Differential Demographic Trajectories and Polygenic Adaptation to Monsoon Seasonality in Sky Island Hercules Beetle Populations of the American Southwest.

Authors

Sean Chien, My-Hanh Le, Heath Blackmon, Jen-Pan Huang

Published in

Molecular ecology. Volume 35. Issue 18. Pages e70551.

Abstract

Sky island mountain ranges of the American Southwest represent isolated habitat fragments surrounded by arid lowland barriers, making them powerful natural experiments for studying population divergence, demographic history and local adaptation. Here, we use whole-genome resequencing of the Western Hercules beetle (Dynastes grantii Horn, 1870) across four primary lineages to characterize the genomic consequences of habitat fragmentation and climate-driven isolation. Population structure analyses revealed strong hierarchical genetic differentiation consistent with isolation-by-distance, while ABBA-BABA tests detected little to no evidence of post-divergence gene flow among lineages. Coalescent modelling revealed synchronous demographic expansions during the Last Glacial Period followed by severe Holocene contractions across all lineages, with the Utah population experiencing the most pronounced bottleneck and maintaining persistently low effective population size (N_e). The elevated F_ST but equivalent D_XY in Utah comparisons and elevated runs of homozygosity (ROH) indicate that its genetic distinctiveness reflects accelerated drift rather than ancient isolation. Genomic-environment association analyses identified 1367 high-confidence candidate loci associated with precipitation seasonality, with precipitation of the wettest quarter driving the strongest signal of polygenic adaptation. Monsoon moisture regimes are the primary selective axis shaping genomic divergence. Genetic offset projections identified Mt. Lemmon as the most vulnerable population under future climate scenarios, and genetic rescue donor analyses identified population-specific sources for assisted gene flow. Our results demonstrate how integrating demographic inference, divergence genomics and landscape genomics with whole-genome data, including historical museum specimens, can simultaneously advance understanding of evolutionary history and inform actionable conservation strategies in the future.

PMID:
42798137
Bibliographic data and abstract were imported from PubMed on 26 Sep 2026.

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