Phenotypic and genetic variability of morphometrical traits in natural populations of

Summary - Within-population variability was investigated in the 2 sibling species Drosophila mela!nogaster and D simulans at both phenotypic and genetic levels. Six quantitative traits were studied in 55 different populations of D melanogaster and 25 populations of D simulans encompassing most of the cosmopolitan range of the 2 species. The phenotypic variabilities of all the traits were compared using the coefficients of variation (CV). Differences among CV’s were broader than expected from their theoretical sampling distribution. Temperate populations were generally less variable than tropical ones. Moreover, in both species, the CVof the 3 size-related traits (fresh weight, wing length and thorax length) were correlated. Comparison of the 2 species showed that the average variabilities (mean values of Ct! were almost identical with the exception of ovariole number which is much less variable in D simulans (6% against 8%). At the genetic level, distributions of intraclass correlations did not show any departure from the expected sampling distributions, suggesting that all populations harbored a similar amount of genetic variability. For most traits, no significant difference was found between the 2 species, except again for the ovariole number which is genetically less variable in D simulans. An overall analysis of the total variability showed that 78% of the total variance was explained by the within-population components in D simulans against 50% in D melanogaster.