Abstract: 【Aim】 Variation in coloration is frequently found in insects, but little is known about its functional value.  Drosophila takahashii exhibits genetically coded discontinuous variation in abdominal melanisation. To determine whether physiological performance is likely to be affected by melanisation pattern, in this study we investigated the variation in abdominal melanisation and stress related traits among individuals belonging to three different color morphs, and tested the hypothesis that seasonal environmental conditions would enhance the adaptation of the corresponding seasonal phenotype. 【Methods】 D. takahashii  flies were collected from altitudinal sites and a Mendelian analysis of genetic crosses from true breeding dark and light color strains confirmed the occurrence of a major locus, with dominance of D allele. Ecophysiological traits in populations as well as flies of three body color phenotypes were statistically analyzed. 【Results】A significant increase in the frequency of the dark allele was observed during the dry season and lighter flies occur in the wet season, which suggests that climatic selection plays a role. However, intermediate flies were abundant in both seasons. There were significant  F  values for increase in all traits for intermediate phenotypes ( P<0.001) due to acclimation but no such acclimation effects were observed in dark and light true breeding strains of D. takahashii (P ≥0.42). 【Conclusion】 As per our hypothesis, significantly higher physiological tolerance was observed in dark morph under cool-dry stress conditions, and in light morph under hot-wet conditions, respectively, as determined by different traits. Interestingly, intermediate phenotypes showed higher capability to acclimation to both conditions. Further, we found seasonal changes in temperature and humidity to confer selection pressures on stress-related traits.

Key words: Drosophila takahashii, allele frequency, life history variation, discrete phenotypes, heterozygote flexibility