PHENOTYPIC AND GENETIC-VARIABILITY OF MORPHOMETRICAL TRAITS IN NATURAL-POPULATIONS OF DROSOPHILA-MELANOGASTER AND DROSOPHILA-SIMULANS .2. WITHIN-POPULATION VARIABILITY

Within-population variability was investigated in the 2 sibling specie s Drosophila melanogaster and D simulans at both phenotypic and geneti c levels. Six quantitative traits were studied in 55 different populat ions of D melanogaster and 25 populations of D simulans encompassing m ost of the cosmopolitan range of the 2 species. The phenotypic variabi lities of all the traits were compared using the coefficients of varia tion (CV). Differences among CV's were broader than expected from thei r theoretical sampling distribution. Temperate populations were genera lly less variable than tropical ones. Moreover, in both species, the C V of the 3 size-related traits (fresh weight, wing length and thorax l ength) were correlated. Comparison of the 2 species showed that the av erage variabilities (mean values of CV) were almost identical with the exception of ovariole number which is much less variable in D simulan s (6% against 8%). At the genetic level, distributions of intraclass c orrelations did not show any departure from the expected sampling dist ributions, suggesting that all populations harbored a similar amount o f genetic variability. For most traits, no significant difference was found between the 2 species, except again for the ovariole number whic h is genetically less variable in D simulans. An overall analysis of t he total variability showed that 78% of the total variance was explain ed by the within-population components in D simulans against 50% in D melanogaster.