They like it cold, but only in winter: Climate-mediated effects on a hibernator

Variations in ambient temperature (T-a) profoundly influence energy consumption in endotherms and therefore their survival and fitness. But depending on whether endotherms are hibernating or active, the same changes inT(a)may have opposing consequences for their energy consumption. The aim of this study was therefore to investigate how variations inT(a), occurring during hibernation and during the active period of a hibernator, affect different fitness relevant traits. To understand whether changes inT(a)impact phenology, body mass and reproduction in a small mammalian hibernator, we analysedT(a)variations and detailed capture-mark-recapture data on edible dormiceGlis gliscollected between 1993 and 2016 in South-West Germany. Results revealed that during hibernation aT(a)increase of 1 degrees C advanced the date of first capture after hibernation by 6 days, but only if food availability during the preceding year was low. In contrast, after years of comparatively high food availability, date of first capture was not affected byT(a), but dormice had a significantly lower body mass after emergence, ifT(a)during hibernation was elevated (3-6 g per 1 degrees C). We presume that an earlier emergence as well as a lower body mass after emergence potentially reduces the chance to survive. During the active period of edible dormice, mean springT(a)did not affect the date of birth but was positively associated with litter size, potentially improving reproductive success. Results of this study highlight that, depending on the physiological state of a hibernator, an increase inT(a)can have positive and negative effects on fitness relevant traits. A freePlain Language Summarycan be found within the Supporting Information of this article.