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Circadian and circannual rhythms in metabolism and ventilation in red-eared sliders (Pseudemys scripta) Reyes, Catalina

Abstract

Temperate reptiles are subjected to drastic daily and seasonal changes in their environment that strongly affect their metabolism. Therefore, reptiles inhabiting in northern latitudes require adaptations that allow them to survive extreme environmental changes. Endogenous biological rhythms such as circadian and circannual cycles are advantageous in allowing organisms to anticipate and prepare for periodic environmental changes. However, to be fully functional these rhythms must be entrained to changing environmental cues. I asked whether redeared sliders showed circadian and circannual rhythms in metabolism and ventilation, and whether daily oscillations varied across the seasons. Turtles were chronically exposed to either natural seasonal or constant indoor conditions. In addition, turtles were acutely placed under either seasonal or indoor conditions in order to determine the role of temperature and photoperiod in entraining the circadian and circannual rhythms. Daily cycles in metabolism and breathing pattern were measured over one year. I found evidence of endogenous circadian and circannual rhythms in metabolism and ventilation. Both thermocycles and photocycles were important zeitgebers and long-term exposure to these changing environmental cues was required for the rhythms to be expressed. Furthermore, I observed daily and seasonal changes in breathing pattern such that apneas were longer at night and in the winter. These results indicate that endogenous circadian and circannual rhythms entrained by seasonal changes in temperature and photoperiod prompt physiological adjustments in metabolism, ventilation and breathing pattern. These changes may reflect adaptations that prolong dive times and reduce surface intervals at night and in winter. This could serve to reduce the cost of transport, and risk of predation.

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