Rapid evolution of thermal plasticity in mountain lake Daphnia populations

Populations at risk of extinction due to climate change may be rescued by adaptive evolution or plasticity. Selective agents, such as introduced predators, may enhance or constrain plastic or adaptive responses to temperature. We tested responses of Daphnia to temperature by collecting populations from lakes across an elevational gradient in the presence and absence of fish predators (long-term selection). We subsequently grew these populations at two elevations in field mesocosms over two years (short-term selection), followed by a common-garden experiment at two temperatures in the lab to measure life-history traits. Both long-term and short-term selection affected traits, suggesting that genetic variation of plasticity within populations enabled individuals to rapidly evolve plasticity in response to high temperature. We found that short-term selection by high temperature increased plasticity for growth rate in all populations. Fecundity was higher in populations from fishless lakes and body size showed greater plasticity in populations from warm lakes (long-term selection). Neither body size nor fecundity were affected by short-term thermal selection. These results demonstrate that plasticity is an important component of the life-history response of Daphnia, and that genetic variation within populations enabled rapid evolution of plasticity in response to selection by temperature.

因气候变化面临灭绝风险的种群，可通过适应性进化（adaptive evolution）或表型可塑性（plasticity）获得拯救。选择因子（selective agents），例如外来捕食者，或可强化或抑制种群对温度的可塑性与适应性响应。本研究以水蚤（Daphnia）为研究对象，通过在覆盖海拔梯度的湖泊中采集存在与缺失鱼类捕食者（长期选择）的种群，探究其对温度的响应。随后，我们将这些种群置于两个海拔高度的野外中型实验生态系（field mesocosms）中培养两年（短期选择），之后在实验室设置两个温度梯度开展共同花园实验（common-garden experiment），以测定其生活史性状（life-history traits）。长期与短期选择均对性状产生了影响，这表明种群内表型可塑性的遗传变异使得个体能够针对高温快速演化出可塑性响应。研究发现，高温介导的短期选择提升了所有种群的生长速率可塑性。无鱼湖泊来源的种群繁殖力（fecundity）更高，而暖湖（长期选择）来源的种群体型可塑性更强。体型与繁殖力均未受到短期温度选择的影响。本研究结果证实，表型可塑性是水蚤生活史响应的重要组成部分，且种群内的遗传变异使得其能够针对温度选择快速演化出可塑性。