Desiccation tolerance and starvation resistance exhibit opposite latitudinal clines in Indian geographical populations of Drosophila kikkawai

1. Desiccation tolerance and starvation resistance demonstrated significant differentiation among seven Indian geographical populations of Drosophila kikkawai, collected along a latitudinal range of 12.6-32.7 degrees N. Lack of significant differences in two successive generations suggested that the se physiological traits were genetically controlled. 2. North Indian populations of D. kikkawai displayed significantly higher d esiccation tolerance than southern populations, whereas there was a reverse trend for starvation tolerance (r > 0.90). Regression slope values indicat ed an increase of 0.61 h for desiccation and a decrease of 1.71 h per degre e latitude for starvation tolerance at 17 degrees C. The traits evidenced o pposite latitudinal dines, and such data also matched thermal climatic cond itions on the Indian subcontinent. The survival duration for such traits wa s significantly higher at 17 than at 25 degrees C. 3. Significantly higher starvation tolerance in south Indian populations mi ght be due to large population size, species interactions, and higher metab olic rates in the humid tropical environments. In contrast, prolonged unfav ourable colder climatic conditions are known to favour starvation tolerance in temperate regions. Thus, the causes of desiccation and starvation toler ance seem quite different under tropical and temperate conditions. 4. Starvation tolerance was correlated negatively with body weight and ovar iole number, which might be due to a trade-off in favour of greater allocat ion to non-lipidic reserves for sustaining starvation tolerance in the trop ics. Reduction in metabolic rate may not be applicable for observed higher starvation tolerance in the tropical populations. 5. Multiple regression analysis demonstrated a major effect of coefficient of variation of mean monthly temperature for both the traits of ecological significance. Thus, Indian geographical populations of D. kikkawai provided evidence of independent genetic divergence for starvation and desiccation tolerance under natural conditions.