Data from: Potential fitness tradeoffs for thermal tolerance in the intertidal copepod Tigriopus californicus

Thermal adaptation to spatially varying environmental conditions occurs in a wide range of species, but what is less clear is the nature of fitness trade-offs associated with this temperature adaptation. Here, populations of the intertidal copepod Tigriopus californicus are examined at both local and latitudinal scales to determine whether these populations have evolved differences in their survival under high temperature stress. A clear pattern of increasing high temperature stress tolerance is seen with decreasing latitude, consistent with temperature adaptation. Additionally, there is also evidence for significant variation in thermal tolerance on a smaller scale. The competitive fitness of pairs of northern and southern copepod populations were also examined under a series of lower, more moderate temperatures. These fitness assays show that the southern populations that have the best survival under extreme high temperatures have lowered competitive fitness at the lower temperatures tested, whereas the fitness of the southern populations exceeded that of the northern populations at the highest temperatures tested. Combined, these results suggest that there may be evolutionary trade-offs between performance at high and stressful temperatures and fitness at moderate temperatures in this species.

针对空间异质性环境条件的热适应广泛存在于诸多物种之中，但与这类温度适应相关的适合度权衡（fitness trade-off）的本质，仍有待阐明。本研究以潮间带桡足类加州虎猛水蚤（Tigriopus californicus）的种群为研究对象，分别从局域尺度与纬度梯度尺度开展实验，以探究这些种群在高温胁迫下的存活率是否已演化出差异。研究结果显示，种群的高温胁迫耐受性随纬度降低而显著提升，这一规律与温度适应的预期相符。此外，研究还发现热耐受性在更小的空间尺度上亦存在显著差异。本研究还在一系列更低且更温和的温度条件下，对南北成对的桡足类种群的竞争适合度进行了检测。适合度检测结果表明：在极端高温下存活率最高的南方种群，在本次实验测试的低温环境中的竞争适合度有所降低；而在本次实验测试的最高温度条件下，南方种群的适合度则高于北方种群。综合上述结果，该物种在高温及胁迫温度下的表现与温和温度下的适合度之间，可能存在演化权衡。