Unpredictable warm spells in winter increase blood cortisol level but lengthen telomeres in a seasonal rodent Phodopus sungorus

Animal performance in the environment significantly determines its fitness. However, global warming and the increased frequency of unpredictable weather events may disrupt the proper timing of seasonal adjustments of a phenotype. This may lead to the deterioration of the animal's condition and shorten its lifespan. We tested whether warm spells in winter affect the baseline and stress-induced cortisol level and leukocyte relative telomere length in two winter phenotypes of Siberian hamster Phodopus sungorus, responding and non-responding to short photoperiod. We found that both phenotypes increased cortisol levels in winter and that warm spells augmented this response. Under stable cold conditions, non-responding individuals were more vulnerable to short-term stress than responding ones. However, telomere length increased, suggesting that animals have a high potential to cope with stress and prevent telomere shortening or that these two variables are not directly related. In responding individuals, the higher incidence of torpor also prevented telomere shortening. These results indicate that both phenotypes, responding and non-responding to short photoperiod, can overcome the challenges posed by an unpredictably changing environment.

Methods
We used 230 Siberian hamsters (Phodopus sungorus) of both sexes: 120 (55 males and 65 females) for relative telomere length study (“RTL group’) and 110 animals (55 males and 55 females) for cortisol and testosterone measurements (“CORT/T group”).  A hamster was classified as a responder if it turned white (at least stage 2 or 3 of winter fur according to the Figala scale (Figala et al. 1973)) and used daily torpor (at least one episode).

Cortisol and testosterone concentrations were measured using liquid chromatography/tandem mass spectrometry (LC-MS-MS).

Relative telomere length (RTL) was measured using the quantitative polymerase chain reaction (qPCR) approach.