Cold adaptation in mammals: mechanisms and genomic insights from bats

Gamze Özbay , Veronika N Laine, Chris Heilakka, Mariia Matlova, Ella Sippola, Alexandra Streicher, Tanya Troitsky, Victoria Twort, Thomas Mikael Lilley

Cold environments impose strong energetic constraints on mammals, driving adaptations including thermogenesis, insulation and torpor. Bats are the only mammals capable of powered flight and inhabit different climates, yet the evolutionary basis of their cold tolerance remains poorly understood. In this study, we screened 571 records and retained 137 studies on mammalian cold adaptation. While physiological research focused mainly on non-shivering thermogenesis and metabolic regulation, studies were concentrated in the Palearctic and Nearctic regions, with Rodentia predominating. In contrast, bats were comparatively underrepresented. Among 478 reported genes, most were reported only once. Using thermogenesis-related genes derived from the review, we tested 33 nuclear genes across published bat genomes for positive selection. Site-level evidence consistent with positive selection was limited to six genes. Meanwhile, none of the branch-site tests across predefined cold-associated lineages remained statistically significant. Notably, uncoupling protein 1 (UCP1), the most frequently reported gene in the cold adaptation literature, showed no significant evidence of positive selection in any model. Overall, thermogenesis-related genes frequently emphasized in the literature did not show a common pattern of coding-sequence positive selection across cold-associated bat lineages. Future studies should examine whether regulatory, expression-level or other genomic mechanisms contribute to cold adaptation in bats.