Hybrid zones, where distinct populations meet and interbreed, give insight into how differences between populations are maintained despite gene flow. Studying clines in genetic loci and adaptive traits across hybrid zones is a powerful method for understanding how selection drives differentiation within a single species, but can also be used to compare parallel divergence in different species responding to a common selective pressure. Here, we study parallel divergence of wing colouration in the butterflies Heliconius erato and H. melpomene , which are distantly related Müllerian mimics which show parallel geographic variation in both discrete variation in pigmentation, and quantitative variation in structural colour. Using geographic cline analysis, we show that clines in these traits are positioned in roughly the same geographic region for both species, which is consistent with direct selection for mimicry. However, the width of the clines varies markedly between species. This difference is explained in part by variation in the strength of selection acting on colour traits within each species, but may also be influenced by differences in the dispersal rate and total strength of selection against hybrids between the species. Genotyping‐by‐sequencing also revealed weaker population structure in H. melpomene , suggesting the hybrid zones may have evolved differently in each species, which may also contribute to the patterns of phenotypic divergence in this system. Overall, we conclude that multiple factors are needed to explain patterns of clinal variation within and between these species, although mimicry has probably played a central role.

中文翻译：

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尽管有不同的基因组差异和选择水平，但Müllerian模仿了定量特征。

杂种区，不同的种群汇聚和杂交，可以深入了解尽管存在基因流，种群之间的差异如何得以维持。研究跨杂交区遗传位点和适应性状的种系是了解选择如何驱动单个物种内分化的有力方法，但也可用于比较不同物种对共同选择压力的平行发散。在这里，我们研究了蝴蝶Heliconius erato和H. melpomene的翅膀着色的平行发散，是遥远相关的Müllerian模拟物，在色素沉着的离散变化和结构颜色的定量变化中均显示出平行的地理变化。使用地理系分析，我们表明这些性状的系在两个物种的大致相同地理区域中定位，这与直接选择拟态一致。但是，种间的株系宽度明显不同。这种差异部分地通过选择强度对每个物种内的颜色性状的变化来解释，但也可能受到针对物种之间杂种的选择的分散速度和总强度差异的影响。通过测序进行基因分型也揭示了H. melpomene的种群结构较弱，表明杂种区在每个物种中的进化可能不同，这也可能导致该系统的表型发散模式。总的来说，我们得出的结论是，尽管模仿可能起着核心作用，但仍需要多种因素来解释这些物种内部和之间的临床变化模式。