Hybridization is among the evolutionary mechanisms most frequently hypothesized to drive the success of invasive species, in part because hybrids are common in invasive populations. One explanation for this pattern is that biological invasions coincide with a change in selection pressures that limit hybridization in the native range. To investigate this possibility, we studied the introduction of the brown anole (Anolis sagrei) in the southeastern United States. We find that native populations are highly genetically structured. In contrast, all invasive populations show evidence of hybridization among native-range lineages. Temporal sampling in the invasive range spanning 15 y showed that invasive genetic structure has stabilized, indicating that large-scale contemporary gene flow is limited among invasive populations and that hybrid ancestry is maintained. Additionally, our results are consistent with hybrid persistence in invasive populations resulting from changes in natural selection that occurred during invasion. Specifically, we identify a large-effect X chromosome locus associated with variation in limb length, a well-known adaptive trait in anoles, and show that this locus is often under selection in the native range, but rarely so in the invasive range. Moreover, we find that the effect size of alleles at this locus on limb length is much reduced in hybrids among divergent lineages, consistent with epistatic interactions. Thus, in the native range, epistasis manifested in hybrids can strengthen extrinsic postmating isolation. Together, our findings show how a change in natural selection can contribute to an increase in hybridization in invasive populations.

杂交是最常被假设为推动入侵物种成功的进化机制之一，部分原因是杂交在入侵种群中很常见。对这种模式的一种解释是，生物入侵与限制天然范围内杂交的选择压力的变化相吻合。为了研究这种可能性，我们研究了棕色 anole ( Anolis sagrei) 在美国东南部。我们发现本地人口具有高度的遗传结构。相比之下，所有入侵种群都显示出本地谱系之间杂交的证据。跨越 15 年的入侵范围内的时间采样表明，入侵遗传结构已经稳定，表明大规模当代基因流动在入侵种群中受到限制，并且保持了混合血统。此外，我们的结果与入侵种群中由于入侵期间发生的自然选择变化导致的混合持久性一致。具体来说，我们确定了一个与肢体长度变化相关的大效应 X 染色体基因座，这是 anoles 中众所周知的适应性特征，并表明该基因座通常在天然范围内被选择，但在侵入范围内很少被选择。此外，我们发现该位点的等位基因对肢体长度的影响大小在不同谱系的杂种中大大降低，这与上位相互作用一致。因此，在原生范围内，杂种中表现出的上位性可以加强外在的交配后隔离。总之，我们的研究结果表明，自然选择的变化如何有助于增加入侵种群的杂交。