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Hybridization and isolating mechanisms in Catostomus commersonii and Catostomus macrocheilus Nelson, Joseph Schieser 1965

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The University of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY B.Sc, The University of B r i t i s h Columbia, 1.960 M.Sc, The University of Alberta, 1962 FRIDAY, JULY 30, 1965, AT 10:30 A.M. IN ROOM 3.332, BIOLOGICAL SCIENCE BUILDING of JOSEPH SCHIESER NELSON COMMITTEE I.N CHARGE Chairman: I. McT. Cowan I. E. Efford W. S. Hoar C. C. Lindsey J. W.. Murray T. G„ Northcote G. G. E„ Scudder D. T. Suzuki External Examiner: CL..:.Hubbs S c r i p p s I n s t i t u t e of Oceanography La J o l l a , C a l i f o r n i a HYBRIDIZATION AND ISOLATING MECHANISMS IN CATOSTOMUS COMMERSONII AND CATOSTOMUS MACROCHEILUS (PISCES: CATOSTOMIDAE) ABSTRACT Catostomus commersonii and Catostomus macrocheilus are sympatric i n three major drainages of B r i t i s h Columbia Morphological analysis employing a character index and discriminant, function analysis of a l l o p a t r i c and sym-pa t r i c populations revealed that hybrids occurred i n nine lakes, representing v i r t u a l l y every lake examined where both species occur. Presumed F l hybrids made up an average of TL of the combined populations where hybrids occurred, There was no evidence of backcrossing or swamping. Spawning migrations were studied i n eight confined i n l e t s of lakes which have both species. Four i n l e t s supported migrations of both species. C o l l e c t i n g was also done throughout the spawning migration i n Cluculz River, an outlet with d i v e r s i f i e d habitat supporting both species. Postulating i s o l a t i n g mechanisms were studied from a r t i f i c i a l crosses of the species, two back-crosses involving hybrid females, and microscopic examination of hybrid testes. An i n t e r a c t i o n of temporal, habitat, and postmating i s o l a t i n g mechanisms was not considered s u f f i c i e n t to prevent swamping. Ethological i s o l a t i o n i s in f e r r e d to be of major importance i n reducing i n i t i a l h y b r i d i z a t i o n , while s e l e c t i o n against hybrid crosses i s in f e r r e d to prevent swamping. Hybridization could not be at t r i b u t e d to environ-mental factors commonly noted i n the l i t e r a t u r e to be associated with h y b r i d i z a t i o n . Males of one species entering the spawning act with males and a female of the other species i s considered the main cause of hybridiza-t i o n . Mis-mated i n d i v i d u a l s , however, have much oppor-tunity for conspecific matings at other times. There was no evidence of reinforcement of i s o l a t i n g mechanisms despite the probable occurrence of h y b r i d i z a t i o n i n some areas for at least several hundred years. Natural s e l e c t i o n against i n d i v i d u a l s producing hybrids i s apparently low. GRADUATE STUDIES F i e l d of Study: Ichthyology Marine F i e l d Course Organic Evolution Ichthyology Po A „ Dehnel Go G< E. Scudder Co C. Lindsey N. J . Wilimovsky PUBLICATIONS Gordon, R.N., R.A. Crouter, and J.S. Nelson, 1960. The f i s h f a c i l i t i e s at the Whitehorse Rapids power development; Yukon T e r r i t o r y . Can.Fish Cult. No. 27: 1-14. Hickman, CP., R.A. McNabb, J.S. Nelson, E„D„ Van Breeman, and D. Comfort, 1964. E f f e c t of cold acclimation on e l e c t r o l y t e d i s t r i b u t i o n i n rainbow trout (Salmo g a i r d n e r i i ) . Can. J . Zool 42 (4): 577-597. J.S. Nelson, 1965. E f f e c t s of f i s h introductions and hydr o - e l e c t r i c development on the fishes of the Kananaskis River System, A l b e r t a . J . Fis h Res. Bd. Canada. 22(3): 721-753. HYBRIDIZATION AND ISOLATING ME,C HANI SMS IN CATOSTOMUS COMMERSONII AND CATOSTOMUS  MACROCHEILUS (PISCESS CATOSTOMIDAE) °y JOSEPH SCHIESER NELSON B . S c , The U n i v e r s i t y of B r i t i s h Columbia, I960 M . S c , The U n i v e r s i t y of A l b e r t a , 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE* REQUIREMENTS OF THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of ZOOLOGY We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1965 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r -m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s . , I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i -c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Z o o l o g y  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date J u l y , 1965 Supervisor ! D r . C . C . Lindsey ABSTRACT Catostomus commersonii and Catostomus macrocheilus are sympatric i n three major drainages of B r i t i s h Columbia. Mor-p h o l o g i c a l a n a l y s i s employing a character index and d i s c r i m -inant funct ion a n a l y s i s of a l l o p a t r i c and sympatric populations revealed that hybrids occurred i n nine lakes , representing v i r t u a l l y every lake examined where both species occur . Presumed F l hybrids made up an average of 7f» of the combined populations where hybrids occurred. There was no evidence of backcrossing or swamping. Spawning migrations were studied i n eight confined i n l e t s of lakes which have both species . Four i n l e t s supported migra-t i o n s of both species . C o l l e c t i n g was also done throughout the spawning migration i n C l u c u l z River , an out le t with d i v e r s i f i e d habitat supporting both spec ies . Postmating i s o l a t i n g mechanisms were studied from a r t i f i c i a l crosses of the species , two back-crosses i n v o l v i n g hybrid females, and microscopic examination of hybrid t e s t e s . An i n t e r a c t i o n of temporal, habi ta t , and postmating i s o l a t i n g mechanisms was not considered s u f f i c i e n t to prevent, swamping. E t h o l o g i c a l i s o l a t i o n i s i n f e r r e d to be of major importance i n reducing i n i t i a l h y b r i d i z a t i o n , while s e l e c t i o n against hybrid crosses i s i n f e r r e d to prevent swamping. H y b r i d i z a t i o n could not be a t t r i b u t e d to environmental f a c t o r s commonly noted i n the l i t e r a t u r e to be associated with h y b r i d i z a t i o n . Males of one species enter ing the spawning act with males and a female of the other species i s considered the main cause of h y b r i d i z a t i o n . Mis-mated i n d i v i d u a l s , however, have much opportunity f o r c o n s p e c i f i c matings at other t imes. There was no evidence of reinforcement of i s o l a t i n g mechanisms despite the probable occurrence of h y b r i d i z a t i o n i n some areas f o r at least several hundred y e a r s . Natural s e l e c t i o n against i n d i v i d u a l s producing hybrids i s apparently low. i v TABLE OF CONTENTS Page INTRODUCTION o « e « o e « « e 9 e « * e o « o a « * < * * s « e « c « s * » t * * e * o * * » c e i i c « c 1 DESCRIPTION OF AREA STUDIED B e FX Sll© S o « « a « « a o o « « 0 9 0 c « * o » e * « * © e « a e o © « « e © e « © < > o « 9 C Q a -L.1 MATERIALS AND METHODS A. Hybrid I d e n t i f i c a t i o n 1• M a t e r i a l Examined « » a e « * * » « « * « « a « e « « » * * c » « e e « * » 12 2« Morphological Counts and Measurements < • • « . » . * » 12 B. F i e l d Study of Species Segregation « • « . . . IS 1. Cluculz River » C. Experimental Study of Species Segregation 1« Hybrid Embryo M o r t a l i t y «•«« 21 2 o Hybrid I n V i a b l l i t y eoooe«©eooe«eee»«.eet>e»«s«e»e 26 3 e Hybrid S t e r i l i t y s » e e e e e » e » e » » » o » o e o e * o e « o » » » o « 26 ZOOGEOGRAPHY OF CATOSTOMUS COMMERSONII AND C . MACROCHEILUS.. 27 IDENTIFICATION AND MORPHOLOGICAL ANALYSIS OF HYBRIDS 31 A . Analys is of Immature Specimens * . . < » . . . « . . . . . . < > » . . . » < = 34 B. A n a l y s i s of Adult Specimens . . . . . . . . . . . 48 ISOLATING MECHANISMS A» Temporal I s o l a t i o n . . . » » • . o » 9 . » . e » . » . » * » » o » » « « » « « « e 51 le CluCUlZ RlVer o e e e « o « o e e » e « 9 o » « » e » » « s « » e « e « 0 » » c 52 2 o Inle tS e » « o » e e o * » « e « » o e « e » e t o « » « » » « » « » » o » » « t » » » 55 B« Habitat I s o l a t i o n o » « » » o » » o « » » » » » « » « o » o » » e » # » « » » « < > » 57 1» C l u c u l z River o * « « e « * « * * « » * * * e « » » « » * » s « * * * * * » * » 57 2 o InletS •»#»##»» e « » e » » e e • » • • » • • « • • « • • • • • • * « » • • < > 60 v Page 3. General Considerations .. ....... 61 C . Ethological I s o l a t i o n .....................»...««•« 62 1. Color Differences .•«•«».••••••••••»•••«««»•«»» 63 2. Morphological Differences .... 64 3* Size Differences . . • • • • • o . . . . . . . « » » » e « » . . » » » » » » 65 D. Hybrid Embryo Mortality ........................... 65 E. Hybrid I n v i a b i l i t y and S t e r i l i t y 71 1 o Hybrid I n v i a b i l i t y < . . . o . * « . . . • « . » . . » » » * . . . . . . . » 72 2. Hybrid S t e r i l i t y ..«•*••.••.«.««....•.•••.•«•«. 75 DISCUSSION A. Extent of Hybridization 76 B. Causes of Hybridization 1. Environmental Factors <>...».... 78 2. Incomplete I s o l a t i n g Mechanisms 8 4 C. Eff e c t of Hybridization 88 1. Selective Advantage of Hybrids 88 2. Selective Disadvantage of Hybrids 90 CONCLUSION 93 LITERATURE CITED 95 V I Table LIST OF TABLES Page I L o c a l i t i e s from which suckers were examined f o r Fig o 9 t O l6 . . . e o . o . . . . . . . . . . . a . . . . . . . . . . . . . «»».»«««. 13 II A r t i f i c i a l crosses reared to permit analysis of hybrids of known parentage •. 15 III Inlets examined f o r spawning suckers from which data Were U t i l i z e d . . . . . . . . . . e . g . . . . . ........ ........ • 20 IV Inheritance of dorsal ray number ...... 38 V Index values assigned to f i v e characters 47 VI Hatching time and mortality of the crosses i n f l a s k s . . 68 VII Hatching time and mortality of the crosses i n VIII Summary of s t a t i s t i c s f o r comparing mortality rates of the crosses o . o . . . . » . « • « . . « . • « . . « . . . . « « • . . . . . . . . . . . 69 IX Daily hatching frequency of crosses i n f l a s k s ........ 70 X Daily hatching frequency of crosses i n baskets 70 XI Survival of offspring of a r t i f i c i a l crosses i n laboratory •••••••••••••••••••••••••••••e.......»•»».. 73 V l l LIST OF FIGURES Figure l e D i s t r i b u t i o n of Catostomus commersonii and £• macrocheilus and accepted l o c a l i t y records i n area Of SyiTipatry e « e o e a o e e e o 0 e * * o » o e o * o » e « a 0 e a » * « * « * * * e « e * 5 2» L o c a l i t i e s where spawning migrations of C_„ commer-s o n i i and C_, macrocheilus were studied and areas examxned f o r hybrids ooeo«c« 0 a«««»«ee»e«*«e»»«»«««*«« 6 3» Area selected to study temporal and habitat i s o l a t i n g mechanisms i n Cluculz River 7 4» C l u c u l z River with the r i f f l e s at end of Area 2 . . . • « « 7 5 o CluCUiZ River i n Area 6 ea««ooe<>»««ee«e«eae«aeei>»*»*» 7 6 . Richmond Creek at s i t e where large numbers of r i p e C_a commersonii and C« macrocheilus were taken • « • « . . » 8 7» Sucker Creek at s i t e where large numbers of r ipe C. commersonii and C_c macrocheilus were taken « • « . . . » 8 8o Baskets and f l a s k s of egg hatching apparatus f o r experimental crosses • • • • •eee»«»«««e«a««»<>««««»«*»«»« 23 9° Rela t ion between r a t i o of d o r s a l - p e l v i c distance to caudal peduncle depth and fork length i n a l l o p a t r i c C_o commersonii (328 specimens, 22 populations) and C_, macrocheilus (328 specimens, 20 populations) • 36 10o D i s c r i m i n a t i o n between a l l o p a t r i c C_. commersonii (200 specimens, 14 populations) and C_» macrocheilus (200 specimens, 19 populations) on b a s i s of d or s a l ray number and r a t i o of distance between dorsal and p e l v i c f i n s to caudal peduncle depth o»« 37 v i i i F igure Page 11. D i s c r i m i n a t i o n between a l l o p a t r i c C . commersonii (40 specimens, 4 populations) and C_. macrocheilus (40 specimens, 4 p o p u l a t i o n s ) o • . . . . . . . . . 0 . . . . . . . » 40 12 . Character a n a l y s i s used to i d e n t i f y immature C_. commersonii (hollow histograms, hollow c i r c l e s f o r selected i n d i v i d u a l s ) , C_. macrocheilus ( s o l i d h i s t o -grams, s o l i d t r i a n g l e s f o r selected i n d i v i d u a l s ) and hybrids (hatched histograms, hollow t r i a n g l e s ) i n B u r n S LctlCS o o e o o « > e e e o e 6 « « e e o e o 9 » « 0 9 0 o o e » « « c * e e * e * « * « e i l l 13« Character a n a l y s i s used to i d e n t i f y immature C_. commersonii, C . macrocheilus, and hybrids (explan-a t ion of symbols i n F i g . 12) i n C l u c u l z River 41 14. Character a n a l y s i s used to i d e n t i f y immature C . commersonii. C . macrocheilus, and hybrids (explan-a t ion of symbols i n F i g , 12) i n Summit Lake . . . . . . . . . 42 15. Character a n a l y s i s used to i d e n t i f y immature C« commersonii. C. macrocheilus. and hybrids (explan-a t ion of symbols i n F i g . 12) i n McLeod Lake . . . . . . . . . 42 16. Summary of d o r s a l - p e l v i c distance to caudal peduncle r a t i o and character i n d i c e s used to i d e n t i f y immature hybrids « . . . « . . . . . » . . . . . • . . . . . . . » . * . • . . . . . . . 43 17. D i s t r i b u t i o n of l a t e r a l l i n e scales and diagonal scales i n C_. macrocheilus, hybr ids , and C. commersonii . . . . .ee*........................ .•...».<>. 45 18. D i s t r i b u t i o n of g i l l r a k e r s , p e r i t o n e a l c o l o r , side c o l o r , and dorsa l rays i n C_. macrocheilus. hybr ids , and C . c o m m e r s o n i i » . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 i x Figure Page 19« Comparison of unknown mature sympatric suckers with known immature a l l o p a t r i c (of F i g . 11) and sympatric suckers (of F i g . 16) to show the existence of mature 2 0 . D i s t r i b u t i o n of adult suckers i n C l u c u l z River . 53 21o Degree of female maturity and water temperature i n Cluculz River f o r 1963 a n < ^ 1964 • • • © • • • • • • • • • • • o » » » » o 9 54 2 2 . Relat ive abundance of C_. commersonii (C), presumed hybrids (H), and C. macrocheilus (M) i n i n l e t spawning migrations where both species were common 56 23« Fork length of C_. commersonii (C), presumed hybrids (H), and C_. macrocheilus (M) i n spawning m i g r a t i o n s . . 66 X ACKNOWLEDGMENTS I wish to express my indebtedness to D r . C . C . Lindsey, who suggested t h i s problem. H i s guidance throughout the study and h i s s t imulat ing c r i t i c i s m of the manuscript are appreciated. D r s . I . E . E f f o r d , H.D.. F i s h e r , J . T . McFa'dden, T . G . Northcote, D. Suzuki , and N . J . Wilimovsky read the manuscript and made many h e l p f u l suggestions. D r s . J . R . H * Dempster and J . T . McFadden helped with the s t a t i s t i c a l computations. I am g r a t e f u l to Drs . N.R. L i l e y , W.H. Mathews, and G«E« Rouse, whose advice I have frequently sought. The assistance of Messrs . P . J . McCart i n 1962 and F . J . Fraser i n the spr ing of 1963 and 1964 made the f i e l d work a pleasure . Mrs . C B . Nelson and Miss M.P. Handcock helped with f i e l d work i n the summer of 1964. Miss Handcock provided much data on the substrates seined f o r suckers. Messrs . V/. G i l l and J . C . Lyons provided h e l p f u l information during the f i e l d work. The National Research Counci l of Canada provided a student-ship from 1962 to I 9 6 4 . F i e l d work was supported by a National Research Counci l of Canada grant made to D r . C . C . Lindsey . The B r i t i s h Columbia F i s h and Game Branch provided a t r a i l e r during the 1962 f i e l d work. I am most g r a t e f u l to my wife , Claudine, who typed the manuscript. INTRODUCTION 1 Speciation may be considered complete when in d i v i d u a l s of a population have acquired properties which enable them to maintain reproductive i s o l a t i o n from t h e i r parental species. Geographic i s o l a t i o n i s generally considered a prerequisite f o r the form-ation of these properties, which become tested when external b a r r i e r s break down. The absence of reproductive i s o l a t i o n when populations come into secondary contact may re s u l t i n a fusion of the forms. The establishment of i s o l a t i n g mechanisms, which prevent interbreeding of sympatric populations, may thus be considered the most important aspect of speciation. The phenomenon of hybridization - defined here as the interbreeding of i n d i v i d u a l s belonging to two d i f f e r e n t species due to imperfect i s o l a t i n g mechanisms - presents, therefore, an i n t r i g u i n g problem i n speciation. The p r i n c i p a l i s o l a t i n g mechanisms have been described by Dobzhansky (1951), Mayr (1963), and Muller (1942). For f i s h with external f e r t i l i z a t i o n the various p o t e n t i a l i s o l a t i n g mechanisms, i n the chronological order i n which they become ef f e c t i v e at mating time, may be c l a s s i f i e d as: temporal, habitat, e t h o l o g i c a l , gamete incompatability, hybrid embryo mortality, hybrid i n v i a b i l i t y , and hybrid s t e r i l i t y . The r e l a t i v e importance of each i s o l a t i n g mechanism varies between animal groups. For example, a s t e r i l i t y b a r r i e r may keep one species group separate while i n another group, where hybrids may be f u l l y f e r t i l e , an ethological b a r r i e r has the same e f f e c t . Within ethological b a r r i e r s , v i s u a l , chemical, and auditory stimuli may each play the dominant role i n i s o l a t i o n (Mayr, 1963). 2 Natural hybrids are known f o r many groups of animals (Mayr, 1 9 6 3 ) and are r e l a t i v e l y common among freshwater fishes i n northern regions. The causes of hybridization are numerous and involve a breakdown of one or several i s o l a t i n g mechanisms. Hubbs ( 1 9 5 5 ) stresses the role of environmental factors i n inducing hybridization and regards the r e l a t i v e l y high rate of hybridization i n freshwater f i s h e s i n northern areas to be the r e s u l t of the changing nature of the environment. Hubbs ( 1 9 5 5 » 1 9 6 1 ) notes the factors commonly associated with and conducive to the breakdown of i s o l a t i n g mechanisms i n f i s h to be (i) cohabitation of large numbers of i n d i v i d u a l s of one species with few i n d i v i d u a l s of a related species ( i i ) l i m i t e d spawning area ( i i i ) disturbances or intergradation of the habitat (iv) introduction of one or both species or recency of natural overlap. In certain cases hybridization has been attributed to the chance meeting of egg and sperm with the two species each spawning c o n s p e c i f i c a l l y i n close proximity, rather than deliberate i n t e r s p e c i f i c mating. In several f i s h e s some or most of the i s o l a t i n g mechanisms have been examined i n considerable d e t a i l (e.g., Hubbs and Hubbs, 1 9 3 3 ; M i l l e r , 1 9 6 4 ) and often with precise experimental work (e.g., Clark, Aronson, and Gordon, 1 9 5 4 ; Clark Hubbs, I 9 6 0 , 1 9 6 l b ; Hubbs and Delco, 1 9 6 2 ; P i c c i o l o , 1 9 6 4 ) . Decisive evidence f o r the importance of c e r t a i n i s o l a t i n g mechanisms, however, can be obtained only from f i e l d studies (e.g., M i l l e r , 1 9 6 4 ) . Many studies discuss various facets of a r t i f i c i a l hybridization, while most works on natural hybridization concern cases where one or both of the parental species were introduced or where the environment had been altered by man. Most studies on i s o l a t i n g mechanisms i n f i s h deal with species which never or ra r e l y hybridize n a t u r a l l y . No previous study examines most of the primary potential i s o l a t i n g mechanisms i n which evidence i s presented of two d i s t i n c t species hybridizing i n many undisturbed l o c a l i t i e s throughout much of t h e i r area of sympatry. In t h i s study the hybridization and i s o l a t i o n mechanisms i n Catostomus commersonii (Lac^pede), the white sucker, and Co macrocheilus Girard, the largescale sucker, were examined through f i e l d and experimental work. These two sim i l a r species of f i s h have come into sympatry i n post-Pleistocene times and occur together i n many B r i t i s h Columbia lakes* Hybridization between them has been reported by Carl, Clemens, and Lindsey (1959) and Geen (MS, 1958) and i s known from the present study to be of wide occurrence. Their area of overlap i s large, e a s i l y accessible to study, covers a wide range of environments, both disturbed and undisturbed, and has resulted from the natural expansion i n range of both species. There were three objectives to t h i s study. The f i r s t was to est a b l i s h a method of i d e n t i f y i n g hybrids and to study specimens from many lakes to determine the extent of h y b r i d i z -ation. The second objective was to study spawning migrations and to make a r t i f i c i a l crosses under p a r t i a l l y controlled con-d i t i o n s i n order to evaluate the role of environmental fac t o r s in causing hybridization and to consider the o r i g i n and effectiveness of the pot e n t i a l i s o l a t i n g mechanisms. With the above information, the t h i r d object ive was to consider the b i o l o g i c a l s i g n i f i c a n c e of h y b r i d i z a t i o n i n these two species , and i t s bearing on t h e i r taxonomic s ta tus . DESCRIPTION OF AREA STUDIED A . GEOGRAPHY The area studied l i e s w i t h i n the zone of sympatry of £ . commersonii and C . macrocheilus ( F i g , l ) , i n the northern i n t e r i o r plateau of B r i t i s h Columbia. Most of the lakes and streams examined ( F i g . 2) occur i n the Endako, Nechako, and Crooked r i v e r v a l l e y s between e levat ions of 64O and 762 m (2100 and 2500 f t ) above sea l e v e l . Forested r o l l i n g h i l l s are common. Clay s o i l , l e f t from a post -Pleis tocene g l a c i a l lake occupying the C l u c u l z - F r a s e r Lake area, i s predominate. A l l creeks where spawning suckers were examined have a rapid flow over g r a v e l . Aquatic vegetation i s sparse. Clucul River ( F i g . 3 to 5), the out le t of C l u c u l z Lake, had an est im-ated flow of from 2000 to 3100 cubic decimeter/sec (70 to 110 cubic f t / s e c ) during l a t e May, while the i n l e t creeks ( e . g . , F i g . 6 and 7) var ied from an estimated 60 to 1700 cubic decimeter/sec (2 to 60 cubic f t / s e c - see Table I I I ) , the flow general ly decreasing during the spawning m i g r a t i o n . Freshets are common. There i s l i t t l e d i v e r s i t y i n these small i n l e t s except f o r short pools about 0.6 to 1.2 m (2 to 4 f t ) deep, common along spawning areas i n Decker, Stearns, Norman, Sucker and Erickson creeks. Gravel from about 1.3 to 10 cm (| to 4 inches) diameter i s common. 5 F i g o 1» D i s t r i b u t i o n of Catostomus commersonii and C. macro-cheilus and accepted l o c a l i t y records i n area of sympatry. Lake outlines are omitted. Doubtful l i t e r a t u r e records are indicated by question marks. S P A W N I N G S P A W N I N G B O T H S P A W N I N G S Y N C H R O N O U S L Y — A C . C O M M E R S O N I I -C . M A C R O C H E I L U S -O A S K E E N A . P E A C E TUDYAH L-55° MCLEOD L/ PALLING «" CR-^ E C K E R " BURNS CR '^.RICHMOND CR. STEARNS CR. BURNS L. ENDAKO R. P R A S E R L -54° N i 0 l -MILES —i KMS 126° i 30 -H 45 INIULK1 L. "3«-CORKSCREW CR. EULATAZELLA-L. CROOKED--^ R. SUMMIT L. ERICKSON CR ,CHIEF L. 125° 1_ 124° I - CLUCULZ R.| >,XLUCULZ L. 1*—NORMAN CR. -SUCKER CR. F R A S E R 123' _ l Fig. 2. L o c a l i t i e s where spawning migrations of C_. commersonii and C. macrocheilus were studied and areas examined f o r hybrids F i g , 4. Cluculz River with the r i f f l e s at end of Area 2. Nay 25, 1964 F i g . 5, C l u c u l z River i n Area 6. K a y 22, 196/+ F i g . 6. Richmond Creek at s i t e where large numbers of ripe Co commersonii and J3. macrocheilus were taken. June 2, 1964. F i g . 7* Sucker Creek at s i t e where large numbers of ripe C. commersonii and C. macrocheilus were taken. May 26, 1964."" Farming p r a c t i c e s have modified the banks adjacent to spawning areas f o r various lengths i n P a l l i n g , Decker, Richmond, and Stearns c r e e k s » The substrate of these creeks has, however, been l i t t l e changed. In 1964 the above i n l e t s were very d i r t y owing to f l o o d i n g c o n d i t i o n s . Burns Creek passes through the v i l l a g e of Burns Lake and i s extremely p o l l u t e d . The channels of Burns and Richmond creeks are disrupted i n t h e i r lower courses . C l u c u l z River has been modified by a b u l l d o z e r i n Areas 6 and 7 ( F i g . 3), Streams such as Corkscrew, Sucker, Norman, and C l u c u l z were poisoned i n a sucker e r a d i c a t i o n program i n the e a r l y 1950Ts. A f i s h t rap f o r d isposing of suckers was a l s o operated at t h i s time on C l u c u l z River between Areas 1 and 2. Except as noted above, the spawning areas f o r suckers appear iinmodified by man. Information on the spawning migration i n the d i v e r s i f i e d C l u c u l z River was c o l l e c t e d i n several l o c a t i o n s . Depths and estimates of surface v e l o c i t y i n m i d - r i v e r , obtained by t iming a f l o a t over a f i x e d dis tance , were taken May 23 to 26, 1964. Temperature and depth records were measured i n Area 5» near the observation tower. Area,,, 1. F i r s t part of the out le t where suckers congregate f o r spawning; v e l o c i t y about 0.14 m/sec; f i n e sand with stones up to 5 cm i n diameter predominate, while decaying organic matter character izes the r i v e r bottom upstream; bottom c lear on both sides but with algae i n middle ; bottom near east bank at depth of about 150 to 220 cm with small stones 3«2 to 6.4 mm. Most g i l l n e t t i n g i n Area 1 was done i n the l a t t e r s e c t i o n . Area 2. Velocity of upper part 0v2 to 0.5 m/sec; stones 3»2 to 76 mm common; depth primarily from 70 to 100 cm; side bay of calm water and mud bottom in middle section; lower section with alternating areas of 3°2 to 9»5 mm and 6.4 to 38 mm stones; velocity and depth similar to upper section; r i f f l e at end of area with 1 m/sec velocity and 25 mm stones common. Gi l lnet t ing was done in the upper and lower sections. Area 3. Relatively uniform stretch of r iver between two r i f f l e s velocity about 0.4 m/sec; stones 25 mm common; depth 80 cm in most places. Area 4. Short stretch beginning at a r i f f l e ; similar to Area 3 in remaining section; ends in shallowest section of the r iver with depth about 40 cm and rocks 12.7 to 76 mm predominating. Area 5. Starts below a shallow r i f f l e ; water deepest, 105 cm, and swiftest, 0.6 m/sec, at the f i r s t bend near southwest shore, bottom sandy; back-eddy on northeast shore of the bend; f i n a l stretch with velocity of about 0.6 to 0.8 m/sec, deepest part 85 cm, rocks 25 to 127 mm common. Gi l lnet t ing in 1964 was done in th is la t ter section. Area 6. Relatively uniform throughout i t s length; main channel (where most g i l lnet t ing done) 70 to 82 cm deep with velocity of 0.8 to 0.9 m/sec; channel in middle section near west bank with sandy bottom; remainder composed mostly of 12.7 to 89 mm stones with velocity of 0.5 to 0.7 m/sec between the main channel and the east shore. Area 7. Consists of small shallow bay and downstream stretch within 1 m of west bank; gravel clean and mostly 12.7 to 50 mm. 11 Area S» Mainly a large expansion of standing water which by June consis ts mostly of exposed rooted aquatic vegetat ion; main channel (where a l l g i l l n e t t i n g was done) with a f i n e gravel bottom; depth i n channel averages about 150 cm and v e l o c i t y about 0 . 1 6 to 0 , 3 0 m/sec. The r i v e r f o r 1 .6 km (1 mile) north of Area S consis ts of many stretches s i m i l a r to that described above. Rapids exis t f a r t h e r downstream with f a l l s , impassible to any upstream move-ment of suckers, near the junct ion with the Kechako R i v e r . B. FISHES Several species of f i s h commonly occur i n the streams during the spawning migration of C, commersonii and C. macrocheilus. C . catostomus precedes both species i n spawning time and adults are u s u a l l y absent when C. commersonii and C. macrocheilus are spawning. Considerable overlap i n time, however, does occur with C, commersonii i n Norman Creek, but there are marked d i f f e r e n c e s i n areas of : synchronous con-c e n t r a t i o n s . Ripe Mylochei lus caurinus i s abundant during c e r t a i n times of the sucker spawning migration i n Decker, Burns, Richmond, Norman, Sucker, and Er ickson creeks. Richardsonius  bal tea tus , Ptychocheilus oregonensis. Salmo g a i r d n e r i i . Lota  l o t a , and Cottus asper are also present i n most of the above creeks . No species of f i s h was common i n areas frequented by spawning suckers i n C l u c u l z R i v e r . Several a d d i t i o n a l species of f i s h occur i n lakes where the majori ty of immature suckers r e s i d e . 12 MATERIALS AND METHODS A c HYBRID IDENTIFICATION lo M a t e r i a l Examined M a t e r i a l employed i n the study included museum specimens, i n d i v i d u a l s c o l l e c t e d during the study, and a r t i f i c i a l l y reared i n d i v i d u a l so Table I l i s t s the mater ia l u t i l i z e d f o r the morphological a n a l y s i s of f i e l d specimens* A l l i n d i v i d u a l s used to e s t a b l i s h the presence and estimate the frequency of h y b r i d i z a t i o n were c o l l e c t e d as part of t h i s study. They were seined and preserved without any conscious e f f o r t to favor p a r t i c u l a r t y p e s . Adul ts , except from C l u c u l z River , were obtained with rotenone (Chem F i s h S p e c i a l ) . A l l specimens not examined i n the f i e l d were f i x e d i n 10% formal in and l a t e r t r a n s f e r r e d to 1+0% i s o p r o p y l a l c o h o l . M a t e r i a l from the a r t i -f i c i a l crosses given i n Table II were employed to a s s i s t the i d e n t i f i c a t i o n of h y b r i d s . 2. Morphological Counts And Measurements Data from immature specimens (<20 cm fork length i n Catos-tomus commersonii and <30 cm i n C . macrocheilus) were obtained i n the l a b o r a t o r y . M e r i s t i c data, except f o r g i l l r a k e r counts, from most adul ts were obtained i n the f i e l d . The majori ty of presumed adult hybrids and a random sample of suckers were preserved and re-examined i n the l a b o r a t o r y . Counts on a random sample were recorded f o r a l l c o l l e c t i o n s that were not preserved. A l l body proportions were made on preserved mater ia l with d i a l c a l i p e r s graduated and read to 0.1 mm. M a g n i f i c a t i o n was used where d e s i r a b l e . Counts and measurements were taken on the l e f t side of the specimen when p o s s i b l e . 13 TABLE lo L o c a l i t i e s from which suckers were examined f o r F i g s 9 to 16o I d e n t i f i c a t i o n s are partly based on these -figures» Ci Catostomus commersonii; Ms C „ macrocheilus: Hs Hybrids BCs University of B r i t i s h Columbia; ROMs Royal Ontario Museum; NMCs National Museum of Canada; S or date? F i e l d number of uncatalogued material, some of which was discarded., L o c a l i t y Lat=N,LongoW Museum No, Total No. of Specimens C H M Fig* 0,0,6 9 0,0,7 9 17,6,8 12 ,16 7,6,8 16 0,4,83 16 0,4,8 16 27,2,1 16 8,2,1 16 81,0,1 16 10,0,0 16 Skeena R. Drainage Owen L. C o l l i n s L, Fraser R. Drainage Burns L. Fraser L. Sucker Cr= Norman Cr. Cluculz R( 54°07», 126°41' S74 54°06», 127°13' BC61-479 5 4 ° 1 3 f , 1 2 5 ° 4 6 ' 5 4 o 0 3 l , 1 2 4 o07 , 5 3 ° 4 3 S 1 2 3 ° 3 4 T 5 3 ° 5 2 % 1 2 3 ° 3 4 ' 5 3 0 5 4 ^ 1 2 3 0 3 5 , BC64-416,427 S139;S169; Sl-64; BC64-409 BC64-260,434 June9/63: June4/64 June8/63; S 1 3 4 J B C 6 4 - 41,9, ,19 13,16 408 , 4 5 1 17,9, , 1 0 16 Chief L. 5 4 ° 0 7 « , 1 2 2 ° 5 9 f BC64-404 2 8 ,4, 8,4i , 2 ,2 1 6 1 6 Tyee L» 52°23f , 1 2 2 ° 0 4 f , 1 2 2 ° 1 7 ' , 1 2 1 ° 5 7 * S 9 0 S 8 7 0,0, , 1 0 9 Duckworth L. 52°23' 0,0, , 1 0 9 Anderson R. 50°42 * BC6O-I85 0,0, , 1 0 9 BC60-187 0,0, 0,0, , 1 0 2 9 1 0 Schkam L. 49°25T , 1 2 1°27T B C 5 9 - 5 9 0 0,0, 0,0, 0,0, 9 5 1 0 9 1 0 11 BC59-591 0,0, 0,0, 1 2 11 9 9 BC59-593 0,0, 1 7 9 49°12* 0,0, 5 1 0 Lower Fraser R. ,122°13' BC59-601 0,0, 0,0, 0,0, 19 19 1 0 9 10 11 Stave R. 49°12» ,122°23t BC56-IO9.565 0,0, 27 9 0,0, 5 1 0 Nicola L, 5 0 ° 1 2 » , 1 2 0 ° 2 9 t BC60-175 0,0, 0,0, 11 3 9 1 0 BC60-232 0,0, 25 9,10 Shuswap L» 51°00« ,119°00» , 1 2 0 ° 0 9 ' BC54-349 0,0, 3 1 0 Walker L. 50°33* BC54-442 0,0, 0,0, 16 13 9 1 0 East Barrier .51°16« ,119°50» BC58-3OO 0,0, 3 9 14 L o c a l i t y LatoNgLongoW Museum No. Total No. of Specimens C H M Fig< Columbia Ro Drainage Missezula L. 49°47%120°30« A l l i s o n Lo 49°42% 120°36* Otter Lo Wolfe Lo Osoyoos L. L i t t l e Sand Cr. Kootenay L. Duck Lo Bush L, 49°34S120°46» 49 o27^120 o19 , 49o02»,119°30t 49°20',115°l8' 49°30»,117°10' 49°14SH6°36 M 51°47»,117°37» Pend-d'Oreille R. 49°05 ,,117°30' Yakima R° Snake R. North Powder Ro Peace RB Drainage Summit L 0 Kerry L, McLeod Lo Tudyah Lo Tacheeda L 0 Moberly L e Charlie Lo Stoddart Cr. Tupper Cr. Swan Lo Saskatchewan Ro System White Mud Cr. A l t a 56°14 ,,120°56» 55o38',120°04* 55°31,,120°03» Meander R. Shank Cr. Unknown Eyebrow Cr« A l t a . A l t a . A l t a . SQ, sic o BC54-310 BC59-3H BC56-58O BC59-582 BC56-89, 57-297 BC53-1B7 BC55-12 BC57-57 BC55-315 B C 5 6 - 4 7 5 BC56-523 Ellensburg, Wash. Pullman, Wash. Haines, Ore. 54°17,,122°38» 54°41f,122°47* 54°56«,122059' 55 o04 f,123°02* 54 0 4 l ' , 122°35 f 55°50t,121°40» 56o15*,120°58» S118 BC58-241 BC64-351 BC56-66 S99;S100; BC64 -400 S109 S113;BC64= 397,398 S 1 1 4 J B C 6 4 -396 July/62 S 1 1 5 B C 5 4 - 2 7 July / 6 2 BC61-312 B C 5 7 - 3 6 7 BC61-343 BC57-358 BC55-I41 BC6I-96 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 56 11 19 5 28 12 56 10 12 19 13 11 6 8 5 10 22 17 10 15 3 15 6 18 X 0 26 0,8 0,13 0,5 0,9 0,8 0,24 0,18 0,19 0,16 0,7 0,10 0,8 0,4 0,18 0,17 0,10 0,9 0,7 0,10 0,6 2 2 2 2 5 5 2 2 0 0 0 0 0 0 0 0 0i Oj 0J 0, 0j o, 0j 0, 0; Oi 19 11 ,6 5 50 12 3 3 0 0 , 0 0 ,0 0 , 0 0 0 0 0 0 0 0 0 0 0 0 1 0 9 , 1 0 9 10 9 1 0 9 1 0 9 1 0 1 0 9 1 0 1 0 9 9 1 0 11 9 1 0 9 , 1 0 , 1 1 1 0 1 4 , 1 6 1 6 16 1 6 1 5 , 1 6 1 6 1 6 1 6 9 9 1 0 9 1 0 9 9 9 , 1 1 9 1 0 1 1 9 1 0 9 1 0 9 1 0 9 15 Total Noo of Specimens L o c a l i t y Lat 0NoLong 0 W Museum No. C H M F i g . Long Ro Man. BC56--93 15,0,0 2,0,0 9 10 Eastern Canada Unknown Onto BC59-544 16,0,0 7,0,0 9 10 Lake of the Woods Onto BC5S-3SO 15,0,0 5,0,0 9 10 Usher 's C r 0 Onto BC59-186 3,0,0 9 R0M19691 6,0,0 9 Mykiss L» Onto BC58-374 3,0,0 9 Unknown Onto BC.Uncato 4,0,0 63,0,0 55,0,0 9 Boyer 's C r . Onto R0M19706 9 10 Near Owen Sound Ont. NMC60-499A 15,0,0 10 Nanticoke Onto NMC6O-527A 25,0,0 25,0,0 10,0,0 9 10 11 Cariboo R» Nova Scot ia NMC59-292 32,0,0 29,0,0 10,0,0 9 10 11 Near Mud and New Brunswick BC59-197 5,0,0 9 S k i f f lakes 3,0,0 10 TABLE IIo A r t i f i c i a l crosses reared to permit a n a l y s i s of hybrids of known parentage* Cj C_o commersonii: M: C_. macrocheilus: H : probable Hybrid F L : Fork Length (cm); DR: Dorsal Rays; LLSc : L a t e r a l Line Scales ; DSc: Diagonal S c a l e s ; GR: G i l l r a k e r s . Cross Parental Characters Date Started O r i g i n of Parents CcT MS FL:39;DR:12;LLSc:60;DSc:9 FL:50;DR:15 May 16 C l u c u l z Ro CcT M ? D R : l l DR:14 May 20 Cluculz R. C ? M <? FL:40;DR:11 FL:4l ;DR:l5 May 19 C l u c u l z Ro C 9 DR:10 DR:14 May 20 C l u c u l z Ro C ? CV FL:4i ;DR: i i :LLSc:65 FL:38;DR:i2;LLSc:60 May 19 C l u c u l z Ro Co7" H? FL:36 ;DR:il;LLSc:64 ;DSc:9 ;GR:23 FL:35;DR:12;LLSc:74;DSc:ll;GR:26 June 2 Stearns C r . Cc/ H? FL:2S;DR:12;LLSc:66;DSc:10;GR:26 FL:32;DRsl2;LLSc:7l;DSc:ll;GR:27 June 2 Stearns C r . 16 The f o l l o w i n g characters were employed i n the i d e n t i f -i c a t i o n of i n d i v i d u a l s . Fork length was measured on f i s h <15 cm with d i a l c a l i p e r s and >15 cm with a meter s t i c k . Dorsal to p e l v i c f i n distance was measured from the o r i g i n of the dorsa l f i n (membrane over f i r s t rudimentary ray) to o r i g i n of p e l v i c f i n . Care was taken not to d i s t o r t the body. Caudal peduncle depth was the v e r t i c a l depth at the narrowest placet. Dorsal rav count i n the d or s a l f i n excluded the anter ior two to four rudimentary r a y s . The l a s t two rays , one branched and one unbranched, were counted as one. The count i s normally the number of branched rays plus one. A l i z a r i n e Red S was used when required on small specimens. No attempt was made to determine at what fork length the number of dorsa l rays i s f i x e d . It i s f e l t , however, that dorsa l ray number was f i x e d i n a l l specimens, both reared and n a t u r a l because ( i ) there was no obvious c o r r e l a t i o n between f i n ray number and fork length w i t h i n the s ize range examined ( i i ) the anal f i n ray number was seven, the maximum number i n a l l specimens except a small number of reared hybrids which had eight ( i i i ) a l l specimens were greater than 20 mm fork l e n g t h . MacPhee (i960) found d o r s a l f i n ray number to be f i x e d by at l eas t the 20 mm stage i n C. macrocheilus . A comparison of MacPhee's work with Stewart (1926), who studied C. commersonii. suggests that f i n ray number i n the l a t t e r species i s f i x e d at a s i m i l a r or e a r l i e r stage than £ . macrocheilus . G i l l r a k e r count was the t o t a l number of anter ior rakers counted under magnif ica t ion on the dissected f i r s t l e f t archc The number of g i l l r a k e r s was counted over a wide length range of specimens and was found to be f i x e d at about 9 cm fork lengtho The asymptotic curve showed a r a p i d increase up to 7 cm. A c o r r e c t i o n f a c t o r was used when immature specimens were analyzed so that a comparison between specimens of d i f f e r e n t lengths could be made. A count of two was added f o r f i s h 5 l to 64 cm while one was added to f i s h 6| to 8 cm fork l e n g t h . Although t h i s c o r r e c t i o n i s crude, the e r r o r i s not l i k e l y to a f f e c t the f i n a l r e s u l t s because (i) species compared w i t h i n a lake were of about the same s ize range ( i i ) the raker number was part of an index. L a t e r a l l i n e scale count was the t o t a l number of scales along the l a t e r a l l i n e . I t inc ludes scales on the caudal f i n . Diagonal scale count extended from the o r i g i n of the dorsa l f i n (anter ior of the f i r s t rudimentary ray) downward and p o s t e r i o r l y t o , but not i n c l u d i n g , the l a t e r a l l i n e * P e r i t o n e a l c o l o r was the degree of black pigmentation on the v e n t r a l abdominal c a v i t y d o r s a l to the p e l v i c f i n s , and was made using a s e r i e s of standards f o r comparison. Four degrees were recognized. Scores were assigned with one given f o r absence of c o l o r and four to i t s f u l l development. T h i s character was u s e f u l only on specimens <15 cm. Side c o l o r was the degree of black pigmentation i n the form of three l a t e r a l b lotches , and was made using a s e r i e s of standards f o r comparison. Four degrees were recognized. Scores were assigned with one given to f u l l development of c o l o r and four to i t s absence. T h i s character was u s e f u l only on specimens ^15 cm. B, FIELD STUDY OF SPECIES SEGREGATION Temporal and habitat segregation i n C . commersonii, C, macrocheilus. and t h e i r hybr id was s tudied i n C l u c u l z River throughout most of the spawning migrat ion i n I963 and 1964. T h i s r i v e r was chosen f o r intensive study because ( i ) both species occur i n large numbers ( i i ) the habi ta t i s d i v e r s i f i e d ( i i i ) i t i s navigable by boat i n the areas of sucker spawning ( iv) the water i s c l e a r , a f f o r d i n g good v i s i b i l i t y . I n l e t s were examined to note the prevalence of both species i n areas where the habitat i s r e l a t i v e l y uniform and conf ined . In a l l streams the degree of gonad development was noted f o r females (ripe, eggs; near maximum s i z e ; cannot be extruded from cavi ty or can be extruded only with manual pressure ; "hard" and y e l l o w i s h - f u l l y r i p e eggs: spontaneously flow out from h a n d l i n g ; j e l l y - l i k e and orangish - spawned out : few or no mature eggs l e f t i n body c a v i t y ) . S i m i l a r degrees of maturity were a lso noted f o r males. Fork length was recorded on a l l captured i n d i v i d u a l s . lo C l u c u l z River G i l l n e t t i n g provided data on the r e l a t i v e abundance of the two species i n each area . Observations from boat, shore, and towers provided comparative data f o r the various areas. Observations, with the a i d of b i n o c u l a r s and Polaro id glasses , 19 were made of spawning acts* Monofilament nylon g i l l n e t s were d r i f t e d f o r a distance of from 0 to 6»1 m (20 feet) f o r 0„5 to 2 minutes on the r i v e r bottom., The nets were c i r c l e d one or more times by b o a t o T h i s method was e f f e c t i v e i n sampling segments of the spawning migrat ion over short p e r i o d s . One or two nets , each 2 4 m (8 f t ) deep and 15*2 m (50 f t ) long of 6.35 cm (2 .5 inches) stretched mesh were employed. Sets were made from the lake out le t to Area 8 ( F i g . 3 K Approximate l o c a t i o n s of net sets i n the l a r g e r Areas from which data are employed have been g i v e n . G i l l n e t t e d suckers were i d e n t i f i e d and recorded as to Area of capture. Two observation towers were constructed. One was i n Area 5 at the r i v e r ' s edge ( r i v e r 14•3 m wide, 85 cm maximum depth) which allowed the observer to be 4»5 m v e r t i c a l l y above the r i v e r l e v e l . The other, i n Area 6 was 9 m from the r i v e r edge ( r i v e r 17»2 m wide, 82 cm maximum depth) and placed the observer 10 m v e r t i c a l l y above r i v e r l e v e l about 23 m from the area of greatest spawning= When the i d e n t i t y of i n d i v i d u a l s was uncertain i n v i s u a l observations the composition of concentrations was assumed to be p r o p o r t i o n a l to the g i l l n e t t e d sample i n the area at that time* A f a i r degree of accuracy was at tained i n i d e n t i f y i n g f i s h from shore (based on s i z e , c o l o r , and shape). No data are shown on doubtful i d e n t i f i c a t i o n s . 2 . I n l e t s Table III l i s t s data on the i n l e t streams which were examined f o r adult suckers and from which data was u t i l i z e d . 20 TABLE I I I , I n l e t s examined f o r spawning suckers from which data were u t i l i z e d o Estimated volume of flow i n cubic decimeter/sec» P a f t e r date examined denotes C»commersonii or Co macrocheilus present; L denotes C<, catostomus present; A denotes Catostomus spp 0 absento Number i n parenthesis denotes number of times creek was examined. Creek Date Examined Temperature Estimated Area C Vole of Collected Flow P a l l i n g May 29S1963P June 2, I964P 10 10 60 420 Highway 16 downstream f o r 200m Decker May 29*1963? June 2.1963? June 2,1964P 11.5 9.5 11 110 110 280 CN Railway downstream to Decker Lo(500m) Burns May 29,1963P June 2,1963P June 1.1964P 13 10.5 11.5 60 60 170 Highway 16 downstream f o r 350m Richmond June 1,1964? 15 140 Stretch f o r 100m located on eastern l i m i t s of Burns Lo townsite Stearns June 2,1963? 8 170 From 50 to 250m downstream from Highway 16 Corkscrew May 13,1962A May 22,1962L June 11,1962P June 25,1962P 6 8c5 10 15 1680 1120 Stretch f o r 450 to 400m from Nulki Lake Sucker May 12,1962LP May 29,1962P June 10,1962P July 15,1962A May 26,1964LP May 28,1964LP 10 13 12 14 15 15 170 220 140 30 140 E u l a t a z e l l a L, upstream f o r 300m Norman May 10-May30,1962,(4)LP 10-15 June 12,1962A 14 July 30,1962A 19 May 12-June9,1963,(7)LP 10-16 May 12-June4,1964,(6)LP 7-16 220-140 110 14 170-60 Cluculz Le upstream f o r 1000m Erickson May 15.1962P May 20.1962P May 26.1962P 9»5 13o5 l6o5 220 220 Stretch f o r 1100 to 1000m from Summit L 21 I n d i v i d u a l s were obtained with rotenone (Chem. F i s h Special ) and c o l l e c t e d i n a seine stretched across the c r e e k » A crude i n d i c a t i o n of the presence of any s p a t i a l i s o l a t i o n was obtained by subsampling i n long stretcheso Water temperature was measured with a Taylor pocket thermometer between 1000 and 1600 hrsc Co EXPERIMENTAL STUDY OF SPECIES SEGREGATION lo Hybrid Embryo M o r t a l i t y (a) Procedure e Embryo m o r t a l i t y t e s t s were conducted at Lakeside Resort , C l u c u l z Lake (Figo 3) from May 16 to June 9$ 1963c Eggs and m i l t were obtained from suckers captured i n g i l l n e t s from C l u c u l z River* F i s h were removed w i t h i n three minutes of captureo T r i a l runs i n f e r t i l i z a t i o n and placement of eggs i n containers were made p r i o r to the f i n a l t e s t s . Procedure of f e r t i l i z a t i o n was based on Davis (1953) and Forney ( 1 9 5 7 ) , and was as uniform as poss ible f o r a l l c rosses . F u l l y r i p e eggs were expressed i n t o a damp p l a s t i c pan. M i l t was immediately added and the mixture gently s t i r r e d by hand f o r two minutesD Care was taken to avoid g e t t i n g slime and blood i n t o the pan. Creek water was added and the eggs were again s t i r r e d f o r two minutes* Afterwards the water was changed several times and then d r a i n e d . One part saturated starch s o l u t i o n to f i v e parts water was added f o r two minutes to reduce adhesion of the eggs. A f t e r a f i n a l washing the eggs were l e f t f o r several hours to water harden. Eggs were counted by sucking them with a syringe bulb through 22 " tygon" p l a s t i c tubing of a 4 mm inside diameter, s l i g h t l y la rger than the swollen eggs. Eggs with a wrinkled membrane, presumably dead, were d iscarded . Eggs were slowly adjusted to d i f f e r e n c e s i n the incubation t e m p e r a t u r e » They were kept out of d i r e c t sunlight at a l l timeso Fungus i n h i b i t o r s or other chemicals were never used. Lots were incubated at temperatures and water q u a l i t y s i m i l a r to that where the donor specimens would have spawned. There were 24 l o t s f o r the four crosses, each l o t with 150 eggs (Tables VI and V I I ) „ Each l o t involved d i f f e r e n t parents and each cross was evenly d i s t r i b u t e d throughout the apparatus. The crosses were uneven i n number because of an i n a b i l i t y to c o l l e c t desired parental types on any one day. Eggs were placed i n a s ingle l a y e r i n 125 ml pyrex e r l e n -meyer f l a s k s or 10 x 10 x 15 cm baskets with an inner l a y e r of nylon c h i f f o n (40 meshes/cm) and an outer l a y e r of nylon c r i n -o l i n e (10 meshes/cm) ( F i g . S ) . The water i n each of the 12 f l a s k s was kept at a depth of 7 cm. A screen was placed over the out le t tube to prevent loss of eggs. The i n l e t tube was 1 cm from the f l a s k bottom. Water flow through each f l a s k was regulated from 100 to 115 cc/min with a screw clamp on the out-l e t t u b i n g . T h i s kept the l i g h t e s t eggs i n a slow motion. The f l a s k s received water siphoned from e i t h e r of two 4 2 - l i t e r a q u a r i a . Six baskets containing eggs were placed i n two rows i n each of the above aquaria and suspended i n 10 cm of water. The flow through each aquarium was 645 c c / m i n . I n s u l a t i o n was placed around the aquaria to reduce temperature extremes. Water was siphoned into these aquaria from two other tanks in which the water was f i l t e r e d and heated. Cluculz Lake water from a depth of 2.3 to 3»4 m was continuously pumped to the aquaria through p l a s t i c hose. Four 50-watt thermostatically controlled heaters were used to rais e the temperature of the cool lake water (7 to 12 C) f o r the duration of the experiment. The temperature at the l e v e l of the eggs i n the baskets and f l a s k s was measured to the nearest 0.25 C at least twice a day at 0900 and 1800 hr. Two maximum-minimum thermometers were used i n each of the aquaria with the baskets. The lowest temperature occurred at about 0600 hr and the highest at about 1800 hr. Although deviations of a few hours occurred i n these extremes they were treated as having occurred at 0600 and 1800 hr. Differences between f l a s k and between basket locations were <0.5 C at any one time. No consistent difference between l o c a t i o n s w i t h i n each type of container was noted. Temperature i n the f l a s k s was c o n s i s t e n t l y lower than i n the baskets . The lowest and highest temperatures f o r the duration of the exper= iment were 8.5 and 13.5 C f o r the f l a s k s and 9°5 and 15 C f o r the baskets . The range i n f l u c t u a t i o n s of the experimental temperature resembled that of the n a t u r a l l y spawned groups. A high l e v e l of oxygen and minimum amount of carbon dioxide was ensured by aerat ing the lake water as i t entered the f i r s t tank and subsequently heating i t . The baskets and f l a s k s were checked every morning and evening. Dead eggs were removed with a pipet te and recorded. The l o s s of yellowish-orange c o l o r a t i o n and a wrinkled membrane was the c r i t e r i a of death. Care was taken not to d is turb the eggs and to t r e a t each l o t the same. During the hatching period the number of hatched and unhatched eggs was recorded twice a day, without removing the eggs from t h e i r container . M o r t a l i t y of newly hatched f i s h was recorded. F u l l y r i p e u n f e r t i l i z e d eggs from the p o s t e r i o r ovary of 15 specimens of each species from C l u c u l z River and f e r t i l i z e d eggs of the four possible crosses at various ages were placed i n a f i x a t i v e of one part acet ic a c i d and three parts ethanol ( C l a r k e ' s f l u i d ) . The diameters of f i v e eggs of each sample were measured with an ocular micrometer. (b) Treatment of da ta . M o r t a l i t y rates were ca lcula ted f o r each l o t . In a l l c a l c u l a t i o n s the a r c s i n percent cor rec t ion (Snedecor, 1956) was employed. The s t a t i s t i c t was used to t e s t the s i g n i f i c a n c e of d i f f e r e n c e of means (Snedecor, 1956* 91)= Hatching times were measured to note any d i f f e r e n c e s between the species and t h e i r hybrids and any r e l a t i o n with m o r t a l i t y r a t e . Since the water temperature var ied between days of incubation and between f l a s k s and baskets and since the l o t s \vere s tar ted at d i f f e r e n t times (Tables IX and X) "days to hatching" must be converted to a measure which accounts f o r these v a r i a t i o n s . Thermal u n i t s (T .U. ) measured i n day c e n t i -grade degrees was chosen as the best approximation and i s sui table f o r the present purpose. The use of T . U . f o r measuring hatching rate i s current ly widespread ( e . g . , Rough. 1 9 6 1 ; and o t h e r s ) . However, there i s evidence that hatching i s not a f i x e d developmental point (Embody, 1 9 3 4 ) nor i s the appearance of any anatomical feature of bet ter value as a measure of developmental rate (Hayes, P e l l u e t , and Gorham, 1 9 5 3 ) ° Hatching time was chosen because of i t s ease of measurement. A lower number of thermal u n i t s i s u s u a l l y required as temperature increases . Thus, c a l c u l -a t ions from f i s h reared at d i f f e r e n t constant temperatures employed to f i n d b i o l o g i c a l zero give d i f f e r e n t r e s u l t s . Toll, were ca lcula ted by measuring the area enclosed each day between 0 C and the temperature l i n e , using an Ott compen-sat ing polar planimeter on a l a r g e - s c a l e vers ion of graphed temperature f l u c t u a t i o n s . Each day was taken to s tar t at 1800 hr , the l a s t time each day that hatched f r y were counted. B i o l o g i c a l zero was a r b i t r a r i l y chosen at 0 C . A i l extremes i n hatching rates were used i n c a l c u l a t i o n s . The mean hatching time was calculated from the formulae? and variances v - ^-t^x - N . N - 1 where t s accumulated thermal units each day (to class markj arithmetic mean of T.U. f o r that day) x s frequency of eggs hatched each day N s number of eggs hatched i n each l o t o 2. Hybrid I n v i a b i l i t y Certain l o t s (Table XI) were reared following completion of the experimental hatching. These were transferred to Vancouver from Cluculz Lake on June 12, 1963. and placed i n p l a s t i c pans fo r two weeks and then placed i n 70 l i t e r plywood tanks located i n the hatchery of the Ins t i t u t e of Fisheries, The University of B r i t i s h Columbia. Temperature was held between 17 and 18 C. A s l i g h t current was maintained with a i r stones. The f i s h were fed protozoa (mostly Paramecium spp.), microworms, brine shrimp n a u p l i i , frozen brine shrimp, and dried f i s h food. 3. Hybrid S t e r i l i t y The offspring from two crosses involving probable hybrid females from Stearns Creek were reared i n the Vancouver laboratory. The testes of 21 presumed adult hybrids i n spawning migrations from several l o c a l i t i e s were sectioned and stained with E h r l i c h ' s haematoxylin. They were compared with similar preparations of C. commersonii and C. macrocheiluso s s C t x 27 ZOOGEOGRAPHY OF CATOSTOMUS COMMERSONII AND Co MACROCHEILUS C_0 commersonii occurs i n a wide v a r i e t y of habi ta ts across North America from Nova Scot ia to B r i t i s h Columbia, and from Arkansas to the North West T e r r i t o r i e s * Co macrocheilus i s confined to western North America from the Sixes River , Oregon, to the Nass River , B r i t i s h Columbia ( F i g » l ) . The two species are sympatric i n the upper Fraser , Peace, and Skeena drainages of B r i t i s h Columbia ( F i g 0 1)« Both species a lso occur i n a l l o p a t r y w i t h i n t h i s general area of sympatry* In the southern area (Fraser River) C_. macrocheilus i s widespread while C_0 commersonii i s s u r p r i s i n g l y rare , known only i n two lakes where Co macrocheilus i s absent (Sixteenmile - 53°04%122°17* and Green - 5 1 ° 2 4 % 1 2 1 ° 1 5 * ) • In upper Peace drainages only C . commersonii has d e f i n i t e l y been found i n a l l o p a t r y (Hart and Bear -shallow lakes with p h y s i c a l b a r r i e r s on the o u t l e t s , and Tacheeda - a deep lake without p h y s i c a l b a r r i e r s ) * In the Nechako drainage both species occur i n a l l o p a t r y * Probably only £ * macrocheilus occurs i n a l l o p a t r y i n the Skeena system* There i s no apparent reason why some i n l e t s of lakes i n which both species are common support only C . commersonii, while both species occur i n other i n l e t s ( F i g . 2)* In Norman and Er ickson creeks C_. macrocheilus i s very rare , despite large numbers of £ . commersonii. However, both species are common i n Sucker, Stearns, Richmond, and Decker creeks, which are s i m i l a r or smaller i n s ize (Table III) and s i m i l a r i n other features to Norman and E r i c k s o n . 28 G i l l n e t t i n g i n C l u c u l z Lake (1962 and 1963) f a i l e d to show any d i f f e r e n c e i n depth d i s t r i b u t i o n or occupancy of d i f f e r e n t substrates between the two species.. In a l l lakes seined no marked d i f f e r e n c e was found i n r e l a t i v e numbers between times at the same l o c a l i t y . Despite the apparent lack of habitat d i f f e r e n c e i n non-spawning suckers there was a marked d i f f e r e n c e i n r e l a t i v e numbers of young seined between l a k e s . This d i f f e r e n c e was consistent between years (1962 and 1964)* For example, p_» commersonii was dominant i n Rose and Tudyah lakes while Co macrocheilus was dominant i n Fraser Lakeo The only g e n e r a l i z a t i o n of the d i f f e r e n c e s i n r e l a t i v e numbers that could be made was that i n the shallowest lakes Co commersonii occurred i n greater numbers than Co macrocheiluso An i n s i g h t in to the invasion routes followed by the two suckers and time of overlap has been gained from a study of t h e i r present d i s t r i b u t i o n and that of other f i s h . T h i s was supplemented by a knowledge of g l a c i a l geology (Holland, 1964, p e r s . comm. D r s . WoH. Mathews and G . E . Rouse). C_. commersonii probably had g l a c i a l r e f u g i a i n both the M i s s i s s i p p i basin area and A t l a n t i c coast drainage, while <3. macrocheilus p e r s i s t e d during the Pleistocene i n the Columbia basin area . At the end of the Wisconsin g l a c i a t i o n C_. commersonii probably extended i t s range westward in to B r i t i s h Columbia through the Peace R i v e r . Access to Fraser drainage p o s s i b l y occurred through an outflow channel 10,000 or more years ago. Several other species of f i s h which had M i s s i s s i p p i r e f u g i a occur i n the Peace River drainage, but those that are not i n Crooked River drainage are also not i n Fraser drainageo Access to Skeena drainage from the Fraser would have been p o s s i b l e through swampy connections at Rose L a k e and p o s s i b l y at the old Stuart-Babine Lake portage routee The common occurrence of C . commersonii i n Nechako drainage at the head-waters of the Fraser suggests that e c o l o g i c a l b a r r i e r s , not recency of i n v a s i o n , account f o r i t s absence from the Thompson and lower Fraser drainage. The nature of the b a r r i e r i s unknown and i t seems paradoxical that such a b a r r i e r e x i s t s when the wide tolerance of C . commersonii i s considered. Several other species have a s i m i l a r anomalous d i s t r i b u t i o n , f o r which no explanation at present i s without c r i t i c i s m . C . macrocheilus. along with several other species , probably had access to Fraser drainage from i t s Columbia refugium through the low Shuswap-Okanagan d i v i d e or the outflow channel between the Nicola and Similkameen v a l l e y s . I t cannot be d e f i n i t e l y es tabl ished when C_. macrocheilus occupied the upper F r a s e r . The most p l a u s i b l e hypothesis i s that i t occupied the Nechako bas in , along with C . commersonii. several thousand years ago. I t seems u n l i k e l y that £ . macrocheilus could have been i n the Nechako area some 10,000 or more years ago, when drainage was to the north , since g l a c i a l dams blocked the middle Fraser River p r i o r to that date . Several species of f i s h which had a Columbia r e f u g i a , i n c l u d i n g C . macrocheilus. occur i n McLeese Lake ( 5 2 ° 2 4 * , 1 2 2 ° 2 0 t ) which has a high f a l l s on the o u t l e t . This out le t i s upstream from the la te g l a c i a l b l o c k . The probable absence of C . macro-c h e i l u s i n the Fraser during ice re t reat suggests that access to McLeese Lake was probably gained by headwater capture from nearby Tyee Lake, which lacks high f a l l s on i t s o u t l e t . Access to Peace drainage may have been through low areas, s i tuated between Fraser and Parsnip drainage, east and south of Summit Lake (head of Crooked R i v e r ) . F a i l u r e to colonize the lower Peace River by <3. macrocheilus and several other species has probably been due to e c o l o g i c a l f a c t o r s and i s not evidence of a recent i n v a s i o n . Access to Skeena drainage, as with C_. commersonii. was probably through Rose Lake. That t h i s or s i m i l a r routes were fol lowed by other species may be i n f e r r e d from the many species ( i n c l u d i n g a l l species that ascend i n l e t s i n the spring) shared between the Parsnip , Nechako, and Skeena r i v e r s (see Lindsey, 1956). Access to the Nass River by C_,, macrocheilus was probably through the Kitsumkallum v a l l e y . Lack of adequate information on the r e l a t i v e times of drainage from p o s t - g l a c i a l lakes and c l i m a t i c condit ions does not permit sound conclusions regarding time of overlap* I t would, however, be d i f f i c u l t to e x p l a i n the d i s t r i b u t i o n of the two species i n the general area of sympatry i f C_. macrocheilus and C_. commersonii d i d not have access to the Nechako basin at l e a s t several hundred years ago. Lakes probably p e r s i s t e d i n the Peace area during the most recent g l a c i a t i o n , commencing some 25,000 years ago (pers . comm. W.H. Mathews). Both species may have had access to the area, but such a hypothesis requires more i n f o r m a t i o n . I t i s apparent from the d i s t r i b u t i o n of these two suckers that the area of sympatry i s a r e s u l t of na tura l d i s -p e r s i o n , not human i n t e r v e n t i o n , and, p a r t i c u l a r l y i n the Nechako area, has probably exis ted at l e a s t f o r several hundred years . 3 1 IDENTIFICATION AND MORPHOLOGICAL ANALYSIS OF HYBRIDS The i d e n t i f i c a t i o n of a specimen as a n a t u r a l hybrid i s based on c i r c u m s t a n t i a l evidence, u s u a l l y morphological i n t e r -mediacy between two spec ies . Crosses made by plant and animal breeders, i n c l u d i n g f i s h c u l t u r i s t s , i n the l a s t century showed that hybrids were general ly intermediate to t h e i r parental s p e c i e s . Forms i n nature intermediate between two species were subsequently i n t e r p r e t e d as hybrids by some workers. Exper-imental studies showing that f i s h hybrids are u s u a l l y intermediate (Hubbs, 1955) have given support to or have been the evidence f o r these interpretat ions ! . The r e c o g n i t i o n and correct i d e n t i f i c a t i o n of hybrids i s v i t a l because of the var ied importance ascribed to the r o l e of h y b r i d i z a t i o n i n evolut ion and i t s s i g n i f i c a n c e to the species concepts The presence of na tura l hybrids cannot be shown using conventional methods i f s t e r i l e hybrids resemble one parental type through dominant i n h e r i t a n c e . A l s o , i n t e r p r e t a t i o n s other than that of hybrid o r i g i n ex is t f o r intermediate specimens. F i r s t l y , the form may represent a species (a) ances t ra l to two divergent species , (b) e s t a b l i s h e d by hybrid o r i g i n but now s e l f - m a i n t a i n e d , or (c) intermediate i n many respects between two species due to p a r a l l e l e v o l u t i o n . Hubbs ( 1 9 5 5 ) reviews the evidence that M o l l i e n e s i a formosa i s of (b) type o r i g i n with both parental species extant . The somewhat intermediacy of Catostomus columbianus with C . macrocheilus and C. catostomus or £ . platyrhynchus may be explained by (c ) . Secondly, such a form could be of t e r a t o l o g i c a l o r i g i n and be " a c c i d e n t l y " intermediate i n c e r t a i n characters . Abnormalit ies are r e l a t i v e l y common i n Catostomidae and i n d i v i d u a l s may have characters which l i e w e l l beyond the normal frequency d i s t r i b u t i o n of the species . For example, a mature C_. macrocheilus from C l u c u l z River had s ix dorsa l f i n rays and one anal f i n ray (normal minima are 12 and 7 r e s p e c t i v e l y ) ; both f i n s appeared free of i n j u r y . L a s t l y , i t could be a var iant of a known species with characters which are at the extreme range and overlap those of another s p e c i e s . Such forms may e x i s t i n species not possessing known characters which separate the species by a d i s t i n c t gap, as i n the adul ts of the present study, and may resemble h y b r i d s . White and Key (1957) found i n a grasshopper that what had been interpreted as i n t r o -gressive h y b r i d i z a t i o n on morphological evidence was r e a l l y an example of convergent e v o l u t i o n . . A l l morphological intermediates could be placed i n one of two species using c y t o l o g i c a l evidence with no i n d i c a t i o n of h y b r i d i z a t i o n . . M i l l e r (1955) described a. hybrid woodpecker and because of i t s resemblance to Dendroconis  b o r e a l i s postulated that the l a t t e r species arose through h y b r i d -i z a t i o n and i n t r o g r e s s i o n . I consider the evidence M i l l e r used i n the hybrid i n t e r p r e t a t i o n as weak. Brown and Wilson (1956) r i g h t l y c r i t i c i z e h i s i n t e r p r e t a t i o n s and those of s i m i l a r works. They point out that before a hybrid i n t e r p r e t a t i o n can be accepted the v a r i a t i o n over the range of the presumed parental species must be known and the a l t e r n a t i v e explanation of displacement must be considered. Rar i ty of d i s t i n c t i v e specimens as evidence to substantiate a hybrid i n t e r p r e t a t i o n must be used with c a u t i o n . Many species are rare i n c o l l e c t i o n s (but several previously described rare cyprinidj, catostcmid, and centrarchid species or aberrant i n d i v i d u a l s are now considered hybrids). Extensive c o l l e c t i n g i n the closed Cluculz Lake drainage produced only one Catostomus columbianus e Conversely, hybrids need not be rare* Hubbs and M i l l e r (1943) found hybrids to constitute about 870 of the parental population i n an entire basin area« Experimental crossing, although often providing conclusive evidence (e.g., Hubbs and Hubbs, 1932) cannot always be used to indicate what natural hybrids should look l i k e , or when i t can, does not necessarily v e r i f y the i d e n t i t y of a presumed natural hybrid. F i r s t l y , crossing two i n d i v i d u a l s need not y i e l d o f f s p r i n g s i m i l a r to those produced under natural con-d i t i o n s . Rough (MS, 196l ) found counts i n several meristic characters exceeding those of natural populations i n crosses at normal temperature within C. commersonii (resembling C. macrocheilus i n dorsal f i n count). This d i f f i c u l t y can be circumvented through the use of controls (known pure crosses) i n hybrid i d e n t i f i c a t i o n . Rough (MS, 1961) also notes v a r i a b i l i t y i s often greater i n a r t i f i c i a l crosses than i n natural ones. Secondly, the interpretation of the form representing a species intermediate between two species i s not disproven. This study employed several c r i t e r i a to reach conclusions on the occurrence and extent of hy b r i d i z a t i o n . The two species were examined both throughout a large part of t h e i r area of allop a t r y and i n a l l o p a t r i c populations within the area of sympatry, thereby e s t a b l i s h i n g the v a r i a t i o n of each character . From t h i s a method was devised which separated both species with a d i s t i n c t gap. Morphological ly intermediate specimens were found only i n those areas which contain both species and were considered to be hybrids* Reared o f f s p r i n g of experimental crosses provided information on the inher i tance of c e r t a i n char-acters i n h y b r i d s . The p o s s i b i l i t y of intermediate specimens representing a d i s t i n c t species was el iminated by f i n d i n g them only sympatric with both presumed parental spec ies . T h i s g l a c i a t e d area of sympatry does not form a "zoogeographical u n i t " . Evidence that p o t e n t i a l i s o l a t i n g mechanisms would permit h y b r i d i z a t i o n was obtained. Ao ANALYSIS OF IMMATURE SPECIMENS Eight characters were selected from 62 p o t e n t i a l characters which had been examined on 20 immature and 10 mature i n d i v i d u a l s seemingly to be of each species chosen from a sympatric pop-u l a t i o n (Summit Lake) . The s e l e c t i o n of characters was based on t h e i r u t i l i t y i n separating the two species and p r e c i s i o n by which they could be measured. The characters were examined i n many a l l o p a t r i c populations of both species and proved equally u s e f u l i n separating the spec ies . The only character separating the species with a d i s t i n c t gap was the r a t i o of the caudal peduncle depth to fork l e n g t h . I t was des i rable to avoid using fork length because of i n -accuracies when using preserved f i s h which often have a frayed caudal f i n . Dorsal to p e l v i c f i n distance was chosen to form the r a t i o , because i t had a low c o r r e l a t i o n with caudal peduncle 35 depth (0.52 and 0.21 i n the 40 specimens each of C . macro-c h e i l u s and Co commersonii r e s p e c t i v e l y of F i g . 11) and d i d i n i t s e l f contribute to separation of the specieso F i g - 9 shows that a d i s t i n c t gap e x i s t s between the two species i n specimens from about 5 to 20 cm fork length when using the body ra t ioo Only specimens 5 to 18 cm fork length were used f o r the a n a l y s i s of hybrids* C o l l e c t i o n s employed i n F i g . 9 (Table II) covered a wide range i n fork length within each species and tended to overlap one another with no suggestion of a c l i n e . A l l o p a t r i c populations w i t h i n the area of sympatry (Co macrocheilus from Bulkley Lake (22 specimens) and N u l k i Lake (48); C_. commersonii from Tacheeda Lake (42) and Hart Lake (36) f e l l w i t h i n the range of t h e i r respect ive species as i n F i g , 9* The body r a t i o was not u s e f u l i n separating small f i s h but experimental f i s h d i d not deviate from n a t u r a l f i s h of s i m i l a r s ize i n t h i s r a t i o . Dorsal f i n ray number was chosen to p l o t against the above r a t i o ( F i g , 10) i n the g r a p h i c a l a n a l y s i s to form the b a s i s of hybr id i d e n t i f i c a t i o n s because ( i ) i t was the only m e r i s t i c character which could be examined i n a l l f i s h (scales and g i l l -rakers are often not countable i n small preserved f i s h ) ( i i ) i t was the only m e r i s t i c character which could be examined i n a l l experimentally reared f i s h ( i i i ) i t i s u s e f u l i n separating the species ( c o r r e l a t i o n of O.33 and 0,38 with body r a t i o i n 40 specimens each of C_. macrocheilus and C. commersonii respect -i v e l y of F i g . 11) ( iv) the a v a i l a b l e evidence from the a r t i f i c i a l crosses showed that hybrids are intermediate i n z Z> a 3 < Q < U J Q . I < o 1. A*A ^  AAA A A A A A A A A .AA A.AA A*A AA A * A A A A A . A A JA A A A AA A A ^ . A A A A * \ " A A A A A A A A A \ AA AAAA A 1 C. MACROCHEILUS =IA1 ' A C COMMERSONII 0 o 0 o o 0 0 ^ 8 OOO O o O n O o o o°§&> o o o o o go ~o ~ o oo OQOO O o o o o o o O 00 Q o ° o o o o o O O QDOOOSD o °99 <£ o o o o o o o o o o o b o o o o ° o Oo ^ A A ooo *AAA  A A* A O°AVA o o — I 1 1 1 I I I I l i I i r , i ff 1 I 10 15 20 JJ 30 50 F O R K L E N G T H — C M F i g . 9. Rela t ion between r a t i o of d o r s a l - p e l v i c distance to caudal peduncle depth and fork length i n a l l o p a t r i c C_. commersonii (328 specimens, 22 populations) and C. macrocheilus (328 specimens, 20 p o p u l a t i o n s ) . VO o 37 u z Q LU Q_ 2 6 [ y 2) LU Q. I 10 11 DORSAL 12 ° cT^io L~1~ FREQUENCY 15 16 COMBINED 60 F i g . 10. D i s c r i m i n a t i o n between a l l o p a t r i c C . commersonii (200 specimens, 14 populations) and C . macrocheilus (200 specimens, 19 popixlations) on b a s i s of dorsa l ray number and r a t i o of distance between dor s a l and p e l v i c f i n s to caudal peduncle depth. d o r s a l ray number with most of the v a r i a t i o n l y i n g w i t h i n the parental number (Table I V ) . Specimens, 5«5 to 13*5 cm fork length , from populations both near to and f a r from the area of sympatry are i n F i g . 10 . Prel iminary a n a l y s i s revealed that some specimens i n sympatric lakes had a body r a t i o which f e l l w i t h i n the gap of a l l o p a t r i c specimens. Since there was no b a s i s f o r knowing whether hybrids overlap the parenta l species i n t h i s body r a t i o another independent a n a l y s i s was made. A character complex i n v o l v i n g f i v e characters was found s u i t a b l e . Of the f i v e characters , l a t e r a l l i n e scales could be counted i n 19 TABLE IV. Inheritance of dorsal ray numberc Species, number of rays ? and sex of parent given under cross. Cs Q.0 commersonii, Ms C. macrocheilus. M; probable hybrid DORSAL FIN RAYS Cross 10 11 12 13 14 15 Mean C12J x Ml 5? 0 0 2 9 2 2 13.2 C l l / x M14? 0 1 12 24 11 2 13 .0 C l l ? x Ml 5 ^ 0 1 2 4 2 0 12 .7 CIO? x M14 cf 1 0 0 0 0 0 10 C11<T x C12? 0 4 5 0 0 0 11.5 C1U x H12? 0 3 24 1 0 0 11.9 i n d i v i d u a l s comprising three hybrid crosses. Their number was intermediate between the species. The highest c o r r e l a t i o n c o e f f i c i e n t within 40 specimens of each species comparing pairs of characters of the seven characters was 0.55, obtained i n C. macrocheilus between diagonal and l a t e r a l l i n e scales. Only 6 of 42 c o r r e l a t i o n s had a r value ">0.36 and s i g n i f i c a n t l y d i f f e r e n t from zero at the .02 l e v e l . The index was based on the range of characters as they exist where the index would be applied by using i n d i v i d u a l s from f i v e sympatric lakes. Individuals were chosen which had a body r a t i o within and varying throughout the f u l l range of the pure species i n F i g . 9 . The i n c l u s i o n of hybrids would give conservative conclusions, that i s , i d e n t i f y fewer hybrids than e x i s t . The combined range of measurements f o r each character f o r equal numbers ( t o t a l of from 80 to 140 f o r each character) of both species was divided into twenty parts with equal numbers of i n d i v i d u a l s i n each twentieth. A score of 0 to 10 was given to each count according to which twentieth i t occupied. The low and high counts correspond to C_. commersonii and C. macro-cheilus respectively. The index f o r each specimen was the average of the f i v e characters (three f o r Burns Lake). The index produced complete separation of the two species i n a l l o p a t r i c populations (Fig. 11) whereas each component character overlaps between species. A l l immature specimens i n the area of sympatry were i d e n t i f i e d using a combination of F i g . 10 and 11 (e.g., F i g . 12 to 15)« Some specimens had a body r a t i o s l i g h t l y higher or lower than the species gap, but had a character index tending i n the opposite d i r e c t i o n . Such specimens are considered hybrids with the intermediates. Evidence from areas not shown was of a similar nature. Specimens i n the character index include, where possible, a l l specimens with a body r a t i o l y i n g i n the gap between the parental species as established i n F i g . 9° Specimens above and below the area of intermediacy were examined u n t i l only the parental species were l e f t . A sample of each species was also included i n the f i g u r e s . Results from a l l areas of sympatry are summarized i n F i g , 16. The percentage of hybrids from these samples of immature suckers varied from 17% i n a sample of 31 from Burns Lake (Fi g . 12) and 13% i n a sample of 69 i n Cluculz River (Fig. 13) to 2.5% i n a sample of 77 from Summit Lake (Fig. IL), Of the t o t a l sample of 499 suckers from areas where hybrids were found 7o2% were hybrids. These hybrids constitute 13.2% and 18.8$ of the specimens, respectively, of £. commersonii and C, macro-che i l u s . Both species were caught i n only three areas without 40 _1 U z 3 Q LU Q-< u u LU a < cr C. MACROCHFII US • LOWER FRASER R.,BC. • PEND-D'OREILL R, B.C. A SCHKAM L, B.C. • SNAKE R. WASH. A a A. Mo ° \ o o v ^ o V O O V v o I • _L_ C.COMMFRSONII 0 SWAN L.. B.C. ? WHITE MUD CR.,ALTA A CARIBOU R., N. S. a NANTICOKE, ONT. 4 5 CHARACTER 6 INDEX 8 F i g . 11. Discrimination between al lopatr ic C. commersonii (40 specimens. 4 populations) and C. macrocheilus (40 specimens 4 populations). Character index calculated from g i l l rakers , la tera l l ine scales, diagonal scales, peritoneal color, and side color. Explanation of character index in text. hybrids s Rose Lake with 117 C. commersonii and 1 C. macro-chei lus: Norman Creek with 81 C, commersonii and 1 C. qiaprp-.cheilus: and Davie Lake with 9 £• commersonii and 13 £• macrocheilus* With the inclusion of these lat ter populations hybrids constitute 5$ of a l l immature specimens. Hybrids were taken only in one lake without both species in the sample. Several hundred C. macrocheiluq but no C. commersonii were seined from Fraser Lake, The la t ter species e x i s t s i n t r i b -utaries and probably occur in Fraser Lake in low numbers. Bias may arise in percents i f the species and hybrids segregate, as Hubbs (1955) notes for sunfish hybrids. Sampling adults with g i l lne ts in Cluculz Lake, 1962-63, fa i led to show any marked 41 V z Q UJ ^3^ _1 < u y ui a. i O ^ Q 10 DORSAL 11 RAYS 12 13 2 ZD 14 L 3 3 l b 3 - I I I I l — L . 4 J 1 ' 1 • CHARACTER INDEX FREQUENCY ^ n H n n ^ i L n i i i i / t . / ' F i g . 12. Character analysis used to i d e n t i f y immature C . commersonii (hollow histograms,'hollow c i r c l e s f o r selected i n d i v i d u a l s ) , C. macrocheilus ( s o l i d histograms, s o l i d t r i a n g l e s f o r selected individuals) and hybrids (hatched histograms, hollow triangles) i n Burns Lake. Character index calculated from g i l l r a k e r s , peritoneal color, and side co l o r . y u z Q UI CL < Q < u UI CL < CC „ 02 Q 11 D O R SAL 12 RAYS 13 2 a 2 10 _ L L FREQUENCY 0 2 CHARACTER INDEX F i g . 13. Character analysis used to i d e n t i f y immature C . commersonii. C. macrocheilus. and hybrids (explanation of symbols i n F i g . 12) i n Cluculz River. Character index calculated from g i l l r a k e r s , l a t e r a l l i n e scales, diagonal scales, peritoneal color, and side color. u z ZD LU J O2-11 DORSAL RAYS 12 ] 0 13 10 FREQUENCY CHARACTER INDEX F i g . 14. Character a n a l y s i s used to i d e n t i f y immature C . _commersonii. C . macrocheilus. and hybrids (explanation of symbols i n F i g , 12) i n Summit Lake. Character index same as i n F i g . 13 , _i u z => LU 3 a. < a < \ y LU CL O • 11 DORSAL 12 2 RAYS 13 1 4 15 7 0 6 0 2 FREQUENCY CHARACTER INDEX F i g . 15 . Character a n a l y s i s used to i d e n t i f y immature C . commersonii. C, macrocheilus. and hybrids (explanation of symbols i n F i g . 12) i n McLeod Lake. Character index same as i n F i g . 13 . 43 C . C O M M E R S O N I I - • HYBRIDS-^) C MACROCHEILUS BURNS L. FRASER L. SUCKER CR. NORMAN CR. CLUCULZ R. CHIEF L. SUMMIT L. KERRY L. M c LEOD L. TUDYAH L. SYMPATRIC POPULATIONS COMBINED _ ALLOP. POP. WITHIN AREA OF SYMPATRY ALLOP POP OUTSIDE AREA OF SYMPATRY I I I L . _ l I I I • 1 t '12 I HO °t 112 L -o 3 L "12 • 6-Jo oL ]12 6" HO of-1 J12 z 111 a.r - I-I—i gr s r - 0 To -112 L U i Q_6r "of-i — n JZ_X T2~ 2 3 DORSAL- PELVIC/CAUDAL PEDUNCLE a J I I ' 1 L_ 1 CHARACTER INDEX F i g . 16. Summary o f d o r s a l - p e l v i c d i s t a n c e t o c a u d a l peduncle r a t i o and c h a r a c t e r i n d i c e s used t o i d e n t i f y immature h y b r i d s . Specimens used i n the body r a t i o r e p r e s e n t random c o l l e c t i o n s . difference between the species i n lake d i s t r i b u t i o n . No obvious difference was noted i n lakes and Cluculz River where several seine hauls were made at d i f f e r e n t times and areas. Discrepancy between actual and expected r e s u l t s occurred i n Sucker Creek. Poisoning revealed 27 immature C, commersonii and 1 £. macro-^ h e i l u s , an opposite r e l a t i o n to that found i n t h e i r parents (1962 year class - F i g . 22). Results from poisoning earler i n the season here and i n Norman Creek suggest that immature C. commersonii ascend the i n l e t s . The p o s s i b i l i t y of segregation influencing the other r e s u l t s cannot be excluded. Each character of the index was intermediate i n the hybrids (Fig. 17 and 18) with considerable spread into the parental species. The indices employed f o r i d e n t i f i c a t i o n (column 1, Table V) were recalculated using data of F i g . 17 and 18 (column 2, Table V). Substantial differences were noted only f o r l a t e r a l l i n e scales. Using the recalculated index changed the index scale and occasionally the r e l a t i v e p o s i t i o n of i n d i v i d -uals, but did not a f f e c t conclusions on the i d e n t i f i c a t i o n of i n d i v i d u a l s . To further evaluate the mathematically crude graphical index, a discriminant function analysis (Williams, 1959) i n -volving f i v e d i f f e r e n t functions, each with d i f f e r i n g numbers of characters, was made on an IBM 7O4O computer. The following data were calculated: ( l ) c o r r e l a t i o n c o e f f i c i e n t s of characters within and between each species from a t o t a l of eight a l l o p a t r i c populations; (2) c o r r e l a t i o n c o e f f i c i e n t s of the f i v e discrim-inant functions between and within each species i n allopatry; C. MACROCHFII US MS HYBRIDS — ^ C. COM MERSONII — D ALLOPATRIC -16 Jo 8 Jo LZ 45 12 0 \2A Jo SYMPATRIC i i i i i i i i_ 60 LATERAL .\y^ I I I I I I I 1 L LINE SCALES 10 J0 -|5 JO 14 -10 V L n rh. -"0 I I— If) L L O 1 or U Z) -i40 JO . J i i i i i DIAGONAL15SC. F i g . 1?« D i s t r i b u t i o n of l a t e r a l l i n e scales and diagonal scales i n C_. macrocheilus, hybr ids , and C, commersonii. A l l o p a t r i c data (top) comprise the four a l l o p a t r i c populations of both species of F i g . 11. Sympatric data (bottom) comprise specimens whose i d e n t i t y was determined by body r a t i o and character index. Only lake systems where hybrids were found are i n c l u d e d . 46 C. MACROCHFILIIS — • H Y B R I D S - ^ CCOMMERSONIKZI ALLOPATRIC J " l i i i i ' • • ' ' • • ' I 20 30 GILLRAKERS 24 -"0 -l24 0 SYMPATRIC T or cr < ^ .Q Q J°° 30 5 J to z U J m flO 1 z JO 1175 Jj25 i i i i PERITONEAL COLOR _i i i 1SIDE 4 COLOR te1-DORSAL RAYS F i g 0 18o D i s t r i b u t i o n of g i l l r a k e r s , peritoneal color, side color, and dorsal rays i n C 0 macrocheilus., hybrids, and C, commersoniio See F i g c 17 f o r further explanation, ~ 4 7 TABLE V . Index values assigned to f i v e characters.. Side and p e r i t o n e a l c o l o r i n d i c e s combined. Column 1 denotes i n d i c e s employed i n a n a l y s i s ( F i g . 11 to 15 and 19)« Column 2 g ives r e c a l c u l a t i o n s of i n d i c e s from r e s u l t s of column 1 ( F i g . 17 and 1 8 ) . Dorsal rays are i n c l u d e d . Diagonal Scales L a t e r a l Line Scales No. 1 2 No. 1 2 No. 1 2 9 1.2 0.4 60 0.2 0.5 71 6.9 8.2 10 3.3 3.7 61 0.7 0.7 72 7.2 8.5 11 5.4 5.3 62 1.3 1.6 73 7.8 9.2 12 7*0 7.2 63 1.8 2.6 74 8.3 9.5 13 8.7 9.3 64 2.4 3.2 75 8.7 9.7 14 9c7 9.9 65 3.4 4.0 76 9.2 9.7 15 10 10 66 3.9 4.9 77 9.5 9.8 67 4 »4 5.4 78 9.7 9.8 68 4.9 6.2 79 9.9 9.9 69 5.8 6.9 80 9.9 9.9 70 6.7 7.8 81 10 10 G i l l r a k e r s Color Dorsal Rays No= 1 2 No. 1 2 No. 2 22 0.7 0.5 2 0 1.4 10 0.1 23 1.4 24 2.6 3 2.5 4.1 11 2.4 2.3 4 3.8 4.9 12 4.7 25 3.6 3.9 5 5 5.3 13 6.7 26 4 .3 54 6 6.2 6.5 14 9.0 27 5.2 6.6 7 7.5 9.3 15 9 . 9 28 6,5 7.8 8 10 10 16 10 29 7.7 9.2 30 9 . 0 9.6 31 9 .7 9.7 (3) evaluat ion of usefulness of each character i n discr iminant f u n c t i o n s ; (4) t h e o r e t i c a l and e m p i r i c a l l y der ived c a l c u l a t i o n s on u t i l i t y of separation of each character ; (5) d iscr iminant funct ions f o r each specimen i n eight a l l o p a t r i c populations and C l u c u l z , Summit, and McLeod l a k e s ; (6) average discr iminate scores f o r each a l l o p a t r i c p o p u l a t i o n ; and (7) d i s c r i m i n a t i o n between species f o r each a n a l y s i s . 4 S There was a complete agreement, except f o r one specimen, i n c l a s s i f i c a t i o n of specimens between the graphica l character index and treatment of the same characters i n the discr iminant funct ion a n a l y s i s . The one exception was c l a s s i f i e d as C . commersonii i n the graphs but as a h y b r i d i n the discr iminant a n a l y s i s . The h y b r i d i n t e r p r e t a t i o n was l a r g e l y due to one character and the o r i g i n a l i d e n t i f i c a t i o n was l e f t . The discr iminant a n a l y s i s provided bet ter separation of the species i n a l l o p a t r y than the index i n which characters were given equal weight. However, as i n the graphica l a n a l y s i s , the subject ive i n t e r p r e t a t i o n on some b o r d e r l i n e specimens i s present . D i f f e r e n t i n t e r p r e t a t i o n s would have been made i n a few cases when fewer or more characters were used but the r e l a t i v e numbers of hybrids to parental types would not be changed. The e a s i l y computed g r a p h i c a l a n a l y s i s was therefore considered s u f f i c i e n t l y accurate i n i d e n t i f y i n g i n d i v i d u a l h y b r i d s . The morphological d i s t i n c t i v e n e s s and intermediacy of c e r t a i n specimens, and t h e i r occurrence only i n areas occupied by the presumed parental species , l e f t no reasonable doubt as to t h e i r hybr id o r i g i n . B . ANALYSIS OF ADULT SPECIMENS The i d e n t i f i c a t i o n of adult h y b r i d s , i n contrast with immature, i s not complete and accurate . Separation of adults with a d i s t i n c t gap and an independent t e s t i n g of intermediates cannot be done using characters employed on immature specimens. Body propor t ion , side c o l o r , and p e r i t o n e a l c o l o r are of l i t t l e or no value i n species separat ion. There was r e l a t i v e l y l i t t l e d i f ference i n the mean discr iminant funct ion between populations when f i v e or more characters were employed, but when only three characters were considered there was much d i f f e r e n c e . A l l o p a t r i c C. macro- c h e i l u s i n Fraser River (BC59-601) were intermediate to .2» macrocheilus of Snake River (BC64-351) and t y p i c a l C . commersonii. No marked di f ference occurred i n sympatric populat ions . T h i s allowed a common score to be used f o r a l l popula t ions . Scores based on three m e r i s t i c characters applied to a l l o p a t r i c specimens, known sympatric immature, and unknown adult specimens, suggested the presence of many adult hybrids ( F i g . 1 9 ) . No attempt was made to include or leave out p a r t i c -u l a r specimens. The importance of t h i s i s apparent by the demonstration that basing scores on extremes of each species may indicate " h y b r i d s " as an a r t i f a c t of the method. Adults were accepted as presumed hybrids i n l a t e r sections only i f they had a m e r i s t i c combination which was more l i k e l y that of a h y b r i d than of the pure species (based on F i g . 19 plus g i l l r a k e r counts f o r preserved specimens). Specimens with high and low counts of two characters each were e s p e c i a l l y p i c k e d . The percent of these i n d i v i d u a l specimens, termed presumed h y b r i d s , of the sampled population var ied from 15$ i n Decker Creek and 9 to 6% i n P a l l i n g , Richmond, Stearns, and Sucker creeks to about 2 .5$ i n Burns, Norman, and Er ickson creeks and C l u c u l z R i v e r . 10-0 20 i/) z LU U UJ Q_ I/) O 0 C.MACRQCHEILUS — • C.COMMERSONII - • HYBRIDS — GROUPED-ALLOPATRIC MMATURE SYMPATRIC IMMATURE SYMPATRIC MATURE 50 6 CHARACTER INDEX ^ . P i g . 19» Comparison of unknown mature sympatric suckers with known immature a l l o p a t r i c (of F i g . 11) and sympatric suckers (of F i g . 16) to show the existence of mature h y b r i d s . Number of hybrids made proportionate to pure types . Sympatric specimens (bottom) are from spawning migrations i n P a l l i n g , Decker, Burns, Richmond, Stearns, C l u c u l z , and Norman streams. Character index based on dorsa l rays , diagonal scales , and l a t e r a l l i n e s c a l e s . 51 ISOLATING MECHANISMS Ac TEMPORAL ISOLATION The purpose of t h i s sect ion i s to determine the extent of any d i f f e r e n c e s i n time of spawning migration of the two species i n sympatry. Many congeneric species and even sympatric " races" are i s o l a t e d only or i n part by d i f f e r e n c e s i n time of breeding. „C. catostomus o f t e n , but not always, has completed spawning before C. commersonii and C. macrocheilus b e g i n . Berg (1934) and Mayr (1963) c i t e other examples of temporal i s o l a t i o n . Suckers occupy the streams studied only during t h e i r spawning migrat ion, except f o r a r e l a t i v e l y small number i n C l u c u l z River which remain behind i n summer. Temperature appears to be the most important f a c t o r i n i n i t i a t i n g the spawning m i g r a t i o n . T h i s i s suggested by the c o r r e l a t i o n of temperature with commencement of the sucker migration both between years w i t h i n a p a r t i c u l a r stream and between streams w i t h i n a p a r t i c u l a r year . Water temperatures i n mid-May were lower i n I964 than 1963 i n the i n l e t (Norman Creek) and out le t of Cluculz Lake. The spawning migration was delayed i n both streams i n I 9 6 4 . Geen (MS, 1958) noted an e a r l i e r spawning migration of •2 s commersonii i n C l u c u l z River i n 1956 and 1957 than during t h i s study when stream temperatures were lower. Migrat ions i n Corkscrew Creek are several weeks l a t e r than i n nearby warmer i n l e t s (1962 observations - Table I I I ; pers . comm. W. G i l l ) , Geen (MS, 1958) and Tremblay (1962) provide f u r t h e r evidence; Dence (1948) a d d i t i o n a l l y notes that temperature governs spawning a c t i v i t y wi thin a p a r t i c u l a r migrat ion i n eastern dwarf C, commersonii. 52 lo C l u c u l z River Results i n g i l l n e t t i n g from Areas 1 to 8 showed that C_. commersonii and C . macrocheilus begin t h e i r spawning migration at about the same time ( F i g . 20). In 1964 the r i v e r had been extensively examined f o r several days before the f i r s t suckers were observed below Area 1. Clear water condit ions p r e v a i l e d thereby permit t ing accurate observat ions . In 1963 g i l l n e t t i n g and shore observations indica ted that C . macrocheilus was present f o r a longer time than C. commersonii. Up to and shor t ly a f t e r May 28 the number of suckers was decreasing and the number present on June 8 and 10 suggested the presence of a second migration of C. macrocheilus ( F i g . 20) which had not yet spawned ( F i g . 2 1 ) . The most meaningful measure of temporal i s o l a t i o n i s not the t iming of spawning migrat ions , but the overlap i n time i n presence of f u l l y r ipe i n d i v i d u a l s . Females were used to i n d i c a t e the amount of temporal overlap between the two species because they were present f o r a shorter period of time than males and t h e i r state of maturity i s easier to assess . The presence of m i l t does not n e c e s s a r i l y indica te presence of spermatozoa. In both 1963 and 1964 females of both species became f u l l y r i p e at about the same time ( F i g . 2 1 ) . Females of both species capable of spawning were present synchronously f o r a period of at leas t 12 days. This represents v i r t u a l l y the ent i re period i n which there were f u l l y r i p e C_. commersonii. Males of both species had f r e e l y running m i l t and spawning c o l o r a t i o n before the females were f u l l y r i p e . In 1963 and 1964 13 14 16 17 18 19 20 21 22 23 24 26 27 28 31 3 -1 0 -MAY 1 9 6 3 . Wo BfflD C COMMERSONII O C.MACROCHFILUS M • r20 1 9 6 4 , mmf J!] S C M=2 MJ MJ BED ttH MS gjja MB Br" I •J__l B i JUNE 1 2 20 • 1)1 J 1_ m 1 H L I ffl_IH_J H L J • Mf~lH BS88n Iggfl JlTI 8I~I mmcn BD •=] L i i m 1=1 H Z I i n E JH !• BB I Wm L P t n H i i BP i p i I 11 .•I I J L _ l L -I L 8 53 AREA. L Dl F i g , » D i s t r i b u t i o n o f a d u l t c o r r e s p o n d t o F i g , 3, R a t i o o f c a l c u l a t e d f r o m g i l l n e t c a t c h e s A r e a 6 b a s e d o n c a t c h p e r u n i t i n t w o n e t s i n a b o u t 1.5 m i n u t e g i l l n e t c a t c h u s e d t o d e t e r m i n e d a y s * C a t c h i n a l l c a s e s e q u a l 3 4 5 6 R I V E R A R E A s u c k e r s i n C l u c u l z R i v e r . A r e a s t w o s p e c i e s w i t h i n e a c h a r e a D i f f e r e n c e s b e t w e e n d a y s i n e f f o r t ( s c a l e c o r r e c t e d t o c a t c h s ) V i s u a l o b s e r v a t i o n s a n d v a r i a t i o n b e t w e e n A r e a s w i t h i n o r e x c e e d s t h a t g i v e n i n f i g u r e . MAY JUNE F i g c 21 . Degree of female maturity and water temperature i n Cluculz River f o r I963 and 1964.. Mid-day temperatures recorded between 1300 and 1500 hrs. See Materials and Methods f o r explanation of degrees of maturity. there was evidence that f u l l y r i p e C . commersonii females outnumbered s i m i l a r C . macrocheilus females ( F i g . 21) at the beginning of t h e i r spawning migrat ion , while an opposite r e l a t i o n held at the end. F u l l y r ipe males of both species were common throughout the p e r i o d . There was no evidence to suggest that d i e l d i f f e r e n c e s exist i n spawning time, but t h i s was not c r i t i c a l l y i n v e s t -i g a t e d . The r e s t r i c t i o n of c l o s e l y re la ted species of f i s h to spawning at d i f f e r e n t times of the day i s not known. Although suckers may spawn mainly at night much spawning a c t i v i t y was observed i n dayl ight i n the present study (Clucul River f o r both species under cloudy and sunny condi t ions , McLeese and Tyee Lake f o r C . macrocheilus, Bear Lake f o r £ . coramersTonii). Reighard (1920) a lso observed spawning i n C. commersonii during d a y l i g h t . 2. I n l e t s Evidence from i n l e t s f u r t h e r suggests that there i s l i t t l temporal i s o l a t i o n between the two species . The duration of the spawning migrat ion was es tabl ished only f o r Norman Creek, i n which C. macrocheilus adults were very r a r e . F u l l y r ipe females of both species were present at the same time i n a l l creeks ( F i g . 22) i n which both species were found (adult or immature). It i s almost c e r t a i n that those creeks i n which only one species was found do not have runs at another time of the other spec ies . These creeks, Burns, Norman, and E r i c k s o n , have large migrations of C . commersonii and d r a i n into lakes where C, macrocheilus i s abundant. 56 M A Y 29, 1963 C H M J U N E 2,1963 C H M J U N E 2, 1964 C H DECKER CR. RICHMOND CR. J U N E 1. 1964 C V/////////////////A STEARNS CR. H M J U N E 2, 1963 C H M SUCKER CR. M A Y 12, 1962 C H R _ M A Y 2 9 , 1 9 6 2 C M J U N E 1Q1962 M V/////A I M A Y 26, 1964 C H M MAY 2 8 1964 C H M vzzz NUMBER 2 0 " 5b Fig, 22. Relative abundance of C. commersonii (C), presumed hybrids (H), and C. macrocheilus (M) in inlet spawning migrations where both species were common. Number of females indicated by bar, number of males indicated by line starting from 0. Stearns Creek had 1 hybrid male. Proportionate number of females in various degree of maturity indicated as in Fig. 21. 57 B. HABITAT ISOLATION Selec t ion of d i f f e r e n t areas f o r spawning often acts as a mechanism f o r reproductive segregation ( C . L . Hubbs, 1961). The purpose of t h i s sec t ion i s to examine areas of occurrence of suckers i n Cluculz River and c e r t a i n i n l e t s to determine i f there was any s p a t i a l i s o l a t i o n between the two spec ies . 1. Cluculz River Marked d i f f e r e n c e s i n area of occurrence were apparent from g i l l n e t catches of the spawning migration ( F i g , 2 0 ) , Data from May 13 t c 28, '1963 and May 13 to June 3 , 1964 were analyzed (Model I , a n a l y s i s of v a r i a n c e ) . During t h i s time both species were about equally common i n the r i v e r as a whole. However, s i g n i f i c a n t d i f f e r e n c e s occurred i n areas occupied, both i n 1963 (F6, 36 = 4 . 1 5 , p < 0 . 0 0 5 ) and I964 ( F 7 , 98 B 6 .12, p < 0 . 0 0 5 ) . In 1963 the greatest d i f f e r e n c e was a t t r i b u t e d to the predominance of C . commersonii i n Area 7 and C. macrocheilus i n Areas 3 and 6 . In 1964 the greatest d i f f e r e n c e was a t t r i b u t e d to the predominance of C . commersonii i n Area 7 and C . macro-c h e i l u s i n Areas 2 and 6 . Considerat ion of f u l l y r i p e females lessened the s i g n i f -icance of some d i f f e r e n c e s . In I963 the marked di f ference i n Area 3 had no i s o l a t i v e value, because equal members of r ipe females of both species were captured on the same day. In 1964 £ e commersonii was rarer than C . macrocheilus i n Area 2, but had a greater number of f u l l y r i p e females (16 compared to 5 r e s p e c t i v e l y ) . There was thus complete temporal overlap i n occurrence of f u l l y r i p e females. 58 The greatest consistent segregation i n f u l l y r i p e i n d i v i d -uals was i n Areas 6 and 7» Only two f u l l y r i p e C, commersonii compared to 1/+ f u l l y r i p e C . macrocheilus females were c o l l e c t e d i n the main channel of Area 6 i n both years . The C» commersonii females were caught before the C. macrocheilus. From May 25 to 28, 1964 s at times between 0830 to 1130 h r , 332 matings ( p a i r i n g of males with a female i n which one or more male passes through a ser ies of tremors) were observed. Of these, 51% occurred i n the main channel over sand bottom while 38 and 11% occurred over gravel adjacent to the channel to the southeast and northwest, r e s p e c t i v e l y . The majority of a l l matings were at depths from 60 to 82 cm. At l e a s t f i v e matings were observed which involved the smaller C. commersonii i n d i v i d u a l s i n adjacent Area 7» Segregation by sex was a lso present i n t h i s area as i n the rest of the r i v e r . Males preferred the swif ter of f -shore water while females occurred near shore. P r i o r to mating the females moved toward midstream. Observation and g i l l n e t t i n g i n 1963 and I964 showed only C . commersonii spawned i n Area 7* Spawning was over gravel at depths u s u a l l y l e s s than 30 cm. No large suckers resembling C.. macrocheilus were observed i n Area 7 while C_. commersonii spawned there (May 21 to 24, I 9 6 3 , and May 27 to 29, I 9 6 4 ) , nor were any f u l l y r ipe C» macrocheilus i n d i v i d u a l s taken there at any t ime. The l a t e r spawning i n 1964 than 1963 was probably due to colder temperatures i n 1964. There seems l i t t l e doubt that s u b s t a n t i a l spawning occurred i n these two adjacent areas with very l i t t l e mixing or i n t e r s p e c i f i c matings. 5 9 It i s possible in Areas other than 6 and 7 that while l i t t l e habitat or temporal i s o l a t i o n i s apparent i n the pooled data, an i n t e r a c t i o n of the two could produce e f f e c t i v e segregation. In l a t e May, 1963, there was a predominance of C. macrocheilus over fi n e gravel 150 cm deep i n the channel of Area 8. The large number of C_. commersonii females e a r l i e r were not f u l l y ripe and were probably migrating farther downstream. In 1964 the only f u l l y ripe i n d i v i d u a l s of both sexes i n Area 8" were Co macrocheilus. Segregation was probably equally marked as i n I963. A greater r e l a t i v e preponderance of C_. commersonii was observed near the observation tower i n Area 5, from at least May 23 to 27, 1964, than suggested i n F i g . 20. Groups of about 50 male and female £. commersonii were present at depths from 60 to 70 cm. Sampling showed many to be f u l l y r i p e . No other such i n t e r a c t i o n was noted. F i g . 20 and additional sampling (May 22, 1963, i n the fi n e gravel section 105 cm deep at the sta r t of Area 5, six C . macro-cheilus females, four spawned and two f u l l y r i p e ; f i v e C . macro-cheilus males f u l l y r i p e ; no C_. commersonii were caught) suggest that where segregation occurred C . commersonii spawned over coarse gravel i n r e l a t i v e l y shallow water while C . macrocheilus preferred to spawn over sand or fi n e gravel i n r e l a t i v e l y deep water. When C . macrocheilus occupied the r i v e r i n the absence of ripe C . commersonii (early June, 1963) i t showed the same pref-erence to areas as when with C . commersonii. 60 Presumed hybrids occurred throughout the spawning migration and i n a l l Areas except 7» They were taken with the parental species and i n small numbers on each occasion. F u l l y ripe i n d i v i d u a l s of both sexes were taken i n close proximity at the same time as f u l l y ripe i n d i v i d u a l s of the pure species* No e x t r i n s i c b a r r i e r appeared to exist which would prevent back» crossing. 2. I n l e t s There was no evidence of species segregation i n i n l e t s where CJ. commersonii and C. macrocheilus were common (Fig. 22). Subsampling over apparently uniform substrate (the uniformity of most i n l e t s r e l a t i v e to sucker size did not allow a l o g i c a l breakdown into discrete areas) showed no meaningful difference. The r e l a t i v e abundance of the various types i n F i g . 22 may be considered representative of any smaller section of the sampled area. Several creeks had only one species common but drained into lakes with both species. P a l l i n g Creek had 1 C, commer- s o n i i and 26* C. macrocheilus. Sampling i n Burns Creek produced 64 small Co commersonii but no C_. macrocheilus. Some 307 £• commersonii and 5 C. macrocheilus were collected i n Norman Creek. Sampling was done throughout the spawning run f o r 3 years. C. macrocheilus adults occurred o f f the mouth of t h i s i n l e t but evidently ascended i t r a r e l y (1962 data). Geen (MS, 1958) also noted C. commersonii i n i n l e t s of Cluculz Lake but did not f i n d C_. macrocheilus. Erickson Creek had 91 C_» commer-so n i i and 1 C« macrocheilus. 61 Burns creek i s much shallower than other i n l e t s . Because C» macrocheilus p o s s i b l y cannot become stunted to the degree of C . commersonii ( F i g . 2 3 ) , mechanical s e l e c t i v i t y to s ize may thus p r o h i b i t the entry of C_« macrocheilus . Creek s ize (Table III) does seem r e l a t e d to the s ize of migrants ( F i g . 2 3 ) . No explanation can be given f o r the disproport ionate number i n i n l e t s other than Burns. 3° General Considerations Although only C_. commersonii spawned i n a shallow gravel area of Cluculz River while f u l l y r i p e C. macrocheilus out-numbered C. commersonii i n deep channels with sand or f i n e g r a v e l , both species spawn i n d i v e r s i f i e d habi ta ts throughout t h e i r range. They spawn i n i n l e t s and out le ts with d i f f e r i n g p h y s i c a l condit ions and appear to overlap the spawning habitat of the other . C_„ commersonii apparently seldom or never spawns i n deep sand bottom areas, although i n eastern North America Raney (1943) has observed i t to spawn i n a r e l a t i v e l y deep quiet pool with g r a v e l . Spawning requirements of C_. commersonii are general ly considered to be r e l a t i v e l y shallow running water over a gravel bottom (Reighard, 1915* 1920; Geen, MS, 1958), but the species i s not r e s t r i c t e d to t h i s . Lake spawning was observed i n a l l o p a t r i c C_. commersonii i n Bear Lake May 26, 1962. There was some suggestion of t h i s species lake-spawning i n C l u c u l z Lake. F u l l y r i p e males and females were g i l l n e t t e d i n early June, 1963* 3 miles from the nearest sui table stream. There i s a lso evidence f o r lake spawning i n C, commersonii i n eastern 62 North America (references i n Geen, MS, 1958). C_. macrocheilus spawns i n deep sandy areas of Cluculz River and i n shallow coarse gravel i n l e t s . A l l o p a t r i c C. macrocheilus were observed to lake- spawn i n McLeese Lake over gravel from at least 0700 to 1030 hr successively from June 14 to 18, 1962. Water depth was 0.3 to 1.2 m (1 to 4 f t ) . F u l l y ripe and spawned males and females were g i l l n e t t e d from the s i t e . Lake spawning also occurred i n Tyee Lake on June 18, 1962 over gravel areas. A nearby creek was too low f o r suckers and was reported lower than i n previous years. In addition to the above, a l l o p a t r i c populations have been found spawning i n outlets (Geen, MS, 1958) and on lake margins and i n i n l e t s (Weisel, 1957)* Keating (1958) and Keating (pers. comm.) found egg deposition f o r C. macro-cheilus at the lower end of pools i n an Idaho stream at 1.2 to 1 .8 m (4 to 6 f t ) depths i n primarily sand with 5 to 10 cm (2 to 4 inch) rubble. In sympatry, reproductive segregation was not apparent i n the confined i n l e t s , but was i n the d i v e r s i f i e d Cluculz River. In general, C_, commersonii preferred shallow gravel areas while C. macrocheilus preferred deep sandy areas. Co ETH0LOGICAL ISOLATION Of the several mechanisms usually operative which prevent interbreeding of animal species, ethological i s o l a t i o n i s generally considered the singly most important (Mayr, 1963). Useful r e s u l t s were not obtained i n mate choice t e s t s conducted i n fenced areas of Cluculz River. The s e n s i t i v i t y of suckers to disturbances, as noted by Reighard (1920) and Stewart (1926), probably explains the f a i l u r e to obtain r e s u l t s on the r e l a t i v e strength of conspec i f i c and i n t e r s p e c i f i c m a t i n g s » Many studies invoke e t h o l o g i c a l i s o l a t i o n to be of major importance i n i s o l a t i o n but few studies a c t u a l l y demonstrate the mechanism. P i c c i o l o (1964) found v i s u a l s t i m u l i the most important of several poss ible methods f o r d i s c r i m i n a t i o n i n four species of anabantids. Hanson (MS, 1965) and Painter (MS, I962) provide evidence that Oncorhvnchus nerka tend to select mates near t h e i r own s i z e . The p o s s i b i l i t y of a basis f o r f a v o r i n g conspec i f i c matings based on c o l o r , morphological , and s ize d i f f e r e n c e s was therefore explored. 1. Color d i f f e r e n c e s Color d i f f e r e n c e s were i n i t i a l l y studied on f r e s h l y caught f i s h held under water. These observations were supplemented by observing undisturbed known f i s h (the c o l o r characters d i f f e r i n captured i n d i v i d u a l s ) . I n d i v i d u a l s used were mainly from C l u c u l z River but suckers from other streams i n the area of sympatry were i n c l u d e d . Catostomus macrocheilus Females - L a t e r a l and dorsal body of greenish yellow to golden color i n mature i n d i v i d u a l s not yet f u l l y r i p e ; f a i n t to d i s t i n c t black band extending v e n t r a l l y from the l a t e r a l l i n e f o r 4 to 5s scale rows, extending anter-i o r l y under the eye and around the snout and p o s t e r i o r l y to the caudal peduncle i n f u l l y r i p e females i n C l u c u l z R i v e r ; black band i n females observed to come from spawning a c t s ; narrow yel lowish s t r i p v e n t r a l to the black band; vent ra l surface w h i t i s h ; band 3 to 5 scale rows wide of an i r i d e s c e n t o l i v e green to a d i r t y yellow color of an ochre nature dorsal to the l a t e r a l l i n e ; dorsal surface greenish gray to dark; a n t e r i o r margin of p e c t o r a l and p e l v i c f i n s u s u a l l y dark. Males - Body color resembles females except the black and o l i v e green bands develop sooner and l a s t longer (therefore males with bands occur i n a greater percentage than s i m i l a r l y colored females) ; black band a deeper black (jet black) than i n females; a n t e r i o r margin of pec tora l and p e l v i c f i n s u s u a l l y dark, but o c c a s i o n a l l y with a d i s t i n c t white l e a d i n g edge. £L» commersonii Females - Uniform s t e e l gray or grayish hue to body extending about 5h scale rows below the l a t e r a l l i n e ; no d i s t i n c t black, y e l l o w i s h , or o l i v e green bands present (yellow-i s h white s t r i p reported i n t h e i r eastern range by Reighard, 1920 ) ; a n t e r i o r margin of pec tora l and p e l v i c f i n s u s u a l l y white . Males - Resemble C . commersonii females up to the time when m i l t can be expressed; brownish gray t inge some-times present; f u l l y r i p e males resemble C, macrocheilus males i n c o l o r ; no br ight reddish s t r i p e ( in place of the dark s t r ipe) was observed i n spawning i n d i v i d u a l s although i t has been noted f o r the species i n t h e i r eastern range ( e . g . , Reighard, 1920); a n t e r i o r margin of pec tora l and p e l v i c f i n s u s u a l l y white . 2. Morphological Dif ferences I n t e r s p e c i f i c d i f f e r e n c e s ex is t i n d o r s a l f i n length , head shape, body shape, and number of s c a l e s . Morphological sexual d i f f e r e n c e s a lso exis t but are s i m i l a r i n both species ( e . g . , males have tuberc les at spawning time and d i s t i n c t i v e l y shaped caudal, anal , p e l v i c , and dorsa l f i n s ) . 65 3 0 Size Differences Within each species , females are u s u a l l y longer than males such that i n conspec i f i c matings the expected p a i r i n g would be f o r males to mate with females of a l a r g e r s i z e . C, macrocheilus i s longer than C t commersonii i n sympatry but there i s much overlap ( F i g . 23). I t i s thus possible f o r i n t e r s p e c i f i c matings of both r e c i p r o c a l s to occur and s t i l l maintain the smaller male to l a r g e r female r e l a t i o n , although i t would be l e s s l i k e l y to occur than conspeci f ic matings. Reighard (1920) describes the p o s i t i o n of males and females i n the p a i r i n g act i n C.commersonii. I t i s not known how important the r e l a t i v e p o s i t i o n s are to successful spawning. The body contacts as described by Reighard (1920) could not l i k e l y occur i f males were l a r g e r than the females or much smal ler . D. HYBRID EMBRYO MORTALITY Congeneric species of f i s h can u s u a l l y be crossed success-f u l l y although marked d i f f e r e n c e s i n mor ta l i ty between r e c i p r o c a l s are known (Hubbs and Drewry, 1959). The hypothesis that C_. commersonii and C . macrocheilus are not s u f f i c i e n t l y d i s s i m i l a r i n t h e i r genetic c o n s t i t u t i o n to r e s t r i c t the production of f i r s t generation hybrids was t e s t e d . There was assumed to be no d i f f e r e n t i a l m o r t a l i t y rate due to s t a r t i n g day of the crosses . Comparable l o t s d i d not suggest otherwise. Egg m o r t a l i t y genera l ly occurred through-out the r e a r i n g period with no obvious d i f f e r e n c e i n the time of death between the four crosses . Pre-hatching m o r t a l i t y PALLING CR. MS | 6 DECKER CR. MS LZ^^M—Tl I 6 BURNS CR. C S , I 1 2 7 RICHMOND CR. Cc? I BBftiia ^  ^ 46 H e / I i ^ ^ H L 1 2 MS I 5 STEARNS CR CS ^ f 5 CORKSCREW CR. Mc? I 5 M$ I 5 ^ SUCKER CR. ^ CS | I 4 H 2 _ ^ I 5 NORMAN CR. Cc? I HH&HB ~I 4 9 C S I BPfll I 49 H e / I 5 CLUCULZ R. 4 Q C? I & I 4 9 H e ? i wntetm I 1 2 H $ I 4 Mc? I BHJBl ~~| 49 ERICKSON CR. c s i i i i imfauuip n i i i i i i 3 0 4 0 5 0 FORK LENGTH CM. F i g . 23-.- Fork length of C. commersonii (C), presumed hybrids (HJ, and C. macrocheilus TM) i n spawning m i g r a t i o n s . Numbers wi thin streams does not n e c e s s a r i l y r e f l e c t r e l a t i v e abundance. Sub-samples are random i n fork l e n g t h . Blackened bar denotes 4 standard er rors of the mean. Black bar plus white bar on e i t h e r side of the mean o u t l i n e s 1 standard d e v i a t i o n . H o r i z o n t a l l i n e represents range. Sample size shown at r i g h t . 67 rate ivas not s i g n i f i c a n t l y d i f f e r e n t between f l a s k s and baskets i n the 16 comparable l o t s ( t - ^ - 0.23, p>0,8). Flasks and baskets were thus combined i n ca l c u l a t i o n s . No s i g n i f i c a n t difference occurred between pre-hatching mortality rates of the four crosses. The hybrid cross with C . commersonii females, however, had the highest mean mortality rate both within fl a s k s and baskets. The highest t value of the four crosses was obtained comparing the two r e c i p r o c a l crosses and was not s i g n i f i c a n t (tio s 1»89» p^0.08). The var i a t i o n in hatching success (Tables V I and V I I ) within each cross seems large even though the l o t s were reared under apparently ident-i c a l conditions. The four C . commersonii controls started i n fl a s k s on May 19, varied from 18 to 38$ i n pre-hatching mortality. In addition to r e f l e c t i n g differences i n the v i a b i l i t y of zygotes from d i f f e r e n t parents t h i s v a r i a t i o n may r e f l e c t differences in stripping technique and condition of the parents. A summary of the s t a t i s t i c s employed i n making t te s t s f o r mortality are given i n Table V I I I with hatching frequency data i n Tables I X and X. Hatching time was not s i g n i f i c a n t l y d i f f e r e n t between f l a s k s and baskets i n the 16 comparable l o t s ( t ^ 5 1.31, p>0 . 2 ) . Flasks and baskets were thus combined i n ca l c u l a t i o n s . Analysis of variance of the mean hatching time showed l i t t l e difference (F3 23 - 3»07, p>0.05)» The hatching time of the hybrid cross with C. commersonii eggs was s i g n i f i c a n t l y shorter than i t s r e c i p r o c a l (11 Q - 2.6, p < 0.05) and the C . commersonii control ( t - i , s 2»7, p<0.02). A l l other combinations were not 68 TABLE VIo Hatching time and mor ta l i ty of the crosses i n f l a s k s (1 s Q." commersonii x C . commersonii; 2 = C_. commersonii? x.,C« macrocheilus rf ; 3 s C . commersonii S x C_0 macrocheilus ? J 4 = C , macrocheilus x C, macrocheTlus)"e Hatching time i n day degrees Centigrade. Each l o t contains 150 eggs. Cross 1 2 3 4 Number ' ~ ' ' ~ ""~*""™° ""*"""' hatched 113 116 93 123 110 136 104 103 106 121 122 110 Mean hatching time 195 182 188 169 174 178 170 159 154 199 178 207 Hatching time 16.8 20.2 16.1 16.6 13.5 21.4 10.2 12.5 11.0 8.7 13.5 17.3 s . d o p Q r*c ent 3 day 39 31 21 24 57 0 20 28 28 0 11 0 m o r t a l i t y Combined percent 54 46 51 38 68 9 44 51 49 18 28 26 m o r t a l i t y TABLE V I I . Hatching time and m o r t a l i t y of the crosses i n baskets . See Table VI f o r explanat ion . Cross Number „• „ -hatched 104 132 121 47 118 115 119 126 110 114 112 122 Mean hatching time 168 174 160 152 172 162 174 161 177 181 167 174 Hatching time 11.5 15.8 6.1 8.1 14.3 13.0 7.1 9.1 21.0 14.8 18.0 16.5 S wd e Percent 3 day 25 37 0 10 69 13 4 3 30 41 15 23 m o r t a l i t y Combined percent 48 44 19 72 76 34 24 18 49 55 36 38 m o r t a l i t y 69 TABLE V I I I . Summary of s t a t i s t i c s f o r comparing m o r t a l i t y rates of the crosses . Number of l o t s shown i n parenthesis a f t e r c r o s s . See Table VI f o r legend. Cross 1(9) 2(6) 3(6) 4(3) Pre-hatching m o r t a l i t y Mean (arcs in [%) Sum of Squares Corrected Mean % 27.8 323 21.8 35.5 541 33.7 27.1 36.7 20.8 29 .0 17*3 23.5 Three day post -hatching m o r t a l i t y Mean (arcsin f%] Sum of Squares Corrected Mean % 27.2 2248 20.9 31 .0 912 2 6 . 6 18.7 1101 10.3 17.3 469 8.9 Combined mor ta l i ty Mean (arcsin J%) Sum of Squares Corrected Mean % 39.9 1099 41.2 47 .8 469 54*9 33.8 487 31.0 35.3 29 33.4 s i g n i f i c a n t . The tendency f o r hybrid r e c i p r o c a l s to approach t h e i r maternal parents was also noted by Hubbs and Strawn (1957a:50) and Clark Hubbs (196la) f o r d a r t e r s . L i t t l e s i g n i f i c a n c e can be attached to the hybrid cross with C . commersonii eggs having both the shortest hatching time and a tendency to have the highest mor ta l i ty r a t e . There was no s i g n i f i c a n t c o r r e l a t i o n between the number of eggs to hatch and the mean hatching time e i t h e r w i t h i n crosses or with crosses combined. The diameter of u n f e r t i l i z e d non-swollen C_. commersonii eggs (x = 2.1mm i n C l a r k e ' s f l u i d ) was s i g n i f i c a n t l y smaller ( t ^ = 1 0 . 4 , p < 0 . 0 0 l ) than those of C . macrocheilus (x - 2.5 mm). This same r e l a t i o n held a f t e r f e r t i l i z a t i o n . Eggs from hybrids between the two species were intermediate i n s ize with the hybrid cross 70 TABLE IX* Daily hatching frequency of crosses in f l a s k s (1 s G o commersonii x C > commersonii: 2 s C . commersonii ? x C_o macrocheilus rf* ; 3 5 5 G . commersonii c? x C o macrocheilus ? ; 4 - C c macrocheilus x £. macrochsTlus")T Accumulated day degrees C given f o r class mark, as used in c a l c u l a t i o n s . Day Started from May 16 May 19 May 20 st a r t Cross Cross Cross Acc. 1 3 Day C Acc. Day C 1 1 1 1 2 2 2 Acc Day C 1 3 4 12 121,0 123.5 1 13 136,1 132.8 2 13 135.2 6 2 14 144»5 3 1 6 3 2 6 15 147.0 10 2 15 14^,0 1 156.3 31 5 8 29 20 14 15 159.4 34 7 2 16 159.3 6 1 168.7 8 5 45 31 54 47 56 I7I.5 15 48 3 17 171.5 11 1 180 • 8 16 19 41 22 23 26 20 I83.O 1 34 12 18 183.3 16 2 191.9 18 33 9 15 4 8 193.3 35 24 13 19 195*7 37 83 202.6 37 25 1 6 1 2 204.8 2 9 4 38 20 207.8 28 27 3 3 4 217.1 20 21 218.9 12 6 229.6 20 22 229.6 2 1 242.1 2 TABLE X. Daily hatching frequency of crosses i n baskets* See Table IX f o r explanation. Day Day Started from May 16 May 19 May 20 st a r t " ~ ~ '—"~~ """ Acc. Cross Acc. Cross Acc- Cros: Day 1 3 3 Day 1 2 Day 1 2 2 3 3 4 4 C C C 12 134.2 16 2 136,8 2 4 4 13 139.8 4 147.3 26 149.9 23 13 37 9 2 26 13 14 152.3 22 5 47 160.4 25 3.8 163.4 96 46 48 51 23 46 48 15 164.9 42 26 61 173.9 48 1 177.4 41 19 18 51 21 29 16 177.9 31 88 14 187.9 30 191.1 11 6 13 22 5 20 17 191.1 9 201.6 13 203.7 5 1 8 11 5 8 18 216.1 2 5 4 5 4 19 229.0 6 1 i n v o l v i n g C. commersonii eggs being smaller than i t s r e c i p r o c a l i n the four ages examined. There i s no evidence that t h i s d i f f e r e n c e produces any c o m p l i c a t i o n s . The tendency f o r the smaller egged r e c i p r o c a l t o have the highest m o r t a l i t y rate i s not n e c e s s a r i l y a causal r e l a t i o n since opposite f i n d i n g s are known from other f i s h {Hubbs and Drewry, 1959)« Although gametic i n c o m p a t a b i l i t y i s a p o t e n t i a l i s o l a t i n g mechanism i n aquatic animals where chance meeting of gametes i s p o s s i b l e , i t has r a r e l y been found i n f i s h . Clark Hubbs (I960) provided evidence that sperm of two species of Etheostoma are more capable of f e r t i l i z i n g c o n s p e c i f i c eggs than i n t e r -s p e c i f i c eggs a f t e r a. time lapse, thereby s e l e c t i n g against a c c i d e n t a l h y b r i d i z a t i o n . No such t e s t s were done i n t h i s study. C e r t a i n l y gametic i n c o m p a t a b i l i t y does not occur wit h -out a time l a p s e . Samples of eggs were taken from the pan used f o r f e r t i l i z a t i o n t o f i l l the f l a s k s and baskets without conscious e f f o r t t o f a v o r p a r t i c u l a r types. Of the 150 eggs f i n a l l y put i n each c o n t a i n e r , only a maximum of 12 per l o t and a t o t a l of 161 eggs f o r a l l l o t s were r e j e c t e d as showing signs of being abnormal. There was no obvious c o r r e l a t i o n with t h i s low number and. the type of cross or the pre-hatching m o r t a l i t y of each l o t . S e l e c t i o n against h y b r i d i z a t i o n could thus not be shown to be present cn the b a s i s of s e l e c t i v e f e r t i l i z a t i o n or embryo m o r t a l i t y . E. HYBRID INVIABILITY AND STERILITY The p o s s i b i l i t y t h a t h y b r i d s , once produced, are at a s e l e c t i v e disadvantage was explored. 72 1. Hybrid I n v i a b i l i t y (a) Post-hatching mortality. A measure of post-hatching mortality was obtained by noting the number of hatched young to die 3 days a f t e r mean hatching time i n each l o t . Mortality was not s i g n i f i c a n t l y d i f f e r e n t between f l a s k s and baskets i n the comparable l o t s ( t ] ^ = 0 . 3 , p > 0 . 7 ) nor was the mortality from f e r t i l i z a t i o n to 3 days a f t e r mean hatching ( t ] ^ = 0.2, p> 0 . 0£)o Flasks and baskets were thus combined i n cal c u l a t i o n s . Post-hatching mortality percents are based on unequal sample sizes caused by pre-hatching mortality. The error involved i n using these percents, however, does not e f f e c t the conclusion that the tendency f o r the hybrid cross with C. commersonii females to have the highest mortality rate was not s i g n i f i c a n t . The highest t value was obtained i n comparing the recip r o c a l s (t]_o = 1*5, p > 0 . 1 ) . Tests made on mortality from f e r t i l i z a t i o n to 3 days after mean hatching showed the hybrid cross with C. commersonii females had a s i g n i f i c a n t l y higher mortality than i t s r e c i p r o c a l (t ^ o ~ 2.48, p < 0 . 0 5 ) . Neither hybrid cross was s i g n i f i c a n t l y d i f f e r e n t from the two controls (conspecific crosses). The most meaningful f i n d i n g was that no s i g n i f i c a n t difference occurred between hybrids and the control crosses ( t 2 2 = 1*3, p > 0 . 2 ) . The tendency f o r hybrids with C, commersonii females to have a higher mortality (Table VIII) than the controls was balanced by the opposite tendency of i t s r e c i p r o c a l . There was no suggestion of selection against the F l hybrids i n the l o t s transferred to the Vancouver laboratory (Table XI). 73 TABLE XI. Survival of o f f s p r i n g of a r t i f i c i a l crosses i n laboratory. Species and sex of parent given under cross. Eggs i n the l a s t two crosses hatched a f t e r t r a n s f e r . C: C. commersonii. M: C. macrocheilus. H: probable hybrid Cross No. that No. a l i v e at Survival hatched transfer Days a f t e r transfer to laboratory 15 68 118 201 281 Ccf xM9 126 110 51 18 9 6 3 Cr/ xM? 122 108 102 52 41 20 6 C? xMo" 103 55 45 10 6 0 0 C? xMo* 115 88 45 1 1 1 1 tV xC? 116 80 55 9 2 1 1 Co* xH? 119 132 103 38 28 15 2 C<J xH? 90 108 38 9 2 0 0 Five out of 19 hybrids longer than 36.5 mm from one cross with C. macrocheilus females had a deformed mouth. The opening was reduced and terminal with the upper jaw compressed. The mouth had moved ve n t r a l l y i n other hybrids at t h i s s i z e . Deformed hybrids died. Since t h i s cross nevertheless had the highest survival rate, mouth deformity cannot be invoked as a fa c t o r of i n v i a b i l i t y . The deformity was not observed i n several hundred s i m i l a r sized suckers from Cluculz River. A r t i f i c i a l l y and natu r a l l y hatched offspring had similar habits. Laboratory hybrids as well as the pure cross remained on the bottom of t h e i r container f o r the f i r s t few weeks u n t i l the elongate yolk sac was absorbed. They then became primarily pelagic. Several months l a t e r and a f t e r t h e i r mouth had moved ve n t r a l l y , they usually fed on the bottom. On June 8 and 10, I963, i n Area 7 of Cluculz River, several hundred dead eggs,-eyed eggs, and hatched f r y with t h e i r yolk sac were c o l l e c t e d . They were under loose clean gravel 2.5 to 7»5 cm i n diameter 74 at a water depth of 8 to IL cm. In t h i s l o c a t i o n on May 22 and 24, C . commerspnii were observed spawning. In la te June and e a r l y July , 1962, young suckers with t h e i r yolk sac absorbed occurred i n schools at the surface near shore while most young i n l a te July were benthic . Ratio of young^to adult natural h y b r i d s . Any changes i n percent hybrids within a year c lass would provide a measure of i n v i a b i l i t y . Time and problems of aging and sampling d i d not allow changes between years i n hybr id proport ions i n a year c l a s s to be s t u d i e d . The same information could be obtained by not ing d i f f e r e n c e s i n percent hybrids between year classes i n any year, i f percent h y b r i d i z a t i o n was the same each year f o r a p a r t i c u l a r area . There i s , however, no reason to be l ieve the rate jis constant . Indeed, i f environmental f a c t o r s l a r g e l y inf luenced the amount of h y b r i d i z a t i o n a constant rate would not be expected. A crude measure of na tura l i n v i a b i l i t y from immature to the mature stage was obtained by grouping a l l samples of immature and a d u l t s . A l l samples included several year c l a s s e s . It was assumed that d i f f e r e n t rates of h y b r i d i z a t i o n between years would be averaged out using t h i s method. F i g . 19 suggests that adult hybrids are more common than young, The inference that hybrids between the immature and adult stage are at a s e l e c t i v e advantage cannot be accepted because the several assumptions needed to reach the conclusion are not l i k e l y t r u e . There i s no reason, however, to bel ieve there i s s e l e c t i o n against i n d i v i d u a l h y b r i d s . The percent of adults termed presumed hybrids through i n d i v i d u a l a n a l y s i s comprised 1$ of the t o t a l population where hybrids were founds 2. Hybrid S t e r i l i t y (a) Crosses* Two crosses which very l i k e l y involved hybrid females and C, commersonii males (characters i n Table II) showed no obvious d i f f e r e n c e between m o r t a l i t y of t h e i r o f f s p r i n g and those of other crosses (Table X I ) . I n d i v i d u a l s of the most successful cross were reared up to 39 mm fork length with one i n d i v i d u a l reared to 56 nun. No obvious morph-o l o g i c a l deformit ies were noted i n the young. (b) Gonads. Both sexes were found i n presumed adult hybrids (53 males and 21 females) . This unequal sex r a t i o i s commonly found i n c o l l e c t i o n s from spawning migrations of the parental species and does not suggest a dis turbed sex r a t i o . A l l stages of maturity ( r ipe , f u l l y r i p e , and spawned) occurred i n presumed h y b r i d s . M i l t and eggs could be expressed from hybrids as i n the pure species . The gonads of hybrids had the same external appearance and appeared as large as the pure types ( c o n t r o l s ) . Much v a r i a t i o n , however, e x i s t s i n a l l types . Ten ovaries of presumed hybrids were examined under low m a g n i f i c a t i o n . Recently spawned i n d i v i d u a l s had a few large ova (about 2.4 mm and orangish) while the remainder of the ovary had small ova (0.1 to 1.2 mm and w h i t i s h ) , which again i s s i m i l a r to the c o n t r o l s . Sections of tes tes from 21 presumed hybrids showed no noticeable d i f ference with the c o n t r o l s . Unspawned males with tubules f u l l of gametes and spawned i n d i v i d u a l s with few 76 or no gametes with col lapsed t u b u l e s o c c u r r e d . The p o s s i b i l i t y of the gametes being i n v i a b l e , however, cannot be discounted. The q u a l i t y of the sect ions was poor and microscopic d e f e c t s may have been present i n the sex cells» DISCUSSION A . EXTENT OF HYBRIDIZATION H y b r i d i z a t i o n between C. commersonii and C. macrocheilus occurs i n at least nine lakes , representing a wide d i v e r s i t y of environments throughout much of the area of sympatry and v i r t u a l l y every lake where a sample was obtained. In a l l l o c a l i t i e s the pure parental forms were dominant i n numbers * D i f f e r e n t numbers of immature hybrids captured i n the lakes , ranging from 2.5 to 17% of the t o t a l sucker number, may not r e f l e c t d i f f e r e n c e s i n rate of h y b r i d i z a t i o n but be a t t r i b -utable to d i f f e r e n t s e l e c t i v e pressures against young hybrids and sampling e r r o r . No consistent trend was noted throughout the area, except f o r a tendency f o r percents to be higher i n lakes of the Nechako than i n the Crooked b a s i n . It was not possible to e s t a b l i s h the presence of backcross i n d i v i d u a l s , but there i s no known reason why they should not occur . Specimens d i f f i c u l t to c l a s s i f y may be products of backcrossing, but a n a l y s i s of hybrid characters ( F i g . 16, 17, and 18) suggests that , i f present, they are very l imited? I f backcrossing d i d occur more f requently than i n i t i a l h y b r i d -i z a t i o n then border l ine or d i f f i c u l t specimens should be more numerous than they are . I t i s doubtful , however,' i f i n d i v i d u a l 77 backcrosses could be d i f f e r e n t i a t e d (even by methods of Anderson, 1953 and others) from var iants of the species unless such back-crosses were common and the various recombinants not selected against* The presence of backcrosses would not be indica ted even i f a high v a r i a b i l i t y existed i n the hybrids (Atz, 1962; Hubbs and Strawn, 1957b), e s p e c i a l l y i f any were produced by delayed f e r t i l i z a t i o n from stray sperm which causes increased v a r i a b i l i t y (Clark Hubbs, 1957)• The extent of h y b r i d i z a t i o n i n these two suckers does not suggest they are not f u l l species . Various studies ( G i l b e r t , 1961 and C L . Hubbs, I 9 6 I f o r f i s h ; B l a i r , 1941 and Cory and Manion, 1955 f o r amphibians; S i b l e y , 1954 and S i b l e y and West, 1958 f o r b i r d s ; Mayr, 1963 f o r other groups) d e s c r i b i n g two forms f a i l i n g to h y b r i d i z e i n some areas but having mass h y b r i d -ized i n other areas, with various t r a n s i t i o n a l cases often present, seem to deal with groups which bridge the gap between good species and c o n s p e c i f i c popula t ions . Many hybr idize only under environmental disturbances , of ten throughout t h e i r area of syrapatry, and probably do not represent various stages of genetic divergence. The presence of hybrids does not n e c e s s a r i l y i n d i c a t e that i s o l a t i n g mechanisms are not keeping the parental species segregated. Hybrid swarms associated with environmental disturbances no more suggest c o n s p e c i f i c i t y than the many a r t i f i c i a l crosses which have shown re la ted f i s h can r e a d i l y produce viable and f e r t i l e hybrids ( C L . Hubbs, 1961; Hubbs and Drewry, 1959) . Forms which fuse (intergrade) whenever they come i n t o secondary contact should be considered c o n s p e c i f i c . But , i f a l l evidence suggests that the forms are remaining d i s t i n c t i n at l eas t one l o c a l i t y , regardless of whether hybrids or hybrid swarms occur elsewhere, the forms, when d i s t i n g u i s h a b l e , should be recognized as d i s t i n c t species . I f there i s main-tenance or divergence of d i f f e r e n c e s i n the area of h y b r i d - , i z a t i o n , without immigration, the process of speciat ion may be considered complete. T h i s i s i n agreement with the b i o l o g -i c a l species concept given by Mayr (I963). C . commersonii and C_. macrocheilus probably represent an i r r e v e r s i b l e d i s c o n t i n u i t y . There i s evidence from many varied environments that they are g e n e t i c a l l y d i s t i n c t and t h e i r status as d i s t i n c t species , which has never been questioned, should remain. B. CAUSES OF HYBRIDIZATION 1. Environmental Factors The environmental f a c t o r s that Hubbs (1955, 1961) notes as having weakened i s o l a t i n g mechanisms and allowed h y b r i d i z -a t i o n i n freshwater f i s h e s , i n c l u d i n g the f i r s t sucker hybrids described (Hubbs, Hubbs, and Johnson, 1943), do not appear to have caused h y b r i d i z a t i o n between C_. commersonii and C. macro-c h e i l u s . I f the suckers encountered these c o n d i t i o n s , however, hybrids would probably occur i n greater numbers. (a) Disproportionate numbers. Stebbins (1959) notes that disproport ionate numbers of i n d i v i d u a l s between plant species have long been known to be condicive to h y b r i d i z a t i o n . In animals, h y b r i d i z a t i o n has often been a t t r i b u t e d to the f a i l u r e of an i n d i v i d u a l to f i n d a c o n s p e c i f i c mate and i t thereby mating with a more abundant species ( e . g . , Hubbs, 1951; Hubbs et a l . , 1943; Hubbs and M i l l e r , 1953; Hubbs and L a r i t s , 1961; New, 1962; Mecham, I960; S i b l e y , 1961). Brower's (1959) data can be s i m i l a r l y in terpre ted and i s preferable to h i s explan-a t ion that natural s e l e c t i o n has improved b a r r i e r s to h y b r i d -i z a t i o n when two species are i n near equal numbers but not when there i s an unequal number. It seems l i k e l y that reinforcement should proceed most r a p i d l y where one species i s r a r e . The above explanation i s made on the assumption that r e l a t i v e numbers of the two parental species c o l l e c t e d with the hybrids are p r o p o r t i o n a l to the year c lass of the parental species which gave r i s e to the h y b r i d s . Marked d i f f e r e n c e s i n r e l a t i v e numbers of sucker species between years are known (author 's data from A l b e r t a ) , but i t i s f e l t from consistency of r e s u l t s of a p a r t i c u l a r size group between years w i t h i n lakes and streams that young from Rose, Fraser , and Tudyah lakes and adults from streams general ly r e f l e c t the species composition of t h e i r parents . In apparent contrast to other works, i n l e t s (Norman and Krickson) and lakes (Rose, Fraser , and Tudyah) which had marked d i f f e r e n c e s i n r e l a t i v e numbers of the two species had low numbers of h y b r i d s . I t i s u n l i k e l y disproport ionate numbers i n i n l e t s r e f l e c t d i f f e r e n c e s i n spawning time, thereby e x p l a i n i n g the low rate of h y b r i d i z a t i o n in Norman and Erickson creeks j because of the marry times these streams were checked. I n l e t s with a low dispropor t ion (Decker, Richmond, and Stearns) had the highest percent of h y b r i d s . C l u c u l z River , with near equal numbers, had a low percent of adult hybr ids , but a high of youngo The percent of adult hybr ids , obtained with rotenone i n streams, i s l e s s l i k e l y a t t r i b u t a b l e to sampling e r r o r than the sample of immature hybr ids , seined i n lakes , and i s thus more r e l i a b l e . In a d d i t i o n , although i d e n t i f i c a t i o n of adult hybrids i s l e s s r e l i a b l e than f o r immature, i t i s more comparable to numbers from areas of a l l o p a t r y , where i d e n t i f i c a t i o n was a lso based on a d u l t s . I f only conspec i f i c matings occur when a choice of mate e x i s t s , but h y b r i d i z a t i o n occurs when there i s no choice , the expected r e s u l t would be an inverted V - l i k e curve i f percent hybrids i s p lo t ted against species r a t i o . Factors such as number of encounters with the opposite species required before i n t e r s p e c i f i c matings occurred would inf luence the shape of the curve . At the s tar t there would be only one species and no h y b r i d i z a t i o n . As the number of a second species increased, i n i t i a l matings of the rare species would be with the common one, during which time the percent of hybrids would increase . T h i s stage i s obviously unstable since the rare species cannot maintain i t s e l f , as perhaps i n the case Hubbs (1951) described and i n C . macrocheilus i n Norman and Erickson creeks which may be s t rays , not c o n s t i t u t i n g a perpetuating p o p u l a t i o n . When s u f f i c i e n t numbers of the second species are reached, conspeci f ic matings would begin to occur and increase i n frequency u n t i l few or no i n t e r s p e c i f i c matings occurred. However, the d ispropor t ion 81 i n Decker, Richmond, and Stearns creeks, where h y b r i d i z a t i o n was highest , was lower than areas noted i n the l i t e r a t u r e where hybrids occur and appear to be caused by f a i l u r e to f i n d a mate. Another explanation of the apparent discrepancy between t h i s study and that of others i s suggested by the data from i n l e t s . An increase i n h y b r i d i z a t i o n with a decrease i n d i s -proport ion of the two species might be explained i f habitat segregation were important and e t h o l o g i c a l segregation weak. In small i n l e t s , a s i m i l a r i t y i n numbers of each species would r e s u l t i n maximum h y b r i d i z a t i o n , while i n a d i v e r s i f i e d environ-ment, such as C l u c u l z R i v e r , habitat segregation would keep h y b r i d i z a t i o n low. It i s f e l t , however, that i f e t h o l o g i c a l segregation were weak the rate of h y b r i d i z a t i o n would be higher than observed. H y b r i d i z a t i o n thus does not appear to be explained by a large d ispropor t ion i n numbers of spawners. The d i f f e r e n c e between C l u c u l z River on the one hand, and the i n l e t s with a small d i s p r o p o r t i o n and apparent high rate of h y b r i d i z a t i o n on the other, seems better explained by the d i f f e r e n c e s i n habitat d i v e r s i t y . In Cluculz River the suggestion of a d ispropor t ion i n f u l l y r ipe i n d i v i d u a l s of both sexes between each species at the beginning and end of the spawning migrat ion , however, i s considered conducive to h y b r i d i z a t i o n . (b) R e s t r i c t e d spawning area . R e s t r i c t e d spawning area which forces species to mate i n close proximity i s often associated with h y b r i d i z a t i o n ( e . g . , Bai ley and Lagler , 1938; Trautman, 1948). There i s no evidence of spawning area being r e s t r i c t e d or having been decreased i n the past where C_. commersonii and C , macrocheilus are sympatric . Density of spawners, however, i s high i n a l l streams. Crowding of i n d i v -i d u a l s suggests the p o s s i b i l i t y of a widely invoked cause of h y b r i d i z a t i o n , acc identa l f e r t i l i z a t i o n ( e . g . Hubbs, 1955; Hubbs and M i l l e r , 1953; M i l l e r , 1964) . In C l u c u l z River , where some segregation i s apparent, the two suckers are not spawning i n such close proximity as the c y p r i n i d s M i l l e r (I964) s tudied . Although laboratory experiments have demonstrated that sperm longevi ty w i l l permit a c c i d e n t a l f e r t i l i z a t i o n (Clark Hubbs, 1957, I 9 6 0 , 1 9 6 l b ) , f i e l d experiments t e s t i n g the hypothesis are l a c k i n g . Clark Hubbs (1957, I 9 6 0 , 1961b) and Hubbs and Drewry (1958) have found gametic incompatabi l i ty a f t e r a time lapse which would reduce the chances of acc identa l i n t e r s p e c i f i c f e r t i l i z a t i o n . Since delayed f e r t i l i z a t i o n may r e s u l t i n lower hatching rates and v a r i a b l e phenotypes, short temporal funct ion of sperm may be a s i g n i f i c a n t i s o l a t i n g mechanism. M i l l e r (1964) noted no di f ference i n f e r t i l i z a t i o n and hatching, nor any abnormal young, with delayed f e r t i l i z a t i o n of eggs of a c y p r i n i d . However, i t seems u n l i k e l y that the r e l a t i v e l y high percent of hybrids found i n the species of t h i s study would be due to a c c i d e n t a l f e r t i l i z a t i o n . ( ° ) Disturbances or in tergradat ion of the environment.. Many cases of h y b r i d i z a t i o n , both i n plants and animals, have been a t t r i b u t e d to disturbances of the environment (Anderson, 1953; Hubbs, 1955, 1961; Mecham, I960; S i b l e y , 1 9 6 l ) . One of S3 t h e m o s t p r o n o u n c e d a r e a s o f h a b i t a t s e g r e g a t i o n i n s u c k e r s o c c u r r e d i n t h e d i s t u r b e d s e c t i o n o f C l u c u l z R i v e r , A r e a s 6 a n d 7° M a n ' s a c t i v i t i e s h a v e p r o v i d e d a s h a l l o w g r a v e l b a n k w h e r e C . c o m m e r s o n i i s p a w n e d s e p a r a t e l y f r o m C . m a c r o c h e i l u s . I t i s t h e u n d i s t u r b e d a r e a s w h i c h g e n e r a l l y a r e l e a s t d i f f e r -e n t i a t e d a n d w h e r e h y b r i d i z a t i o n i s l i k e l i e s t t o o c c u r . M o s t o f t h e a r e a o f h y b r i d i z a t i o n h a s n o t b e e n d i s t u r b e d b y man i n a n y way w h i c h m i g h t d i s t u r b t h e i s o l a t i n g m e c h a n i s m s . I n l e t s w h e r e d i s t u r b a n c e s h a v e o c c u r r e d show n o o b v i o u s h i g h e r p e r c e n t o f h y b r i d s t h a n u n d i s t u r b e d i n l e t s . ( d ) S p e c i e s i n t r o d u c t i o n . H y b r i d i z a t i o n o f t e n a p p e a r s a t t r i b u t a b l e t o t h e i n t r o d u c t i o n o f one o r b o t h p a r e n t a l s p e c i e s i n t o a new e n v i r o n m e n t ( e . g . , H u b b s a n d H u b b s , 1947; H u b b s e t a l . , 1943)» S p e c i e s w h i c h h y b r i d i z e when i n t r o d u c e d i n t o t h e r a n g e o f a n o t h e r o f t e n o c c u r t o g e t h e r n a t u r a l l y w i t h o u t h y b r i d -i z i n g ( C L . H u b b s , 1 9 6 l ) . T h e c a u s e i n some c a s e s may b e due t o i n i t i a l d i s p r o p o r t i o n a t e n u m b e r s . T h e o v e r l a p o f G i l a a n d S j p h a . t e l e s . w h i c h p r o d u c e d l a r g e n u m b e r s o f h y b r i d s , was o r i g i n a l l y f e l t t o be n a t u r a l ( H u b b s a n d M i l l e r , 1943), b u t H u b b s (1955) b e l i e v e s G i l a was i n t r o d u c e d . E n v i r o n m e n t a l c h a n g e s p r o b a b l y a l s o c o n t r i b u t e d t o t h e h y b r i d i z a t i o n . O v e r l a p i n C a t o s t o m u s c o m m e r s o n i i a n d C . m a c r o c h e i l u s i s c o n s i d e r e d n a t u r a l . T h e r e i s n o a p p a r e n t r e a s o n why h y b r i d -i z a t i o n h a s n o t o c c u r r e d f o r t h e p r o b a b l e s e v e r a l h u n d r e d y e a r p e r i o d o f s y m p a t r y . 84 2. Incomplete I s o l a t i n g Mechanisms (a) Temporal i s o l a t i o n . Temporal i s o l a t i o n i s i n e f f e c t i v e i n C l u c u l z River and a l l i n l e t s examined. The period of overlap of f u l l y r ipe i n d i v i d u a l s appears to exceed the period when only c o n s p e c i f i c matings could occur. Apparently, both C_. commer-s o n i i and C. macrocheilus began t h e i r migration at about 6 to 9 C and spawning at about 10 to 12 C . C, commersonii i n eastern North America (Dence, 1948; Raney and Webster, 1942; Tremblay, 1962) and C, macrocheilus i n Idaho (Keating, 1958) appear to have s i m i l a r temperature responses. As noted above, s l i g h t time d i f f e r e n c e s i n the presence of f u l l y r ipe i n d i v i d u a l s of both sexes i n both species i n Cluculz River i s considered conducive to h y b r i d i z a t i o n . (b) Habitat i s o l a t i o n . No habitat i s o l a t i o n was demon-strated i n the i n l e t s . This was not s u r p r i s i n g since these streams have few d i s t i n c t i v e areas which could permit s i g n i f -icant segregation i n these large f i s h . Both species t o l e r a t e a wide v a r i e t y of condit ions f o r spawning and can spawn under i d e n t i c a l c o n d i t i o n s . C l u c u l z River had a d i v e r s i f i e d environment and species segregation i s probably explained by d i f f e r e n c e s i n habitat preference, rather than e x c l u s i o n . Segregation was stable i n time and afforded g e n e r a l i z a t i o n s ( i . e . , C_. commersonii spawned i n shallow gravel areas and £ . macrocheilus i n deep sandy areas ) . (c) E t h o l o g i c a l i s o l a t i o n . The incomplete nature of the other p o t e n t i a l i s o l a t i n g mechanisms and the low number of hybrids compared to parental types suggests that i n £ . commer-_spnii and C, macrocheilus. as i n most species (Mayr, 1963), e t h o l o g i c a l b a r r i e r s are of major importance. Evidence from mate preference t e s t s i s l a c k i n g , but there i s a basis f o r species recogni t ion based on s i z e , morphology, and c o l o r . With dayl ight spawning these mechanisms could be employed. There i s no evidence that any of the p h y s i c a l d i f f e r e n c e s are used f o r species r e c o g n i t i o n . P i c c i o l o (1964) has shown several morph-o l o g i c a l d i f f e r e n c e s i n anabantids to be unimportant (although v i s u a l d i f f e r e n c e s were important) . Males i n C l u c u l z River were often observed to move quickly downstream several meters or more and court females which had just moved o f f from shore to mid-stream. This suggested that auditory s t i m u l i may be involved which may tend to be species s p e c i f i c . Contact between mating males and females i s short with no elaborate courtship (Reighard, 1920; present observat ions) . Mating i s promiscuous with several males to each female. Animals with a short p a i r bond, as i n the present species , u s u a l l y have w e l l developed mate recogni t ion (S ibley , 1957). I t i s c l e a r , however, that there i s much opportunity f o r h y b r i d i z a t i o n . In both species , females genera l ly move out from the r i v e r bank (usually to near mid-stream i n C. macrocheilus) when ready to spawn and are pursued by several males. Even i f females tended to p a i r with c o n s p e c i f i c males the opportunity f o r a male of the opposite species to enter the f e r t i l i z a t i o n act with the other males does e x i s t . In support of t h i s , i n several matings i n Area 6 which involved mainly C. macrocheilus. 86 small males (probably C. commersonii) entered the spawning act with la rger males (probably C. macrocheilus) . Males have general ly been found to be l e s s s e l e c t i v e than females i n f i s h and other ver tebra tes . (d) Hybrid embryo m o r t a l i t y . F inding no evidence that i n t e r s p e c i f i c crosses were l e s s successful than conspec i f i c crosses was expected. Related species can u s u a l l y be r e a d i l y crossed ( C . L . Hubbs, I96I). Since there i s no reason to bel ieve i n t r o g r e s s i o n has occurred (see l a t e r ) , and the donors were t y p i c a l of t h e i r species , i t i s considered u n l i k e l y that i n t e r -s p e c i f i c crosses using a l l o p a t r i c populations would have been l e s s successful than those obtained by taking donors from an area of h y b r i d i z a t i o n . (e) Hybrid i n v i a b i l i t y and s t e r i l i t y . Many species produce f e r t i l e and v i a b l e hybrids without l o s i n g t h e i r genetic i d e n t i t y ( C . L , Hubbs, 1 9 6 1 ) . C . commersonii and C. macrocheilus a lso appear capable of producing large numbers of v i a b l e hybrids with no evidence of any e f f e c t i v e postmating i s o l a t i n g mechanism. Dif ferences i n v i a b i l i t y between hybrids and the parental species , however, could e x i s t and be b i o l o g i c a l l y s i g n i f i c a n t . S i b l e y (1961) f e e l s that hybrids between c l o s e l y r e l a t e d species may be selected against by t h e i r intermediate characters ( i ) being i l l adaptive ( i i ) reducing the chance f o r f i n d i n g a mate. The biology of the two suckers appears so s i m i l a r that no intermediate t r a i t can be construed as i l l - a d a p t e d . Presumed female hybrids can be backcrossed to at l eas t C. commersonii, There i s no evidence that presumed hybrid males are f e r t i l e , but no d i f f e r e n c e with controls could be detected by examining s l i d e preparations of gonads. Hubbs and Hubbs (1933), Hubbs and Drewry (1959), and Hubbs and L a r i t z (1961) have found s t e r i l e hybrids with abnormal meiotic segregation i n the t e s t e s . S imi lar disorders could have existed i n the sucker hybrids but been undetected. Presumed male hybrids did produce m i l t as r e a d i l y as the parental species . The sex r a t i o of hybrids was s i m i l a r to that of the parental species . Hubbs and M i l l e r (1953) a lso reported a normal sex r a t i o i n other sucker h y b r i d s . Some f i s h hybrids are known only from females (New, 1962) while others are mostly males (Hubbs and Hubbs, 1933)* (f) Interac t ion of i s o l a t i n g mechanisms. An i n t e r a c t i o n between habitat i s o l a t i o n and temporal i s o l a t i o n i n C l u c u l z River has been shown i n some cases to produce e f f e c t i v e segreg-a t i o n . The degree of habitat segregation would be expected to vary i n d i f f e r e n t areas . The apparent high h y b r i d i z a t i o n i n i n l e t s probably r e f l e c t s a reduced opportunity f o r habitat i s o l a t i o n . I n t e r s p e c i f i c encounters must be very frequent i n a l l . streams. An i n t e r a c t i o n of temporal, habi ta t , and postmating i s o l a t i n g mechanisms i s not considered s u f f i c i e n t to prevent swamping. Mate s e l e c t i o n would appear to be of major importance In each l o c a l i t y the percentage of F l * s , which probably con-s t i t u t e the majori ty of hybr ids , would be a crude measure of the e f f e c t i v e n e s s of i s o l a t i o n . The number of a r t i f i c i a l crosse made using suckers caught wi thin a distance of 25 m was due to the lack of an e f f e c t i v e i n t e r a c t i o n of i s o l a t i n g mechanisms, excluding e t h o l o g i c a l i s o l a t i o n . Co EFFECT OF HYBRIDIZATION H y b r i d i z a t i o n appears to be occurring under natural con-d i t i o n s * T h i s makes the study of i t s e f f e c t s more meaningful than i f i t had been a t t r i b u t a b l e to man's a c t i v i t i e s which may or may not have been simulations of past n a t u r a l occurrences. S ibley (1957) described the possible e f f e c t s when an e x t r i n s i c b a r r i e r i s broken and two p r e v i o u s l y i s o l a t e d pop-u l a t i o n s come i n t o sympatry. I f i s o l a t i n g mechanisms have not been f u l l y es tabl ished h y b r i d i z a t i o n w i l l r e s u l t . The e f f e c t s of h y b r i d i z a t i o n var ies depending on whether the hybrids are (i) at a s e l e c t i v e advantage ( r e s u l t i n g i n swamping of the parental species , or perhaps i n t r o g r e s s i o n and change of the parental species to new adaptive peaks i f only part of the hybrid gene complex i s at an advantage) ( i i ) at a s e l e c t i v e disadvantage ( r e s u l t i n g i n reinforcement and establishment of complete i s o l a t i n g mechanisms between the parental spec ies ) . In r e l a t i v e l y recent overlaps the d i r e c t i o n of s e l e c t i o n may be d i f f i c u l t to determine. 1. Se lec t ive Advantage of Hybrids Since h y b r i d i z a t i o n i s not a t t r i b u t a b l e to man's a c t i v i t i e s hybrids may have been produced since the s tar t of sympatry, at leas t several hundred years ago. I f hybr ids , presently con-s t i t u t i n g on the average of 7% of the sucker populat ion, were at a s e l e c t i v e advantage then f u s i o n of the parental species should have proceeded r e l a t i v e l y f a s t . C e r t a i n l y , because of 89 i t s s e l f - a c c e l e r a t i n g nature, i t would have gone to completion i n at l eas t a few l o c a l i t i e s . Instead, the parental species are dominant i n every l o c a l i t y . There was no evidence f o r i n t r o g r e s s i o n (regarded here as the incorporat ion of genes of one species i n t o another species through backcrossing and natural se lec t ion on the recombinants) i n any character examined. Sympatric and a l l o p a t r i c populations were s i m i l a r i n v a r i a b i l i t y and the mean of a l l characters f e l l w i t h i n the geographic v a r i a t i o n of a l l o p a t r i c populat ions . I t could be argued that £ . commersonii i n Burns Creek are products of i n t r o g r e s s i o n using i n t e r p r e t a t i o n s s i m i l a r to C . L . Hubbs ( 1 9 6 l ; 1 3 - 1 4 ) , M i l l e r (1955), and Stebbins (1959) . This species had a higher g i l l r a k e r count (25 to 28) than other sympatric populations (22 to 2 7 ) . I t seems more p l a u s i b l e that the high g i l l r a k e r number was selected f o r i n t h i s creek without i n t r o -g r e s s i o n . High scale counts f o r C_. commersonii. resembling j2 • macrocheilus. occur wel l w i t h i n the area of a l l o p a t r y and are obviously not a t t r i b u t a b l e to h y b r i d i z a t i o n . An apparent c loser resemblance i n spawning c o l o r a t i o n i n the zone of sympatry than a l l o p a t r y i s a lso a t t r i b u t e d to geographic v a r i a t i o n . The resemblance has af fec ted only one color character , a red band i n males at spawning. Color d i f f e r e n c e s which cannot be a t t r i b u t e d to i n t r o g r e s s i o n occur throughout the range of other species ( e . g . , Hybopsis plumbea). Brown and Wilson (1956) and White and Key (1957) have shown that morphological evidence must be used with caution and that i t may be u n r e l i a b l e i n showing i n t r o g r e s s i o n . 90 It i s concluded that swamping i s evident ly not occurr ing , and that therefore hybrids are selected agains t . 2. Se lec t ive Disadvantage Of Hybrids Selec t ion may occur against hybrids and be e f f e c t i v e i n preventing swamping but not be detectable from laboratory observat ions . The e f f e c t s of s e l e c t i o n against hybrids may sometimes be detected by examining the parental species f o r evidence of reinforcement of the i s o l a t i n g mechanisms. Rein-forcement occurs i f s e l e c t i o n acts against hybr ids , thereby promoting conspec i f i c matings, u n t i l the i s o l a t i n g mechanisms have been p e r f e c t e d . V a r i a b i l i t y i n the parental species which permits h y b r i d i z a t i o n must be selected a g a i n s t . The i n t e n s i t y of s e l e c t i o n determines the speed and extent of reinforcement* Sibley (1961) reviews the evidence i n Parus where i n the past 100 years h y b r i d i z a t i o n has become.reduced due to reinforcement. Hubbs and Strawn (1956) note l o c a l i t i e s where f e r t i l e Notropis hybrids were dominant, and h y b r i d i z a t i o n apparently induced by habitat disturbance, but these populations now consist p r i m a r i l y of the parental species . However, C»L» Hubbs (196l) reports mummified hybrids of several hundred years age from a population which presently has hybrids but where the parental species are s t i l l d i s t i n c t . Hybrids may also be at a s e l e c t i v e advantage i n some areas but at a disadvantage i n others (Mayr, 1942: 265-266) . Cha rac ters 3. f f e c t e d by s e l e c t i o n and associated p l e i o t r o p i c e f f e c t s w i l l be those which govern the meeting of d i f f e r e n t spec ies . Reinforcement has been suggested f o r a l l i s o l a t i n g mechanisms but the most convincing evidence e x i s t s f o r premating mechanisms. I t i s d i f f i c u l t to expla in reinforcement of post -mating mechanisms by the d i r e c t e f f e c t s of s e l e c t i o n . Indeed, i t i s d i f f i c u l t to separate the e f f e c t s of reinforcement from geographic v a r i a t i o n spuriously corre la ted with a l l o p a t r y and sympatry, This i s suggested from Mecham's (1961:45) review of hybr id i n v i a b i l i t y i n toads . I n v i a b i l i t y was leas t developed i n sympatry, probably due to random genetic divergence. Hubbs and Strawn (1957a) describe a s i m i l a r example i n d a r t e r s . Explanations of divergence i n sympatry by reinforcement, without information on v a r i a t i o n throughout a l l o p a t r y or considerat ion of competition, must be held with doubt. In Catostomus commersonii and C. macrocheilus no evidence was found of d i f f e r e n c e s i n spawning temperature between the zones of sympatry and a l l o p a t r y , nor between the species wi thin the area of sympatry. No major d i f f e r e n c e i n spawning habitat was ; found between the species w i t h i n the area of sympatry. Of the characters examined which were considered as a poss ible b a s i s f o r e t h o l o g i c a l i s o l a t i o n no displacement was noted. The i n a b i l i t y to demonstrate hybrid embryo m o r t a l i t y and hybrid s t e r i l i t y thus leaves no evidence of reinforcement i n the inves t iga ted i s o l a t i n g mechanisms. I t i s u n l i k e l y that r e i n -forcement has occurred i n any other mechanism. From the beginning of sympatry, s e l e c t i o n has not been severe enough to have prevented h y b r i d i z a t i o n i n any known l o c a l i t y . This i s not al together unexpected from the postulated cause of h y b r i d i z a t i o n . Males are capable of f e r t i l i z i n g the eggs of many females and i n d i v i d u a l s of both sexes u s u a l l y spawn i n successive years . A mis-mated male or female thus has much opportunity i n c o n t r i b u t i n g to i t s own species through con-s p e c i f i c mating. Se lec t ion against such an i n d i v i d u a l would be extremely low. This i s s i m i l a r to Mayr's ( 1 9 6 3 ; 1 2 9 ) acceptance that s e l e c t i o n pressures are not nearly so high i n favor of high f e r t i l i t y i n perennial p lants as i n s h o r t - l i v e d animals . The lack of evidence f o r reinforcement of i s o l a t i n g mech-anisms i n C. commersonii and C. macrocheilus suggests that the mechanisms present were developed i n a l l o p a t r y . As such, the present mechanisms would be i n c i d e n t a l by-products of divergence a r i s i n g through s e l e c t i v e pressures unrelated to reproductive i s o l a t i o n . T h i s i s general ly regarded to be the o r i g i n of i s o l a t i n g mechanisms by Mayr (1942, 1959* 1963), Mecham (196l), Moore ( 1 9 5 7 ) , and M u l l e r (1942). It i s poss ible that some of the mechanisms arose through reinforcement with other species . Dobzhansky (1940, 1951:207-211) suggests that reinforcement i s general ly necessary to complete specia t ion and f u l l y e s t a b l i s h i s o l a t i n g mechanisms. C . commersonii was probably sympatric with C_. catostomus (with which i t h y b r i d i z e s i n one area of i n t r o d u c t i o n , Hubbs et a l . , 1943) and several r e l a t e d species during the l a s t g l a c i a t i o n . C_. macrocheilus was sympatric with several species of Catostomus i n i t s Columbia refugium and h y b r i d i z e s with C. columbianus (Hubbs et a l . , 1943; author ' s work). From the apparent time during which h y b r i d i z a t i o n has occurred and evidence that swamping i s not occurr ing , i t i s concluded that there are s e l e c t i v e pressures preventing hybrids from c o n t r i b u t i n g to the gene pool of the parental species . Weak s e l e c t i o n against p a r t i c i p a n t s of h y b r i d i z a t i o n would account f o r the apparent absence of reinforcement of the i s o l a t i n g mechanisms at the present stage. In agreement with the contention of Mayr (1963) that i n vertebrates there i s l i t t l e evidence that h y b r i d i z a t i o n has contributed to s p e c i a t i o n , there i s no evidence here that h y b r i d i z a t i o n has had any e f f e c t i n specia t ion of the suckers. CONCLUSIONS Catostomus commersonii and C. macrocheilus have been i n secondary contact i n some areas f o r at least several hundred years . Presumed F l hybrids made up an average of 7% of the combined populations of the nine lakes where hybrids were found. H y b r i d i z a t i o n i s occurr ing i n undisturbed areas and could not be a t t r i b u t e d to the environmental fac tors f requently invoked as conducive to h y b r i d i z a t i o n i n f i s h . There was no evidence of backcrossing or i n t r o g r e s s i o n nor reinforcement of the i s o l a t i n g machanisms. An i n t e r a c t i o n of temporal, habitat and several inves t iga ted postmating i s o l a t i n g mechanisms i s not considered s u f f i c i e n t to explain the absence of swamping. E t h o l o g i c a l i s o l a t i o n i s i n f e r r e d to keep F l hybrids low while unknown fac tors prevent swamping by s e l e c t i o n against backcrosses-Accidenta l f e r t i l i z a t i o n may account f o r some hybrids but the main cause of h y b r i d i z a t i o n i s considered to be males of. one species entering the spawning act with males and a female of another species . Since mis-mated males can contribute to conspec i f i c matings at other times, s e l e c t i o n against such i n d i v i d u a l s would be low. This i s i n agreement with the con-tent ion that h y b r i d i z a t i o n has probably been occurring since the beginning of sympatry although there i s no evidence of reinforcement. E f f e c t i v e i s o l a t i n g mechanisms were es tabl ished i n a l l o p a t r y and a slow process of reinforcement i s probably o c c u r r i n g . LITERATURE CITED Anderson, E . 1953« Introgressive h y b r i d i z a t i o n , B i o l . Rev. 28(3)S280~307° A t z , J.W, 1962. E f f e c t s of h y b r i d i z a t i o n on pigmentation i n f i s h e s of the genus Xiphophorus. Zoologica 47(4)$153-181. B a i l e y , R . M . , and K . F . L a g l e r . 1938. An a n a l y s i s of h y b r i d i z -a t ion in a population of stunted sunfishes i n New York* Pap. M i c h , Acad. S c i . , Arts and Let ters 2 3 ( 1 9 3 7 ) : 5 7 7 - 6 0 6 . Berg, L . S . 1934= Vernal and hiemal races among anadromous f i s h e s . T r a n s l . W.E, R i c k e r . 1959» J« F i s h . Res. 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