Abstract：
Amphibian diversity is most prominent in the warm and humid tropical and subtropical regions across the globe. Nonetheless, amphibians also inhabit high-altitude tropical mountains and regions at medium and high latitudes, exposing them to subzero temperatures and requiring behavioural or physiological adaptations to endure freezing events. While freeze tolerance has been predominantly reported in high-latitude zones where species endure prolonged freezing (several weeks or months), less is known about mid-latitudes amphibians exposed to occasional subzero temperatures. In this study, we employed a controlled ecological protocol, subjecting three frog species from the Iberian Peninsula (Rana parvipalmata, Epidalea calamita, and Pelobates cultripes) to a 2-h exposure to temperatures of -2 °C to investigate the accumulation of urea and glucose as physiological mechanisms associated with survival at freezing temperatures. Our results revealed a moderate response in the production of cryoprotectant metabolites under experimental freezing conditions, particularly urea, with notable findings in R. parvipalmata and E. calamita and no response in P. cultripes. However, no significant alterations in glucose concentrations were observed in any of the studied frog species. This relatively weak freezing tolerance response differs from the strong response exhibited by amphibians inhabiting high latitudes and enduring prolonged freezing conditions, suggesting potential reliance on behavioural adaptations to cope with occasional freezing episodes.
摘要：
两栖动物的多样性在全球温暖潮湿的热带和亚热带地区最为突出。尽管如此，两栖动物还居住在高海拔的热带山脉和中高纬度地区，将它们暴露在零度以下的温度下，并需要行为或生理适应才能忍受冻结事件。虽然耐冻性主要在高纬度地区报道，在这些地区，物种可以忍受长时间的冻结（几周或几个月），人们对中纬度两栖动物偶尔暴露于零度以下温度的了解较少。在这项研究中,我们采用了受控的生态协议，来自伊比利亚半岛的三种青蛙（Ranaparvipalmata，Epidaleacalamita,和Pelobatescultripes）暴露于-2°C的温度下2小时，以研究尿素和葡萄糖的积累作为与在冷冻温度下存活相关的生理机制。我们的结果表明，在实验冷冻条件下，冷冻保护剂代谢产物的产生有适度的反应，特别是尿素，在R.parvipalmata和E.calamita中发现了显着的结果，而在P.cultrypes中没有反应。然而,在所研究的任何青蛙物种中均未观察到葡萄糖浓度的显着变化。这种相对较弱的耐冻性反应不同于居住在高纬度地区和长期冻结条件下的两栖动物表现出的强烈反应，提示可能依赖行为适应来应对偶尔的冻结事件。
