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 investigated on a large number of populations (ie 55 and 25, respectively) for 6 morphometrical traits concerning weight, size, reproductive capacity and bristle numbers. For 21 populations, sympatric samples of the 2 species were available. For most traits, the mean values of D melanogaster 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-European axis, in both hemispheres, and on the American continent. In D simulans, a latitudinal dine that is parallel to those observed in D melanogaster was observed suggesting that variability between populations is partially adaptive. In addition to these parallel variations, in which the mean values of all traits increase with latitude, inter-continental variations were also detected in D melanogaster when populations sampled at similar latitudes were compared (eg, West Indian and Far Eastern populations). Different demographic strategies (r or K) could explain such variations. Analysis of morphological distances (Mahalanobis generalized distance D-2) between populations of the 2 species, showed that D melanogaster is much more diversified than D simulans. All the traits except the sternopleural bristle number are involved in these differences.