Data from: Gape-limited predators as agents of selection on the defensive morphology of an invasive invertebrate

Invasive species have widespread and pronounced effects on ecosystems and adaptive evolution of invaders is often considered responsible for their success. Despite the potential importance of adaptation to invasion, we still have limited knowledge of the agents of natural selection on invasive species. Bythotrephes longimanus, a cladoceran zooplankton, invaded multiple Canadian Shield lakes over the past several decades. Bythotrephes have a conspicuous caudal process (tail spine) that provides a morphological defense against fish predation. We measured viability selection on the longest component of the Bythotrephes spine, the distal spine segment, through a comparison of the lengths of first and second instar Bythotrephes collected from lakes differing in the dominance of gape-limited predation (GLP) and non-gape-limited predation (NGLP) by fish. We found that natural selection varied by predator gape-limitation, with strong selection (selection intensity: 0.20-0.79) for increased distal spine length in lakes dominated by GLP, and no significant selection in lakes dominated by NGLP. Further, distal spine length was 17% longer in lakes dominated by GLP, suggesting the possibility of local adaptation. As all study lakes were invaded less than twenty years prior to our collections, our results suggest rapid divergence in defensive morphology in response to selection from fish predators.

外来入侵物种会对生态系统造成广泛且显著的影响，而入侵物种的适应性进化常被视作其入侵成功的核心驱动因素。尽管适应入侵环境的进化过程具有重要研究价值，但目前学界对入侵物种所经历的自然选择作用因子仍知之甚少。长肢薄皮溞（Bythotrephes longimanus）是一种枝角类浮游动物（cladoceran zooplankton），在过去数十年间已成功入侵加拿大地盾区的多个湖泊。该物种具有醒目的尾突（尾棘），可通过形态特征抵御鱼类捕食。本研究通过对比采自两类湖泊的一龄和二龄长肢薄皮溞个体的远端棘段长度，分析了该结构所承受的生存选择压力：这两类湖泊分别以鱼类的限制型口捕食（gape-limited predation, GLP）和非限制型口捕食（non-gape-limited predation, NGLP）为主导。研究结果显示，自然选择强度随捕食者的限制型口捕食特征发生变化：在以GLP为主导的湖泊中，存在对更长远端棘段的强烈选择（选择强度为0.20~0.79）；而在以NGLP为主导的湖泊中，则未检测到显著的选择作用。此外，GLP主导湖泊中的长肢薄皮溞，其远端棘段长度较NGLP主导湖泊长17%，这暗示了本地适应的可能性。由于所有研究湖泊均在采样前不到20年的时间内被入侵，本研究结果表明，长肢薄皮溞的防御形态在鱼类捕食者的选择压力下发生了快速分化。