MORPHOLOGICAL VARIATION IN NATURAL AND EXPERIMENTAL POPULATIONS OF <i>DROSOPHILA PSEUDOOBSCURA</i> AND <i>DROSOPHILA PERSIMILIS</i>

Abstract

Drosophila pseudoobscura and its sibling D. persimilis are two species of fruit flies which have received considerable attention from the standpoint of population genetics. Examination of the arrangements (inversions) in the third chromosome in salivary gland cells of the larval progeny of flies derived from many geographic localities throughout the distribution of these species reveals that (1) populations within a locality are largely polymorphic; (2) populations from different altitudes and latitudes differ in the frequency of chromosomal arrangements; (3) the frequency of these arrangements varies from season to season; and (4) there are secular changes in the frequency of these inversions (see Dobzhansky, 1951, p. 138, for map showing frequency of the different inversions in D. pseudoobscura through most of its distribution, and Dobzhansky et al., 1964, for the most recent survey of inversion frequencies in this species). Laboratory studies showing that the frequency of these inversions is modified through natural selection and manipulation of environmental conditions are too numerous to mention (review in Strickberger, 1963). A few of these studies (for example, Beardmore et al., 1960; Tantawy, 1961) have combined the use of inversions and quantitative traits to measure the relative fitness of different gene arrangements under different constant and fluctuating temperatures, and one study (Druger,