Data from: Evolutionary stasis despite selection on a heritable trait in an invasive zooplankton

Invasive species are one of the greatest threats to ecosystems and there is evidence that evolution plays an important role in the success or failure of invasions. Yet, few studies have measured natural selection and evolutionary responses to selection in invasive species, particularly invasive animals. We quantified the strength of natural selection on the defensive morphology (distal spine) of an invasive zooplankton, Bythotrephes longimanus, in Lake Michigan across multiple months during three growing seasons. We used multiple lines of evidence, including historic and contemporary wild-captured individuals and paleoecology of retrieved spines, to assess phenotypic change in distal spine length since invasion. We found evidence of temporally variable selection, with selection for decreased distal spine length early in the growing season and selection for increased distal spine length later in the season. This trend in natural selection is consistent with seasonal changes in the relative strength of non-gape-limited and gape-limited fish predation. Yet, despite net selection for increased distal spine length and a known genetic basis for distal spine length, we observed little evidence of an evolutionary response to selection. Multiple factors likely limit an evolutionary response to selection, including genetic correlations, trade-offs between components of fitness, and phenotypic plasticity.

入侵物种（Invasive species）是对生态系统的重大威胁之一，且已有证据表明，进化在生物入侵的成败过程中发挥着关键作用。然而，针对入侵物种（尤其是入侵动物）的自然选择（natural selection）及其演化响应的相关研究仍较为匮乏。本研究在三个生长季的多个月份内，量化了密歇根湖（Lake Michigan）内入侵性浮游动物长肢滑囊溞（Bythotrephes longimanus）的防御形态结构——远端棘（distal spine）所承受的自然选择强度；研究借助多类证据，包括历史与当代野生捕获个体、以及回收棘刺的古生态学分析，以评估该物种自入侵以来远端棘长度的表型（phenotypic）变化。研究结果显示存在时间可变选择（temporally variable selection）：在生长季早期，自然选择倾向于缩短远端棘长度；而在生长季后期，则倾向于延长远端棘长度。这种自然选择趋势与非口限捕食（non-gape-limited）和口限捕食（gape-limited）鱼类的相对捕食强度的季节变化相一致。然而，尽管净自然选择（net selection）倾向于延长远端棘长度，且已知远端棘长度具有遗传基础，但我们几乎未观测到针对选择的演化响应。多种因素可能限制了演化响应的产生，包括遗传相关性、适合度（fitness）组分间的权衡关系（trade-offs），以及表型可塑性（phenotypic plasticity）。