Adaptive associations between total body color dimorphism and climatic stress‐related traits in a stenothermal circumtropical Drosophila species

Abstract

Low desiccation resistance of Drosophila ananassae reflects its rarity outside the humid tropics. However, the ability of this sensitive species to evolve under seasonally varying subtropical areas is largely unknown. D. ananassae flies are mostly lighter during the rainy season but darker and lighter flies occur in the autumn season in northern India. We tested the hypothesis whether seasonally varying alternative body color phenotypes of D. ananassae vary in their levels of environmental stress tolerances and mating behavior. Thus, we investigated D. ananassae flies collected during rainy and autumn seasons for changes in body melanization and their genetic basis, desiccation‐related traits, cold tolerance and mating propensity. On the basis of genetic crosses, we found total body color dimorphism consistent with a single gene model in both sexes of D. ananassae. A significant increase in the frequency of the dark morph was observed during the drier autumn season, and body color phenotypes showed significant deviations from Hardy‐Weinberg equilibrium, which suggests climatic selection plays a role. Resistance to desiccation as well as cold stress were two‐ to three‐fold higher in the dark body color strain as compared with the light strain. On the basis of no‐choice mating experiments, we observed significantly higher assortative matings between dark morphs under desiccation or cold stress, and between light morphs under hot or higher humidity conditions. To the best of our knowledge, this is the first report on the ecological significance of seasonally varying total body color dimorphism in a tropical species, D. ananassae.

Contrasting strategies of resistance vs. tolerance to desiccation in two polar dipterans

“…We speculate that the initial composition and change in the cuticle layer is more biased towards a greater number and length of hydrocarbons in H. borealis than either Antarctic dipteran. Differences in melanization between the two Diptera may also offer an explanation for the differing levels of resistance in the current study, as has been shown between Drosophila Parkash et al 2009;Parkash et al 2012;Ramniwas et al 2013).…”

Direct and correlated responses to laboratory selection for body melanisation inD. melanogaster: support for melanism- desiccation resistance hypothesis.

“…The laboratory-selected desiccation-resistant and -sensitive strains of D. melanogaster have shown similar amounts of cuticular lipid mass (Gibbs et al, 1997), and there is also a lack of differences in the amount of cuticular lipid mass in northern versus southern populations of D. melanogaster (Parkash et al, 2008a). However, in two cases (Melanoplus sanguinipes and Z. indianus), there are significant intrapopulation differences in the amount of cuticular lipid mass per cm 2 (Rourke, 2000;Parkash et al, 2008a;Parkash et al, 2012).…”

“…Phenotypic variation of body melanisation in some lepidopterans and coelopterans are represented by discrete morphs (melanic and nonmelanic) consistent with a major locus (Da Cunha, 1949;Martinez and Cordeiro, 1970). Several studies have shown changes in the frequencies of two or more allelic variants in response to temporally or spatially variable climatic conditions (Umina et al, 2005;Parkash et al, 2009;Parkash et al, 2012). In contrast, variation in body melanisation in a D. melanogaster population follows a bell-shaped curve and such a quantitative trait is expected to respond quickly to laboratory as well as field selection.…”

Invasion and adaptation of a warm adapted species to montane localities: effect of acclimation potential

“…All acclimation experiments were carried out on 10 homozygous (for phenotype) strains for the dark as well as light morphs (see Parkash et al, 2012). These strains were originally derived from true breeding (for body color) iso-female lines from Solan.…”

“…The adult acclimation for cold resistance in D. melanogaster increases the lifespan, reduces mortality and recovery time after exposure to subzero temperatures (Rako and Hoffmann, 2006;Le Bourg, 2007). Further, the dark morph of D. ananassae is more resistant to cold and desiccating conditions as compared to the light morph; while the latter is more resistant to heat stress (Parkash et al, 2012). Thus, we may expect evolutionary responses to natural selection on traits related to desiccation and cold stress in subtropical populations of D. ananassae.…”