Adaptive Radiation in High-Altitude Rodent Species

Abstract

High-altitude environments impose severe physiological and ecological constraints on vertebrate life — including hypoxia, low temperatures, high UV radiation, and compressed growing seasons — that have repeatedly driven convergent and divergent adaptive radiation in montane rodent lineages worldwide. This study investigated the mechanisms, tempo, and morphological correlates of adaptive radiation in three high-altitude rodent genera — Microtus (voles), Ochotona (pikas), and Cricetulus (hamsters) — across elevational transects (1,200–4,800 m) in the Scandinavian mountains, Carpathians, and eastern Alps, combining geometric morphometrics, comparative genomics (whole-genome resequencing of 186 individuals), and Bayesian phylogenetic divergence dating. Geometric morphometric analysis of 1,842 skull specimens across 24 populations revealed significant cranial shape divergence correlated with altitude (Procrustes ANOVA: F = 18.6, R2 = 0.42, p < 0.001), with high-altitude populations showing enlarged braincases, shortened rostra, and wider zygomatic arches consistent with enhanced thermoregulatory capacity and altered dietary mechanics. Whole-genome resequencing identified 284 high-FST SNPs between high- and low-altitude populations, with gene ontology enrichment revealing significant overrepresentation of hypoxia response, haemoglobin affinity, and energy metabolism pathways. Divergence dating placed high-altitude lineage formation primarily in the Pleistocene (0.8–0.1 Ma), coinciding with glacial-interglacial cycles that repeatedly isolated montane populations. Trait-phylogeny decoupling analysis revealed that morphological divergence rates exceeded neutral expectation by 4.2–8.6× in the three high-altitude genera, consistent with active natural selection rather than genetic drift. These results provide a comprehensive multi-evidence framework for understanding adaptive radiation in European high-altitude rodents and identify candidate genomic loci for altitude adaptation relevant to conservation genomics under climate change