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The regulation of numbers in Tribolium confusum by means of selective migration Carl, Ernest A 1970

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i THE REGULATION OF NUMBERS IN TRIBOLIUM  CONFUSUM BY MEANS OF SELECTIVE MIGRATION by Ernest A. C a r l M.A., U n i v e r s i t y of C a l i f o r n i a , 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR 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 t o the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1970 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 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 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 t u d y . 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 p u r p o s e s 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 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 Zoology  The U n i v e r s i t y o f B r i t i s h Co lumbia V a n c o u v e r 8, Canada ABSTRACT i i A lengthy, and a t times heated, debate on the r e g u l a t i o n of animal numbers has proceeded i n the l i t e r a t u r e f o r over h a l f a century. A wide v a r i e t y of c a u s a l agents - from sun spots to a shortage of t r a c e elements - has been proposed t o e x p l a i n the observed d e n s i t i e s , and a wide v a r i e t y of mechanisms has a l s o been proposed - from n a t u r a l s e l e c t i o n to chance. Only oc-c a s i o n a l l y have any of these proposals been r i g o r o u s l y t e s t e d , and the s u r v i v a l of p a r t i a l l y or t o t a l l y c o n f l i c t i n g hypotheses has been correspondingly high. I have attempted to t e s t j u s t one of these proposals: the polymorphism hypothesis of C h i t t y (Proc. E c o l . Soc. A u s t r a l i a 2:51-78, 1967.) According to t h i s hypothesis, any n a t u r a l population which l i v e s i n a h i g h l y favourable h a b i t a t can r e g u l a t e i t s numbers through the a c t i o n of two morphs, one c h a r a c t e r i z e d by a high f e c u n d i t y and the other by a s u p e r i o r a b i l i t y to hold i t s p o s i t i o n i n the environment. Population d e n s i t y i s postulated to be a f u n c t i o n of the r e l a t i v e frequency of the morphs and to change i n a p r e d i c t a b l e way. I have conducted f i v e experiments t o i n v e s t i g a t e the e x i s t e n c e o f , and the mode of i n t e r a c t i o n between, these presumed morphs i n T r i b o l i u m confusum. the questions asked being: 1 ) Is the d e n s i t y achieved by open populations ( i . e . those from which emigration i s allowed) d i f f e r e n t from t h a t i n c l o sed populations ( i . e . those from which emigration i s pre-vented)? 2) Is the mechanism of r e g u l a t i o n i n open populations d i f f e r e n t from that i n closed populations? 3) Is the tendency to migrate a constant property of i n d i v i d u a l s ? A) Is the d e n s i t y achieved by populations founded by migrants d i f f e r e n t . f r o m that of populations founded by non-migrants? 5) Is the d e n s i t y achieved by open populations ( w i t h m i g r a t i o n by s e l f - s e l e c t i o n ) d i f f e r e n t from t h a t achieved by closed populations from which an equal number of animals are removed a t random? I found the answers to a l l these questions t o be 'yes', and the d i f f e r e n c e s i n each case to be i n the d i r e c t i o n pre-d i c t e d by the polymorphism hypothesis. I suggest that the polymorphism hypothesis i s u s e f u l f o r p r e d i c t i n g f u t u r e den-s i t i e s of populations from which emigration i s o c c u r r i n g , but i s not u s e f u l f o r p r e d i c t i n g d e n s i t i e s i n populations 1) from which animals cannot escape or 2) i n which m o r t a l i t y caused by e x t r i n s i c f a c t o r s i s so great t h a t , d e s p i t e high f e c u n d i t y , the populations are unable to produce a m i g r a t i n g s u r p l u s . I argue tha t 1) and 2) are r a r e i n nature, or at l e a s t have been st u d i e d r a t h e r seldom. Table of Contents i v 1 « T X t ILQ j P c l ^ G « e • e o a e o 0 0 0 0 0 0 0 2 » A t ) S t l ? 3 . C t o o o o o o o o o o o o o o o o o e 3 . Table of Contents... 4 . L i s t of Tables 5 . L i s t of Figures 6 . Acknowledgement 7 . I n t r oduct ion « 3 B I^lOtlnOClS o e o o o o o o e o o o e o e o o o o 9 . The Experiments. a. Experiment 1 b. Experiment 2 . . . c. Experiment 3 . d. Experiment 4 . . e. Experiment 5 1 0 . General D i s c u s s i o n 1 1 . References... 1 2 . Appendix 1 1 3 . Appendi 2al ^ o e e o o o o o © o o * o o a e • o o o o o * o c • 0 0 • * i 0 0 0 O 0 0 0 0 ft • 0 900400090 0 0 0 0 0 0 0 * ft O 0 O 0 0 0*0 o o o e o o • 00* 0 0 0 0 0 0 0 0 0 0 0 0 0 O 0 O 0 0 0 0 0 0 0 0 0 0 * 0 ft o o o e o o o e o o c o * 0 o * o O ft o o ft ft 0 ft ft 0 0 0 0 * O 0 O O 0 0 O ft'* o o O0O00O ftOO X i i i v V v i v i i 1 8 1 3 1 3 1 7 1 9 2 3 2 8 3 2 4 1 4 8 5 2 L i s t of Tables v Table I . Age composition of Gen. 2 open c u l t u r e s by o * ") month 16 Table I I . A d u l t b e e t l e s per c u l t u r e f o r v a r i o u s s e t s of r e p l i c a t e s r e f e r r e d t o i n the t e : : t . . . . . . . . . . . . . . 52 Table III.Number of migrants per c u l t u r e f o r v a r i o u s sets o f r e p l i c a t e s r e f e r r e d t o i n the t e x t . . . . . " 55 Table IV. Ascending ranlc order of d e n s i t y among 10 Gen. 2 open c u l t u r e s used i n Experiments 1, 2, and 5... 58 v i L i s t of Figures ! F i g u r e 1. Performance of a d u l t beetles i n open and c l o s e d c u l t u r e s 14-15 Figure 2. Performance of a d u l t beetles i n mimic , c u l t u r e s and t h e i r models 20-21 Figu r e 3. Performance of a d u l t beetles i n c u l t u r e s founded by migrants, non-migrants and uns e l e c t e d stock.... 25-26 Fig u r e 4. Performance of a d u l t beetles i n normal open c u l t u r e s and i n c u l t u r e s where migrants are chosen a t random. 30-31 v i i ACKNOWLEDGMENT This work was done under the s u p e r v i s i o n of Dr. D. C h i t t y , whom I wish t o thank f o r support, a d v i c e , and en~ couragement throughout the study. I wish to thank Mrs. J e n n i f e r Fawcett, Miss Karen Uldall-Ekman, and Mrs. P a t r i c i a Wilson f o r t e c h n i c a l a s s i s t a n c e , a l s o Drs. A. B. Acton, N. R. L i l e y , J . E. P h i l l i p s , and G. G. E. Scudder f o r advice and c r i t i c a l reading of the manuscript. This work was supported by a grant to Dr. C h i t t y from the N a t i o n a l Research C o u n c i l of Canada. 1 INTRODUCTION ' T h i s t h e s i s r e p o r t s an e x p e r i m e n t a l t e s t o f C h i t t y ' s p o l y -morphism h y p o t h e s i s of a n i m a l p o p u l a t i o n r e g u l a t i o n ( C h i t t y , 1960, 1965, 1967) . In t r y i n g to a c c o u n t f o r c y c l e s i n v o l e p o p u l a t i o n d e n s i t i e s , C h i t t y suggested t h a t when v o l e numbers a r e low, n a t u r a l s e l e c t i o n f a v o r s t h a t p a r t o f the p o p u l a t i o n t h a t has the h i g h e s t i n t r i n s i c r a t e of n a t u r a l i n c r e a s e (Lo tka 1925; Andrewar tha and B i r c h 1954) . S e l e c t i o n i n t h i s d i r e c t i o n i n i t i a t e s an i n c r e a s e i n d e n s i t y . As d e n s i t y i n c r e a s e s , compet-i t i o n f o r space i n c r e a s e s and a h i g h i n t r i n s i c r a t e o f n a t u r a l i n c r e a s e becomes i n c o n s e q u e n t i a l as the a c t u a l r a t e of i n c r e a s e f a l l s t o z e r o . In s t a t i o n a r y p o p u l a t i o n s o n l y t h o s e an ima ls w h i c h can remain i n the h a b i t a t w i l l l e a v e any descendants t h e r e ; t h o s e t h a t emigra te o r a r e u n a b l e t o breed w i l l c o n -t r i b u t e n o t h i n g t o the gene p o o l . S e l e c t i o n s h o u l d now f a v o u r t h o s e a n i m a l s h a v i n g whatever form o f b e h a v i o u r e n a b l e s them t o preempt the most f a v o r a b l e b r e e d i n g s i t e s . These an ima ls a r e presumably l e s s t o l e r a n t o f o t h e r i n d i v i d u a l s o f the same s p e c i e s and p o p u l a t i o n d e n s i t y s h o u l d d e c r e a s e under c o n t i n u e d s e l e c t i o n f o r the a b i l i t y t o preempt r e s o u r c e s . Thus p o p u l a t i o n s a r e v iewed as c o n s i s t i n g of two g e n e t i c morphs: one s e l e c t e d f o r a h i g h i n t r i n s i c r a t e of n a t u r a l i n c r e a s e , w h i c h would tend t o push d e n s i t i e s ^ u p , and one s e l e c t e d f o r some form of h o s t i l e b e h a v i o u r , ( i n the sense o f T i n b e r g e n , 1957) w h i c h would tend t o push d e n s i t i e s down. C h i t t y assumed t h a t the l a t t e r form of s e l e c t i o n would a l s o i n v o l v e s e l e c t i o n a g a i n s t the genotypes w i t h a h i g h i n t r i n s i c r a t e of n a t u r a l i n c r e a s e . A l t h o u g h he envisaged t h i s mechanism as applicable to a l l species, he did not say i t was the only mechanism of regulation or that i t would operate in a l l populations at a l l times. Two classes of s i t u -ations can be excluded: 1) Populations e x i s t i n g in habitats so unfavorable that mortality from e x t r i n s i c factors exceeds the i n t r i n s i c rate of natural increase and 2) populations in which something a t y p i c a l frustrates the separation of the hypothesized morphs. In the f i r s t case, one would expect the population to move toward raono-morphism, the morph with the high i n t r i n s i c rate of natural i n -crease being always favoured. Populations which could increase t h e i r mean f e r t i l i t y enough to exceed the e x t r i n s i c mortality would then come within the scope of the polymorphism hypothesis; those that could not, would-not long p e r s i s t without immigrants from elsewhere. In the second of the cases above, the method of f r u s t r a t i n g the separation of the morphs would depend on how the separation is u s u a l l y effected in the species involved. From the natural h i s t o r y l i t e r a t u r e (e.g. Errington (1951) for muskrats) one would guess that the separation is usually by migration, since animals do not usually seem to k i l l conspecifics d i r e c t l y (Lorenz, 1952, 1966). By whatever means separation of the morphs is frustrated, such populations should increase in density u n t i l further r i s e i s stopped by some other mechanism such as stress - induced reduction i n f e r t i l i t y (Christian and Davis, 1964), cannibalism (Chapman, 1928; Park 1934; Paine, 1965), 3 food shortage (e.g. Lack, 1954), or disease (Elton, 1931). Proponents of the polymorphism hypothesis are obliged to show that populations, which are in situations 1) or 2) above are there through the agency and control of man, or are there tem-p o r a r i l y and w i l l become extinct unless conditions change. The hypothesis bears some s i m i l a r i t y to MacArthur and Wilson's (1967) r and K s e l e c t i o n , but whereas Chitty compared genetic morphs of a single species, MacArthur and Wilson compared strategies of related species. It i s very s i m i l a r to ideas proposed by L i d i c k e r (1962). Later (1965) Chit t y pointed out that insects might be e s p e c i a l l y good experimental animals on which to t e s t his hypo-thesis since i t s assumptions were completely general. Since Chitty put f o r t h his view of regulation, arguments supporting the existence of the required morphs have been elaborated (Krebs, 1964; S a d l e i r , 1965; Healey, 1967; Munro, 1967; d e l Solar, 1968). Wellington (1960) showed that cater-p i l l a r s of Malacpsoma p l u v i a l e (Dyar), occur in types showing d i f f e r e n t properties a f f e c t i n g population dynamics but f e l t that the phenotypic differences were not genetic. He implied that the frequencies of the types changed as populations of the moth were founded and then died out. Birch (1960) suggested a mechanism by which natural selection on individuals could favour lower fecundity without involving any linkage of fecundity-pro-ducing and other genes. Although Birch f e l t his mechanism of limited a p p l i c a b i l i t y , the scheme can be e a s i l y extended to any p o p u l a t i o n whose b r e e d i n g s i t e s have a f i x e d r e a r i n g c a p a c i t y ' and whose members l a y eggs w i t h o u t r e g a r d to how many eggs have a l r e a d y been l a i d on the r e s o u r c e . C r a i g e t a l (1965) showed t h a t s o c i a l dominance can have a g e n e t i c b a s i s . C h r i s t i a n and Dav is (1964) s u g g e s t e d t h a t g e n e t i c changes c o u l d n o t o c c u r r a p i d l y enough t c f i t C h i t t y ' s h y p o t h e s i s t o n a t u r a l p o p u l a t i o n s , but B r o a d h u r s t (1960) was a b l e t o produce b e h a v i o u r a l l y d i s -t i n c t p o p u l a t i o n s o f l a b o r a t o r y mice i n two o r t h r e e g e n e r a t i o n s . As long ago as 1948, Dobzhansky demonst ra ted r a p i d l y o c c u r r i n g g e n e t i c changes i n w i l d p o p u l a t i o n s of D r o s o p h i l a . In an i n -g e n i o u s l y s i m p l e exper iment Thoday (1963) found a c l o s e c o r -r e l a t i o n between the f r e q u e n c y of a mutant a l l e l e and p o p -u l a t i o n d e n s i t y t h r o u g h s e v e r a l d e n s i t y f l u c t u a t i o n s i n l a b -o r a t o r y c u l t u r e s o f D r o s o p h i l a . , S h o r r o c k s (1970) , a l s o u s i n g l a b o r a t o r y c u l t u r e s o f D r o s o p h i l a . but o f w i l d o r i g i n , showed t h a t d e n s i t y c y c l e d w i t h a 4 - g e n e r a t i o n p e r i o d , t h a t i n d i v i d u a l s f rom "peak" p o p u l a t i o n s had lower f e r t i l i t y than t h o s e from " n o n -peak" p o p u l a t i o n s when removed from the p o p u l a t i o n and p l a c e d i n a s t a n d a r d i z e d s i t u a t i o n , and t h a t t h i s low f e r t i l i t y had a g e n e t i c component. He a l s o found t h a t p o p u l a t i o n s had low i n -t r i n s i c r a t e s of n a t u r a l i n c r e a s e a t low d e n s i t i e s and i m p l i e d t h a t t h i s was because t h e s e low p o p u l a t i o n s had been preceeded by a h i g h d e n s i t y p o p u l a t i o n . Krebs and h i s c o l l e a g u e s (Krebs e t aJL, 1969; Tamar in and K r e b s , 1969; Krebs 1970) have t e s t e d C h i t t y ' s h y p o t h e s i s u s i n g f i e l d p o p u l a t i o n s o f two s p e c i e s o f M i c r o t u s . They were a b l e t o show t h a t g e n e t i c s e l e c t i o n was o c c u r r i n g as the p o p u l a t i o n s proceeded t h r o u g h a c y c l e o f abundance, and t h a t changes i n male a g g r e s s i v e n e s s p a r a l l e l e d t h i s g e n e t i c change. In popu-l a t i o n s l i v i n g w i t h i n a f e n c e d a r e a and thus u n a b l e t o e m i g r a t e , t h e g e n e t i c a l and b e h a v i o u r a l changes d i d n o t o c c u r and n o r m a l r e g u l a t i o n f a i l e d : t h e mice a t e up a l l t h e g r a s s and s t a r v e d . From t h e s e o b s e r v a t i o n s , Krebs s u g g e s t e d t h a t g e n e t i c s e l e c t i o n was e f f e c t e d i n p a r t by d i f f e r e n t i a l m i g r a t i o n between morphs i n n a t u r a l p o p u l a t i o n s . r Meanwhile, o t h e r s ( R i c h , 1956; S o n l e i t n e r , 1961; P a r k , M e r t z , G r o d z i n s k i and P r u s , 1965; L l o y d , 1958, 1968) were d e v e l o p i n g a d i f f e r e n t h y p o t h e s i s o f r e g u l a t i o n o r i g i n a l l y s u g g e s t e d by Chapman (1928) and P a r k (1932), W orking w i t h c l o s e d l a b o r a t o r y p o p u l a t i o n s o f T r i b o l i u m . t h e s e w o r k e r s i n -f e r r e d t h a t t h e b e e t l e s r e g u l a t e t h e i r d e n s i t i e s by e a t i n g eggs, s m a l l l a r v a e , and pupae a t r a t e s t h a t a r e d e n s i t y depen-d e n t . As p o p u l a t i o n d e n s i t y i n c r e a s e s t h e environment becomes more h o s t i l e t o eggs, l a r v a e , and pupae u n t i l f i n a l l y none s u r v i v e s t o produce more a d u l t s . The p o p u l a t i o n s i z e t h e n f a l l s because o f n a t u r a l d eaths o f a d u l t s u n t i l a few pupae s u r v i v e t o a d u l t h o o d i n t h e now l e s s h o s t i l e e n v i r o n m e n t . In h i s 1965 p a p e r , C h i t t y extended t h e scope of t h e p o l y -morphism h y p o t h e s i s t o i n c l u d e a l l s p e c i e s o f a n i m a l s . In so d o i n g he opened h i s h y p o t h e s i s t o t h e r i s k o f b e i n g r e f u t e d by t e s t s u s i n g i n s e c t d a t a , i n c l u d i n g , o f c o u r s e , t h e T r i b o l i u m d a t a o u t l i n e d above: r e g u l a t i o n had been e x p l a i n e d i n c l o s e d T r i b o l i u m c u l t u r e s w i t h o u t i n v o k i n g any g e n e t i c change. I f 6 T r i b o i i u m populations c o n t a i n C h i t t y ' s morphs, and u s u a l l y e f f e c t a s e p a r a t i o n of these morphs by means of s e l e c t i v e mig-r a t i o n , then c l o s e d c u l t u r e s from inbred stocks would f a l l n i c e l y i n t o the second type of s i t u a t i o n , a l r e a d y excluded from the polymorphic mechanism. But, as discussed above, the burden of proof f a l l s on the proponents of the polymorphism hypothesis. Since the hypothesis c l e a r l y s p e c i f i e s what changes must occur when the c o n d i t i o n of no m i g r a t i o n and l i m i t e d g e n e t i c v a r i a -b i l i t y are r e l a x e d , i t seemed to me t h a t a c l e a r t e s t of the polymorphism hypothesis was p o s s i b l e using T r i b o i i u m . The p r e d i c t e d changes are: 1) Open c u l t u r e s must maintain lower d e n s i t i e s than c l o s e d c u l t u r e s . 2) P r o p e n s i t y to migrate must be a property of the i n -d i v i d u a l b e e t l e . 3) Open c u l t u r e s founded by migrants must maintain higher d e n s i t i e s than open c u l t u r e s founded by non-migrants. 4) Changes i n age s t r u c t u r e must be i n s u f f i c i e n t to e x p l a i n changes i n d e n s i t y ; changes i n the q u a l i t y of the i n d i v i d u a l s making up the p o p u l a t i o n must be i n v o l v e d . 5) Cultures subject to random losses must maintain higher d e n s i t i e s than c u l t u r e s subject to losses of the same magnitude through n a t u r a l emigration (which, under the hypothesis i s presumed to be non-random). Since these p r e d i c t i o n s r e q u i r e c u l t u r e s of T r i b o i i u m to per-form d i f f e r e n t l y from a l l p r e v i o u s l y reported c u l t u r e s , I under-took the experiments reported below. Although i n the l o g i c of the experimental design the experiments are s e q u e n t i a l , they were i n f a c t done l a r g e l y simultaneously. In t h i s way I was a b l e to use some c u l t u r e s t o o b t a i n data f o r s e v e r a l d i f f e r e n t experiments; even so over 5 m i l l i o n l i v i n g stages had to be counted t o complete the work. . - ,-I , There i s a l a r g e l i t e r a t u r e on the nature and maintenance of polymorphisms i n p o p u l a t i o n s , much of i t t h e o r e t i c a l . Beardmore (1970) has r e c e n t l y reviewed t h i s l i t e r a t u r e , and i t i s i n a p p r o p r i a t e t o comment on the s u b j e c t i n any depth. Here I am u s i n g the term i n i t s broadest sense t o r e f e r to a range of g e n e t i c morphs i n a p o p u l a t i o n , w i t h no assumptions about linkages or h e t e r o s i s . However, f o r s i m p l i c i t y of argument, I s h a l l , i n t h i s paper, assume t h a t only two d i s t i n c t morphs are present. :- * - • Throughout the paper I s h a l l keep the data presented down to the minimum r e q u i r e d f o r understanding the argument. Sup-plemental data and comments w i l l be found i n the appendices. In Appendix 1 two a l t e r n a t i v e explanations f o r some of the r e s u l t s are discussed (and dismissed) and data are presented on the v a r i a t i o n of i n d i v i d u a l r e p l i c a t e s . Appendix 2 includes the means used i n c o n s t r u c t i n g the graphs, together w i t h t h e i r standard e r r o r s (Table I I ) , the number of emigrants (Table I I I ) , and evidence t h a t r e p l i c a t e s tend t o maintain a charac-t e r i s t i c rank (Table IV). 8 METHODS On 16 September 1968, I c o l l e c t e d about 2,000 a d u l t T r i b o i i u m confusum D u v a l ( C o l e o p t e r a : T e n e b r i o n i d a e ) from some c h i c k e n mash i n a henhouse on t h e U n i v e r s i t y o f B r i t i s h Columbia Campus and a l l o w e d them t o l a y eggs f o r a week. I t h e n d i s -c a r d e d t h e o r i g i n a l a d u l t s and r e a r e d t h e eggs t o a d u l t h o o d . I randomly w i t h d r e w a sample of 1,000 o f t h e s e new a d u l t s and c a l l e d them ' G e n e r a t i o n 1 (Gen. 1) s t o c k s ' . Then I t o o k about 2000 Gen. 1 eggs and r e a r e d them t o a d u l t h o o d t o produce Gen. 2 s t o c k s . S i n c e I k e p t d e n s i t i e s low by c h o o s i n g o n l y a few eggs t o be s u r v i v o r s and chose t h e s e a t random, t h e p o p u l a t i o n was, g e n e t i c a l l y , e x p a n d i n g i n t o an ' i n f i n i t e h a b i t a t ' . In e f f e c t , I a p p l i e d a m i l d s e l e c t i v e p r e s s u r e f o r f e c u n d i t y between Gen. 1 and Gen. 2:- t h e more fecund a n i m a l s i n Gen. 1 would be o v e r -r e p r e s e n t e d i n Gen. 2 s i m p l y because t h e y l a i d more eggs. I t h e n m a i n t a i n e d t h e s e two s t o c k s w i t h o u t r e c r u i t m e n t by t r a n s -f e r r i n g t h e a d u l t s t o new f l o u r each week f o r about a y e a r , a f t e r w h i c h t h e y began d y i n g i n a p p r e c i a b l e numbers>• The f l o u r from w h i c h t h e a d u l t s had been removed was i n c u b a t e d f o r f i v e weeks. In t h i s way, 52 s u c c e s s i v e l o t s of b e e t l e s o f each s t o c k were produced o v e r a p e r i o d of a y e a r , each l o t presumably b e i n g g e n o t y p i c a l l y e q u i v a l e n t t o t h e o t h e r s s i n c e each l o t had t h e same p a r e n t s . E x p e r i m e n t a l a n i m a l s were drawn from t h e s e l o t s as r e q u i r e d . A l l s t o c k and e x p e r i m e n t a l c u l t u r e s were k e p t i n d a r k i n c u b a t o r s a t 27±2°. R e l a t i v e h u m i d i t y i n t h e f l o u r was d i f f i c u l t t o d e t e r m i n e , but t h e a i r i n t h e i n c u b a t o r s was k e p t a t about 10% R . H . w i t h pans of water p l a c e d n e a r the h e a t e r and f a n . Each c u l t u r e was housed i n a c y l i n d r i c a l s t y r e n e box (91 mm I .D. by 68 mm h i g h : #420, T r i s t a t e P l a s t i c Mould ing C o . , H e n d e r s o n , Kentucky) w i t h a c l o s e - f i t t i n g l i d and a 14 mm h o l e bored i n the s i d e and f i t t e d w i t h a 21 mm f l e x i b l e p o l y u r e t h a n e p l u g . Each box c o n t a i n e d 30g of f l o u r . In a d d i t i o n , ' o p e n ' c u l t u r e s had a 3-dram s h e l l v i a l (19x65.mm) taped u p r i g h t a g a i n s t the i n s i d e of the box . B e e t l e s c o u l d c l i m b from the f l o u r p l a c e d i n the b o x , up a s t r i n g , and drop i n t o the v i a l , w h i c h remained empty of f l o u r ; they c o u l d n o t r e t u r n f rom the v i a l t o t h e box because the s t r i n g d i d no t r e a c h the bottom of the v i a l . T h i s arrangement was m o d i f i e d f rom Prus (1963): the s t r i n g was a 12 cm l e n g t h of 12 l b . t e s t d a c r o n f i s h i n g l i n e ( B . F . G l a d i n g and C o . , S o u t h O t s e l i c , New Y o r k ) w i t h a loop t i e d i n the end t h a t hung i n t o the v i a l . In open c u l t u r e s , a d u l t s w h i c h had dropped i n t o the v i a l s were counted as m i g r a n t s , but t h o s e on the s t r i n g a t census t ime were counted as n o n - m i g r a n t s s i n c e they s t i l l had the o p t i o n of r e t u r n i n g t o the c u l t u r e . M i g r a n t s were removed p e r i o d i c a l l y w i t h an a s p i r a t o r and a t a l l y was kept o f t h e i r numbers. To f i n d out i f the s i n g l e s t r i n g o f f e r e d t o o r e s t r i c t e d an o p p o r t u n i t y f o r m i g r a t i o n , I s e t up the f o l l o w i n g t h r e e s e t s of c u l t u r e s : 5 c u l t u r e s w i t h 3 s t r i n g s each 5 c u l t u r e s w i t h 1 s t r i n g e a c h 5 c u l t u r e s w i t h 1 s t r i n g e a c h removed on a l t e r n a t e weeks . 10 I c o u l d f i n d no d i f f e r e n c e i n e m i g r a t i o n r a t e between t h e s e groups of c u l t u r e s so I conc luded t h a t my a p p a r a t u s n e i t h e r r e s t r i c t e d e m i g r a t i o n n o r en t rapped i n d i v i d u a l s d u r i n g t h e i r normal movements around the h a b i t a t . In t h i s p a p e r , ' f l o u r 8 i s used t o r e f e r t o a c u l t u r e medium wh ich c o n s i s t s o f p r e - s i f t e d , ' a l l - p u r p o s e ' wheat f l o u r mixed w i t h 5% by we ight T o r u l a y e a s t (Canada Soya I n d u s t r i e s , Vancouver , C a n a d a . ) . The f l o u r has been e n r i c h e d i n manufacture w i t h 0.44 mg T h i a m i n e , 0,26 mg R i b o f l a v i n , 3 . 5 mg N i a c i n , and 2 .9 mg I ron per 100 g f l o u r (Robin Hood M i l l s , L t d . , M o n t r e a l , C a n a d a ) . The medium was mixed i n 20 l b . l o t s and s e m i - s t e r i l i s e d i n a d r y oven f o r 24 hours a t 6 5 ° b e f o r e ' u s e . A census was made o f a l l e x p e r i m e n t a l c u l t u r e s once per month; e a c h c u l t u r e was passed t h r o u g h a n e s t o f two s i e v e s ( U . S . S t a n d a r d , 20 and 60 mesh w i t h openings o f 0.84 and 0.25 mm r e s p e c t i v e l y ) and a r e c e i v e r . A t f i r s t I i n c u b a t e d the m a t e r i a l w h i c h passed t h r o u g h t o the r e c e i v e r f o r f i v e weeks, but a f t e r r e c o v e r i n g o n l y two b e e t l e s , h a v i n g s i e v e d out o v e r 20 ,000 l a r v a e and e g g s , I t h e r e a f t e r d i s c a r d e d the c o n t e n t s o f the r e c e i v e r . "Mesh S e r i e s " s i e v e s c o u l d no t pass t h i s t e s t : l a r g e numbers of l a r v a e pass t h r o u g h the 60 mesh s i e v e . A p -p a r e n t l y the openings i n "Mesh S e r i e s " s i e v e s a r e l a r g e r than t h o s e i n U, S . S t a n d a r d s i e v e s d e s p i t e the same mesh r a t i n g . The f i r s t s i e v e r e t a i n e d a l l the a d u l t s , pupae , and l a r g e l a r v a e and some of the medium l a r v a e and c a s t s k i n s . These were dumped' i n t o an enameled t r a y , the c a s t s k i n s blown away - 11 by mouth , and the l i v e s t a g e s counted by p i c k i n g them up one by one w i t h an a s p i r a t o r . The second s i e v e r e t a i n e d t h e r e m a i n d e r o f the medium l a r v a e and the s m a l l l a r v a e , e g g s , c a s t s k i n s and f r a s s . T h i s f r a c t i o n was s p r i n k l e d on t o b l a c k c o n s t r u c t i o n p a p e r , where the l a r v a e tended t o c l i n g t o the paper w h i l e the r e s t o f the m a t e r i a l was shaken o f f . The l a r v a e were then counted as t h e y were f l i c k e d o f f the paper one a t a t ime w i t h a s m a l l b r u s h . Two p a s s e s on the paper removed o v e r 99% o f the l a r v a e , and the few r e m a i n i n g s m a l l l a r v a e and the eggs were s e p a r a t e d f rom the c a s t s k i n s and f r a s s i n an a i r s e p a r a t o r . The a i r s e p a r a t o r was a l i g h t c a r d b o a r d c o n i c s e c t i o n 5 cm D i a . a t the b o t t o m , 8 cm D i a . a t the t o p and 10 cm. h i g h , w i t h a 5 cm D i a . l u c i t e r i n g a t t a c h e d t o the bottom f o r s u p p o r t . The bottom was c o v e r e d w i t h a p i e c e of f i n e b o l t i n g c l o t h and the a p p a r a t u s was h e l d a t o p a 1000 ml E r l e n m e y e r c f l a s k w h i c h had been packed w i t h spun g l a s s . Compressed a i r was passed t h r o u g h a wa te r t r a p and a d iaphragm r e g u l a t o r s e t at- 12 p s i . , then t h r o u g h a c o n t r o l v a l v e and i n t o the E r l e n m e y e r f l a s k t h r o u g h a p o r t n e a r the b o t t o m . In o p e r a t i o n a sample was p l a c e d i n t h e cone and the a i r was t u r n e d on s l o w l y . The d r y c a s t s k i n s and f r a s s were c a r r i e d out o f the cone by the a i r s t ream and s e t t l e d on t o the t a b l e w h i l e the l a r v a e , eggs and a few odd p i e c e s o f c u t i c l e , b e i n g much d e n s e r , remained on the b o l t i n g c l o t h . About 10% o f the f i r s t i n s t a r l a r v a e were e j e c t e d f rom the a p p a r a t u s , p r o b a b l y because they tended t o c l i n g t o c a s t s k i n s . However, s i n c e l e s s than 1% of the l a r v a e were p l a c e d i n the s e p a r a t o r t o b e g i n w i t h , the l o s s was l e s s than 0..1% and was i g n o r e d . A f t e r t rea tment i n the a i r s e p a r a t o r , the egg f r a c t i o n was a g a i n s p r i n k l e d on t o the paper to check f o r the p r e s e n c e of s m a l l l a r v a e , w h i c h were c o u n t e d . Upon c o m p l e t i o n of c o u n t i n g , a l l l i v i n g s t a g e s were p l a c e d i n a new c o n t a i n e r w i t h f r e s h f l o u r . The eggs were no t c o u n t e d , but were r e t a i n e d w i t h the o t h e r s t a g e s . Open c u l t u r e s were a l l o w e d t o s e t t l e down f o r s i x days b e f o r e the s t r i n g s were r e p l a c e d . A l l a p p a r a t u s was s t e r i l i z e d between uses i n a d r y oven a t 8 5 ° o r i n an a u t o c l a v e a t 15 p s i . s team. Counte rs were r e g u l a r l y washed w i t h 95% e t h y l a l c o h o l . Much of the c o u n t i n g p rocedure was m o d i f i e d from Park (1948) , Watt (1955) and L l o y d (1968) . The l a r v a e were p l a c e d i n t h r e e s i z e c l a s s e s a f t e r the method of L l o y d . THE EXPERIMENTS 13 Experiment 1_. Open and closed c u l t u r e s . '.Introduction and Methods: I f open c u l t u r e s do not r e g u l a t e t h e i r d e n s i t i e s below those of closed c u l t u r e s , then e i t h e r the presumed polymorphism doesn't e x i s t , or the separation of the morphs i s not e f f e c t e d through emigration. In e i t h e r case, C h i t t y ' s hypothesis i s wrong. A d d i t i o n a l l y , i f the g e n e t i c v a r i a b i l i t y and the a s s o c i a t i o n between f e c u n d i t y and d o c i l i t y r e q u i r e d by C h i t t y ' s hypothesis e x i s t s , the Gen. 2 o f f s p r i n g w i l l be more fecund and should reach higher d e n s i t i e s than those reached by Gen. 1 o f f s p r i n g . To t e s t these i m p l i c a t i o n s , I set up 71 c u l t u r e s of 50 a d u l t s each (11 Gen. 1 open; 50 Gen. 2 open; 10 Gen. 2 c l o s e d ) , and f o l l o w e d t h e i r performance over a p e r i o d of from nine to twelve months. Controls from'changing c o n d i t i o n s , aging of a d u l t s , and disease i n f e s t a t i o n s are discussed i n Appendix 1. R e s u l t s : ( F i g . 1, Table 1). D e n s i t i e s i n c l o s e d (D) c u l t u r e s were s i g n i f i c a n t l y higher (p<,05, t - t e s t ) • t h a n those i n Gen. 1 open c u l t u r e s (A) from the t h i r d month on, and s i g n i f i c a n t l y higher than the Gen. 2 c u l t u r e s (B) from the f o u r t h month on. Gen. 2 c u l t u r e s were higher (p<p5, t - t e s t ) than Gen. 1 c u l t u r e s from the second month on. ( C a p i t a l l e t t e r s i n parenthesis r e f e r to column headings i n Appendix 2). D i s c u s s i o n : The polymorphism hypothesis has been placed a t r i s k F i g . 1„ Performance of a d u l t b e e t l e s i n open and closed c u l t u r e s , ( • . • . each of 30 g. f l o u r . • mean of 11 open c u l t u r e s Gen. 1 stock O mean of 50 open c u l t u r e s Gen. 2 stock ® mean of 10 c l o s e d c u l t u r e s Gen. 2 stock MONTHS in Table I. Age Composition of Gen. 2 Standard Error are Shown. Open Cultures by Month. Means and Their Month Adults Pupae 0 50.0 ( 0.0) 0.0 ( 0.0) 1 40.0 ( 0.5) 47.7 ( 3.5) 2 361.8 (14.0) 22.2 ( 1.7) 3 258.4 (13.1) 51.7 ( 6.9) 4 201.8 (12.8) 23.5 ( •3.5) 5 135.5 (10.1) 5.5 ( 1.4) 6 108.5 ( 9.0) 18.8 ( 6.5) 7 74.0 (7.6) 0.1 ( 0.1) 8 48.1 (4.5) 0.0 ( 0.0) 9 31.8 ( 2.9) 0.0 ( 0.0) 10 19.1 ( 1.6) 0.1 ( 0.1) Large Medium Small Larvae Larvae Larvae 0.0 ( 0.0) 0.0 ( 0.0) 0.0 (0.0) 146.9 ( 6.3) 213.9 10.0) 223.4 (9.3) 23.5 ( 2.1) 46.6 ( 3.2) 172.3 (5.8) 9.8 ( 1.7) 27.4 ( 3.7) 198.5 (14.5) 7.3 ( 1.3) 30.4 ( 4.6) 220.5 (15.1) 4.7 ( 1.2) 36.5 ( 6.2) 276.8 (15.0) 3.1 ( 1.1) 29.4 ( 2.8) 305.7 (18.1) 0.4 ( 0.2) 4.6 ( 1.3) 306.1 (17.7) 1.0 ( 0.4) 42.3 ( 3.8) 257.9 (20.7) 0.3 ( 0.2) 70.9 ( 5.8) 124.4 (14.5) 0.5 ( 0.3) 35.2 ( 4.7) 68.7 (11.5) 17 and has n o t been r e f u t e d , as t h e r e s u l t s conform t o i t s p r e -d i c t i o n s . The c a n n i b a l i s m h y p o t h e s i s has n o t been p l a c e d a t r i s k , s i n c e t h e a d d i t i o n o f a n o t h e r form o f ' m o r t a l i t y ' (emig-r a t i o n ) c o u l d s i m p l y have s h i f t e d t h e e q u i l i b r i u m p o i n t o f t h e r e g u l a t i o n . D e n s i t i e s a c h i e v e d by c l o s e d c u l t u r e s i n t h i s work a r e l o w e r t h a n t h o s e r e p o r t e d by P a r k (1954). T h i s e f f e c t i s c o n s i s t e n t w i t h t h e polymorphism h y p o t h e s i s because my s t o c k s were p r o b a b l y l e s s i n b r e d t h a n t h o s e o f P a r k . The d a t a can n o t be used t o t e s t t h i s p o i n t however, s i n c e P a r k used a d i f f e r e n t s i z e c u l t u r e (8 g v s . my 30 g) and i t i s known t h a t numbers a r e n o t l i n e a r l y p r o p o r t i o n a l t o f l o u r volume (McDonald, 1969). As t h e s e p o p u l a t i o n s have o v e r l a p p i n g g e n e r a t i o n s , e s t i m -a t i n g t h e mean number o f g e n e r a t i o n s p e r u n i t t i m e i s impos-s i b l e w i t h o u t p e d i g r e e d a t a . The development t i m e i s about 32 days (egg t o s e x u a l l y mature a d u l t ) but t h e a d u l t s can c o n t i n u e t o be p r o d u c t i v e f o r o v e r a y e a r . As t h e p o p u l a t i o n i s i n c r e a ? s i n g , mean g e n e r a t i o n t i m e must be l e s s t h a n when t h e p o p u l a t i o n i s d e c r e a s i n g . By means of r o u g h , and l a r g e l y i n d e f e n s i b l e c a l -c u l a t i o n s , I e s t i m a t e d t h a t t h e Gen. 2 open c u l t u r e s a veraged about 4 g e n e r a t i o n s i n t h e i r f i r s t ' 9 months. Experiment 2_. C u l t u r e s w i t h a r t i f i c i a l age s t r u c t u r e s . I n t r o d u c t i o n and methods: I now w i s h e d t o s e e , i f , i n s p i t e o f t h e i r l o w e r d e n s i t i e s , t h e open c u l t u r e s were n e v e r t h e l e s s b e i n g k e p t i n check by mechanisms n o t i n v o l v i n g a q u a l i t y change i n ; t h e i n d i v i d u a l s making up t h e p o p u l a t i o n . I f no q u a l i t y change o c c u r s , t h e n d e n s i t y a t t i m e T n i s d e t e r m i n e d by d e n s i t y and age s t r u c t u r e at T n - 1 , According t o the polymorphism hypothesis, however, d e n s i t y a t T n would a l s o depend on the amount of s e l e c t i o n to which the population had been subjected. I t h e r e f o r e chose randomly 1 0 of the 5 0 Gen. 2 open c u l t u r e s (G) from Exp. 1 t o serve as model c u l t u r e s . Using the data from these, I r e c o n s t r u c t e d the d e n s i t y and age s t r u -c t u r e of each model a t month 1 , using unselected Gen. 2 o f f -s p r i n g , t o produce 1 0 open mimic c u l t u r e s ( F ) . Thus, each mimic was given the same d e n s i t y and age s t r u c t u r e as i t s model had a t but the same ge n e t i c composition as .its model had a t T 0, For i n s t a n c e , model r e p l i c a t e Number 1 was s t a r t e d w i t h 5 0 a d u l t s of Gen. 2 o f f s p r i n g . One month l a t e r the census revealed 4 0 a d u l t s , 2 5 pupae, 1 5 1 large l a r v a e , 3 5 3 medium l a r v a e , 1 2 5 s m a l l l a r v a e and an estimated 1 0 0 eggs. I then made up mimic 1 by going t o the Gen. 2 o f f s p r i n g stock and counting out the app r o p r i a t e numbers of each stage and combining them i n an open c u l t u r e . One month l a t e r , I censused both c u l t u r e s and compared the numbers of a d u l t s present i n each. I made s i m i l a r comparisons f o r d e n s i t i e s and age s t r u c t u r e s a t months 2 (G), 3 (H), and 4 ( I ) , and f o r month 7 ( j ) using unselected Gen. 1 o f f s p r i n g , making a t o t a l of 5 0 mimic c u l t u r e s . I f no s e l -e c t i o n had occurred i n the models, there should have been no d i f f e r e n c e between the two kinds of c u l t u r e s ; i f s e l e c t i o n had occurred, the mimics should have maintained higher den-s i t i e s than t h e i r models s i n c e a l l mimics had the genet i c c o n s t i t u t i o n f o r T Q > a time of r i s i n g d e n s i t i e s i n the models. R e s u l t s : ( F i g . 2 ) . In a l l cases d e n s i t i e s were s i g n i f i c a n t l y higher i n the mimics than the models (p<.05; o n e - t a i l e d t - t e s t ) D i s c u s s i o n : Changes i n age s t r u c t u r e are not s u f f i c i e n t to e x p l a i n the r e g u l a t i o n of numbers i n the open c u l t u r e s . F i g . 2 shows t h a t the mimic c u l t u r e s c o n t a i n a propensity to i n c r e a s e , which i s being l o s t w i t h time i n the r e g u l a r open c u l t u r e s . E s p e c i a l l y i n months 3, 4, and 7, the performance of the mimic c u l t u r e s resembles t h a t of the r e g u l a r open c u l t u r e s i n months 1 and 2. I t appears they are performing more l i k e t h e i r 'genetic age' ( T Q ) than t h e i r 'age s t r u c t u r e age' ( T 3 , T 4 ? and T y ) . Experiment 3. The constancy of m i g r a t i n g behaviour. I n t r o d u c t i o n and methods: I f the d i f f e r e n c e between.open and clos e d c u l t u r e s i s , i n f a c t , t r a c e a b l e t o a d i f f e r e n c e i n mig-r a t i o n r a t e between two morphs, then i t f o l l o w s t h a t a migrant, i f put back i n t o the c u l t u r e i t migrated from, should tend to migrate again. To t e s t t h i s I m p l i c a t i o n , I set up 10 open c u l t u r e s , each w i t h 150 a d u l t Gen. 2 o f f s p r i n g of the same age. A f t e r a l l o w i n g the animals to s e t t l e down f o r sw: days, I put s t r i n g s i n place and c o l l e c t e d a l l the migrants f o r the next 14 days ( f i r s t m i g r a t i o n p e r i o d ) , marking each w i t h a spot of pai n t ( L i q u i d e x A c r y l i c Polymer Emulsion, Permanent Pigments Inc., C i n c i n n a t i , Ohio). At the end of the 14 days, I removed to o F i g . 2. .Performance of a d u l t b e e t l e s i n mimic c u l t u r e s and t h e i r models. • mean of 11 model c u l t u r e s , Gen. 1 st o c k O mean of 10 model c u l t u r e s , Gen, 2 s t o c k © mean of 10 mimic c u l t u r e s F i v e s e t s of mimic c u l t u r e s are shown, each set made t o mimic the stage of the model c u l t u r e represented by i t s j u n c t i o n w i t h the model c u l t u r e l i n e . F u r t h e r e x p l a n a t i o n i n t e x t . 600r 500h MONTHS 22 the non-migrants and marked them with a d i f f e r e n t colour', the colour code being reversed in half of the cultures. I then re-combined the emigrants and non-migrants, placed them in-a new 30 g of f l o u r and, a f t e r the six-day s e t t l i n g down period, recorded the colour of those bettles emigrating during the next eight days (second migration period). Results: Of the 1466 beetles.which survived to the end of the f i r s t migration period, 1131 were non-migrants and 335 were migrants. During the second migration period, 198 beetles migrated, of which 105 had also been migrants during the f i r s t migration period. The p r o b a b i l i t y that migrants of the f i r s t period have no greater propensity to migrate in the second period than the non-migrants i s less than .001 (Con-tingency O C 2 (df = 1) =118). Discussion: Had t h i s t e s t shown the second migration to be random with respect to the f i r s t , the hypothesis that d i f f e r e n t morphs were being separated by migration would have been unten-able. Yet, showing' that individuals are segregating non-randomly i s not the same as showing that these individuals• are the postulated morphs. That i s to say, migration could be non-random in terms of some genetic t r a i t s , but random in terms of others. This t e s t does not show that there is a genetic d i f -ference between the migrants and non-migrants. However, Ogden (1970) selected migrant and non-migrant lines of both Triboiium  confusum and T. castaneium for f i v e generations and was able to show that migration behaviour has a genetic component. Lemer 23 and Inouye (1968) showed t h a t a r e l a t e d form o f b e h a v i o u r , maze r u n n i n g , was a l s o under g e n e t i c c o n t r o l i n t h e same two s p e c i e s . Whether o r n o t t h e s e g e n e t i c d i f f e r e n c e s had any demographic consequences remains t o be seen. Experiment 4. M i g r a n t and non-migrant c u l t u r e s . I n t r o d u c t i o n and Methods: I f e m i g r a t i o n i s s e l e c t i v e , and i s s e p a r a t i n g t h e presumed morphs, t h e n c u l t u r e s s t a r t e d v / i t h mig-r a n t s must r e a c h h i g h e r d e n s i t i e s t h a n t h o s e s t a r t e d w i t h non-m i g r a n t s . T h i s i s so because, t o e x p l a i n t h e dr o p i n t h e d e n s i t i e s o f t h e r e g u l a r open c u l t u r e s , I presumed t h a t t h o s e i n d i v i d u a l s w h i c h c o u l d h a v e . p r e v e n t e d t h e dr o p were no l o n g e r p r e s e n t . The m i g r a n t s a r e t h e a n i m a l s w h i c h have l e f t , so t h e y must have t h i s p r o p e n s i t y t o form dense c u l t u r e s . To t e s t t h i s p r e d i c t i o n , I c o l l e c t e d t h e m i g r a n t s from t h e v i a l s o f t h e 50 Gen. 2 c u l t u r e s i n Exp. 1. A t t h e end o f e a c h o f s i x c o n s e c u t i v e months I w i t h d r e w a t random f i v e l o t s e a c h o f 50 a d u l t s , w i t h w h i c h I s t a r t e d f i v e open m i g r a n t c u l t u r e s . (K-P) A t t h e same t i m e , I s t a r t e d 50 r e p l i c a t e s o f t h e Gen. 2 Exp 1 c u l t u r e s , and, a t t h e end o f each month, broke up enough o f t h e s e c u l t u r e s t o y i e l d 250 a d u l t s w h i c h had n o t m i g r a t e d . W i t h t h e s e I s t a r t e d f i v e open non-migrant c u l t u r e s (Q-V) each month. I c o u l d n o t draw t h e m i g r a n t s and n o n - m i g r a n t s from t h e same s e t o f r e p l i c a t e s because as I s e q u e n t i a l l y d e s t r o y e d c u l t u r e s t o o b t a i n n o n - m i g r a n t s , I would have been d r a w i n g t h e subsequent m i g r a n t samples from a d i f f e r e n t sub-s e t o f c u l t u r e s . T h e r e f o r e , t h e n e x t b e s t t h i n g was t o g e t t h e 24 m i g r a n t s and no n - m i g r a n t s from d i f f e r e n t , but g e n e t i c a l l y and e x p e r i m e n t a l l y e q u i v a l e n t s e t s o f r e p l i c a t e s . R e s u l t s : ( F i g . 3 ) . C u l t u r e s founded by m i g r a n t s o f f i v e o f th e s i x p e r i o d s r e a c h e d h i g h e r d e n s i t i e s t h a n d i d t h e i r r e s -p e c t i v e non-migrant c u l t u r e s (p<.05; one t a i l e d t - t e s t ) . F o r p e r i o d 5 t h e d i f f e r e n c e was n o t s i g n i f i c a n t . D i s c u s s i o n : The p r e d i c t i o n s o f t h e polymorphism h y p o t h e s i s were c o n f i r m e d . The m i g r a n t group l e a v i n g t h e c u l t u r e s d u r i n g any p a r t i c u l a r p e r i o d e x h i b i t e d a g r e a t e r a b i l i t y t o i n c r e a s e t h e p o p u l a t i o n d e n s i t y t h a n d i d t h e non-migrants o f t h e same p e r i o d . Of p a r t i c u l a r i n t e r e s t i s t h e performance o f t h e second p e r i o d m i g r a n t s ( F i g . 3 B ) . To be a second p e r i o d m i g r a n t , an a n i m a l had t o be e i t h e r (1) a non-migrant in;.the f i r s t p e r i o d and a m i g r a n t i n t h e n e x t o r (2) a m i g r a t i n g o f f s p r i n g of a non-m i g r a n t . I t i s n o t s u r p r i s i n g , t h e r e f o r e , t h a t t h e performance of t h i s group i s s i m i l a r t o t h a t o f t h e s t o c k p o p u l a t i o n . A f t e r p e r i o d 2, a l l m i g r a n t s had been s u b j e c t e d t o more non-migrant s e l e c t i o n t h a n m i g r a n t s e l e c t i o n , and t h e i r performance was a c c o r d i n g l y l o w e r t h a n t h a t o f . t h e s t o c k p o p u l a t i o n s . I t ap-pea r s t h a t i n e a c h s u c c e s s i v e p e r i o d , t h e p o p u l a t i o n ' s a v e r a g e a b i l i t y t o d r i v e out o t h e r s i n c r e a s e s , and so phenotypes w h i c h a r e n o t d i s p l a c e d i n one p e r i o d , may be d i s p l a c e d i n a l a t e r p e r i o d . T h i s r e s u l t s i n e x t r e m e l y ' s o f t ' s e l e c t i o n ( W a l l a c e , 1 968), w h i c h I d i d n o t p r e d i c t . By ' s o f t ' s e l e c t i o n , W a l l a c e means t h a t , w h i l e f i t n e s s d e t e r m i n e s t h e o r d e r i n w h i c h a n i m a l s a r e e l i m i n a t e d , t h e number e l i m i n a t e d depends on some Performance of a d u l t b e e t l e s i n c u l t u r e s founded by migrants, non-migrants and unselected stock. O mean of 50 open c u l t u r e s , unselected s t o c k ©mean of 5 open c u l t u r e s , migrant stock O mean of 5 open c u l t u r e s , non-migrant stock Each graph shows migrant and non-migrant c u l t u r e s founded by a d u l t s taken from a d i f f e r e n t p o i n t i n the development of r e g u l a r open c u l t u r e s i n d i c a t e d by A . 27 other f a c t o r . In the migrant-founded c u l t u r e s , one expects a decrease i n the average a b i l i t y to d i s p l a c e o t h e r s , and t h i s shov;s up i n the high d e n s i t i e s recorded f o r these c u l t u r e s . I f a simple tendency to migrate, or a h i g h general a c t i v i t y was the prime c h a r a c t e r i s t i c of migrants, the migrant-founded popul-c' a t i o n s should have a h i g h tendency t o migrate, and consequently, a low pop u l a t i o n d e n s i t y , the opposite of what was observed. In some i n s e c t s , the a c t of mi g r a t i n g r e l e a s e s b e h a v i o u r a l or p h y s i o l o g i c a l i n h i b i t i o n s and an increase i n f e c u n d i t y r e s u l t s (Johnson, 1963). In my c u l t u r e s , the s t i m u l u s , i . e . one a c t of m i g r a t i n g , i s i d e n t i c a l f o r migrants of a l l p e r i o d s . I f t h i s mechanism was r e s p o n s i b l e f o r the high p o p u l a t i o n d e n s i t i e s observed i n migrant-founded p o p u l a t i o n s , I would expect t h a t the higher gains achieved by the f i r s t p e riod migrants would be repeated by the migrants of subsequent p e r i o d s ; i t i s not. n o t i c e t h a t c u l t u r e s s t a r t e d w i t h migrants from the s i x t h p e r i o d ( F i g . 3F) reached r e l a t i v e l y h i g h d e n s i t i e s , r e v e r s i n g a t r e n d seen across the other f i v e p e r i o d s , I i n t e r p r e t t h i s to mean t h a t , as the d e n s i t y of the supplying c u l t u r e f a l l s , p o t e n t i a l d i s p e r s e r s can remain i n the c u l t u r e longer and l a y more eggs. Even though they are e v e n t u a l l y d r i v e n out and the po p u l a t i o n as a whole' continues to f a l l , the frequency of these p o t e n t i a l d i s p e r s e r s should increase among the progeny of each suc c e s s i v e generation. Under s o f t s e l e c t i o n , the 'samples' taken by m i g r a t i o n should i n c r e a s i n g l y c o n s i s t of d i s p e r s i n g type animals, which, by the polymorphism hy p o t h e s i s , i m p l i e s i n c r e a s i n g f e c u n d i t y . This would r e s u l t i n the good performance 28 of the migrant-founded c u l t u r e s . Since these d i s p e r s e r s are e v e n t u a l l y d r i v e n out of the supplying c u l t u r e , a sample of a d u l t s drawn from the c u l t u r e should continue t o be l a r g e l y non-d i s p e r s i n g types,.and t o found c u l t u r e s which do not reach hig h peak d e n s i t i e s . Experiment 5. Numeric and gen e t i c e f f e c t s of m i g r a t i o n . I n t r o d u c t i o n and Methods: J u s t because a demographic d i f f e r -ence e x i s t s between migrants and non-migrants, i t does not n e c e s s a r i l y f o l l o w t h a t t h i s d i f f e r e n c e i s r e s p o n s i b l e f o r the r e g u l a t i o n observed i n open c u l t u r e s . The idea i s amenable t o t e s t , however. One can imagine emigration a f f e c t i n g a p o p u l a t i o n i n two ways: i t can reduce current d e n s i t y merely by removing members of the p o p u l a t i o n , and i t can reduce f u t u r e d e n s i t y by s e l e c t i v e l y removing those members of the po p u l a t i o n whose o f f -s p r i n g would have c o n t r i b u t e d most to the maintenance of d e n s i t y . I t i s not p o s s i b l e t o remove genotypes from a po p u l a t i o n w i t h -out removing i n d i v i d u a l s , but i t i s p o s s i b l e t o remove i n d i v -i d u a l s without s e l e c t i v e l y removing genotypes. In the f o l l o w i n g experiment I compared the performance of two types of c u l t u r e s : one from which i n d i v i d u a l s were l e a v i n g of t h e i r own accord (and presumably not a t random), and another from which an equal number was removed a t random. I f the two types of c u l t u r e s perform a l i k e , then the polymorphism hypothesis, i s r e f u t e d . To do t h i s experiment, I randomly nominated 10 of the open Gen. 2 c u l t u r e s from Exp. 1 t o serve as models i n which n a t u r a l m i g r a t i o n r e s u l t e d i n b o t h n umeric and g e n e t i c l o s s . W i t h g e n o t y p i c a l l y e q u i v a l e n t s t o c k , I e s t a b l i s h e d 10 mimic c u l t u r e s under i d e n t i c a l c o n d i t i o n s , e x c e p t t h a t t h e y were c l o s e d and were s e t up two months l a t e r . I t h e n a s s i g n e d , a t random, one mimic t o e a ch model. A t each monthly c e n s u s , I randomly removed from t h e mimics t h e same number of a d u l t s as had m i g r a t e d from t h e c o r r e s p o n d i n g model d u r i n g t h e h a l f month b e f o r e and t h e h a l f month a f t e r t h e comparable model census. T h i s m a n i p u l a t i o n r e s u l t s i n two d e n s i t i e s e a ch month f o r t h e mimic c u l t u r e s , one b e f o r e and one a f t e r r e m o v a l . In t h i s way t h e mimics were s u b j e c t e d t o t h e same numeric l o s s as were t h e m o dels, but t o none of t h e assumed d i f f e r e n t i a l g e n e t i c l o s s . R e s u l t s : ( F i g . 4 ) . The d e n s i t i e s o f t h e two t y p e s of c u l t u r e s a r e n o t d i f f e r e n t a t months 1, 3 and 4. The mimics a r e l o w e r a t month 2, as i s t r u e o f c l o s e d c u l t u r e s i n Exp. 1. From month 5 onward, t h e y a r e s i g n i f i c a n t l y h i g h e r t h a n ' t h e models. (p<.01) D i s c u s s i o n : The p r e d i c t i o n s o f t h e polymorphism h y p o t h e s i s have been f u l f i l l e d . Numeric l o s s a l o n e was n o t s u f f i c i e n t t o e x p l a i n t h e b e h a v i o u r of open c u l t u r e s a f t e r t h e f o u r t h month. D u r i n g t h e f i r s t f o u r months, numeric l o s s was s u f -f i c i e n t t o e x p l a i n t h e b e h a v i o u r o f open c u l t u r e s , w h i c h was n o t u n e x p e c t e d , s i n c e g e n e t i c l o s s e s a f f e c t f u t u r e g e n e r a t i o n s and a r e c u m u l a t i v e . Performance of a d u l t beetles i n normal open c u l t u r e s and i n cu l t u r e s where migrants are chosen a t random. O mean of 10 open c u l t u r e s , Gen. 2 stock © mean of 10 closed c u l t u r e s , Gen. 2 stock i n which migrants are chosen a t random. Two po i n t s f o r each month i n random m i g r a t i o n c u l t u r e s represent the numbers before and a f t e r removal. 32 GENERAL DISCUSSION As C h i t t y (1967) has p o i n t e d o u t , "the s i n e qua non f o r any s c i e n t i f i c h y p o t h e s i s i s t h a t i t be s t a t e d i n a way t h a t can be t e s t e d , w h i c h means t h a t some form o f g e n e r a l i z a t i o n i s r e q u i r e d . T e s t i n g c o n s i s t s of t r y i n g t o f a l s i f y t h i s g e n e r a l -i s a t i o n , s i n c e e v i d e n c e i n f a v o u r o f a h y p o t h e s i s i s g e n e r a l l y u s e l e s s e x c e p t when i t r e s u l t s from a f a i l u r e o f s u c h a t - . ." ... tempts...". F o r any outcome, an a l t e r n a t i v e h y p o t h e s i s can u s u a l l y be o f f e r e d i n e x p l a n a t i o n a p o s t e r i o r i , but an a p r i o r i h y p o t h e s i s must t a k e precedence o v e r i t , o t h e r t h i n g s b e i n g e q u a l (Popper, 1963). I t i s always hazardous t o e x t r a p o l a t e from l a b o r a t o r y t o f i e l d s i t u a t i o n s , where many t h i n g s a r e c h a n g i n g , but perhaps l a b o r a t o r y s t u d i e s can h e l p i d e n t i f y some p r o c e s s e s as impos-s i b l e o r i m p r o b a b l e and d e f i n e o t h e r s more c o n c i s e l y , s u c h t h a t t h e l a b o r of f i e l d t e s t i n g i s r e d u c e d . In t h i s r e s e a r c h I have p l a c e d T r i b o i i u m p o p u l a t i o n s i n f i v e s p e c i f i c s i t u a t i o n s , and i n e a c h s i t u a t i o n I have d e f i n e d one outcome out of t h e c l a s s o f a l l p o s s i b l e outcomes w h i c h , i f n o t o b s e r v e d , would r e f u t e t h e polymorphism h y p o t h e s i s o u t l i n e d i n . t h e I n t r o d t i c t i o n . F i r s t l y , I compared open w i t h c l o s e d c u l t u r e s (Exp. 1) s i n c e I t h o u g h t t h a t i n open c u l t u r e s numbers s h o u l d be r e g -u l a t e d a t d e n s i t i e s below t h o s e o f c l o s e d ones. The d e n s i t i e s o f t h e c l o s e d c u l t u r e s i n c r e a s e d s t e a d i l y f o r s i x months, ; t h e n f e l l s l o w l y f o r t h e n e x t t h r e e months. However, t h e open 33 c u l t u r e s rose s h a r p l y , reaching a much lower peak d e n s i t y i n two months, then f e l l p r e c i p i t o u s l y , l e v e l l i n g o f f at very low d e n s i t i e s ( F i g . 1 ) . Although I had p r e d i c t e d the eventual lower l e v e l of the open c u l t u r e s , I was unprepared f o r the r a p i d and sp e c t a c u l a r way i n which t h a t l e v e l was reached. Next, I wanted t o see i f any change had occurred i n the demographic q u a l i t y of the members of the.open c u l t u r e s during t h e i r r i s e and then p r e c i p i t o u s f a l l i n d e n s i t y , so I put together sets of a r t i f i c i a l p o p u l a t i o n s , each made up according t o the d e n s i t y and age s t r u c t u r e observed i n a r e g u l a r open c u l t u r e a t some point i n i t s development (Exp. 2 ) . Since I used stock which was g e n e t i c a l l y e q u i v a l e n t t o the stock used t o s t a r t the r e g u l a r c u l t u r e s , the only d i f f e r e n c e between the a r t i f i c i a l and r e g u l a r c u l t u r e s should have been m o d i f i c a t i o n s of the phenotypic c o n s t i t u t i o n of the l a t t e r which had occurred s i n c e the c u l t u r e s were founded. I reasoned t h a t i f the den-s i t i e s of the two types of c u l t u r e s followed each other f a i r l y w e l l i n the ensuing few months, none of the p r e d i c t e d changes could have occurred. The a r t i f i c i a l c u l t u r e s and the r e g u l a r ones reacted very d i f f e r e n t l y ( F i g . 2) so I concluded, t h a t some change had occurred i n the i n d i v i d u a l s of the r e g u l a r c u l t u r e s s i n c e the c u l t u r e s ' founding. But how was i t occurring? Assuming the polymorphism hypothesis, I p r e d i c t e d t h a t the change occurred because the frequency of one demographic type of animal was being reduced i n the c u l t u r e , s i n c e t h a t type was emigrating a t a d i s p r o p o r -t i o n a t e l y h i g h r a t e . I f t h i s i s t r u e , i t must a l s o be t r u e t h a t 34 the tendency t o m i g r a t e i s a p r o p e r t y of the i n d i v i d u a l a n i m a l , so t h a t i f an i n d i v i d u a l m i g r a t e s o n c e , and i s r e t u r n e d t o the c u l t u r e , i t w i l l tend t o m i g r a t e a g a i n . I t e s t e d t h i s i n E x p . 3 and i t t u r n e d out t o be t r u e . S i n c e Ogden (1970) had shown m i g -r a n t T r i b o i i u m t o be g e n e t i c a l l y d i f f e r e n t from n o n - m i g r a n t s , i t seemed l i k e l y t h a t my m i g r a t i o n c l a s s e s were a l s o the demo-g r a p h i c morphs r e q u i r e d by the polymorphism h y p o t h e s i s . I f s o , they must have s p e c i f i c demographic p r o p e r t i e s . A c c o r d i n g l y , I p r e d i c t e d t h a t those i n d i v i d u a l s wh ich m i g r a t e d under a g i v e n s e t o f c o n d i t i o n s would found c u l t u r e s w h i c h would r e a c h h i g h e r peak d e n s i t i e s than would c u l t u r e s founded by i n d i v i d u a l s wh ich had been n o n - m i g r a n t s under t h e s e same c o n d i t i o n s . I t e s t e d the p r e d i c t i o n (Exp . 4) and found i t t o be c o r r e c t ( F i g , 3 ) , A t t h i s p o i n t , a l l the ' p a r t s ' r e q u i r e d by the po lymorphism h y p o t h e s i s seemed t o o p e r a t e as p r e d i c t e d and t h e y seemed t o work i n c o n c e r t . I now d e c i d e d t o t r y a s l i g h t l y d i f f e r e n t a t t a c k . U s i n g the polymorphism h y p o t h e s i s , I p r e d i c t e d a c i r c u m s t a n c e under wh ich norma l r e g u l a t i o n would f a i l , a c i r -cumstance under w h i c h no o t h e r r e g u l a t i o n h y p o t h e s i s known t o me would p r e d i c t a s i m i l a r f a i l u r e . I f s e l e c t i v e m i g r a t i o n i s r e s p o n s i b l e f o r the observed r e g u l a t i o n , then random m i g r a t i o n a t the same r a t e i n o t h e r w i s e comparable c u l t u r e s shou ld thwart t h a t r e g u l a t i o n . I conducted t h i s t e s t (Exp . 5) by removing a n i m a l s a t random from ' m i m i c ' c u l t u r e s a t the same r a t e t h a t they were l e a v i n g of t h e i r own 35 v o l i t i o n , and nonrandomly, from a set of 'model' c u l t u r e s founded w i t h g e n e t i c a l l y e q u i v a l e n t stock. Normal r e g u l a t i o n was indeed thwarted i n the 'mimic' c u l t u r e s ( F i g . 4 ) . Regulation i n open c u l t u r e s of T r i b o i i u m confusum appears t o be by means of s e l e c t i v e m i g r a t i o n . The l i t e r a t u r e on T r i b o i i u m i s voluminous, a t l e a s t 2000 published works. Of the e c o l o g i c p o r t i o n , almost a l l deals w i t h the behaviour of closed c u l t u r e s and, as regards r e g u l a t i o n , most expresses the view, i n whole or i n p a r t , t h a t changes i n age s t r u c t u r e feed back on d e n s i t y by means of cannibalism such t h a t r e g u l a t i o n i s achieved without modifying the gene po o l . The idea i s i l l u s t r a t e d w e l l by Park et a l ' (1965), i n d i s c u s s i n g a s t r a i n of T. castaneum. c i : "As a s i n g l e species p o p u l a t i o n , c i must be c o n t i n u a l l y engaged i n a s t r u g g l e between i t s impressive n a t a l i t y and developmental r a t e , on the one hand, and i t s e q u a l l y impressive c a n n i b a l i s t i c s e l f - d e s t r u c t i o n of eggs and pupae, on'the other hand. These counter processes of input and output.are r a r e l y , i f ever, i n e q u i l i b r i u m . The balance between them changes w i t h the s i z e of the p o p u l a t i o n and i t s immature-a d u l t age s t r u c t u r e . Eggs c o n s t a n t l y are being added to the ecosystem. This v a r i e s i n amount w i t h the number of fecund females, the extent to which they are crowded, and their- ages. But c i , w i t h i t s h i g h i n t r i n s i c r a t e of i n c r e a s e , i s always 36 a b l e t o s u p p l y eggs i n good measure... In a r e a l sense c l i s so s u c c e s s f u l , by any c r i t e r i o n , because i t s c a p a c i t y t o r e c r u i t i s tempered by i t s p r e d a t i o n ( c a n n i b a l i s m ) ; t h e f o r m e r p e r m i t t i n g s i z a b l e p o p u l a t i o n s t o be m a i n t a i n e d w h i l e t h e l a t t e r p r e v e n t s t h e s o r t o f g r o s s o v e r c r o w d i n g t h a t c h a r a c t e r i z e s b i a s t r a i n o f T. confusurn A t t h i s t i m e , two s i g n i f i c a n t f a c t s were known: , (1) t h a t t h e v e r y demographic c h a r a c t e r i s t i c s c i t e d above a r e under g e n e t i c c o n t r o l and d i f f e r among known s t r a i n s ( L e r n e r and Ho, 1961; P a r k e t a l , 1964) and (2) " t h a t a n y t h i n g w h i c h a f f e c t s y°, t h e p r o b a b i l i t y o f a p o t e n t i a l r e c r u i t b e i n g d e s t r o y e d by an a d u l t , i s l i k e l y t o have a p r o f o u n d e f f e c t on t h e number o f a d u l t s i n t h e p o p u l a t i o n " , ( L l o y d , 1968). N o t i c e s p e c i f i c a l l y t h a t P i s a p r o p e r t y o f one i n d i v i d u a l , n o t a p o p u l a t i o n . Even though he d e f i n e s P g e n e r a l l y , L l o y d o b v i o u s l y equated i t v / i t h c a n n i b a l i s m , f o r i n e x p l a i n i n g a d i s c r e p a n c y i n t h e p o p u l a t i o n t r e n d s o f s t r a i n c l , he i n v o k e d a change i n P and s u g g e s t e d i t was due t o a change i n t h e egg c a n n i b a l i s m r a t e . G e n e r a l l y , however, he adopts t h e p r e v a i l i n g v i e w t h a t P i s c o n s t a n t . Indeed, c l o s e d c u l t u r e s have, by and l a r g e , o n l y one form of d e a t h : c a n n i b a l i s m . A d u l t s cannot c a n n i b a l i z e o t h e r a d u l t s ( P a r k e t a l , 1965), so t o e f f e c t any l o n g term change i n P , one'must h y p o t h e s i s e t h a t t h e p r e d a t o r y s t a g e s can d e t e c t l a t e n t c a n n i b a l i s t i c t r a i t s i n t h e p r e y s t a g e s and p r e y on them s e l e c -t i v e l y . T h i s has n o t been shown, n o r does i t , s e e m p r o b a b l e . I n open c u l t u r e s the p i c t u r e changes. A new form o f 37 'death', e m i g r a t i o n , i s p o s s i b l e , and s e l e c t i o n f o r or a g a i n s t m i g r a t i o n can f a l l on the same stage that e x h i b i t s the t r a i t . Now an i n d i v i d u a l can be e l i m i n a t e d as a r e c r u i t without being k i l l e d and a group of t r a i t s which could not a f f e c t P i n closed c u l t u r e s are now f r e e t o do so. Since cannibalism i s s t i l l o c c u r r i n g , i t f o l l o w s t h a t opening a c u l t u r e can only change p upward, r e s u l t i n g i n a lower a d u l t d e n s i t y ( L l o y d , 1968). In my open c u l t u r e s t h i s lower d e n s i t y i s observed. In f a c t , the p o p u l a t i o n d e n s i t y approaches an asymptote which can-not be d i s t i n g u i s h e d from zero over the time spans reported here. The polymorphism hypothesis p r e d i c t s a balance between the morphs, not the slox-7 e x t i n c t i o n of one of them as these r e s u l t s seem to i n d i c a t e . But the polymorphism hypothesis addresses i t s e l f t o problems of n a t u r a l p o p u l a t i o n s , i n which both immigration and emigration are presumably o c c u r r i n g . My -experiments t e s t o n l y one p a r t of the system, the downward phase. I would speculate t h a t the upward phase i s c o n t r o l l e d by immigration, a t l e a s t i n p a r t . Some emigrants from 'optimal' areas might s u r v i v e i n l e s s s u i t a b l e areas, where they experience heavy s e l e c t i o n i n favour of upward phase morphs (see I n t r o d u c t i o n ) . They, or t h e i r progeny, could c o n s t i t u t e a supply of p o t e n t i a l immig-ran t s to the o p t i m a l areas. Such p o t e n t i a l immigrants would have an i n c r e a s i n g l y good chance of r e - e n t e r i n g the optimal area as the endemic population there decreased. 'No data are a v a i l a b l e on these matters and so f u r t h e r s p e c u l a t i o n , w h i l e i t c a r r i e s e x c i t i n g i m p l i c a t i o n s , i s f u t i l e . 38 C a r r i e d t h i s f a r , however, t h e model has i m p l i c a t i o n s as t o whether o r n o t n a t u r a l p o p u l a t i o n s a r e u s u a l l y open o r c l o s e d . I s u g g e s t t h a t as l o n g as members o f a p o p u l a t i o n have a c c e s s t o h a b i t a t s i n w h i c h t h e y would e x p e r i e n c e d i f f e r e n t s e l e c t i o n p r e s s u r e s , t h e p o p u l a t i o n must be open. A f u n c -t i o n a l l y c l o s e d p o p u l a t i o n would be one w h i c h e x i s t e d i n a p a t c h o f u n i f o r m h a b i t a t so l a r g e t h a t m i g r a t i o n a t i t s edges had no s i g n i f i c a n t e f f e c t on i n d i v i d u a l s i n t h e c e n t e r . I n t u i t -i v e l y , i t i s d i f f i c u l t f o r me t o e n v i s a g e s u c h a s i t u a t i o n i n n a t u r e . As mentioned i n t h e i n t r o d u c t i o n , C h i t t y o r i g i n a l l y c o n c e i v e d o f t h e polymorphism h y p o t h e s i s i n c o n n e c t i o n w i t h s m a l l mammals. One might p r e v i o u s l y have argued t h a t t h e model has been f i t t e d t o some p e c u l i a r i t y o f mammals and i s a p p l i c a b l e o n l y t o them. I b e l i e v e t h a t I have shown t h a t t h e polymorphism h y p o t h e s i s can be used t o p r e d i c t t h e p o p u l a t i o n t r e n d s o f a s p e c i e s . p h y l o g e n e t i c a l l y f a r removed from mammals, p r o v i d e d t h e p o p u l a t i o n i s c a p a b l e o f p r o d u c i n g e m i g r a n t s . I t h e r e f o r e s u g -g e s t t h a t t h e polymorphism h y p o t h e s i s w i l l be u s e f u l i n p r e -d i c t i n g p o p u l a t i o n t r e n d s i n a w i d e v a r i e t y o f s p e c i e s , , t h o u g h under c e r t a i n c o n d i t i o n s o n l y . I t w i l l p r o b a b l y be o f l i t t l e u se i n c l o s e d h a b i t a t s u n l e s s t h e s p e c i e s can e f f e c t a d e n s i t y dependent s e l e c t i o n by some means o t h e r t h a n m i g r a t i o n . Thoday's (1963) and S h o r r a c k ' s (1970) work on D r o s o p h i l a i n d i c a t e s t h a t s e l e c t i o n o f demographic morphs by o t h e r means i s p o s s i b l e . The d e n s i t y a t w h i c h r e g u l a t i o n o c c u r s i n t h e i r c u l t u r e s seems v e r y h i g h , a l t h o u g h I can f i n d i n t h e l i t e r a t u r e 39 no r e l i a b l e estimates f o r n a t u r a l populations of t h i s s p e c i e s . Perhaps Drosophila can e f f e c t a s e p a r a t i o n of morphs by two d i f f e r e n t agencies, each a c t i n g a t i t s own d e n s i t y . This appears to be an area r i p e f o r i n q u i r y . The other s i t u a t i o n i n which the polymorphism hypothesis w i l l be of l i t t l e or no value i n p r e d i c t i n g numbers i s i n the case of populations l i v i n g i n harsh h a b i t a t s . ('Harsh' and 'Kind 1 h a b i t a t s are used by Andrewartha and B i r c h , 1954). To be harsh v/ith regard to a given s p e c i e s , a h a b i t a t must be so unfavourable t h a t , on the average, losses to e x t r i n s i c f a c t o r s exceed gains from r e p r o d u c t i o n . Such s i t u a t i o n s must produce a strong s e l e c t i o n pressure f o r higher f e c u n d i t y , and t h e r e f o r e , assuming the t r u t h of polymorphism hypothesis, lead toward f i x -a t i o n of the h i g h f e c u n d i t y morph. Populations i n harsh hab-i t a t s can p e r s i s t o n l y i f the d i f f e r e n c e between m o r t a l i t y and f e c u n d i t y i s made up by immigration, i n v/hich case they a c t as absorbers of the surplus animals from b e t t e r h a b i t a t and as a g e n e t i c reserve of h i g h f e c u n d i t y morphs. Although the p o l y -morphism hypothesis would be of no use i n p r e d i c t i n g d e n s i t i e s i n harsh h a b i t a t s , these h a b i t a t s may, through gene f l o w , i n t e r -a c t v/ith k i n d h a b i t a t s and a f f e c t the f u n c t i o n i n g of the polymorphism mechanism i n the l a t t e r p l ace. Harsh h a b i t a t s have r e c e i v e d l i t t l e study, probably because population d e n s i t i e s there are correspondingly l e s s and s t a t i s t i c a l i n f e r e n c e becomes le s s c e r t a i n . This neglect i s unfortunate. In c o n c l u s i o n , I suggest that the polymorphism hypothesis 40 w i l l be u s e f u l i n p r e d i c t i n g population trends i n kind h a b i t a t s where (a) the f e c u n d i t y of a species exceeds e x t r i n s i c m o r t a l i t y , and (b) i n t r i n s i c mechanisms are being used to d i s -pose of the r e s u l t i n g s u r p l u s . Although we do not know the r e l a t i v e extent o f . h a r s h and k i n d h a b i t a t s c e r t a i n l y kind h a b i t a t s harbor the populations which account f o r the s u r v i v a l of a species f o r long periods of time. REFERENCES 41 Andrewartha, H.G. and L.C. B i r c h 1954. The d i s t r i b u t i o n and abundance of animals. Univ. of Chicago Press, Chicago, I l l i n o i s . 782 p. Beadmore, J . 1970. E c o l o g i c a l f a c t o r s and the v a r i a b i l i t y of gene-pools i n Drosophila. In Hecht, M.K. and W.C. Steere (Eds.) Essays i n e v o l u t i o n and genetics i n honor of Th. 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C o n t r o l C u l t u r e s f o r Exp. 1 The 50 Gen. 2 open and 10 Gen. 2 closed c u l t u r e s were set up a t the same time and run i n the same incubator, a procedure which c o n t r o l l e d f o r any s u b t l e d i f f e r e n c e s i n techniques or c o n d i t i o n s w i t h time. As a f u r t h e r check, 1 s t a r t e d 2 a d d i t i o n a l open c u l t u r e s ('sequential c u l t u r e s ' ) each month f o r the f i r s t s i x months of the run, using Gen. 2 stock. I reasoned that i f these 12 r e p l i c a t e s d i d not perform d i f f e r e n t l y from one another, then there was no s i g n i f i c a n t d i f f e r e n c e i n technique through the experiment. They were not d i f f e r e n t from one another, and the general shape of t h e i r a d u l t d e n s i t y curves was the same as th a t f o r the 50 Gen. 2 open c u l t u r e s . However, these s e q u e n t i a l c u l t u r e s held g e n e r a l l y higher d e n s i t i e s than d i d the 50 Gen. 2 open c u l t u r e s . Since s m a l l d i f f e r e n c e i n f e c u n d i t y and some beha v i o u r a l t r a i t s (e.g. egg cannibalism) were known (Mertz, 1965), I con-t r o l l e d f o r these e f f e c t s by s e t t i n g a s i d e one l o t of a d u l t Gen. 2 o f f s p r i n g a t the'time I s t a r t e d the 50 Gen. 2 open c u l t u r e s and, w i t h these, s t a r t e d two open c u l t u r e s ('sequential aged c u l t u r e s ' ) each month f o r the f i r s t s i x months of the run. In t h i s way the founders of each successive p a i r of c u l t u r e s were one month o l d e r than those of the p a i r before them. I reasoned t h a t i f there w e r e . n o ' s i g n i f i c a n t d i f f e r e n c e s between these s e q u e n t i a l aged c u l t u r e s and the s e q u e n t i a l c u l t u r e s , then a d u l t aging e f f e c t s were not s i g n i f i c a n t . The s e q u e n t i a l aged c u l t u r e s were not s i g n i f i c a n t l y d i f f e r e n t from the s e q u e n t i a l 49 c u l t u r e s , but shared w i t h the l a t t e r the tendency t o hold higher d e n s i t i e s than those i n the 50 Gen. 2 open c u l t u r e s . I do not know the reason f o r the d i f f e r e n c e between both sets of seq u e n t i a l s and the r e g u l a r open c u l t u r e s . 1 suspect that i t was due to a bias i n choosing founders. When I set up the 50 Gen. 2 open c u l t u r e s and the 10 Gen. 2 clo s e d c u l t u r e s , I used a t o t a l of 3000 a d u l t s (50 x 50+10 x 50) as founders, which represents n e a r l y the e n t i r e week's production f o r the Gen. 2 stocks (ca, 3 2 0 0 ) . When I set up the s e q u e n t i a l s , I used only 200 a d u l t s (2 x 50 + 2 x 5 0 ) . I f there was some unknown bias i n the o r i g i n a l sub-sampling of the week's production, i t would be most pronounced i n the s m a l l e r sample ( 2 0 0 ) . Since the time r e l a t i o n s h i p between the r e p l i c a t e s was important, I could not repeat these t e s t s without r e p e a t i n g the e n t i r e experiment. T r i b o i i u m i s subject t o a number of diseases ( c f . S o k o l o f f , 1966) the best known being A d e l i n a t r i b o l i i i n f e s t a t i o n (Park, 1948; Park and Frank, 1950). Although i t i s d i f f i c u l t to see how diseases would a f f e c t open c u l t u r e s more than closed ones, 1 had p r e d i c t e d lower d e n s i t i e s i n the open c u l t u r e s and 1 wished t o be as sure as p o s s i b l e t h a t any observed d i f f e r e n c e s were not due t o some diseas e . I t h e r e f o r e s e l e c t e d 11 of the lowest d e n s i t y r e p l i c a t e s from among the 50 Gen. 2 open c u l t u r e s and, inst e a d of throwing away t h e i r used f l o u r a f t e r the t h i r d census, I used i t t o s t a r t 11 new c u l t u r e s i n . There was no s i g n i f i c a n t d i f f e r e n c e between the performance of these 11 new c u l t u r e s and t h a t of the 50 Gen. 2 open c u l t u r e s . There was a s i g n i f i c a n t d i f f e r e n c e between the new c u l t u r e s and the 11 low .. • 50 r e p l i c a t e s from which the f l o u r had come. I t appears t h a t , i f a disease i s r e s p o n s i b l e f o r the low d e n s i t i e s i n the open c u l t u r e s , i t a f f e c t s open c u l t u r e s more than c l o s e d ones, i t a f f e c t s non-migrant stock more than migrant s t o c k , and i t can-not be t r a n s m i t t e d t h r o u g h contaminated c u l t u r e medium. I would say t h a t such a disease i s u n l i k e l y . Throughout t h i s work I was impressed by the tendency of the r e p l i c a t e s t o perform s i m i l a r l y to others i n t h e i r groups, and t h e r e f o r e I f e e l t h a t the means and standard e r r o r s of the means g i v e an adequate p i c t u r e of the o v e r a l l performance of a l l the r e p l i c a t e s . In a l l c u l t u r e s s t a r t e d w i t h f i f t y a d u l t s , the general shape of the t i m e / d e n s i t y curve f o r each r e p l i c a t e Is l i k e the mean. There was a strong tendency f o r r e p l i c a t e s that, developed h i g h peak d e n s i t i e s e a r l y i n t h e i r h i s t o r y t o r e t a i n above mean d e n s i t i e s f o r the r e s t of the experiment, and conversely, those showing low peak d e n s i t i e s tended t o remain below the mean. An example of t h i s can be seen i n Table IV. . ' ' The 50 Gen. 2 open c u l t u r e s i n Exp. I showed the g r e a t e s t range between the r e p l i c a t e s ; the standard e r r o r s are s m a l l because of the large number of r e p l i c a t e s . This group con-t a i n e d two markedly 'abnormal' r e p l i c a t e s whose d e n s i t i e s pro-gressed from month 0 t o month 10 as f o l l o w s : 50/39/32/13/3/3/ 2/1/1/1/1 and 50/38/120/50/29/8/4/1/1/1. I do not know the reason f o r these unusual performances, but I t e s t e d the f l o u r from both c u l t u r e s f o r disease i n the manner noted above and, ' / ° 51 finding no evidence of disease in the te s t population, I could not r e j e c t the r e p l i c a t e s . For comparison, the next lowest rep-l i c a t e from the 50 Gen. 2 open cultures had densities of 50/44/ 258/116/63/32/21/13/8/5/4 and the highest r e p l i c a t e had den-s i t i e s of 50/33/37^/288/268/238/239/258/146/53... This l a t t e r r e p l i c a t e has the d i s t i n c t i o n of being the only culture of a l l open cultures started with 50 adults which increased i n adult density a f t e r the fourth month and was one of three which increased a f t e r the t h i r d month, The 10 Gen. 2 closed cultures had larger standard errors than any of the open cultures, but even the lowest r e p l i c a t e held higher densities than the highest r e p l i c a t e of the 50 Gen. 2 open cultures. The closed culture with the lowest peak den-s i t y had monthly densities of 50/77/248/452/444/378/259/222. Again i n experiments 2 and 4, the several r e p l i c a t e s of a r t i f i c i a l cultures, migrant cultures, and non-migrant cultures each tended to exhibit the same'time/adult density curve shapes as the others in t h e i r groups, and so I f e e l that means and standard errors again adequately describe the data. Appendix 2. Tabular Data Table II. Adult Beetles per culture f o r various sets of r e p l i c a t e s refered to in the text. Means and t h e i r standard errors are shown. Column l e t t e r codes are those used i n the experiments section. Months A B C D E . 0 50.0 ( 0.0) . 50.0 ( 0.0) 50.0 ( 0.0) 50.0 ( 0.0) 50.0 ( 0.0) 1 46.6 ( 3.2) 40.0 ( 0.4) 40.4 ( 1.4) 69.3 ( 3.4) 54.3 ( 3.4) 2 267.5 (34.1) 361.8 (14.0) 420.4 (28.9) 241.6 (12.2) 347.2 (15.3) 3 213.1 .(47,2) 258.4 (13.1) 281.7 (28.9) 345.3 (24.7) 368.5 (28.9) 4 '-, 107.5 (24.0) 201.8 (12.7) 238.7 (29.4) 447.7 (37.8) 335.3 (28.9) 5 50.5 (12.6) 135.5 (10.1) 156.9 (22.7) 513.9 (49.7) 347.9 (58.4) •6 30.1 ( 7.4) 108.5 ( 9.0) 121.3 (21.0) 595.3 (74.4) 363.1 (78.2) 7 18.1 ( 4.2) 74.0 ( 7.6) 96.6 (21.2) 545.1 (93.1) 386.8 (48.3) 8 12.8 ( 2.9) 48.1 ( 4.5) 62.0 (12.1) 491.4 (90.8> '9 10.1 ( 2.2) 31.8 ( 2.8) 43.2 ( 8.3) 379.7 (58.6) 10 9.6 ( 2.2) 19.1 ( 1.6) 26.5 ( 5.0) 11 7.3 ( 1.5) 12 6.3 ( 1.0) Table I I , Continued Months F i G i H I J 0 40.4 ( 1.5) 420.4 (28.9) 281.7 (28.9) 238.7 (29.4) 15.6 ( 3.8) 1 453.5 (22.4) 420.8 (28.9) 347.5 (13.4) 359.6 (31.1) 132.2 (28.9) 2 218.2 (15.1) 285.0 (17.0) 325.7 ( 9.1) 349.6 (18.3) 245.1 (12.2) 3 185.7 (19.2) 183.0 (11.5) 282.0 (16.6) 301.0 (19.6) 265.9* (23.6) 4 115.8 (13.7) 108.6 ( 9.2) 164.2 (14.4) 1 Months K L M N C i 0 50.0 ( 0.0) 50.0 ( 0.0) 50.0 (0.0) 50.0 ( 0.0) 50.0 ( 0.0) 1 33.0 ( 1.2) 43.2 ( 1.0) 52.2 ( 2.6) 43.2 ( 1.9) 42.2 ( 2.2) 2 487.2 (31.0) 344.0 (36.9) 221.2 (31.5) 233.4 (29.1) 140.2 (46.5) 3 382.8 (31.9) 200.4 (33.1) 169.4 (35.9) 185.8 (36.0) 101.4 (49.1) ,4 363.8. ( 9.4) 174.2 (52.1) 152.8 (38.1) 113.2 (26.5) 57.6 (29.9) Table II, Continued. Months F Q 0 50.0 ( 0.0) 50.0 ( 0.0) 1 44.4 ( 1.9) 43.4 ( 1.6) 2 251.4 (35.5) 247.6 (39.2) 3 126.3 (35.5) 187.4 (35.6) 4 91.4 (25.3) 132.4 (47.3) Months U V 0 50.0 ( 0.0) 50.0 ( 0.0) 1 32.8 ( 2.3) 36.8 ( 3.4) 2 100.4 (24.6) ^  16.2 ( 1.5) > O 38.8 (11.8) 9.2 (1.4) 4 24.4 ( 6.4) R 50.0 ( 0.0) 47.4 ( 0.4) 230.8 ( 7.0) 176.0 (21.8) 100.0 (10.8) S 50.0 ( 0.0) 74.3 ( 8.4) 124.2 (12.8) 87.0 (14.4) 60.8 (21.3) T 50.0 ( 0.0) 48.8 ( 1.9) 105.4 (16.8) 67.6 (13.4) 42.2 (10.8) Table I I I . Number of migrants per culture for various sets of r e p l i c a t e s referred to in the text. Means and t h e i r standard errors are shown. Column l e t t e r codes are those used in the experiments section. Months A B C F G 0 0.0 ( : 0.0) 0.0 ( 0.0) 0.0 < : o.o) 0.0 ( 0.0) 0.0 ( 0.0) 1 4.3 { : 1 . 4 ) 9.9 ( 0.5) 9.9 < : 1 . 6 ) 45.4 ( 7.8) 105.6 (13.5) 2 41.2 ( : 9.1) 39.6 ( 3.7) 32.7 ( : 5.6) 80.7 ( 8.0) 133.8 (11.2) . 3 , 96.9 ( :i9.2)- 129.8 ( 7.1) 153.6 < :i3.6) 26.8 ( 7.4) 68.2 ( 6.3) 4 64.3 < ;i6.7) 71.6 ( 5.0) 69.7 :ii.o) 27.9 ( 3.4) 85.1 ( .5.7) 5 35.7 ( : 3.3) 75.7 ( 6.6) 81.2 < :i6.2) 6 9.2 ( : 3.4) 15.9 ( 1.8) 22.7 ( : 5.o) 7 4.7. < : 1.3) 19.5 ( 3.0) 8.5 < : 3.2) 3V. 2.1 < : 0.7) 18.3 ( 2.2) 14.6 ( : 6.5) "t. 9 1.9 < : o.8) 3.0 ( 0.5) 2.5 ( : 0.9) •10.*. 0.2 < : o.i) J . J V. 0.5) 5.6 ( : 1.5) 11 0 . 4 ( : o.2) 12 0.2 ( : o.i) -Table I I I , Continued Months H I 0 0.0 ( 0.0) 0.0 ( 0.0) 1 63.3 (13.0) 55.1 (10.2) 2 77.3 (13.5) 82.2 (14.7) 3 45.3 ( 4.2) 52.4 ( 8.8) 4 75.9 ( 6.5) Months M N 0 0.0 ( 0.0) 0.0 ( 0.0) 1 5.4 ( 0.5) 6.6.(2.0) > 2 28.6 ( 7.0) 17.2 ( 2.0) 3 41.0 (13.0) 49.6 (14.5) 4 31.6 (11.5) 31.0 ( 7.6) J 0.0 ( 0.0) 1.0 ( 0.4) 70.6 ( 7.2) 94.0 (12.4) K 0.0 ( 0.0) 20.0 ( 2.0) 63.6 ( 2.9) 169.2 (30.4) 143.8 (21.8) L 0.0 ( 0.0) 5.4 ( 0.8) 35.8 ( 4.4) 77.6 (12.3) 26.0 (10.5) 0 0.0 ( 0.0) 6.6 ( 1.7) 19.8 ( 7.8) 22.2 (10.2) 14.2 ( 6.8) P 0.0 ( 0.0) 4.2 ( 1.5) 42.8 ( 4.5) 63.8 (21.6) 19.6 ( 6.8) Q 0.0 ( 0.0) 13.0 ( 1.3) 59.2 (13.3). 36.6 (17.1) 13.8 ( 3.7) > <—\ > o CO CO • * • • o CM O o CM o • • • • • o CM t-1 en /-~\ o CO o o • • • • ft o t—l CM CM o o vO CM • • • • • o CM . i — l I - I o o r - l • • • • • o o CM o CM o o O o CM o CO CM o O i—I o CO co r - l i—I o r - l <f m o 00 vO o • • • • o CM CM . CO CO 3. a O O Pi o CM VD • • • • « o o CO o o o o CM • • • • • o CO m o CM CO m M 1—1 r - l OT si O r - l CM CO Table IV. Ascending rank order of density among 10 Gen. 2 open cultures used in Experiments 1 , 2 , and 5. Months Rank I 2 3 4 5 6 7 8 9 10 1 1 10 3 3 3 3 3 3 3 3 2 2 4 4 4 4 4 4 4 10 4 3 3 1 10 10 10 10 10 10' 4 10 L. 4 2 9 9 2 9 2 2 9 9 5 5 9 1 1 9 2 9 9 2 8 6 • r 6 3 2 6 8 7 5 8 5 2 7 7 8 8 7 5 8 8 5 8 7 8 8 7 6 8 7 5 7 7 7 5 o 9 6 7 2 1 6 . 6 6 6 6 10 10 5 5 5 6 1 1 1 1 1 

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