Understanding mechanisms that underlie species range limits is at the core of evolutionary ecology. Asymmetric gene flow between larger core populations and smaller edge populations can swamp local adaptation at the range edge and inhibit further range expansion. However, empirical tests of this theory are exceedingly rare. We tested the hypothesis that asymmetric gene flow can constrain local adaptation and thereby species’ range limits in an endemic US salamander (Ambystoma barbouri) by determining if gene flow is asymmetric between the core and peripheries of the species’ geographic distribution and testing whether local adaptation is swamped at range edges with a reciprocal transplant experiment. Using putatively neutral loci from populations across three core‐to‐edge transects that covered nearly the entire species’ geographic range, we found evidence for asymmetric, core‐to‐edge gene flow along western and northern transects, but not along a southern transect. Subsequently, the reciprocal transplant experiment suggested that northern and western edge populations are locally adapted despite experiencing asymmetric gene flow, yet have lower fitness in their respective home regions than those of centre population. Conversely, southern populations exhibit low deme quality, experiencing high mortality regardless of where they were reared, probably due to harsher edge habitat conditions. Consequently, we provide rare species‐wide evidence that local adaptation can occur despite asymmetric gene flow, though migration from the core may prohibit range expansion by reducing fitness in edge populations. Further, our multitransect study shows that multiple, nonmutually exclusive mechanisms can lead to range limits within a single species.

中文翻译：

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对基因流的混合支持是对局部适应的限制，并且是地方sal的有限地理范围的贡献者。

了解构成物种范围限制的机制是进化生态学的核心。较大核心种群和较小边缘种群之间的不对称基因流会淹没范围边缘的局部适应性，并抑制范围进一步扩大。但是，这种理论的实证检验极为罕见。我们检验了以下假设：不对称基因流会限制局部适应，从而限制了美国US的物种范围限制（Ambystoma barbouri），通过确定该物种的地理分布的核心与周边之间的基因流是否不对称，并通过对等移植实验来测试局部适应性是否在范围边缘处被淹没。利用覆盖了几乎整个物种地理范围的三个核心到边缘样带的种群的推定中性位点，我们发现了证据表明沿西部和北部样带而不是沿着南部样带不对称，核心到边缘的基因流动。随后，相互移植实验表明，尽管经历了不对称的基因流动，北部和西部边缘种群仍是局部适应的，但在其各自的家乡地区的适应性却低于中心人群。相反，南部人口的人品质量较低，无论将它们饲养在何处，死亡率都很高，这可能是由于边缘生境条件更加恶劣所致。因此，我们提供了稀有物种范围的证据，尽管基因流不对称，但局部适应仍会发生，尽管从核心迁移可能会通过降低边缘种群的适应性来阻止范围扩大。此外，我们的多样点研究表明，多种非互斥机制可导致单个物种内的范围限制。