PHENOTYPIC AND GENETIC-VARIABILITY OF MORPHOMETRICAL TRAITS IN NATURAL-POPULATIONS OF DROSOPHILA-MELANOGASTER AND DROSOPHILA-SIMULANS .1. GEOGRAPHIC VARIATIONS

Geographical variability between natural populations of the 2 related cosmopolitan species Drosophila melanogaster and D simulans was invest igated on a large number of populations (ie 55 and 25, respectively) f or 6 morphometrical traits concerning weight, size, reproductive capac ity and bristle numbers. For 21 populations, sympatric samples of the 2 species were available. For most traits, the mean values of D melano gaster are higher than those of D simulans, with the exception of the sternopleural bristle number, for which the species are similar. In D melanogaster, similar latitudinal variations exist along an African-Eu ropean axis, in both hemispheres, and on the American continent. In D simulans, a latitudinal dine that is parallel to those observed in D m elanogaster was observed suggesting that variability between populatio ns is partially adaptive. In addition to these parallel variations, in which the mean values of all traits increase with latitude, inter-con tinental variations were also detected in D melanogaster when populati ons sampled at similar latitudes were compared (eg, West Indian and Fa r Eastern populations). Different demographic strategies (r or K) coul d explain such variations. Analysis of morphological distances (Mahala nobis generalized distance D-2) between populations of the 2 species, showed that D melanogaster is much more diversified than D simulans. A ll the traits except the sternopleural bristle number are involved in these differences.