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Demographic consequences of artificial selection at the LAP locus in voles Microtus townsendi LeDuc, Janice Irene 1974

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DEMOGRAPHIC CONSEQUENCES OF ARTIFICIAL SELECTION AT THE LAP LOCUS IN VOLES jHICBOTUS TORNSENDI) by JANICE IRENE leCDC B.Sc, , u n i v e r s i t y of A l b e r t a , 1971 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE CF MASTER OF SCIENCE i n the Eepartment of Zoology We accept t h i s t h e s i s as conforming to the r e g u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA AUGUST, 1974 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Co lumb ia , I ag ree that the 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 tudy . I f u r t h e r agree 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 purposes may be g r a n t e d by the 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 . It i s u n d e r s t o o d that 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 thout my w r i t t e n p e r m i s s i o n . Department o f _ / a The U n i v e r s i t y o f B r i t i s h Co lumbia Vancouver 8, Canada Date Jejrfi- I X /97V ABSTRACT A number of s t u d i e s on s m a l l mammals have shewn that changes i n the frequency of a l l e l e s a t polymorphic l o c i are c o r r e l a t e d with p o p u l a t i o n f l u c t u a t i o n s . To determine whether t h i s a s s o c i a t i o n between demography and g e n e t i c s i s c a u s a l , I a l t e r e d gene f r e q u e n c i e s i n two f i e l d p o p u l a t i o n s of M*. townsendi^ Using s t a r c h g e l e l e c t r o p h o r e s i s , I detected a l e u c i n e aminopeptidase (LAP) polymorphism i n M_. townsendi_. The f a s t a l l e l e , LAP-F, was present i n a c o n t r o l p o p u l a t i o n at a frequency of about .35 from J u l y 1971 to J u l y 1973. By removing homozygous SS v o l e s from one experimental p o p u l a t i o n I maintained an LAP-F frequency of about .75. Removal of FF homozygotes from a second p o p u l a t i o n r e s u l t e d i n an LAP-F frequency of about .25. I monitored demographic v a r i a b l e s of the p o p u l a t i o n s while the s e l e c t i o n was being a p p l i e d . The p o p u l a t i o n s went through i n c r e a s i n g and peak phases and then d e c l i n e d s h a r p l y during the s p r i n g of 1973. There were i n d i c a t i o n s t h a t d i f f e r e n t genotypes had an advantage i n s u r v i v a l and r e p r o d u c t i o n during d i f f e r e n t phases of p o p u l a t i o n d e n s i t y . The s e l e c t i o n t h a t maintained the polymorphism on the c o n t r o l area c o u l d be c o r r e l a t e d with p o p u l a t i o n d e n s i t y . However, the o v e r a l l f i t n e s s of each experimental population was not a f f e c t e d by i t s genotypic composition at t h i s l o c u s . TABLE OF CONTENTS I n t r o d u c t i o n 1 Methods Study Area . 4 Trapping Schedule 5 E l e c t r o p h o r e s i s . . 6 T r a n s f e r s 7 Sources Of E r r o r 8 R e s u l t s 11 Population Density 11 A l l e l e Frequency . 12 A l l e l e Frequency And Density 13 Demography And Genotypes 15 S u r v i v a l And Genotype . 16 Breeding C o n d i t i o n And Genotype 17 Eody Weights And Growth Rates 19 LAP And Demography 20 D i s c u s s i o n ; . 21 L i t e r a t u r e C i t e d 61 LIST OF TABLES Table 1. LAP Types For Colony Crosses Of M.. townsendi Tested For Chi-square Goodness Of F i t . 26 Table 2. Number Of T r a n s f e r r e d M._ townsendi Remaining On The Experimental G r i d s U n t i l At Lea s t The Next Trapping S e s s i o n . . ; 27 Table 3. Percentage Maximum T r a p p a b i l i t y Of Tagged Mj_ townsendi Grouped By Time Of Year. 2 8 Table 4. Mean Body Weight At The Time Of F i r s t Capture Of M_j_ townsendi On The C o n t r o l G r i d I. 29 Table 5. Instantaneous Rates Of P o p u l a t i o n Increase For Ik i2«£sendi On A l l G r i d s Expressed As Percent Per Week. _30 Table 6. Percent Bi-weekly Change In LAP-F Frequency For Hi townsendi.. . 31 Table 7. C o r r e l a t i o n Of Density And LAP-F Frequency In !k i o a i j s e n d i ^ 3 2 Table 8. Minimum Two-week S u r v i v a l Rates In B, townsendi On G r i d G. 3 3 Table 9. Minimum Two-week S u r v i v a l Rates F c r M._ townsendi On G r i d H. I I 34 Table 10. Minimum Two-week S u r v i v a l Rates For MA townsendi On C o n t r o l G r i d I . 35 Table 11. Percentage Of Adult M^ townsendi Males With S c r o t a l T e s t e s On G r i d G. 36 Table 12. Percentage Of Adult |, townsendi Males With S c r o t a l Testes On G r i d H. _ _ 37 Table 13. Percentage Of Adult townsendi Males With S c r o t a l T e s t e s On C o n t r o l G r i d I. 38 Table 14. Percentage Of Adult M.. townsendi Females L a c t a t i n g On G r i d G. 39 Table 15. Percentage Of Adult fU townsendi Females L a c t a t i n g On G r i d H. 40 Table 16. Percentage Of Adult M. townsendi Females L a c t a t i n g On C o n t r o l G r i d I. . 41 Table 17. Mean Body Weight Of Male MA townsendi On Gr i d G i i i For Each Season. 42 Table 18. Mean Body Weight Of Male M^ townsendi On Gri d H For Each Season. 43 Table 19. Mean Body Weight Of Male MA townsendi On G r i d I For Each Season. 44 Table 20. Average Growth Bates {% Per Day.) Adjusted By Regression To A Standard 35 G Vole, Of M_. townsendi Males On G r i d G. ~_ " _ ~ Z Z Z 4 5 Table 21. Average Growth Rates {% Per Day) Adjusted By Regression To A Standard 35 G Vole, Of M_. townsendi Males On G r i d H. ~ 46 Table 22. Average Growth Rates (% Per Day) Adjusted By Regression To A Standard 35 G Vole, Of M.. townsendi Males On C o n t r o l G r i d I . LIST OF FIGURES F i g u r e 1. Westham I s l a n d R e c e i v i n g S t a t i o n : L o c a t i o n Of Study G r i d s . 48 F i g u r e 2. S t a r c h Gel Showing LAP S t a i n i n g P a t t e r n In Mi c r o t u s Townsendi Serum. 4 9 Fi g u r e 3. P o p u l a t i o n Density Of Microtus Townsendi On G r i d G. . ZZZZZ—Z—ZZZ ~ ~ 5 0 F i g u r e 4. P o p u l a t i o n D e n s i t y Of Microtus Townsendi On G r i d H. ZZZZZZZ ZZZ—ZZZZ 5 1 F i g u r e 5. P o p u l a t i o n Density Of Microtus Townsendi On G r i d I. Z Z Z , Z 52 F i g u r e 6. A l l e l e Frequency Of F On Grid G, From Which A l l SS Voles Were Removed. 53 Fi g u r e 7. A l l e l e Frequency Of F On G r i d H, From Which A l l FF Voles Were Removed, 54 F i g u r e 8. A l l e l e Frequency Of F On G r i d I, The C o n t r o l G r i d . 55 Fi g u r e 9. Histogram Of Mean Bi-weekly S u r v i v a l Rates Of Male Microtus Townsendi During The Three Summers. 56 Fi g u r e 10. Histogram Of Mean Bi-weekly S u r v i v a l Rates Of Female Microtus Townsendi During The Three Summers. 57 F i g u r e 11. Histogram Of Body Weight D i s t r i b u t i o n s Of Male Microtus Townsendi On G r i d G. 58 Fi g u r e 12. Histogram Of Body Weight D i s t r i b u t i o n s Of Male MiSSSiSS Townsendi On G r i d H. 59 F i g u r e 13. Histogram Of Body Weight D i s t r i b u t i o n s Of Male Microtus Townsendi On G r i d I. _ _ 60 1 INTRODUCTION M i c r o t i n e rodents undergo p e r i o d i c f l u c t u a t i o n s i n p o p u l a t i o n d e n s i t y which are not d i r e c t l y r e l a t e d to known changes i n the environment of the p o p u l a t i o n ( C h i t t y 1960; Krebs 1966; Krebs et a l 1969). The absence of obvious e x t r i n s i c r e g u l a t i o n of such p o p u l a t i o n s has l e d C h i t t y (1967,1969) to suggest that g e n e t i c changes are a necessary p a r t of the c o n d i t i o n s l e a d i n g to numerical f l u c t u a t i o n s . During the p e r i o d of low numbers and p o p u l a t i o n i n c r e a s e , so the s t o r y gees, c e r t a i n genotypes are favored by s e l e c t i o n . As d e n s i t y i n c r e a s e s , an a g g r e s s i v e genotype gains the s e l e c t i v e advantage through the e l i m i n a t i o n from the breeding p o p u l a t i o n of those l e s s able to withstand crowding. A d e c l i n e i n numbers w i l l occur when the i n c r e a s i n g s e l e c t i o n f o r a g g r e s s i v e i n d i v i d u a l s has decreased the t o t a l p o p u l a t i o n f i t n e s s with regard to f o r c e s other than i n t r a - s p e c i f i c c o m p e t i t i o n . The above hypothesis assumes t h a t the p o p u l a t i o n c o n t a i n s g e n e t i c v a r i a t i o n capable of responding to short-term s e l e c t i v e p r e s s u r e s . E l e c t r o p h o r e t i c s t u d i e s of p r o t e i n s have r e v e a l e d l a r g e amounts of a p p a r e n t l y p e r s i s t e n t a l l e l i c v a r i a t i o n i n n a t u r a l p o p u l a t i o n s (e.g., Lewontin and Hubby 1966; Selander e t a l 1971). Evidence t h a t s e l e c t i o n does maintain such v a r i a t i o n and can be e f f e c t i v e over s h o r t p e r i o d s has been found (Yarbrough and Kojima 1967; Kojima and T o b a r i 1969). It i s at l e a s t reasonable, then, to use e l e c t r o p h o r e t i c v a r i a n t s as g e n e t i c markers when one i s i n v e s t i g a t i n g the i m p l i c a t i o n s of 2 C h i t t y 1 s hypothesis of p o p u l a t i o n r e g u l a t i o n through g e n e t i c change. S e v e r a l authors have monitored e l e c t r o p h o r e t i c markers durin g d e t a i l e d demographic s t u d i e s on f l u c t u a t i n g p o p u l a t i o n s . Semeonoff and Robertson (1968) found that the a l l e l e frequency of an e s t e r a s e polymorphism changed during a p o p u l a t i o n d e c l i n e of Microtus a g r e s t i s ^ Canham (1969) reported that the r e l a t i v e f i t n e s s e s of the genotypes of a t r a n s f e r r i n and of an albumin polymorphism were r e l a t e d to changes i n d e n s i t y of Peromyscus manjculatus and Clethriononjys <jaj3j3eri p o p u l a t i o n s . Changes i n a l l e l e f r e q u e n c i e s at a t r a n s f e r r i n locus (Tamarin and Krebs 1969) and a t both t r a n s f e r r i n and l e u c i n e aminopeptidase l o c i (Gaines and Krebs 1971) have been c o r r e l a t e d with changes i n d e n s i t y i n Microtus E^nnsy l y a n i c u s and M_. cchrogas t e r p o p u l a t i o n s . The r e s u l t s of these s t u d i e s are" compatible with C h i t t y ' s hypothesis t h a t the changes i n f l u e n c i n g numerical f l u c t u a t i o n s are g e n e t i c . They are a l s o c o n s i s t e n t with the view t h a t g e n e t i c changes have no c a u s a l r e l a t i o n s h i p with p o p u l a t i o n f l u c t u a t i o n s , but are only a s i d e - e f f e c t of the numerical changes (Charlesworth and G i e s e l 1972). This t h e s i s d e s c r i b e s an attempt to d i s c o v e r the r e l a t i o n s h i p between the a l l e l e frequency of an e l e c t r o p h o r e t i c marker, l e u c i n e aminopeptidase (LAE) , and the demography of a f i e l d p o p u l a t i o n of Microtus townsendi. I chose to work with LAP because the genotypes c o u l d be a c c u r a t e l y typed i n the l a b , but I had no reason to suspect t h a t the p a r t i c u l a r polymorphism was maintained by the same f o r c e s t h a t operated on the LAP 3 polymorphism s t u d i e d by Gaines and Krebs (1971). On each of two experimental areas, I c o n t i n u o u s l y s e l e c t e d f o r one a l l e l e of the LAP polymorphism by i n t r o d u c i n g v o l e s homozygous f o r the chosen a l l e l e and removing v o l e s homozygous f o r the a l t e r n a t e a l l e l e . Demographic v a r i a b l e s were monitored while the s e l e c t i o n was being a p p l i e d . My o b j e c t was to determine whether changing the a l l e l e frequency of the e l e c t r o p h o r e t i c marker would be s u f f i c i e n t to change the demographic p a t t e r n s between the p o p u l a t i o n s . I made no attempt to d i s t i n g u i s h between e f f e c t s due to the i n d i v i d u a l a l l e l e s and those due to p o s s i b l e l i n k a g e complexes. 4 M E T H O D S Study, Area The study area was on Westham I s l a n d i n the F r a s e r R i v e r d e l t a , 4 miles west of Ladner, B. C. , and about t w e n t y - f i v e road miles from the U n i v e r s i t y of B r i t i s h Columbia campus. Trapping was c a r r i e d out from J u l y 1971 to J u l y 1973 at the Department of N a t i o n a l Defense r a d i o r e c e i v i n g s t a t i o n on the i s l a n d . The ground was g e n e r a l l y f l a t , with an o l d i n t r o d u c e d pasture-mix v e g e t a t i o n . The land was p r o t e c t e d from f l o o d i n g by d i k e s and drainage d i t c h e s , but standing water covered some s e c t i o n s during the winter o f both years. Three s i t e s were marked out with 100 stakes each, i n a ten by ten p a t t e r n . Each stake was 25 f e e t from the next, and each g r i d covered 1.5 a c r e s . The s i z e and r e l a t i v e p o s i t i o n of each g r i d are shown i n F i g . 1. From November to March 1971-72, about 20% of g r i d G, about 30% of g r i d I, and about 40% of g r i d H were covered with standing water. About h a l f these amounts was present on each g r i d through December and January 1972-73. 5 Trapping Schedule Longworth l i v e - t r a p s were placed i n M._ townsendi runways near each stake on the g r i d s . An attempt was made to have an excess of t r a p s a v a i l a b l e to the voles at a l l times. T h e r e f o r e , one or two t r a p s , depending on the p o p u l a t i o n d e n s i t y , were pla c e d near each stake. Every second week, tr a p s were set Monday afternoon and checked Tuesday morning and a f t e r n o o n and Wednesday morning. The t r a p s were locked open i n p l a c e to serve as p r e b a i t s t a t i o n s between t r a p p i n g p e r i o d s . During hot weather, t r a p p i n g was done only over the two n i g h t s to avoid m o r t a l i t y i n the t r a p s during the heat of the day. My t r a p p i n g schedule was a f f e c t e d by v a r i o u s a c t s of God, such as a heavy r a i n f a l l during October 1971, which n e c e s s i t a t e d my s a c r i f i c i n g the t h i r d check that week, and a c t s of man, such as the mowing of the e n t i r e area i n September 1971 and of the areas around the g r i d s at other times. These emergencies a f f e c t e d a l l g r i d s at the same time and I have not considered t h e i r consequences i n t h i s t h e s i s . A v o l e caught f o r the f i r s t time was bled from the s u b o r b i t a l s i n u s and given a numbered ear-tag. Tag number, l o c a t i o n on the g r i d , and weight to the nearest gram were recorded f o r each animal caught during a t r a p p i n g p e r i o d . Breeding c o n d i t i o n was assessed from t e s t i s p o s i t i o n i n the males and from v a g i n a l p e r f o r a t i o n , n i p p l e development, and pubic symphsis c l o s u r e i n the females. L i t t e r s i n t r a p s and n o t i c e a b l e pregnancies were recorded. 6 Si®£tro£horesis I used a h o r i z o n t a l s t a r c h g e l e l e c t r o p h o r e t i c method with Connaught s t a r c h (Connaught Medical Research L a b o r a t o r i e s , Toronto, Canada) and the plasma p r o t e i n b u f f e r system of Selander (1969). The g e l molds, t r a y s , and s l i c i n g procedure were adapted from those d e s c r i b e d by Tsuyuki et a l (1966). I a p p l i e d the serum from the blood samples to the g e l s l o t s with f i l t e r paper i n s e r t s , s u bjected the g e l s to 150 v f o r 3 hr, and then incubated them f o r 2 hr i n the s t a i n i n g s o l u t i o n of Brewer (1970) at pH 5.2. The f u n c t i o n a l name l e u c i n e aminopeptidase has been a p p l i e d to " v a r i o u s amino a c i d naphthylamidases" which reduce the s u b s t r a t e 1 - l e u c y l - -naphthyl amide (Smith et a l 1965). S t a i n i n g r e v e a l e d the zones of L A P - a c t i v i t y shown i n F i g . 2. A zone of slower m o b i l i t y appeared to be monomorphic i n a l l animals typed; the second zone was polymorphic, and the three s t a i n i n g p a t t e r n s were l a b e l l e d FF, FS, and SS. The polymorphism conformed to a t w o - a l l e l e autosomal i n h e r i t a n c e model. A breeding colony was maintained to provide i n f o r m a t i o n on the g e n e t i c c o n t r o l of the polymorphism, but only 29 c r o s s e s were s u c c e s s f u l i n the two ye a r s . However, the r e s u l t s of typing the 271 o f f s p r i n g f o r LAP showed no evidence a g a i n s t the assumed mode of i n h e r i t a n c e (Table 1) . Based on these e l e c t r o p h o r e t i c a l l y determined genotypes, a program of a r t i f i c i a l s e l e c t i o n was c a r r i e d out i n the f i e l d . Mice typed as SS on g r i d G were removed and r e l e a s e d cn g r i d H; 7 those typed as FF on g r i d H were removed and r e l e a s e d on g r i d G (see F i g . 1). The s e l e c t i o n was c a r r i e d on throughout the study as new mice entered the p o p u l a t i o n . G r i d I was the c o n t r o l g r i d ; a l l new mice were typed f o r LAP but none was removed or added. T r a n s f e r s During the study, a t o t a l of 66 animals, r e p r e s e n t i n g 8.6% of the t o t a l catch on g r i d H, were typed as FF and removed. These animals were r e l e a s e d on g r i d G, but only 19 (27%) of these 66 stayed on g r i d G u n t i l at l e a s t the next t r a p p i n g p e r i o d . These a d d i t i o n a l 19 represented 1.7% of the t o t a l of 1110 animals caught on g r i d G during the study. Of the 10U (9.3%) animals typed as SS on g r i d G and removed, 61 (59%) were caught at l e a s t one t r a p p i n g p e r i o d a f t e r r e l e a s e on g r i d H. These represented of 7,9% of the t o t a l of 765 animals caught on g r i d H. During both breeding and non-breeding seasons a g r e a t e r p r o p o r t i o n of the animals t r a n s f e r r e d to g r i d H took up r e s i d e n c e than d i d those t r a n s f e r r e d to g r i d G (see Table 2). For the p r e s e n t a t i o n of r e s u l t s and the d i s c u s s i o n that f o l l o w s I w i l l r e f e r to breeding seasons d e f i n e d by the percentages of v o l e s i n breeding c o n d i t i o n on the g r i d s . During the study f i v e p e r i o d s of breeding performance could be d i s t i n g u i s h e d as f o l l o w s : 8 Summer 1971 J u l y 1 to Nov. 1 1971 breeding Winter 1971-72 Nov. 15, 71 t o Feb. 7, 72 non-breeding Summer 1972 Feb. 21 to Sept 18 1972 breeding Winter 1972-73 Oct. 2, 72 to Feb. 5, 73 ncn-breeding Summer 1973 Feb. 18 to J u l y 23, 73 breeding Most t a b l e s w i l l be presented with the data grouped over these breeding seasons and the graphs of d e n s i t y and a l l e l e frequency w i l l be shown with the non-breeding seasons shaded. S-SiliSlS of E r r o r A d i s c u s s i o n o f the genotypic and demographic d i f f e r e n c e s between the g r i d s must f i r s t cover the p o s s i b l e sources of e r r o r i n t r o d u c e d by the experiment. M o r t a l i t y d i r e c t l y a t t r i b u t a b l e to the experiment appeared to be low with the t r a p p i n g program employed. The t o t a l s of animals found dead i n t r a p s not p r o p e r l y p r e b a i t e d , a c c i d e n t l y k i l l e d d u r i n g handling, and found dead of unknown causes were 43 (4%) out of 1110 on g r i d G, 36 {5%) of 765 on g r i d H, and 35 (4%) of 959 on the c o n t r o l g r i d I. I found no evidence that t h i s m o r t a l i t y was non-random with r e s p e c t to sex or genotype. Within t h i s study, I had no s a t i s f a c t o r y method of e s t a b l i s h i n g the e f f e c t t h a t b l e e d i n g had on the s u r v i v a l of the i n d i v i d u a l v o l e s . Of the t o t a l of 2,834 animals caught, 2,774 (98%) were bled , and the m a j o r i t y of these were bled a t the time of f i r s t 9 c a p t u r e . I assume f o r the purposes of t h i s d i s c u s s i o n t h a t the e f f e c t s of b l e e d i n g were the same over both sexes and a l l genotypes. As d i s c u s s e d by Krebs (1966) and H i l b o r n (1974), the t r a p p i n g procedure was designed to enumerate a l l animals present i n the t r a p p a b l e p o p u l a t i o n to a v o i d the n e c e s s i t y of one 's assuming random sampling when e s t i m a t i n g p o p u l a t i o n parameters. An index of t r a p p a b i l i t y was c a l c u l a t e d to determine the e f f i c i e n c y of t h i s enumeration. I estimated the t r a p p a b i l i t y of Ma. i2iiSS®lidi by comparing the a c t u a l number caught during one t r a p p i n g p e r i o d with the minimum number known to be a l i v e at t h a t t r a p p i n g . The minimum number known to be a l i v e c o n t a i n s those p r e v i o u s l y tagged mice t h a t are missed during the t r a p p i n g p e r i o d but caught a t some l a t e r t r a p p i n g . Between 815? and 98% of a l l animals i n the t r a p p a b l e p o p u l a t i o n present cn a g r i d were caught during each t r a p p i n g p e r i o d . I found no d i f f e r e n c e between the t r a p p a b i l i t i e s of males and females during any time of year on any g r i d , nor were there any d i f f e r e n c e s between g r i d s . During the l a t e winter on a l l g r i d s , t r a p p a b i l i t y was u n i f o r m l y good, but during the summer t r a p p a b i l i t y was lower probably owing to the a l t e r e d t r a p p i n g program mentioned above. These data are presented i n Table 3, summarized by time of year and g r i d . Very sm a l l v o l e s were r a r e l y caught i n Longworth t r a p s , but t h i s would a f f e c t my a n a l y s i s only i f the p r o b a b i l i t y cf capture was d i f f e r e n t between g r i d s or genotypes. I c o n s i d e r e d mean tody weight at the time of f i r s t capture as an index of r e l a t i v e 10 t r a p p a b i l i t y (Table 4) . I compared the d i f f e r e n t genotypes on the c o n t r o l g r i d with a K r u s k a l - W a l l i s one-way ANOVA ( S i e g e l 1956). I found no s i g n i f i c a n t d i f f e r e n c e s i n mean body weight at the time of f i r s t capture between i n d i v i d u a l s of d i f f e r e n t genotypes. Mean body weight a t f i r s t capture was lower f o r the males dur i n g summer 1971 than d u r i n g the summers of 1972 or 1973, and was lower f o r females than f o r males at a l l times. I concluded from these data t h a t the i n d i v i d u a l s of the d i f f e r e n t genotypes were e n t e r i n g the trapped p o p u l a t i o n at comparable s i z e s , and assumed t h a t they were e q u a l l y s u s c e p t i b l e to t r a p p i n g throughout l i f e . 11 RESULTS I attempted to d i s c o v e r whether or not a d i f f e r e n c e i n a l l e l e f r e q u e n c i e s would l e a d to a change i n demographic processes. An answer to t h i s q u e s t i o n could be obtained only i f the p o p u l a t i o n d i d indeed show the phenomenon of i n t e r e s t , numerical f l u c t u a t i o n , and i f I was s u c c e s s f u l i n a l t e r i n g the LAP a l l e l e frequency. P2EMiaii2£ Density The minimum numbers of males and females known to be a l i v e are graphed f o r each g r i d ( F i g u r e s 3, 4, and 5). G r i d H' had a c o n s i s t e n t l y lower d e n s i t y than t h a t on e i t h e r g r i d G or g r i d I, but the three p o p u l a t i o n s underwent s i m i l a r numerical changes. D e n s i t i e s on g r i d G and g r i d I were s i m i l a r , and the low frequency of LAP-F on g r i d I was not a s s o c i a t e d with a low d e n s i t y of townsendi. I concluded that the low d e n s i t y of the g r i d H p o p u l a t i o n was not a s s o c i a t e d with the LAP composition of the p o p u l a t i o n . Numbers dropped on g r i d H d u r i n g the autumn of 1971, when standing water reduced the a v a i l a b l e g r i d area. On a l l g r i d s , v o l e d e n s i t y i n c r e a s e d throughout the winter of 1971-72, dropped s l i g h t l y i n the e a r l y s p r i n g of 1972, and i n c r e a s e d throughout the summer. A f t e r a s h o r t d e c l i n e i n the f a l l of 1972, d e n s i t i e s reached t h e i r h i g h e s t on a l l g r i d s d u r i n g December 1972. The p o p u l a t i o n s d e c l i n e d u n t i l Hay 1973, then i n c r e a s e d u n t i l the end of the study. The mean weekly r a t e s 12 of p o p u l a t i o n i n c r e a s e (Table 5) r e f l e c t these p a t t e r n s . The d i r e c t i o n of d e n s i t y change between t r a p p i n g p e r i o d s ( + ,0,-) was compared between the g r i d s . Density changed i n the same d i r e c t i o n on a l l three g r i d s between 34 of 50 t r a p p i n g p e r i o d s f o r males and between 38 of 50 periods f o r females. Large f l u c t u a t i o n s i n d e n s i t y occurred on each g r i d during the study, but a l l g r i d s changed with s i m i l a r r a t e s a t the same times. V a r i a b i l i t y among study s i t e s i s t r a d i t i o n a l l y d e a l t with through r e p l i c a t i o n of c o n t r o l and experimental a r e a s , but i n t h i s study I had no r e p l i c a t e s . The c o n t r o l d i f f e r e d from g r i d G i n a l l e l e frequency (see below) and from g r i d H i n M_. townsendi p o p u l a t i o n d e n s i t y . The frequency of LAP-F was low on both g r i d I and g r i d H, and i n s p i t e of the a r t i f i c i a l s e l e c t i o n a g a i n s t LAP-F on g r i d H, was s i m i l a r on the two g r i d s during the study. Peak d e n s i t i e s maintained on g r i d s I and G were about 200 v o l e s , but on g r i d H were about 130 v o l e s . G r i d s I and G were l e s s s u b j e c t to winter f l o o d i n g than g r i d H, and r e d u c t i o n of a v a i l a b l e h a b i t a t i s the s i m p l e s t e x p l a n a t i o n f o r the lower d e n s i t y . A l l e l e Frequency I found no s i g n i f i c a n t LAP-F frequency d i f f e r e n c e s between the sexes on any g r i d . A K r u s k a l - W a l l i s one-way ANOVA gave s i g n i f i c a n t a l l e l e frequency d i f f e r e n c e s between the three g r i d s f o r a l l p e r i o d s . The graphs of a l l e l e frequency, (Figures 6, 7, and 8) i l l u s t r a t e t h a t the d i f f e r e n c e between the experimental 13 g r i d s G and H was s u s t a i n e d from the middle c f the f i r s t b r e eding p e r i o d u n t i l the end of the study. The mean bi-weekly changes i n LAP-F frequency are shown i n Tab l e 6. A l l e l e frequency was changing on a l l g r i d s between J u l y 1971 and September 1971 before I began the experimental s e l e c t i o n , and some a l l e l e frequency d i f f e r e n c e was already e s t a b l i s h e d between the experimental g r i d s . The mean bi-weekly change i n a l l e l e f requency from the time the experiment began i n September 1971 u n t i l the end of the study was g r e a t e r on both experimental g r i d s {+.37% on g r i d G and -.32% on g r i d H) than cn the c o n t r o l (+.03%). The experimental technique was appa r e n t l y s u c c e s s f u l s i n c e a l l e l e f r e q u e n c i e s changed on the experimental g r i d s by about the same amounts and i n d i r e c t i o n s c o n s i s t e n t with the s e l e c t i o n a p p l i e d . A l l e l e Frequency, and Densit y Having e s t a b l i s h e d t h a t there was indeed an a l l e l e frequency s e p a r a t i o n between the two experimental areas, I then t e s t e d f o r an a s s o c i a t i o n of a l l e l e frequency with d e n s i t y . The r e s u l t s of a c o r r e l a t i o n of d e n s i t y and a l l e l e frequency f o r each season are shown i n Table 7. For males, durin g summer 1972 on g r i d H, winter 1972-73 on g r i d I , and summer 1973 on g r i d s G and I , there were s i g n i f i c a n t p o s i t i v e a s s o c i a t i o n s . Negative c o r r e l a t i o n s were found on both G and H during summer 1973. For males over the e n t i r e study, t h e r e was a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between a l l e l e frequency and 14 d e n s i t y on g r i d I and a s i g n i f i c a n t negative c o r r e l a t i o n on g r i d H. For females, s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n s of d e n s i t y with a l l e l e frequency were found during winter 1971-72 on g r i d s I and H, summer 1972 on g r i d G and summer 1973 on g r i d I. During summer 1972, s i g n i f i c a n t negative c o r r e l a t i o n s were found on g r i d s I and H. Over the e n t i r e study, the d e n s i t y of females on g r i d G was s i g n i f i c a n t l y p o s i t i v e l y c o r r e l a t e d with the a l l e l e frequency and on g r i d H was s i g n i f i c a n t l y n e g a t i v e l y c o r r e l a t e d with a l l e l e frequency. These c o r r e l a t i o n s c o n t a i n l i t t l e i n f o r m a t i o n on the experimental g r i d s s i n c e I cannot remove the e f f e c t of t r a n s f e r s . D e n s i t y of v o l e s i n c r e a s e d during most of the study on a l l g r i d s , while LAP-F frequency dropped on g r i d H and rose on g r i d s I and G. I would expect the o v e r a l l p o s i t i v e c o r r e l a t i o n o f d e n s i t y and a l l e l e frequency on g r i d G, since the experimental s e l e c t i o n f o r LAP-F was continued over the study. The o p p o r t u n i t y f o r s e l e c t i o n i n c r e a s e d when numbers i n c r e a s e d , and s e l e c t i o n r e s u l t e d i n a higher frequency o f LAP-F. On g r i d vH the o p p o s i t e s e l e c t i o n was c a r r i e d out, and by s i m i l a r reasoning the n e g a t i v e c o r r e l a t i o n of LAP-F frequency and d e n s i t y could be expected. I i n t e r p r e t the s i g n i f i c a n t a s s o c i a t i o n s of a l l e l e f r e g u e n c i e s and d e n s i t i e s on the experimental g r i d s t o be only an e x p r e s s i o n of the experimental s e l e c t i o n . The s t r o n g e s t c o r r e l a t i o n occurred on the c o n t r o l g r i d when numbers were dropping i n l a t e winter 1972-73, and i n d i c a t e d that LAP-S had a s e l e c t i v e advantage a t t h a t time. However, the evidence f o r an 15 a s s o c i a t i o n between numbers and a l l e l e f r e q u e n c i e s i s s l i g h t , and must be s u b s t a n t i a t e d with i n d i v i d u a l demographic i n f o r m a t i o n . De mograpjiy and Genotypes I f the genotypes of the LAP polymorphism have d i f f e r e n t s e l e c t i v e advantages depending on the population changes, then one should be able to d i s c o v e r t h i s from demographic i n f o r m a t i o n . I con s i d e r e d minimum two-week s u r v i v a l r a t e s , r e p r o d u c t i v e performance, and body weights of males i n order to d i s c o v e r any such r e l a t i o n s h i p . I wished to separate g e n e t i c e f f e c t s on demography from area e f f e c t s . The l o g i c a l method was to co n s i d e r the demographic i n f o r m a t i o n a v a i l a b l e f o r each genotype on each g r i d . However, a l l SS homozygotes were removed from g r i d G as they entered the p o p u l a t i o n . Any es t i m a t e s of demographic v a r i a b l e s f o r t h a t genotype on g r i d G were based on a small sample of the new animals i n the p o p u l a t i o n , and could not be considered r e p r e s e n t a t i v e . A s i m i l a r bias e x i s t e d on g r i d H, where FF homozygotes were removed. On the c o n t r o l g r i d I, a l l three genotypes could be considered f o r comparisons of demographic v a r i a b l e s . T h e r e f o r e , I f o l l o w e d a standard procedure i n my a n a l y s i s . When t e s t i n g f o r e f f e c t s due to g r i d s I compared the heterozygotes between a l l three g r i d s , the FF homozygotes between g r i d G and g r i d I, and the SS homozygotes between g r i d H and g r i d I . When l o o k i n g f o r g e n e t i c e f f e c t s I compared the 16 genotypes w i t h i n each g r i d : FF homozygotes, heterozygotes, and SS homozygotes on g r i d I; FF homozygotes with heterozygotes on g r i d G; and SS homozygotes with heterozygotes on g r i d H. S u r v i v a l and Genotyjge In order to i n v e s t i g a t e the g e n e t i c component of s u r v i v a l , I compared the average minimum s u r v i v a l r a t e s f o r genotypes on each g r i d (Tables 8, 9, and 10) by means of a chi-square contingency t e s t . T r a n s f e r r e d animals were not i n c l u d e d i n the c a l c u l a t i o n of s u r v i v a l r a t e s on the experimental g r i d s . On c o n t r o l g r i d I duri n g summer 1973 f o r males and summer 1973 f o r females, s i g n i f i c a n t d i f f e r e n c e s were found between s u r v i v a l of the t h r e e genotypes FF, SS, and FS. On the experimental g r i d s only the males showed s i g n i f i c a n t d i f f e r e n c e s among genotypes. On g r i d G during summer 1971 the s u r v i v a l of the FF homozygotes was s i g n i f i c a n t l y higher than that of the heterozygotes. On g r i d H dur i n g summer 1971, the s u r v i v a l of the SS homczygcte males was s i g n i f i c a n t l y h i g h e r than t h a t of the hete r o z y g o t e s . The d i f f e r e n c e s i n male s u r v i v a l between genotypes on both experimental g r i d s during summer 1971 are not p a r a l l e l e d fcy d i f f e r e n c e s between these genotypes on the c o n t r o l g r i d during the p e r i o d . Nor i s the r e l a t i v e l y low s u r v i v a l of heterozygote males on g r i d I r e f l e c t e d on the experimental g r i d s during summer 1973. Average minimum s u r v i v a l r a t e s were compared between g r i d s ( F i g u r e s 9 and 10) f o r i n d i v i d u a l genotypes. During summer 1971 / 17 s u r v i v a l r a t e s of heterozygotes on g r i d I were s i g n i f i c a n t l y b e t t e r f o r both males and females than those o f the heterozygotes on e i t h e r experimental g r i d . S u r v i v a l of the SS homozygotes on g r i d I was s i g n i f i c a n t l y b e t t e r than t h a t on g r i d H f o r both males and females during summer 1971. For males durin g summer 1973 s u r v i v a l r a t e s of the SS homozygotes on g r i d H and the FF homozygotes on g r i d G were s i g n i f i c a n t l y lower than those of the corresponding homozygotes on the c o n t r o l g r i d . The d i f f e r e n c e s i n s u r v i v a l r a t e s between g r i d s were more c o n s i s t e n t than those between genotypes. Breeding C o n d i t i o n and Genotyjje I used the p o s i t i o n of the t e s t i s as an index of breeding c o n d i t i o n i n male M.. townsendi.. Only a d u l t males, those weighing more than 44 g, were c o n s i d e r e d s i n c e the sample s i z e s of j u v e n i l e s and suba d u l t s were s m a l l . T a b l e s 11, 12, and 13 show the percentages of a d u l t males with s c r o t a l t e s t e s . On g r i d I during the summer of 1971 there were s i g n i f i c a n t l y fewer SS males i n breeding c o n d i t i o n than e i t h e r FS or FF males. On g r i d G during summer of 1973 there were s i g n i f i c a n t l y fewer FS males breeding than FF males. On g r i d H during the winter of 1972 there were fewer SS males i n breeding c o n d i t i o n than FS males. Between the g r i d s , during the winter of 1972-73 there was a s i g n i f i c a n t l y higher percentage of FS males i n breeding c o n d i t i o n on g r i d H. There was a higher percentage of FS males i n breeding c o n d i t i o n on g r i d H than cn e i t h e r g r i d G or g r i d I 18 over the e n t i r e study. For FF homozygotes during the winter of 1971-72 there was a higher percentage i n breeding c o n d i t i o n on g r i d G than on g r i d I . During the summer o f 1971 g r i d B had a higher percentage o f SS males breeding than d i d g r i d I . The s i z e of the n i p p l e s i s c o n s i d e r e d the most u s e f u l f i e l d index of breeding c o n d i t i o n i n a. townsendi (Tamarin and Krebs 1967). L a c t a t i n g females have medium or l a r g e n i p p l e s . Chi-square t e s t s f o r d i f f e r e n c e s between genotypes i n numbers of females l a c t a t i n g (Tables 14, 15, and 16) r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s on g r i d I during the summer of 1971, g r i d G during the summer of 1972, and on g r i d G over the e n t i r e study. T e s t s f o r d i f f e r e n c e s between g r i d s r e v e a l e d s i g n i f i c a n t l y fewer breeding FS females on g r i d H than on the other g r i d s d u r i n g summer 1971. Although s i g n i f i c a n t d i f f e r e n c e s between genotypes and between g r i d s showed up i n the percentages of v o l e s i n breeding c o n d i t i o n , these d i f f e r e n c e s f o l l o w e d no obvious p a t t e r n . Only on g r i d I during summer 1971 d i d both males and females have the same r e l a t i o n s h i p (FF>FS>SS) f o r percentages of each genotype i n breeding c o n d i t i o n . During that p e r i o d the LAP-F frequency i n c r e a s e d on g r i d I, but I found no such r e l a t i o n s h i p between breeding and a l l e l e .frequency change during any other p e r i o d of the study. The most n o t i c e a b l e p a t t e r n i n breeding performance was the d i f f e r e n c e between the years of the study. Breeding was maintained at a low l e v e l on a l l g r i d s throughout the winter of 1971-1972, but had stopped by the end of September 1972. 19 However, the percentages of v o l e s i n breeding c o n d i t i o n were not d i f f e r e n t between summers. No d i f f e r e n c e s were apparent between the g r i d s i n the obvious year-to-year v a r i a t i o n of length of breeding seasons. Body Weights and Growth Bates The d i s t r i b u t i o n of male body weights changed on each g r i d d u r i n g the study (Figures 11, 12, and 13). The change was most n o t i c e a b l e on g r i d I , where the average weight of males went from about 50 g durin g summer 1971 and winter 1971-72, to about 60 g during summer 1972, then down to about 45 g i n winter 1972-73 and back up to about 56 g i n summer 1973 (see Tables 17, 18, and 19). On the two experimental g r i d s the average weights were not as high as on the c o n t r o l during summer 1972, but d i d drop to about 46 g during winter 1972-73.' except f c r summer 1972, the changes i n body weight d i s t r i b u t i o n were c o n s i s t e n t between a l l three g r i d s throughout the study. Instantaneous r e l a t i v e growth r a t e s , adjusted to a standard 35 g vo l e by r e g r e s s i o n , were c a l c u l a t e d f o r males (see Krebs e t a l 1969). The mean growth r a t e s f o r each p e r i o d and genotype are shown i n Tables 20, 21, and 22. During a l l three summers on g r i d I, growth r a t e s were lowest f o r the FF homozygotes. Growth r a t e s f o r the heterozygotes were lower than those f o r the SS homozygote duri n g a l l t h r e e summers on g r i d H and during the summers of 1971 and 1972 on g r i d I. On g r i d G, the growth r a t e of FF homozygotes was higher than t h a t of the heterozygotes i n 20 summer 1971, but lower during summer 1973. Growth r a t e s were not c o n s i s t e n t l y d i f f e r e n t between g r i d s f o r any genotype. LAP and Demographer My experiment was based on c o r r e l a t i v e evidence from other s p e c i e s t h a t a l l e l e f r e q u e n c i e s of e l e c t r o p h o r e t i c polymorphisms are r e l a t e d t o demography. I w i l l now summarize the evidence from my c o n t r o l g r i d f o r such a r e l a t i o n s h i p between LAP and p o p u l a t i o n processes i n M.. townsendi^ During the study there was a p o s i t i v e c o r r e l a t i o n between numbers and LAP-F a l l e l e frequency, although t h i s was s i g n i f i c a n t only f o r the males. T h i s a s s o c i a t i o n was most ev i d e n t d u r i n g s p r i n g 1972 and. s p r i n g 1973 when numbers were dropping, and there was s e l e c t i o n i n fa v o r of the LAP-S a l l e l e . During summer 1973 a steep d e c l i n e i n numbers {-3.5% per week) was fo l l o w e d by a r a p i d i n c r e a s e (1.69? per week). Male heterozygotes s u r v i v e d very p o o r l y during both phases, both male and female FF homozygotes showed an enhanced s u r v i v a l during the i n c r e a s e , and SS homozygotes a decreased s u r v i v a l (Table 8). During summer 1971, when numbers were i n c r e a s i n g there were fewer SS homozygotes i n breeding, c o n d i t i o n i n both males and females, and a corresponding r i s e i n LAP-F frequency was e v i d e n t . So there was some evidence t h a t the d i f f e r e n t genotypes of LAP had v a r i a b l e f i t n e s s e s a s s o c i a t e d with demographic events on the c o n t r o l g r i d d u r i n g my study. 21 DISCUSSION The o v e r a l l c o n c l u s i o n must be t h a t the a l t e r e d a l l e l e f r e q u e n c i e s on the experimental g r i d s d i d not produce any c o n s i s t e n t e f f e c t s on demography. Any d i f f e r e n c e s between the genotypes on the c o n t r o l g r i d were i n g e n e r a l not r e f l e c t e d i n demographic d i f f e r e n c e s between the experimental g r i d s . The changes i n LAP-F frequency had no d i s c e r n a b l e e f f e c t on the changes i n numbers on g r i d G and g r i d H. There was an obvious p a t t e r n of changes between years i n numbers, breeding c o n d i t i o n , and body weights of v o l e s on a l l g r i d s and no g r i d d e v i a t e d p a r t i c u l a r l y from t h i s p a t t e r n . The s i g n i f i c a n t d i f f e r e n c e s t h a t I found between genotypes and g r i d s f o r demographic v a r i a b l e s d i d not a f f e c t the o v e r a l l p a t t e r n of change between years. Owing to p o s s i b l e i n t e r f e r e n c e with r e p r o d u c t i o n and s o c i a l s t r u c t u r e , the t r a n s f e r r i n g of animals throughout the study may have been a major e r r o r i n experimental des i g n . One might p o s t u l a t e that the i n t r o d u c t i o n of a l i e n FU_ townsendi onto the experimental g r i d s produced some s o c i a l d i s t u r b a n c e i n the p o p u l a t i o n s . Davis and C h r i s t i a n (1956) claimed t h a t the i n t r o d u c t i o n of animals i n t o expanding po p u l a t i o n s of r a t s would stop the i n c r e a s e , and i n t r o d u c t i o n s i n t o s t a t i o n a r y p o p u l a t i o n s would r e s u l t i n d e c l i n e s , o n g r i d H i n t h i s study, i n t r o d u c t i o n s formed 7.9% of the t o t a l p o p u l a t i o n , and t h i s l e v e l of d i s t u r b a n c e may have been a f a c t o r i n keeping p o p u l a t i o n d e n s i t i e s low. I n t r o d u c t i o n s to g r i d G formed only 1.7% of the t o t a l p o p u l a t i o n , and d e n s i t i e s were c e r t a i n l y no d i f f e r e n t from 22 those on the c o n t r o l g r i d . In g e n e r a l , few were t r a n s f e r r e d d u r i n g any one t r a p p i n g period, and whatever s o c i a l e f f e c t s were produced by the strange v o l e s would presumably have d i s s i p a t e d by the next t r a p p i n g . Terman (1962) reported that the i n t r o d u c t i o n of a l i e n Perom^yscus would i n h i b i t homing behavior i n r e s i d e n t s f o r only the f i r s t two days a f t e r i n t r o d u c t i o n . The p o p u l a t i o n t h a t the voles were r e l e a s e d i n t o appeared to have an e f f e c t on r e c r u i t m e n t of the t r a n s f e r s . Orr (1966) found t h a t removing r e s i d e n t s before r e l e a s i n g a l i e n Peronryscus r e s u l t e d i n 40% r e c r u i t m e n t of the new mice. In t h i s study, 27% of the mice t r a n s f e r r e d to g r i d G stayed u n t i l the next t r a p p i n g p e r i o d , and 59% o f those t r a n s f e r r e d to g r i d H stayed u n t i l a t l e a s t the next t r a p p i n g p e r i o d . The r e l a t i v e l y high p o p u l a t i o n d e n s i t y on g r i d G was probably r e s p o n s i b l e f o r the poor r e c r u i t m e n t of the t r a n s f e r s . The voles t r a n s f e r r e d - to g r i d H were suddenly exposed t o a l e s s crowded area and t h i s change i n t h e i r environment might account f o r the r e l a t i v e l y high r a t e of r e c r u i t m e n t . Experimental attempts a t t e s t i n g C h i t t y ' s hypothesis have i n v o l v e d the cropping of a d u l t r e s i d e n t s from popu l a t i o n s of m i c r o t i n e s (Krebs 1966, Smyth 1968). T h e i r experiments were undertaken e x p r e s s l y to have an e f f e c t on the s o c i a l processes i n the p o p u l a t i o n s . While the cropping of animals was done on a much l a r g e r s c a l e by those authors, I d i d not c o n s i d e r the p o s s i b i l i t i e s of s o c i a l d i s r u p t i o n through the removal of r e s i d e n t s i n t h i s experiment, A more i n f o r m a t i v e design would be t o a l t e r the a l l e l e f r e q u e n c i e s o n l y at the beginning o f the 23 study r a t h e r than to continue the s e l e c t i o n process throughout. As w e l l as minimizing the s o c i a l d i s t u r b a n c e , such an experiment would r e t a i n a l l genotypes on the g r i d s , one could t h e r e f o r e compare d i r e c t l y between g r i d s using t o t a l v alues f o r demographic v a r i a b l e s . The r e t u r n to o r i g i n a l a l l e l e f r e q u e n c i e s , i f i t occurred, c o u l d i n d i c a t e s p e c i f i c s e l e c t i o n p r e s s u r e s on the polymorphism. v A number of authors have shown t h a t the a l l e l e frequency of an e l e c t r o p h o r e t i c marker can determine the f i t n e s s of an i n d i v i d u a l i n a p o p u l a t i o n . Yarbrough and Kojima (1967) found the s e l e c t i v e advantage among the genotypes of an E s t e r a s e 6 l o c u s i n Droso£hila JSglanogaster cage p o p u l a t i o n s to depend upon the frequency of the a l l e l e s i n the p o p u l a t i o n . Kojima and T o b a r i (1969) found t h a t e i t h e r homozygote of an a l c o h o l dehydrogenase l o c u s i n D r o s o p h i l a melanogaster had an enhanced v i a b i l i t y i f present at a low frequency, but had reduced v i a b i l i t y i f present i n a high frequency. There were i n d i c a t i o n s i n M^, townsendi t h a t d i f f e r e n t genotypes had the r e l a t i v e advantage at d i f f e r e n t p e r i o d s , but such d i f f e r e n c e s apparently had l i t t l e e f f e c t on the demographic events of the p o p u l a t i o n s . When I began t h i s experiment, I had no evidence t h a t the l e u c i n e aminopeptidase polymorphism i n f l u e n c e d demography. Other s t u d i e s have shown that the a l l e l e f r e q u e n c i e s of e l e c t r o p h o r e t i c markers chosen e s s e n t i a l l l y a t random are c o r r e l a t e d with demographic events. B e d f i e l d (1972), from a study on c o l o n i z i n g blue grouse, found t h a t both age of h a b i t a t and the d e n s i t y of the p o p u l a t i o n were c o r r e l a t e d with the 24 frequency of the heterozygotes of an Ng l o c u s . Tamarin and Krebs (1969) found that a d e f i n a b l e ' i n c r e a s e ' genotype e x i s t e d i n both Microtus ochrogaster and M i c r c t u s i e n n s ^ l v a n i c u s ^ T h i s t r a n s f e r r i n genotype was s e l e c t e d f o r during i n c r e a s i n g and peak p e r i o d s of d e n s i t y , and s e l e c t e d a g a i n s t during the d e c l i n e . These ' i n c r e a s e ' and ' d e c l i n e ' genotypes were again d e f i n e d by Gaines (1970) f o r t r a n s f e r r i n and l e u c i n e aminopeptidase. The above s t u d i e s i n d i c a t e d t h a t a s e l e c t i v e advantage can be d e t e c t e d f o r a p a r t i c u l a r e l e c t r o p h o r e t i c genotype although the b i o c h e m i c a l b a s i s f o r the advantage i s not known. However, i n an experimental a n a l y s i s of the r e l a t i v e f i t n e s s e s of t r a n s f e r r i n genotypes i n Microtus o c h r o ^ a s t e r ^ Gaines et a l (1971) found no s i g n i f i c a n t e f f e c t of t r a n s f e r r i n genotype cn r a t e of p o p u l a t i o n i n c r e a s e , percentage of l a c t a t i n g a d u l t s , recruitment index, or s u r v i v a l r a t e o f v o l e s i n fenced e n c l o s u r e s . The r e s u l t s of my study i n d i c a t e t h a t the a l l e l e frequency of l e u c i n e aminopeptidase i n the ^ townsendi p o p u l a t i o n had no e f f e c t on the p o p u l a t i o n processes during the experiment. T h e r e f o r e , any a s s o c i a t i o n s of a l l e l e frequency and numbers were probably an e f f e c t of numbers on the polymorphism r a t h e r than the converse. The d i f f e r e n c e s I found between genotypes f o r s u r v i v a l , r e p r o d u c t i o n , and growth r a t e s i n d i c a t e that the a l l e l e frequency changes on the c o n t r o l g r i d were due to the s e l e c t i o n which maintains the polymorphism. Apparently, s e l e c t i o n does a c t on the v a r i o u s genotypes of e l e c t r o p h o r e t i c markers, yet these genotypes dc not have an a b s o l u t e f i t n e s s . Sved, Reed, and Bodmer (1966) were the f i r s t to suggest that great numbers of genetic polymorphisms i n a 25 p o p u l a t i o n would tend to obscure the optimal genotype. With some hundreds of independently s e g r e g a t i n g l o c i , there would be thousands of i n d i v i d u a l s i n a p o p u l a t i o n with e s s e n t i a l l y the same f i t n e s s . King (1967) makes the point t h a t the l o s s of f i t n e s s s u f f i c i e n t to maintain a polymorphism need not s i g n i f i c a n t l y reduce the f i t n e s s of a p o p u l a t i o n . Therefore changes i n a l l e l e frequency a t such l o c i during numerical f l u c t u a t i o n s would be determined by the degree of f a v c r a b i l i t y of the environment, and the polymorphism i t s e l f would have no e f f e c t on the demographic processes of the p o p u l a t i o n . My work with LAP was e s s e n t i a l l y a 'shot-in-the-dark» approach, although i t was a l o g i c a l next step i n i n v e s t i g a t i n g the c o r r e l a t i o n s of a l l e l e frequency with demography. In the l i g h t of t h i s study, an e x p l a n a t i o n that a l l e l e frequency change causes demographic change cannot be accepted. However, t h i s does not n e c e s s a r i l y i n d i c a t e a g e n e r a l r e l a t i o n s h i p s i n c e LAP may have been a bad c h o i c e of marker. LAP was chosen f o r the same reason that other polymorphisms have been s t u d i e d : the f a c i l i t y of t y p i n g i t i n the l a b . T h e r e f o r e , the s t u d i e s tc date which have invoked e l e c t r o p h o r e t i c polymorphisms as markers f o r demographic change c o n t a i n no i n f o r m a t i o n on g e n e t i c i n f l u e n c e s on demography. An e f f o r t must be made to determine the g e n e t i c a l b a s i s of p o p u l a t i o n processes, such as a g g r e s s i o n , which are thought to be d i r e c t l y i n v o l v e d i n numerical f l u c t u a t i o n s , b e f o r e the hypothesis t h a t g e n e t i c change i n f l u e n c e s numerical f l u c t u a t i o n s i n m i c r o t i n e s can be evaluated. 26 T a b l e 1. LAP t y p e s f o r c o l o n y c r o s s e s of M., t o w n s e n d i t e s t e d f o r c h i - s q u a r e goodness of f i t . LAP No. o f No. of C r o s s : L i t t e r s : O f f s p r i n g : SS FS FF SS x SS 40 SS x FS 11 53 51 >.98 SS x FF 3 15 0 FS x FS 6 FS x FF 11 15 20 10 >.50 22 >.90 FF x FF 34 27 Table 2. Number of t r a n s f e r r e d M. townsendi remaining cn the experimental g r i d s u n t i l at l e a s t the next t r a p p i n g s e s s i o n . T o t a l number t r a n s f e r r e d i n parentheses. To G r i d G To G r i d H Males Females Males Females Summer 1971 0 (5) 1 (3) 8 (9) 4 (8) Winter 1971-72 6 (9) 3 (4) 6 (11) 9 (10) Summer 1972 3 (16) 3 (9) 6 (16) 7 (13) Winter 1972-73 0 (2) 2 (10) 12 (17) 5 (13) Summer 1973 0 (4) 1 (<0 1 (3) 3 (3) T o t a l s 10 (30) 9 (36) 33 (56) 28 (47) 28 Table 3. Percentage maximum t r a p p a b i l i t y of tagged M.. townsendi grouped by time of year. The minimum number known to be a l i v e i n parentheses. G r i d G G r i d H G r i d I Males Females Males Females Males Females J u l y - S e p t 1971 91 88 88 96 100 97 (54) (118) (42) (68) (24) (34) Oct 71-Jan 72 82 84 93 86 85 98 (325) (430) (194) (212) (456) (508) Feb-May 1972 94 90 96 91 94 92 (322) (509) (249) (369) (408) (727) June-Sept 1972 85 83 91 84 87 81 (51 1) (630) (310) (430) (415) (702) Oct 72-Jan 73 83 91 90 88 89 86 (883) (908) (497) (512) (618) (1007) Feb-May 1973 96 95 92 95 92 93 (375) (454) (180) (283) (224) (460) Jun-July 1973 89 91 93 90 91 89 (164) (222) (94) (144) (1 18) (173) Average 87 89 92 90 91 92 29 Table 4. Mean body weight at the time o f f i r s t capture of townsendi on the c o n t r o l g r i d I. Number of vo l e s i n parentheses. Males Females Summer 1971 FF 46.00 ± 4.94 (7) 40.50 ± 6.07 (6) FS 43. 31 ± 2. 47 (26) 38.93 ± 2.15 (29) SS 47.94 ± 3.80 (17) 41.14 ± 2.87 (21) Winter 71-72 FF 37. 80 ± 5.05 (5) 38.27 + 2.11 (11) FS 42.48 + 1 .84 (42) 35.24 ± 1.00 (46) SS 42. 05 2. 53 (22) 33.04 ± 1.59 (26) Summer 1972 FF 57.69 + 1.95 (13) 41.06 ± 2.77 (17) FS 51 .15 ± 1 .42 (72) 40.28 ± 1.68 (57) SS 45. 45 ± 1.57 (64) 40.22 + 1.44 (68) Winter 72-73 FF 39.67 + 3.31 (18) 34.06 ± 2. 15 (17) FS 41. 96 ± 1.57 (52) 37.12 ± 1.07 (77) SS 39.79 + 1.71 (43) 38.72 ± 1.73 (39) Summer 1973 FF 51.00 + 4. 52 (8) 43.00 ± 6.03 (3) FS 44. 15 + 2. 36 (26) 38.00 ± 2.20 (26) SS 43.52 ± 2.71 (25) 35.83 + 2.07 (29) 3 0 Table 5. Instantaneous r a t e s of p o p u l a t i o n i n c r e a s e f o r Hi i2*£5§Sdi on a l l g r i d s expressed as percent per week. Grid G G r i d H G r i d I Summer 1971 3.5 3.0 9.6 Winter 71-72 3.2 3.2 1.5 Summer 1972 1.6 0.8 -0.6 Winter 71-72 1.2 0.2 0.6 Summer 1973 * (a) -3.6 -2.8 -3.5 (b) 2.4 3.1 1.6 * Voles were breeding during summer 1973, but a d e c l i n e i n numbers on a l l g r i d s was pronounced enough to warrant my s e p a r a t i n g the pe r i o d i n t o " d e c l i n e " and " i n c r e a s e " phases given i n (a) and (b). Table 6. Percent bi-weekly change i n LAP-F frequency f o r M. townsendi. G r i d G Grid H Grid I Summer 1971 2.24 -3.82 1.67 Winter 71-72 1.20 -0. 11 0.78 Summer 1972 0.09 0.24 -0. 10 Winter 72-73 -0.05 -0.67 0.09 Summer 1973 (a) 1 .35 1.06 1.63 (b) 0.03 -0.46 0.05 A verage* 0. 53 -0.83 0.16 Average** 0.37 -0.32 0.03 * From J u l y 1971 to J u l y 1973 ** From September 1971, when experiment began, to end. Table 7. C o r r e l a t i o n of a e n s i t y ana LAP-F freguency Ha. fowi}SS£dii. Number of sampling p e r i o d s i n parentheses. G r i d G Grid fi Gria I N r N r N r Summer 1971 Males (8) .15 (8) -.18 (6) .58 Females (8) .37 (8) -.59 (7) .42 Winter 71-72 Males (7) .23 (7) -.42 (7) .58 Females (7) .46 (7) .79* (7) .89** Summer 1972 Males (16) -.43 (16) .51* (16) -.21 Females (16) .80** (16) -. 57* (16) -.53* Winter 71-72 Males (10) -.39 (10) .00 (10) .82** Females (10) .23 (10) -.13 (10) .25 Summer 1973 Males (12) -.58* (12) -. 59* (12) .60 Females (12) -.14 (12) .32 (12) .66 T o t a l s Males (53) . 17 (53) -.64** (51) .34* Females (53) .43* (53) -.55** (52) . 25 * p < 0.05 ** p < 0.01 33 Table 8. Minimum two-week s u r v i v a l r a t e s i n M A townsendi on g r i d G. Number of v o l e s r e l e a s e d i n parentheses. Voles were breeding duri n g Summer 1973, but a d e c l i n e i n numbers was pronounced enough to warrant my s e p a r a t i n g the pe r i o d i n t o • d e c l i n e * and • i n c r e a s e ' phases g i v e n i n (a) and (b). G r i d G Males FF FS Females FF FS Summer 1971 Winter 71-72 Summer 1972 Winter 72-73 Summer 1973 (a) (b) .82 (44) .84 (106) .76 (276) .92 (366) .74 (102) .76 (112) .55** (40) .79 (117) .76 (330) .88 (400) .70 (101) .74 (147) .79 (58) .89 (118) .84 (409) .88 (370) .89 (95) .89 (82) .84 (90) .87 (176) .84 (440) . 88 (482) .86 (144) .86 (112) ** p < .01 34 Table 9. Minimum two-week s u r v i v a l r a t e s f o r M. townsendi on g r i d H. Number of v o l e s r e l e a s e d i n parentheses. Voles were breeding during summer 1973, but a d e c l i n e i n numbers on a l l g r i d s was pronounced enough-to warrant my s e p a r a t i n g the p e r i o d i n t o ' d e c l i n e ' and ' i n c r e a s e phases given i n (a) and (b). G r i d H Males Females SS FS SS FS Summer 1971 .71 .59** .70 .70 (14) (29) (23) (30) Winter 71-72 .84 .85 .82 .90 (50) (52) (61) (71) Summer 1972 .65 .71 .85 .86 (199) (174) (331) (201) Winter 72-73 .87 .85 .90 .86 (233) ( 169) (250) (161) Summer 1973 (a) .47 .79** .84 . 84 (32) (48) (79) (67) (b) .75 .62 .82 . 78 (28) (56) (82) (60) ** p < .01 35 Table 10. Minimum two-week s u r v i v a l r a t e s f o r M.. townsendi on c o n t r o l g r i d I. Number of voles r e l e a s e d i n parentheses. Voles were breeding d u r i n g summer 1973, but a d e c l i n e i n numbers on a l l g r i d s was pronounced enough t o warrant my s e p a r a t i n g the p e r i o d i n t o • d e c l i n e * and 'i n c r e a s e phases given i n (a) and (b). G r i d I Males Females FF FS SS FF FS SS Summer 1971 Winter 71-72 .85 .89 .85 (13) (53) (39) • 86 • 88 • 88 (35) (213) (116) .78 .94 .89 (9) (65) (76) .94 .92 .88 (49) (242) (162) Summer 1972 Winter 72-73 Summer 1973 (a) (b) .72 .72 .76 .80 .86 .84 (47) (339) (287) (107) (564) (475) .80 .83 .86 .87 .86 .88 (88) (259) (241 ) (111) (485) (343) .87 .67 .84 .66 .78 .88* (14) (4U) (62) (22) (138) (98) .91 .53 .76** .90 .80 .82 (24) (38) (63) (10) (94) (95) ** p < .01 36 Table 11. Percentage of a d u l t |L townsendi males with s c r o t a l t e s t e s on g r i d G. T o t a l number of a d u l t males i n parentheses. G r i d G FF FS T o t a l s Summer 1971 Winter 71-72 Summer 1972 Summer 1973 97 N (31) 53 N (79) 72 N (260) Winter 72-73 13 N (263) 84 N (212) 97 (30) 48 (87) 77 (299) 16 (254) 74* (142) 97 (61) 49 (166) 75 (559) 15 (517) 80 (354) * p < .05 37 Table 12. Percentage of a d u l t H A townsendi males with s c r o t a l t e s t e s on g r i d H. T o t a l number of a d u l t males i n parentheses. G r i d H SS FS T o t a l s Summer 1971 95 89 92 N (21) (18) (39) Winter 71-72 55 65 59 N (62) (46) (112) Summer 1972 82 80 80 H (212) (154) (366) Winter 72-73 16 29* 21 N (169) (97) (266) Summer 1973 75 84 80 N (76) (98) (174) * P < :05 38 Table 13. Percentage of ad u l t townsendi males with s c r o t a l t e s t e s on c o n t r o l g r i d I. T o t a l number of a d u l t males i n parentheses. G r i d I FF FS SS TotaIs Summer 1971 100 94 69** 84 ."N (10) (32) (32) (74) Winter 71-72 26 46 51 45 N (30) (160) (84) (278) Summer 1972 87 83 77 81 U (46) (313) (255) (614) Winter 72-73 17 10 9 11 S (53) (146) (150) (349) Summer 1973 88 74 78 79 N (44) (77) (122) (243) ** p < .01 39 Table 14. Percentage of a d u l t H._ townsendi females l a c t a t i n g on g r i d G. T o t a l number of ad u l t females i n parentheses. G r i d G FF FS T o t a l s Summer 1971 42 N (43) Winter 71-72 Summer 1972 Winter 72-73 Summer 1973 27 8 (88) 25 N (346) 6 H (176) 38 N (187) 47 (76) 41 (69) 39** (338) 9 (221) 43 (184) 45 (119) 33 (157) 32 (684) 8 (397) 40 (371) ** p < .0 1 40 Table 15. Percentage of a d u l t EL townsendi females l a c t a t i n g on g r i d H. T o t a l number of a d u l t females i n parentheses. G r i d H SS , FS T o t a l s Summer 1971 15 36 22 N (27) (14) (41) Winter 71-72 17 28 21 N (54) (39) (93) Summer 1972 40 38 39 N (365) (181 ) (546) Winter 72-73 7 6 7 N (161) (80) (241) Summer 1973 36 32 34 N (140) (93) (233) 41 Table 16. Percentage of a d u l t M A townsendi females l a c t a t i n g on c o n t r o l g r i d I. T o t a l number of a d u l t females i n parentheses. G r i d I FF FS SS T c t a I s Summer 1971 75 H (4) 48 (48) 27** (59) 38 (111) Winter 71-72 H (24) 21 (112) 20 (101) 19 (237) Summer 1972 35 H (85) 34 (470) 32 (387) 33 (942) Winter 72-73 6 (32) 5 (182) 5 (151) 5 (365) Summer 1973 33 (21) 33 (132) 39 (139) 36 (292) ** p < .01 42 Table 17. Mean body weight of male Mj_ townsendi on g r i d G f o r each season. T o t a l number of males i n parentheses. G r i d G FF FS Summer 1971 49.14 ± 1.72 53.64 + 1.82 (42) (36) Winter 1971-72 49.34 ± 1.17 51.76 ± 1.26 (122) (117) Summer 1972 54.62 ± 0.68 55.85 ± 0.56 (315) (333) Winter 1972-73 48.01 + 0.48 47.15 ± 0.55 (375) (400) Summer 1973 55.02 ± 0.71 53.45 ± 0.77 (245) (168) 43 Table 18. Mean body weight of male M._ townsendi on g r i d H f o r each season. T o t a l number of males i n parentheses. G r i d H FS SS Summer 1971 50.31 ± 2.05 50.96 ± 2.43 (26) (26) Winter 1971-72 54.55 ± 1.74 48.29 ± 1.31 (55) (103) Summer 1972 56.07 ± 0.74 52.44 ± 0.82 (175) (281) Winter 1972-73 45.71 ± 0.99 44.50 ± 0.61 (170) (296) Summer 1973 52.29 ± 1.04 50.06 ± 1.14 (117) (99) i 44 Table 19. Mean body weight of male M_. townsendi cn g r i d I f o r each season. Number of males i n parentheses. G r i d I FF FS SS Summer 1971 47.29 ± 2.58 47.96 ± 1.59 52.23 ± 2.05 (14) (54) (39) Winter 1971-72 52.48 ± 2.06 50.71 ± 0.74 52.03 ± 1.17 (35) (213) (116) Summer 1972 64.13 ± 1.11 60.79 ± 0.58 55.75 ± 0.66 (47) (339) (289) Winter 1972-73 46.06 ± 1.24 44.28 ± 0.60 45.28 ± 0.63 (88) (254) (244) Summer 1973 60.85 ± 1.46 55.41 ± 1.22 55.44 ± 0.98 (46) (93) (142) 45 Table 20. Average growth r a t e s {% per day) adjusted by r e g r e s s i o n to a standard 35 g v o l e , of M A tojjnsendi males on g r i d G. Sample s i z e i n parentheses. G r i d G FF FS Summer 1971 1.87 ± .21 1.20 ± 34 (31) (19) Winter 71-72 0.64 ± .11 0.84 + .13 (94) (91) Summer 1972 1.08 ± .12 1.09 ± .15 (213) (240) Winter 72-73 0.25 ± .08 0.22 ± .06 (334) (349) Summer 1973 0.51 ± .13 0.85 ± .16 (160) (106) 46 Table 21. Average growth r a t e s (f per day) ad j u s t e d by r e g r e s s i o n to a standard 35 g v o l e , of H._ townsendi males on g r i d H. Sample s i z e i n parentheses. G r i d H FS SS Summer 1971 0.75 ± .35 1.19 ± .36 (17) (13) Winter 71-72 0.76 + .18 0.79 ± .12 (82) (43) Summer 1972 0.56 ± .16 1.70 + .11 (181) (123) Winter 72-73 0.41 ± .09 0.31 ± .08 (249) (141) Summer 1973 1.30 ± .22 1.65 ± .23 (55) (71) d_ ; 47 Table 22. average growth r a t e s (% per day) adjusted by r e g r e s s i o n to a standard 35 g v o l e , of M._ townsendi males on c o n t r o l g r i d I. Sample s i z e i n parentheses. G r i d I FF FS SS Summer 1971 0.84 ± .34 1.25 ± .19 1.64 ± .21 (1 1) (42) (32) Winter 71-72 0.75 ± .21 0.66 ± .09 0.71 ± .10 (30) (178) (99) Summer 1972 0.41 + .40 0.54 + .10 1.29 ± .12 (34) (241) (213) Winter 72-73 0.19 ± .13 0.18 ± .08 0.29 ± .07 (68) (210) (202) Summer 1973 0.79 ± .40 1.59 ± .30 1.32 ± .19 (34) (49) (99) 4 8 F i g u r e 1. Westham I s l a n d r e c e i v i n g s t a t i o n : l o c a t i o n of study g r i d s . The c e n t r a l g r i d , I , was the c o n t r o l . Homozygous FF v o l e s were removed from g r i d H and t r a n s f e r r e d to g r i d G, and homozygous SS v o l e s were moved i n the opposite d i r e c t i o n . H :^I-AV"1V^ /I:/-'''I->W-"'!'" -'. 1 I . ' N i ' V. / ' - ' I ix r „ \ , • _' -O ' station farmland 1 cm = 1 2 5 ft 00 4 9 F i g u r e 2. S t a r c h g e l showing LAP s t a i n i n g p a t t e r n i n M i c r o t u s townsendi serum. 49a • 5 0 F i g u r e 3 . P o p u l a t i o n d e n s i t y of K i c r o t u s townsendi on g r i d G. 3 " .3 3 E oj CD — CO CD . CO • MINIMUM NO. ALIVE < m > DO 51 F i g u r e 4. P o p u l a t i o n d e n s i t y of Microtus townsendi on g r i d H. ® 3 3 » 03 CD — CO 0 CO • MINIMUM NO. A L I V E -< m > 33 F i g u r e 5. P o p u l a t i o n d e n s i t y of H i c r o t u s townsendi on g r i d LU > < o males D females 2 5 Of 100f 5 0 1 2 5 f 10 .. H:::::: n . \ / • \ /::H: m :::: / a . : . : . • • : : : : / • a • • a-•... : o : a , j 1 : 1 r; \ B' . \ / c • • • • • „ Sept Dec Mar Jun Sept Dec 1971 1972 YEAR Mar Jun 1973 53 F i g u r e 6. A l l e l e frequency of F on g r i d G, from which a l l SS v o l e s were removed. — H CD 3 3 oj 0) CD CO L A P - F CD CO • • o . ai L A P _ F A L L E L E F R E Q U E N C Y O L 54 F i g u r e 7. A l l e l e frequency of F on g r i d H, from which a l l FF v o l e s were removed. > o z LU =) O LU CC LL LU _J LU LL I Q_ < .751 o • o .50 h .25 m a l e s f e m a les o o o o \ MM** o °o° °° o o o o o o O' o / .... n«¥rT . . . . o o : : : : Q : . < r > a . . 0 . . . Sept Dec Mar Jun Sept Dec 19 71 1972 YEAR Mar Jun 1973 F i g u r e 8 . A l l e l e frequency of F on g r i d I, the c o n t r o l g r i d . Bgc 56 F i g u r e 9. Histogram of mean bi-weekly s u r v i v a l r a t e s of male Mic r o t u s townsendi during the three summers. ** p < .01 * p < .05 56a < > > rx 100-90 -80 -70 60- n G S U M M E R 1971 F S F F H G S S * < > > cn Z) if) 100] 90] 80-70 6 0 F S S U M M E R 1972 F F G I H G I S S H I < > > DC z> CO 100^ 90-80-6 0 i S U M M E R 1 9 7 3 F S F F S S G I H G I H I 57 F i g u r e 10. Histogram of mean bi-weekly s u r v i v a l r a t e s of female Microtus townsendi during the three summers. ** p < .01 5 7 a < > > DC co 100 90 80 70 60 S U M M E R 1971 F F G I H G I S S H _1 100 • < 90-> > 80-DC 70-CO •\* 60-_ l 100" < > go-> so"-DC Z) 70-CO 60-S U M M E R 1972 F S F F S S G l H G I S U M M E R F S F F H I 1973 S S G I H G H I 5 8 F i g u r e 11. Histogram of body weight d i s t r i b u t i o n s of male Microtus townsendi oh g r i d G. 58a CL i r r r m T h O " r-v-n r->-^ ~i „n m • r-r-i <-n ( I—i i f i i _JD n rm n i-i - n — rr-r-n -» n r-C - 3 03 CO CD JT~lnir-iM O Q a CO r-m-n ,m-n-m. n-. J~Lrtn X L m:n-i: -in,. XfcLi (^•^^•••••nnH •—' rVn - . •-. i~i' i-i PI r-i r-i c 03 n n n n XL. XI *-» n r-r-i C - n m r h n • O CD Q a CO - f — o CO - 4 -o CD + — f -o -+— o CM I S- < CD •IAI0 uj -IAA 59 F i g u r e 12. Histogram of body weight d i s t r i b u t i o n s of male Microtus townsendi on g r i d H. 59a n — -J 3 = - n r - f l r f T H - i n-TTh-n r f T h - r h n-v— CD c ZD t CC o CD Q CO CD n i T*\ 11 -a- a co n rHtM-^n iin — i . r m J T h r-i n~t-3_ r - n - i - i c 03 C\J DC < L U >-• f U T T . •irri-n O n r f t ^ ^ • - 1 • IT"! - i i ifT-"^"!"**--- i i •fTi—n- :rvjh'f-i " ^ i r i : : : IA n. H : '/-jfT-TTTH-wJ JlW-itii o CD a r-m a n r~i H I 1 -I o CO. —f— o CD — f -O — I — o CM CL CD CO CD •IAI0 U| » 1 M 60 F i g u r e 13. Histogram of body weight d i s t r i b u t i o n s of male Microtus townsendi on g r i d I . 6 0 a r~r-r-T-(~n~l r W h fTr-i — X L r r U T T -- n r f f l o_ r - r r - t -^rw. rT-t-rn-. i •JTlTili 11 iiih •rtTTT-rfTJi-. TTTrviraa^: X L rrf-r-TVfTTr-t • rt~i I H - —(~1 __TJL -n-rTVi- J 11 n Q_ r-f~0~>-i f-i-i rnJ"h m. 1 llnl I I I i n d I I PI I - n r-i r-n-i —f— o CO O CD — r -O C D 03 O CD Q CL CD CO c Z3 03 O CD Q a CD CO o CM CO CD CM DC < LU >-•l/MO u ! I M 61 LITERATURE CITED Brewer, G. J . 1970. An i n t r o d u c t i o n to isozyme techniques. Academic Press. New York. pp 186. Canham, R. P. 1969. Serum p r o t e i n v a r i a t i o n and s e l e c t i o n i n f l u c t u a t i n g p o p u l a t i o n s of c r i c e t i d rodents. Ph.D. T h e s i s , U n i v e r s i t y of A l b e r t a . 121 p. Charlesworth, B. And G e i s e l , J . T. 1972. S e l e c t i o n i n p o p u l a t i o n s with o v e r l a p p i n g g e n e r a t i o n s . I I . R e l a t i o n s h i p between gene frequency an demographic v a r i a b l e s . The Amer. Nat. V o l . 106 #949 pp 388-401 C h i t t y , d. 1960. P o p u l a t i o n processes i n the vole and t h e i r r e l e v a n c e to g e n e r a l theory. Can. J. Zool. 38:99-133 C h i t t y , D. 1967. The n a t u r a l s e l e c t i o n of s e l f - r e g u l a t o r y behavior i n animal p o p u l a t i o n s . Proc. E c o l . Soc. Aust. 2:51-78 Davis, D. E. And C h r i s t i a n , J . J . 1956. Changes i n Norway r a t p o p u l a t i o n s induced by the i n t r o d u c t i o n of r a t s . J . W i l d l . Mgt. 20:378-383 Gaines, M. S. And C. J . Krebs. 1971. G e n e t i c changes i n f l u c t u a t i n g v o l e p o p u l a t i o n s . E v o l u t i o n 25:702-723 Gaines., M. S, J . H. Myers, and C. J . Krebs. 1970. Experimental a n a l y s i s of r e l a t i v e f i t n e s s i n t r a n s f e r r i n genotypes of Microtus o c h r o g a s t e r . E v o l u t i o n . V o l . 25:443-450 H i l b o r n , R. 1974. Ph.D T h e s i s . The U n i v e r s i t y o f B. C. Fates of d i s a p p e a r i n g i n d i v i d u a l s i n f l u c t u a t i n g p o p u l a t i o n s of Ht townsendi.. King, J. L. 1967. "Continuously d i s t r i b u t e d f a c t o r s a f f e c t i n g f i t n e s s . " G enetics 55:483-492 Kojima, K. I. And Y. N. T o b a r i . 1969. The p a t t e r n of v i a b i l i t y changes a s s o c i a t e d with genotype frequency at the a l c o h o l dehydrogenase l o c u s i n a p o p u l a t i o n of Droso_p_hila JSelanogaster.. G e n e t i c s 61:201-209 Krebs, C. J . 1966. Demographic changes i n f l u c t u a t i n g p o p u l a t i o n s of Microtus c a l i f o r n i c u s ^ E c o l . Monog. 36:239-273 Krebs, C. J . , B. L. K e l l e r , and R. H. Tamarin. 1969. Microtus p o p u l a t i o n b i o l o g y : demographic changes i n f l u c t u a t i n g p o p u l a t i o n s of M±. Ochrogaster and M. Pennsjflvanicus i n Southern Indiana. Ecology 507587-607~ Lewontin, R. C. And J. L. Hubby. 1966 "A molecular approach to the study of genie h e t e r o z y g o s i t y i n n a t u r a l p o p u l a t i o n s . I I : Amount of v a r i a t i o n and degree of h e t e r o z y g o s i t y i n n a t u r a l 62 p o p u l a t i o n s of D._ Pseudobscura_. Ge n e t i c s 54: 595-609 Orr, H. D. 1966. Behavior of t r a n s l o c a t e d white-footed mice. J . Mamm. 47:500-506 S e i g e l , S. 1956. Nonparametric s t a t i s t i c s f o r the b e h a v i o r a l s c i e n c e s . Mcgraw-Hill book Co. Toronto. 312 p. Selander, R. K. , M. H. Smith, S. Y. Yang, S. E. Johnson, and J. B. Gentry. 1971. Biochemical polymorphism and s y s t e m a t i c s i n the o l d f i e l d mouse. Univ. Of Texas Pub. #7103 Selander, R. K. And Suh Y. Yang. 1969. P r o t e i n polymorphism and genie h e t e r o z y g o s i t y i n a w i l d p o p u l a t i o n of the house mouse. Ge n e t i c s 63:653-667 Semeonoff, R. And F. W. Robertson. 1968. A biochemical and e c o l o g i c a l study of plasma e s t e r a s e polymorphism i n n a t u r a l p o p u l a t i o n s of the f i e l d v o l e , microtus a c j r e s t i s L. Biochem. Genet. 1: 205-227 Smith, E. E., J . T. Kaufman, and A. M. Rutenburg. 1965. J . B i o l . Chem. 240:1718. Smyth, M, 1968. The e f f e c t s of the removal of i n d i v i d u a l s from a p o p u l a t i o n of bank v o l e s Clethrionomys g l a r e ! u s J . Anim. E c o l . 37:167-183 Sved, J . A., T. E. Reed, and W. F. Bodmer. 1966 the number of balanced polymorphisms t h a t can be maintained i n a n a t u r a l p o p u l a t i o n . G e n e t i c s 55:469-481 R e d f i e l d , J. A. 1972. Phd T h e s i s . The U n i v e r s i t y of A l b e r t a . Demography and G e n e t i c s i n c o l o n i z i n g p o p u l a t i o n s of Elue Grouse D§Si.E§aS£!i2 obscurus. Tamarin, R. H. And C. J . Krebs. 1969. M i c r o t u s populaton b i o l o g y I I : G e n e t i c changes at the t r a n s f e r r i n l o c u s i n f l u c t u a t i n g p o p u l a t i o n s of two v o l e s p e c i e s . E v o l u t i o n 23:183-211 Terman, C. R. 1962. S p a t i a l and homing consequences of the i n t r o d u c t i o n of a l i e n s i n t o s e m i - n a t u r a l p o p u l a t i o n s of p r a i r i e deermice. Ecology 43:216-223 Ts u y a k i , H. , E. Roberts, R. H. Kerr, and A. P. Ronald. 1966 j o u r n a l of f i s h . Res. Board of can. Micro s t a r c h g e l e l e c t r o p h o r e s i s . 23 (6) 929-933. Yarbrough, K. M. And K. I. Kojima. 1967. The mode of s e l e c t i o n a t the polymorphic esterase-6 l o c u s i n cage popu l a t i o n s of 2£5§2£iiilS 1122^2ter_j_ G e n e t i c s 57:677-686 

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