Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK.
Biology Program, Faculty of Natural Sciences and Mathematics, Universidad del Rosario, Bogota, Colombia.
Mol Ecol. 2020 Jun;29(11):2016-2030. doi: 10.1111/mec.15460. Epub 2020 Jun 18.
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.
杂种区是不同种群相遇和杂交的地方，它让我们深入了解尽管存在基因流，但种群之间的差异是如何得以维持的。研究杂种区内遗传基因座和适应性特征的梯度变化是理解选择如何在一个物种内推动分化的有力方法，但也可以用于比较不同物种对共同选择压力的平行趋异。在这里，我们研究了蝴蝶海伦娜凤蝶和海伦娜波斑蝶翅膀颜色的平行趋异，这两种蝴蝶是远缘的缪勒拟态种，它们在色素离散变异和结构颜色的定量变异方面都表现出平行的地理变异。通过地理梯度分析，我们发现这两个物种的这些特征的梯度大致位于同一地理区域，这与直接的拟态选择一致。然而，梯度的宽度在不同物种之间有显著差异。这种差异部分可以用每个物种中颜色特征的选择强度的变化来解释，但也可能受到物种之间对杂种的扩散率和总选择强度差异的影响。基因分型测序还揭示了海伦娜波斑蝶中较弱的种群结构，这表明这两个物种的杂种区可能以不同的方式进化，这也可能是该系统表型趋异模式的原因之一。总的来说，我们得出结论，需要多个因素来解释这些物种内部和之间的梯度变化模式，尽管拟态可能发挥了核心作用。
