Population Structure of the Jewel Scarab Chrysina gloriosa

The sky-island mountain ranges of the southwestern United States offer a natural setting for examining how climate and geography impact population structure and gene flow. The jewel scarab, Chrysina gloriosa, is a charismatic beetle restricted to high-elevation habitats in these mountains, where isolation and environmental change may be driving population divergence. We used low-coverage whole-genome resequencing and species distribution modelling to study population structure, gene flow, and demographic history across five mountain ranges in Arizona and West Texas. Our results indicate strong genetic differentiation among most populations, with recent gene flow detected only between two neighboring ranges, possibly through male-mediated dispersal. Demographic analyses reveal a decline in effective population size following late Pleistocene climate shifts, consistent with habitat contraction inferred from paleo-vegetation records. Future climate projections suggest further habitat loss and increasing isolation. Together, these results show how past and ongoing climatic changes have and continue to shape population structure in C. gloriosa, with important implications for its long-term evolutionary potential. These findings mirror patterns documented across sky-island taxa globally, supporting a general model in which climate-driven habitat dynamics and dispersal limitation interact to generate recurrent cycles of population fragmentation, genetic erosion, and demographic instability in montane systems.