Evol Ecol Res 2: 685-699 (2000)     Full PDF if your library subscribes.

Evidence of independent climatic selection for desiccation and starvation tolerance in Indian tropical populations of Drosophila melanogaster

Ravi Parkash1 and Ashok K. Munjal2

1Genetics Research Laboratory, Department of Biosciences, Maharshi Dayanand University, Rohtak 124 001 and 2Department of Bioscience and Biotechnology, Banasthali Vidyapith, Banasthali 304 022, India

Address all correspondence to Ravi Parkash, U.H.-9, Medical Enclave, Rohtak 124 001 (Haryana), India.
e-mail: mdu@mdul.ernet.in


On the Indian subcontinent, geographical populations (8.0° to 33.0°) of Drosophila melanogaster demonstrate opposite latitudinal clines for desiccation (r = 0.83) and starvation (r = −0.88). Desiccation tolerance is significantly and positively correlated with body size and abdominal pigmentation, whereas starvation is negatively correlated with body size and life-history characteristics. Analysis of variance and analysis of covariance show a substantial direct effect of body size for both traits. For the Indian geographical populations, both latitudinal and altitudinal variations can explain the observed divergence of these two traits of ecological significance. Regression analysis of climatic variables (i.e. Tmax, Tmin and Taverage), which are not significantly correlated with latitude, are positively and significantly associated with starvation and can explain trait variability (R2 = 0.78–0.88). In contrast, TCV (R2 = 0.65), rainfall and precipitation (R2 = 0.32) are significantly but positively associated with desiccation tolerance. The observed negative correlation between climatically selected starvation and desiccation in Indian geographical populations is not in line with the correlated selection response of these traits on the basis of laboratory selection experiments. For south Indian tropical populations, higher starvation tolerance might be selected because of temperature variables (Tmax, Tmin and Taverage), higher metabolic stress in relation to smaller body size, greater competition and involve a trade-off for life-history traits. In contrast, significantly higher desiccation tolerance in subtropical (northern) populations might be selected because of TCV, rainfall and precipitation, which reflect seasonal variations. Desiccation and starvation tolerance are independent traits that reveal rapid evolutionary trends in tropical and subtropical climates.

Keywords: climatic selection, Drosophila melanogaster, opposite latitudinal clines, starvation and desiccation tolerance, tropical populations.

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