Studies of the Relative Fitnesses of Experimental Populations of Drosophila melanogaster

TLDR: Estimates of fitness of several experimental populations of D. melanogaster are regarded as further evidence for the retention of genes in large populations on the basis of their action in heterozygous condition and difficulties encountered in interpreting such information are discussed.

Abstract: This paper deals with an attempt to estimate the relative fitnesses of several experimental populations of D. melanogaster. The measure of fitness used was the number of offspring produced by single pairs of individuals. Each experiment consisted of a study of two "competing" populations. Fifty males and 50 virgin females from each of two populations were mated as single pairs in vials. The number of sterile matings was recorded; the offspring produced by fertile pairs were counted fourteen days after mating. Males and virgin females were collected from these vials to establish a second generation of 50 single pairs in vials. The experiments were continued in this way for ten generations. All possible pairs of eight populations (see table 1) were studied. Among the flies representing populations 1 and 3, frequencies of sterile matings increased in successive generations to a high level; this increase must be ascribed to selection of sterility genes in heterozygous condition. In contrast with the increase ...