1. 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.
2. Using geometric morphometrics, stable isotopes, and elemental composition analyses, we quantified phenotypic variability (morphological, trophic, and stoichiometric traits) within and among invasive populations of two crayfish species with distinct invasion histories over 23 gravel pit lakes in southwest France. We sampled 12 populations of the red swamp crayfish (Procambarus clarkii Girard, 1852) and 11 populations of the spiny-cheek crayfish (Faxonius limosus Rafinesque, 1817). We aimed at unravelling the ecological determinants and the mechanisms (neutral or adaptive) underlying the phenotypic variability among invasive populations.
3. We demonstrate that, for each group of traits, P. clarkii and F. limosus display contrasting patterns of variance distribution across three ecological scales (population, sex, individual). Then, we demonstrate that P. clarkii 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 F. limosus vary with ecological factors only (i.e. predation pressure and abundance of P. clarkii). 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 F. limosus.
4. Overall, these results indicate that F. limosus has already gone through local adaptation in the meta-population while this has not yet occurred for P. clarkii, which was introduced later. This highlights that these two invasive species might have contrasting effects across ecological scales.
5. Our study emphasises 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.

中文翻译：

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两种入侵小龙虾物种表型变异的模式和决定因素

1. 关于在野外形成种内变异的生态决定因素和进化过程的知识仍然很少。在生物入侵的背景下，特别需要充分了解入侵物种对接收生态系统功能的影响。
2. 使用几何形态计量学、稳定同位素和元素组成分析，我们量化了在法国西南部 23 个砾石坑湖中具有不同入侵历史的两种小龙虾物种的入侵种群内部和之间的表型变异性（形态、营养和化学计量特征）。我们采样了 12 个红沼泽小龙虾种群 ( Procambarus clarkii Girard, 1852) 和 11 个棘颊小龙虾种群 ( Faxonius limosus Rafinesque, 1817)。我们旨在阐明入侵种群之间表型变异的生态决定因素和机制（中性或适应性）。
3. 我们证明，对于每组性状，P. clarkii和F. limosus在三个生态尺度（人口、性别、个体）上显示出差异分布的对比模式。然后，我们证明了P. clarkii身体形态和化学计量学的性状变异与生态和历史决定因素（即捕食压力、种内入侵和入侵年龄）有关，并且F. limosus 的形态特征仅随生态因素而变化（即P. clarkii 的捕食压力和丰度）。最后，我们强调中性和适应性过程的不同组合塑造了两个物种的表型变异性，在F. limosus中适应性过程的贡献更大。
4. 总体而言，这些结果表明F. limosus已经在元种群中经历了局部适应，而对于后来引入的P. clarkii尚未发生这种情况。这突显出这两种入侵物种可能在生态尺度上产生截然不同的影响。
5. 我们的研究强调，研究入侵物种可以提供关于种内变异及其生态决定因素和野生进化过程的大量知识。我们的结果还强调需要关注生物入侵背景下的种内变异，因为它在广泛的地理区域中可能很大。