Shadows of Adaptation: Phenotypic Polymorphism and Climate Vulnerability in a Genetically Weakly Structured Damselfly

Background : Insects comprise one of Earth's most diverse animal groups, but the resilience and adaptive capacity of most species remains understudied. Psolodesmus mandarinus is an endemic damselfly in Taiwan, where its populations show latitudinal variation in wing pigmentation, with dark-winged populations in the north and clear-winged populations in the central and south. In this study, we aim to investigate the mechanisms underlying the observed phenotype-geography relationship in this species by analysing their genetic and phenotype-environment associations. Results : Despite apparent phenotypic variation ( P _ST ) in wings among geographical populations, we detected weak genetic structure ( F _ST ), with genetic variations explained mostly by geographic distance. Conversely, we identified outlier loci and individuals whose allele frequencies vary with environmental variables, suggesting local adaptation beyond genome-wide differentiation. Our niche modelling further shows dark and clear-winged populations occupy different ecological niches and may respond differently to climate change: clear-winged populations may expand their ranges, while dark-winged ones face geographic constraints. Conclusion : Our study demonstrates that integrating genomics, phenotypes, and ecological data can effectively identify adaptive units and inform climate-resilient conservation strategies for mobile insects. This approach is essential for anticipating responses of biodiversity under environmental change and contributing to broader climate action goals.