Marked daily variation in spring temperature induces variation in Caspase-3, Bcl-2 and HSP60 in Asian Short-toed Larks: how do wild birds maintain cellular homeostasis to cope with the ambient temperature variation?

Abstract

Daily variation in ambient temperature is marked during the spring at middle and high latitudes, when birds have to physiologically prepare for the subsequent breeding period. The ability of birds to maintain homeostasis during this period is important to survival and reproduction. We compared levels of the apoptotic proteins Caspase-3 and B cell lymphoma 2 (Bcl-2) and of the stress response heat shock protein 60 (HSP60) in peripheral blood cell samples of wild Asian Short-toed Larks (Calandrella cheleensis) collected on specific dates in the spring of 2014 and 2015 at different ambient temperatures. We also conducted a controlled temperature experiment to confirm the effect of temperature on the secretion of these proteins. Our results show that levels of Caspase-3, Bcl-2 and HSP60 in the blood of Asian Short-toed Larks varied with daily variations in temperature. Caspase-3 levels were higher but Bcl-2 levels were lower in blood samples collected on days when the mean daily temperature had dramatically increased or decreased, and this trend was confirmed by the results of our laboratory experiment on the effects of temperature on Caspase-3 and Bcl-2 levels. HSP60 levels in the blood of wild-caught Asian Short-toed Larks were higher in samples collected on days with higher temperatures in 2014 and in the high-temperature treatment group in our laboratory experiment. These results indicate that marked daily variation in ambient temperature may increase Caspase-3 levels to initiate apoptosis and that Bcl-2 and HSP60 maintain cellular homeostasis by inhibiting this increase in Caspase-3, suggesting a possible molecular mechanism by which birds cope with the effects of ambient temperature variation at the cellular level.