Search

Introduction: Structural colour patterns and their functions in insect wings are less known. Wing interference patterns (WIPs) are colour patterns apparent when wings are viewed against black backgrounds; the angle of incident light and wing surface structures also influence the resulting wing colour pattern. To date, WIPs are correlated with mate attraction, while the impact of geography and environment on WIPs remains unexplored. We explore WIP variation in Drosophila melanogaster populations collected from three altitudes and also compare WIP variation in sibling species D. melanogaster and D. simulans reared at three different temperatures to understand if local selection pressures could also influence WIPs. Methodology: Wings of D. melanogaster males were collected from three different altitudes, and D. melanogaster and D. simulans males reared at three different temperatures were imaged. Images were analysed for their relative red, green and blue content in the RGB colour space. In representative images, wing thickness was assessed using the Newton colour series. Results: An altitudinal cline in WIPs was observed in the cosmopolitan D. melanogaster collected from the Western Himalayas. Relative RGB values and increase in altitudes were negatively correlated. Thermal responses in WIPs were parallel for both D. melanogaster and D. simulans. Relative RGB values were negatively correlated with rearing temperature. In both species, wing thickness measurements indicated that the wings of flies reared at low temperatures had greater blueness (cyan and magenta) compared to flies reared at moderate to high temperatures; the latter had more green and yellow content. Wing thickness pattern was also consistent for D. melanogaster flies collected from low versus higher altitudes. Discussion: We find WIPs to be a plastic trait in response to temperature. WIP response to thermal variation corroborates with the temperature of the geographic origin in D. melanogaster. The adaptive significance of WIP variation and associated wing thickness remains unclear. Future studies could explore the underlying adaptive significance of structural colour patterning under different environmental conditions. [ABSTRACT FROM AUTHOR]

The pupal colour of many butterflies is plastic, being green or brown depending on the environment in which they develop. In most species with pupal colour plasticity (PCP), larvae that pupate on leaves tend to develop into green pupae whereas those that pupate off‐leaf (e.g., on the stem or soil) tend to become brown. This correlation between background and pupal colour has been hypothesized to protect the butterflies against predation by allowing them to match their background, although experimental evidence is scarce. Furthermore, not all butterflies exhibit PCP, and the extent to which substrate choice influences PCP remains unclear. We use a comparative approach involving multiple, closely related species varying in the degree of PCP to test predictions related to the correlation between pupal colour and pupation substrate. We studied PCP in response to larval density in five common satyrine species (Nymphalidae), two dimorphic and three monomorphic. As predicted, species with monomorphic green pupae preferred to pupate on leaves whereas those with monomorphic brown pupae preferred off‐leaf substrates. In species with dimorphic pupae, pupal colour correlated with pupation substrate. We also predicted that higher larval density induces a greater proportion of off‐leaf pupation in the dimorphic species, but not in the monomorphic species. However, this prediction was not supported. Overall, we found a strong across‐species correlation between pupation substrate choice and pupal colour plasticity, and our results support the idea that pupal colour plasticity can be an adaptation against predation. [ABSTRACT FROM AUTHOR]

Clines are observable gradients that reflect continuous change in biological traits of species across geographical ranges. Clinal gradients could vary at geographic scales (latitude and altitude). Since clinal variations represent active genomic responses at the population level they (clines) provide an immense power to address questions related to climatic change. With the fast pace of climate change i.e. warming, populations are also likely to exhibit rapid responses; at both the phenotypic and genotypic levels. We seek to understand how clinal variation could be used to anticipate climatic responses using Drosophila, a pervasively used inter-disciplinary model system owing to its molecular repertoire. The genomic information coupled with the phenotypic variation greatly facilitates our understanding of the Drosophilidae response to climate change. We discuss traits associated with clinal variation at the phenotypic level as well as their underlying genetic regulators. Given prevailing climatic conditions and future projections for climate change, clines could emerge as monitoring tools to track the cross-talk between climatic variables and organisms. [ABSTRACT FROM AUTHOR]

Lepidopteran insects have provided excellent study systems for understanding adaptive phenotypic plasticity. Although there are a few well-studied examples of adult plasticity among tropical butterflies, our understanding of plasticity of larval and pupal stages is largely restricted to temperate butterflies. The environmental parameters inducing phenotypic plasticity and the selective pressures acting on phenotypes are likely to differ across tropical and temperate climate regimes. We tested the influence of relative humidity (RH), a prominent yet under-appreciated tropical climatic component, along with pupation substrate, larval development time, pupal sex and weight in determining pupal colour in the tropical satyrine butterfly Mycalesis mineus. Pupae of this butterfly are either brown or green or very rarely intermediate. Larvae were reared at high (85%) and low (60%) RH at a constant temperature. Proportions of green and brown pupae were expected to vary across low and high RH and pupation substrates in order to enhance crypsis. Brown pupae were more common at low RH than at high RH, as predicted, and developed faster than green pupae. Pupal colour was correlated with pupation substrate. Choice of pupation substrate differed across RH treatments. It is unclear whether pupal colour influences substrate selection or whether substrate influences pupal colour. Our study underscores the need for further work to understand the basis of pupal plasticity in tropical butterflies. [ABSTRACT FROM AUTHOR]