Data from: Behavioural and physiological adaptations to low-temperature environments in the common frog, Rana temporaria

Background: Extreme environments can impose strong ecological and evolutionary pressures at a local level. Ectotherms are particularly sensitive to low-temperature environments, which can result in a reduced activity period, slowed physiological processes and increased exposure to sub-zero temperatures. The aim of this study was to assess the behavioural and physiological responses that facilitate survival in low-temperature environments. In particular, we asked: 1) do high-altitude common frog (Rana temporaria) adults extend the time available for larval growth by breeding at lower temperatures than low-altitude individuals?; and 2) do tadpoles sampled from high-altitude sites differ physiologically from those from low-altitude sites, in terms of routine metabolic rate (RMR) and freeze tolerance? Breeding date was assessed as the first day of spawn observation and local temperature recorded for five, paired high- and low-altitude R. temporaria breeding sites in Scotland. Spawn was collected and tadpoles raised in a common laboratory environment, where RMR was measured as oxygen consumed using a closed respiratory tube system. Freeze tolerance was measured as survival following slow cooling to the point when all container water had frozen.Results: We found that breeding did not occur below 5°C at any site and there was no significant relationship between breeding temperature and altitude, leading to a delay in spawning of five days for every 100 m increase in altitude. The relationship between altitude and RMR varied by mountain but was lower for individuals sampled from high- than low-altitude sites within the three mountains with the highest high-altitude sites (≥900 m). In contrast, individuals sampled from low-altitudes survived freezing significantly better than those from high-altitudes, across all mountains. Conclusions: Our results suggest that adults at high-altitude do not show behavioural adaptations in terms of breeding at lower temperatures. However, tadpoles appear to have the potential to adapt physiologically to surviving at high-altitude via reduced RMR but without an increase in freeze tolerance. Therefore, survival at high-altitude may be facilitated by physiological mechanisms that permit faster growth rates, allowing completion of larval development within a shorter time period, alleviating the need for adaptations that extend the time available for larval growth.研究背景：极端环境可在局地尺度施加强烈的生态与进化选择压力。变温动物（ectotherms）对低温环境尤为敏感，低温会导致其活动周期缩短、生理过程放缓，且暴露于亚零温环境的概率升高。本研究旨在探究有助于生物在低温环境中存活的行为与生理响应机制，具体设置了两个科学问题：1) 相较于低海拔个体，高海拔普通林蛙（Rana temporaria）成体是否会通过选择更低温度下产卵，以延长幼体生长可利用的时长？2) 从高海拔位点采集的蝌蚪与低海拔位点采集的蝌蚪，在常规代谢率（routine metabolic rate, RMR）与冻耐受能力方面是否存在生理差异？本研究针对苏格兰境内5对配对的高、低海拔普通林蛙产卵位点，以首次观测到蛙卵的日期作为产卵时间，并记录当地气温；采集蛙卵并在统一实验室环境中饲养蝌蚪，采用封闭呼吸管系统测定耗氧量以表征常规代谢率；冻耐受能力则通过将受试个体缓慢降温至容器内水体完全冻结后的存活率进行评估。 研究结果：所有位点的产卵活动均未在5℃以下发生，且产卵温度与海拔之间无显著关联，由此导致海拔每升高100米，产卵时间延迟5天。海拔与常规代谢率的关联因山地而异，但在高海拔位点海拔≥900米的3座山地中，高海拔采集个体的常规代谢率显著低于低海拔采集个体。与之相反，在所有山地中，低海拔采集个体的冻耐受能力均显著高于高海拔采集个体。 研究结论：本研究结果表明，高海拔普通林蛙成体并未通过选择更低温度产卵的行为策略实现适应性进化。然而，蝌蚪似乎具备通过降低常规代谢率以适应高海拔存活的生理进化潜力，但冻耐受能力并未同步提升。因此，高海拔环境下的存活或可通过允许更快生长速率的生理机制实现，从而在更短时间内完成幼体发育，无需通过延长幼体生长可用时长的适应性策略。