Section 9 — Population Genetics 



equally. To ascertain which sex was controlling 

 rate of mating, observations were made on ten 

 pairs from uniform cultures in small plexiglass 

 chambers for 1 hr. Pairs were introduced without 

 etherization; mating pairs were withdrawn and 

 time recorded. Cumulative rate curves for 60 

 to 100 matings give these results: (1) W/W X 

 W/W matings are most rapid, 85 percent within an 

 hour; (2) K/K x K/K are slowest, 15 per cent 

 within an hour. WT $$ x KL <$<$ were 20 per 

 cent less rapid than W x W, while KL $$ x 

 WToo were about that much faster than K x K. 

 Females control the rate of mating then, and 

 substitution of a WT $ of for a KL $ increases 

 mating speed. WT <$(§ court persistently and 

 indiscriminately while KL <$$ court very 

 little. KL $$ refuse to mate by extruding the 

 ovipositor or decamping while WT $$ accept 

 mates more frequently. F2 flies from homo- 

 karyotype sib matings maintain about the same 

 rates. Heterokaryotypes (W/K, K/W) mated 

 within cultures had intermediate rate (55 per cent 

 in 1 hr) but when mated to WT as either sex, 

 mating is increased to 80 per cent while to 

 KL it is lowered to 20 per cent. Maternal ef- 

 fect in heterokaryotypes was evidenced by su- 

 perior mating of both sexes with WT mothers 

 than those with KL mothers when mated to 

 W/W. Therefore these chromosomal rearrange- 

 ments contain genie complexes controlling 

 mating behavior, especially receptivity of $$ and 

 activity of <$<§. 



9.71. Selection for Rate of Development and Gene 

 Arrangement Frequency in Drosophila persi- 

 milis. Luretta D. Spies and Eliot B. Spiess 

 (Pittsburgh, U.S.A.). 



It was demonstrated by Spiess (1958) that the 

 third chromosome arrangement Whitney (W/W) 

 surpassed Klamath (K/K) by approximately 

 3 days in rate of development. To evaluate the 

 rate of development difference as a major com- 

 ponent of fitness in controlling frequencies 

 of these arrangements, 6 experimental popula- 

 tions were initiated in which food was changed 

 rapidly (3 "Fast" Cages) to favor fast developing 

 larvae (W/W) or changed slowly (3 "Slow") to 

 allow other karyotypes (W/K and K/K) to 

 eclose. KL decreased in fast and slow cages at 

 about the same rate to about 10 per cent KL 

 equilibrium. A second pair of populations (DF, 

 DS) were initiated in which (1) all emerging indi- 

 viduals were counted each generation and (2) 

 the first 500 (DF) or last 500 (DS) adults to 

 emerge were used to establish each discrete 

 generation. Selection curves were parallel ap- 



proaching equilibrium at 10-15 per cent KL after 

 6-8 generations. That WT is superior in other res- 

 pects is evident from studies on mating behavior 

 (Spiess), but possibilities remained that (1) the 

 rate of development difference was reduced 

 under population cage conditions or (2) se- 

 lection was not sufficiently intense to effect a 

 change in frequencies. New discrete generation 

 populations were initiated with the same strains 

 (WT = KL = 50 per cent) but with selection 

 intensified 20-fold (DIF, DIS). These popula- 

 tions diverged immediately and KL increased 

 in slow (DIS) to 80 per cent but decreased in 

 fast (DIF) populations to 15 per cent. Selec- 

 tion was reversed after 4-6 generations in subpop- 

 ulations while continuing the original selection 

 scheme. Reversed selection was effective. Rate 

 of emergence increased under fast but was 

 unaltered in slow selection; progeny per $ parent 

 increased from 3 initially to 1 1 after ten genera- 

 tions in DF and DS populations, indicating 

 improved total fitness. Therefore K/K and W/W 

 differ in rate of development under population 

 cage conditions, but moderate selection does not 

 discriminate between these karyotypes. 



9.72. Heritability of Wing Length in Natural Po- 

 pulations of Drosophila melanogaster and D. 

 similans. Abdel-Azim Osman Tantawy (Alex- 

 andria, Egypt). 



The genetic variance of wing lenght in natural 

 populations of Drosophila melanogaster and D. 

 simulans has been studied. Flies were captured 

 twice a month from the same locality for six- 

 teen successive months, from October 1961 to 

 December 1962. Heritability of wing length in 

 both species was estimated by the half-sib anal- 

 ysis and all experimental work was carried out 

 at 250°C. 



The results are summarized as follows: 



1 . Wing length in both species measured on the 

 F2 generation of captured females remained 

 constant from October 1961 up to April 1962 

 (mild temperature) after which it declined grad- 

 ually from May 1962 to August 1962 (hottest 

 months of the year) after whichit showed a 

 steady rise again to the end of the experimental 

 period. Thus, the results are in agreement with 

 these reported on populations captured from 

 high altitude and from northern geographical 

 regions, as compared with low altitude and south- 

 ern regions, respectively. 



2. Heritability estimates indicate that popu- 

 lations of Drosophila melanogaster possess 

 higher significant values for the h 2 each month 

 than those found in D. simulans populations, 

 but the species behaved differently. Populations 



167 



