Euthalia formosana phylogeography and conservation genomics
Global climate change poses disproportionate risks to island endemics, which are geographically constrained and often lack opportunities for range shifts. Effective conservation therefore requires not only documenting contemporary genetic structure, but also understanding how recent diversification histories shape present-day resilience and future vulnerability. Here, we test how rapid within-island diversification can generate lineage-specific climate vulnerability using the Formosan Duke, a Taiwan endemic butterfly associated with low to mid elevation evergreen broad-leaved forests, one of the islands long-standing zones of human nature conflict. Integrating population genomics with environmental association analyses, we reveal a deep east west split structured by the Central Mountain Range, followed by fine-scale subdivision, with stronger diversification in western populations despite Taiwans young geological age. Among these lineages, the southwestern group is of particular concern, exhibiting the lowest genetic diversity, significant identity disequilibrium, and elevated inbreeding. Moreover, we identify a climatic specialization trap in which this lineage is restricted to a narrow, precipitation dependent environmental space. Genetic offset projections further indicate likely exposure to non-analog future climates, suggesting limited capacity to track rapid environmental change. Together, our results show that even highly mobile forest-dependent butterflies can diversify rapidly through the interplay of topographic barriers, historical connectivity, and climatic heterogeneity, yet this process can also create cryptic pockets of vulnerability. We propose a practical conservation framework integrating habitat restoration with lineage specific connectivity to enhance genetic resilience while preserving locally adapted variation, and highlight the Formosan Duke as a flagship for promoting science-based stewardship under accelerating climate change.