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：极端环境可在局部尺度施加强烈的生态与进化压力。变温动物对低温环境尤为敏感，低温会导致其活动周期缩短、生理进程减缓，且暴露于亚零温度环境的概率增加。本研究旨在评估助力生物在低温环境中存活的行为与生理响应。具体而言，我们提出两个研究问题：1）高海拔普通蛙（Rana temporaria）成体是否通过比低海拔个体在更低温度下繁殖，以延长幼体生长的可用时长？2）从高海拔位点采集的蝌蚪，在常规代谢率（RMR）与耐寒性方面，是否与低海拔位点的蝌蚪存在生理差异？本研究针对苏格兰的5对配对高、低海拔普通蛙繁殖位点，以首次观测到蛙卵团的日期作为繁殖日期，并记录当地温度。研究人员采集蛙卵团并在统一实验室环境中饲养蝌蚪，采用封闭呼吸管系统测量耗氧量以表征常规代谢率。耐寒性则通过缓慢降温至所有容器内水体完全结冰后的存活率进行评估。研究结果：我们发现所有位点的繁殖均未在5℃以下发生，且繁殖温度与海拔之间无显著关联，这导致海拔每升高100米，产卵延迟5天。海拔与RMR的关联因山脉而异，但在三个拥有最高海拔位点（≥900米）的山脉中，高海拔位点采集的个体RMR低于低海拔个体。与之相反，在所有山脉中，低海拔个体的耐寒存活率均显著高于高海拔个体。研究结论：我们的结果表明，高海拔成体并未通过在更低温度下繁殖展现出行为适应性。然而，蝌蚪似乎具备通过降低RMR来适应高海拔生存的生理潜力，但耐寒性并未得到提升。因此，高海拔环境下的生存或可借助允许更快生长速率的生理机制，从而在更短时间内完成幼体发育，无需依赖延长幼体生长可用时长的适应性策略。