Patterns and determinants of phenotypic variability within two invasive crayfish species

Knowledge on the ecological determinants and evolutionary processes shaping intraspecific variability in the wild remains scarce. It is particularly needed in the context of biological invasions to fully understand the consequences of invasive species on the functioning of recipient ecosystems.We quantified phenotypic variability (morphological, trophic and stoichiometric traits) within and among invasive populations of two crayfish species (<i>Procambarus clarkii</i> and <i>Faxonius limosus</i>) with distinct invasion histories. We aimed at unraveling the ecological determinants and the mechanisms (neutral or adaptive) underlying the phenotypic variability among invasive populations.We demonstrate that, for each group of traits, <i>P. clarkii</i> and <i>F. limosus</i> display contrasting patterns of variance distribution across three ecological scales (population, sex, individual). Then, we demonstrate that<i> P. clarkii</i> trait variation in body morphology and stoichiometry is associated with both ecological and historical determinants (i.e. predation pressure, intraspecific invasion and invasion age), and morphological traits in <i>F. limosus</i> vary with ecological factors only (i.e. predation pressure and abundance of<i> P. clarkii</i>). Finally, we highlight that different combinations of neutral and adaptive processes shaped the phenotypic variability in the two species, with a higher contribution of adaptive processes in <i>F. limosus</i>.Overall, these results indicate that <i>F. limosus</i> has already gone through local adaptation in the meta-population while this has not yet occurred for <i>P. clarkii</i> which was introduced later. This highlights that these two invasive species might have contrasting effects across ecological scales.<br>Our study emphasizes that studying invasive species can provide great knowledge on intraspecific variability and its ecological determinants and evolutionary processes in the wild. Our results also stress the need to focus on intraspecific variability in the context of biological invasions as it can be substantial across wide geographic areas.

目前学界对野生状态下驱动种内变异的生态决定因子与进化过程的认知仍较为匮乏。而在生物入侵研究框架下，为全面解析入侵物种对受纳生态系统功能的影响，这类研究尤为关键。
本研究针对两种具有不同入侵历史的螯虾物种——克氏原螯虾（*Procambarus clarkii*）与奥氏美螯虾（*Faxonius limosus*）的入侵种群内部及种群间的表型变异（涵盖形态、营养及化学计量性状）进行了量化分析，旨在阐明入侵种群间表型变异背后的生态决定因子与作用机制（中性机制或适应性机制）。
研究结果显示，针对每一类性状而言，克氏原螯虾与奥氏美螯虾在三个生态尺度（种群、性别、个体）上的方差分布模式均呈现显著差异。进一步分析表明，克氏原螯虾的躯体形态与化学计量性状的变异同时与生态及历史决定因子（即捕食压力、种内入侵压力与入侵时长）相关；而奥氏美螯虾的形态性状变异仅与生态因子相关（即捕食压力与克氏原螯虾种群丰度）。最后，本研究揭示，中性与适应性过程的不同组合塑造了两种螯虾的表型变异，其中奥氏美螯虾的表型变异受适应性过程的贡献更高。
综合来看，研究结果表明奥氏美螯虾已在其集合种群中发生了本地适应，而入侵时间较晚的克氏原螯虾尚未出现此类现象；这凸显出两种入侵物种在不同生态尺度上可能产生截然不同的生态影响。
本研究强调，针对入侵物种的研究可极大丰富学界对野生状态下种内变异及其生态决定因子与进化过程的认知；同时本研究结果也凸显出，在生物入侵研究框架下需重点关注种内变异，因为其在大范围地理区域内的变异程度可能十分显著。