Morphological variation of tropical lepidoptera communities across environmental gradients and implications for climate change

Abstract

Climate change has resulted in broad-scale impacts for numerous taxa and ecosystems globally. Yet the responses of species vary significantly and their vulnerability to warming is dependent upon a wide variety of factors. Traits can explain how species adapt to certain environments and may therefore be instrumental in understanding species’ responses to global warming. Ectotherms have been identified as potentially vulnerable to warming impacts due to limitations in their thermoregulation and sensitivity to environmental changes. Morphology in particular can affect ectotherm thermal adaptation and may thus constrain species distributions along thermal gradients. As a result, morphological traits, structured by evolutionary history and phylogeny, could also play a role in future climate change responses. Body color and body size have been identified as important morphological traits affecting thermoregulation of ectotherms. The Thermal Melanism Hypothesis (TMH) and Bergmann’s rule have each been proposed as patterns that could explain color and body size patterns respectively across environmental gradients. Lepidoptera has been used as an ideal system in studying both ectotherm thermoregulation and functional morphology in natural selection. However, the effects of morphology on general distribution patterns across species of Lepidoptera at small scales such as habitat and elevation, and how they are influenced by evolutionary processes remain unclear especially in the tropics. I investigated thermally important morphological traits in diurnal (butterfly) and nocturnal (moth) Lepidoptera groups across different scales in the tropics to determine how their distributions have been constrained by those traits. I employed a phylogenetic framework into trait-based approaches to further explore the role of phylogeny and evolutionary history in shaping those patterns. Thermal experiment showed that butterflies with darker colors and larger sizes can transfer solar energy into heat gain more efficiently than those with lighter colors and smaller sizes. Within butterflies, at the habitat scale, darker and larger individuals were found to be more prevalent in relatively cold microhabitats in a tropical rainforest system in Australia. Across elevation in subtropical and tropical China, butterflies were found to be generally darker and bigger at higher elevations at both the individual and species level. These patterns remained consistent after accounting for phylogeny. Within moths in Yunnan, China, color lightness of communities also increases with elevation and the relationship is most apparent at high elevation and high latitude sites. These studies together emphasize the relationship between morphology and climate; darker colors and larger body sizes are associated with cold environments at multiple scales in the tropics and such patterns have been influenced by evolutionary history within Lepidoptera. The findings highlight the important role of morphological traits in the thermal adaptation and distribution of ectothermic species. Finally, the results of this research further emphasize that body size and color, and morphological traits generally, should be considered when assessing species vulnerability to climate change.