Local climate and genetic influence on intraspecific variation in torpor physiology of a cave-roosting bat

Many small endotherms employ torpor as a survival strategy to reduce energy expenditure during periods with low food availability and cold temperatures. The expression and physiology of torpor can vary substantially within species because of phenotypic plasticity and local adaptation. Understanding how plasticity and genetics influence intraspecific variation is fundamental to identifying the drivers of phenotypic variance in nature. Using a widely distributed bat species, the eastern bent-wing bat (Miniopterus orianae oceanensis), we exposed individuals from two thermally distinct sites to cold temperature regimes (ranging from 15 to 5°C). We measured oxygen consumption, and carbon dioxide production (proxies for torpor metabolic rate, TMR), and water loss during torpor (TEWL) using open-flow respirometry, and quantified skin surface temperature (T_sk) using temperature-sensitive telemetry. Analysis of the data using phylogenetically controlled, multilevel models indicated that bats from both sites exhibited a similar TMR at low T_sk, whereas bats from the colder site had a higher TMR at higher T_sk. We found no evidence of genetic differentiation of bats between the sites and estimates of heritability for TMR and TEWL showed broad credible intervals, yielding high uncertainty in interpreting genetic effects. Differences in torpor physiology responses between warm and cold sites were likely driven by phenotypic plasticity, with among-individual variation in responses partially explained by genetic effects. Such flexibility in the expression of thermoregulatory strategies is important for a highly mobile and widely distributed endotherm to be successful across a large range of thermal climates. Read the free Plain Language Summary for this article on the Journal blog.