Geographical divergence for quantitative traits in colonising populations of Drosophila kikkawai from India

There are significant geographical variations for four quantitative traits among eight natural populations of Drosophila kikkawai along the Indian latitudinal transect (8.29 to 33 degrees N). Body weight, wing length, thorax length, and ovariole number exhibit significant clinal variation with increase in latitutde. Genetic correlations between all the four traits are significantly higher. Slope values for body weight and wing length are higher (2.32 per degree latitude) while lower for thorax length (0.70) and ovariole number (0.56). South Indian populations are characterised by lower mean values but higher variances as well as CV values as compared with northern populations. Multiple regression analyses (on the basis of temperature related climatic variables) evidence significantly higher association between all the four traits and coefficient of variation of mean annual temperature (seasonal thermal amplitude; TCV). Thus, genetic differentiations for quantitative traits in D. kikkawai are due to selective pressure from variable seasonal environmental conditions occurring on the southern tropical versus northern subtropical regions of the Indian subcontinent.