Asymmetrical evolution of cross inhibition in zooplankton: Insights from contrasting phosphorus limitation and salinization exposure sequences

Understanding the evolutionary responses of organisms to multiple stressors is crucial for predicting the ecological consequences of intensified anthropogenic activities. While previous studies have documented the effects of selection history on organisms' abilities to cope with new stressors, the impact of the sequence in which stressors occur on evolutionary outcomes remains less understood. In this study, we examined the evolutionary responses of a metazoan rotifer species to two prevalent freshwater stressors: nutrient limitation and increased salinization. We subjected rotifer populations with distinct selection histories (salt-adapted, low phosphorus-adapted, and ancestral clones) to a reciprocal common garden experiment and monitored their population growth rates. Our results revealed an asymmetric evolutionary response to phosphorus (P) limitation and increased salinity. Specifically, adaptation to low P conditions reduced rotifer tolerance to increased salinity, whereas adaptation to saline conditions enhanced tolerance to P limitation, and such evolved cross-tolerance was more pronounced under moderately saline conditions. Our findings, therefore, underscore the importance of considering historical stressor regimes to improve our understanding and predictions of organismal responses to multiple stressors, and also have significant implications for ecosystem management.

解析生物对多重胁迫因子（multiple stressors）的进化响应（evolutionary responses），对于预判人类活动加剧所引发的生态后果至关重要。尽管既往研究已阐明选择历史（selection history）对生物应对新型胁迫因子（stressor）能力的影响，但胁迫因子出现顺序对进化结局（evolutionary outcomes）的调控作用仍有待深入探究。本研究以一种后生动物轮虫（metazoan rotifer）为对象，探究其对两种典型淡水胁迫因子（freshwater stressors）——营养限制（nutrient limitation）与盐度升高（increased salinization）——的进化响应。我们将具有不同选择历史的轮虫种群（盐适应种群、低磷适应种群及祖先克隆株）置于互置同质园实验（reciprocal common garden experiment）中，并监测其种群增长率（population growth rates）。研究结果显示，轮虫对磷（P）限制与盐度升高的进化响应呈现不对称性。具体而言，适应低磷环境会降低轮虫对盐度升高的耐受能力，而适应盐胁迫环境则可提升其对磷限制的耐受能力；且这种进化获得的交叉耐受性（cross-tolerance）在中度盐度条件下表现更为显著。因此，本研究结果凸显了纳入历史胁迫因子作用模式（stressor regimes）的重要性，这有助于深化我们对生物应对多重胁迫因子响应的认知与预测能力，同时也为生态系统管理（ecosystem management）提供了重要参考依据。