混合区域,不同种群相遇并杂交的地方,深入了解尽管基因流动,种群之间的差异是如何保持的。研究杂交区的遗传基因座和适应性特征是一种有效的方法,可以了解选择如何驱动单个物种内的分化。但也可用于比较不同物种对共同选择压力的平行发散。这里,我们研究了蝴蝶Helconiuserato和H.melpomene的翅膀颜色的平行发散,它们是远缘相关的穆勒模拟物,它们在色素沉着的两个离散变化中都显示出平行的地理变化,和结构颜色的定量变化。使用地理cline分析,我们表明,这些性状中的Clines位于两个物种的大致相同的地理区域,这与模仿的直接选择是一致的。然而,物种之间的神经宽度明显不同。这种差异部分是由作用于每个物种颜色性状的选择强度的变化来解释的。但也可能受到物种之间杂种的分散速率和选择总强度差异的影响。通过测序进行基因分型还揭示了莫尔波明的种群结构较弱,表明混合带可能在每个物种中都有不同的进化,这也可能导致该系统中表型差异的模式。总的来说,我们得出的结论是,需要多种因素来解释这些物种内部和之间的物种变异模式,虽然模仿可能发挥了核心作用。
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.