Data from: Multifarious selection through environmental change: acidity and predator-mediated adaptive divergence in the moor frog (Rana arvalis)

Environmental change can simultaneously cause abiotic stress and alter biological communities, yet adaptation of natural populations to co-changing environmental factors is poorly understood. We studied adaptation to acid and predator stress in six moor frog (Rana arvalis) populations along an acidification gradient, where abundance of invertebrate predators increases with increasing acidity of R. arvalis breeding ponds. First, we quantified divergence among the populations in anti-predator traits (behaviour and morphology) at different rearing conditions in the laboratory (factorial combinations of acid or neutral pH and the presence or the absence of a caged predator). Second, we evaluated relative fitness (survival) of the populations by exposing tadpoles from the different rearing conditions to predation by free-ranging dragonfly larvae. We found that morphological defences (relative tail depth) as well as survival of tadpoles under predation increased with increasing pond acidity (under most experimental conditions). Tail depth and larval size mediated survival differences among populations, but the contribution of trait divergence to survival was strongly dependent on prior rearing conditions. Our results indicate that R. arvalis populations are adapted to the elevated predator pressure in acidified ponds and emphasize the importance of multifarious selection via both direct (here: pH) and indirect (here: predators) environmental changes.

环境变化可同时引发非生物胁迫（abiotic stress）并改变生物群落，但目前学界对自然种群如何适应共同变化的环境因子仍知之甚少。本研究以沿酸化梯度分布的6个沼蛙（Rana arvalis）种群为研究对象，探讨其对酸性与捕食者胁迫的适应机制——该物种的繁殖池塘酸度越高，无脊椎捕食者的丰度也随之升高。首先，我们在实验室不同饲养条件下（酸性/中性pH值与有无笼养捕食者的析因组合），量化了各种群在反捕食性状（行为与形态）上的分化。其次，我们将不同饲养条件下培育的蝌蚪暴露于自由活动的蜻蜓幼虫捕食中，以此评估各种群的相对适合度（存活率）。我们发现，在多数实验条件下，蝌蚪的形态防御性状（相对尾深）以及捕食压力下的存活率均随池塘酸度升高而提升。尾深与幼体体型介导了种群间的存活率差异，但性状分化对存活率的贡献程度强烈依赖于前期饲养条件。本研究结果表明，沼蛙种群已适应酸化池塘中升高的捕食压力，并强调了由直接（此处指pH值）与间接（此处指捕食者）环境变化共同驱动的多重选择的重要性。