Geographical clines for quantitative traits in natural populations of a tropical drosophilid: Zaprionus indianus

We analyzed natural populations of Zaprionus indianus in 10 Indian localiti es along a south-north transect (latitude: 10-31 degrees3 N). Size traits ( body weight, wing length and thorax length) as well as a reproductive trait (ovariole number) followed a pattern of clinal variation, that is, trait v alue increased with latitude. Wing/thorax ratio, which is inversely related to wing loading, also had a positive, but non-significant correlation with latitude. By contrast, bristle numbers (sternopleural and abdominal) exhib ited a non-significant but negative correlation with latitude. Sex dimorphi sm, estimated as the female/male ratio, was very low in Z. indianus, contra sting with results already published in other species. Genetic variations a mong populations were also analyzed according to other geographic parameter s (altitude and longitude) and to climatic conditions from each locality. A significant effect of altitude was found for size traits. For abdominal br istles, a multiple regression technique evidenced a significant effect of b oth latitude and altitude, but in opposite directions. Genetic variations w ere also correlated to climate, and mainly with average year temperature. T aking seasonal variations into account failed however to improve the predic tability of morphometrical variations. The geographic differentiation of Z. indianus for quantitative traits suggests adaptive response to local condit ions, especially to temperature, but also reveals a complex situation accor ding to traits investigated and to environmental parameters, which does not match results on other drosophilid species.