Centre d'Ecologie Fonctionnelle et Evolutive, University of Montpellier, CNRS, EPHE, IRD, Montpellier, France.
Institut de Systématique, Evolution et Biodiversité, Muséum National d'Histoire Naturelle, Paris, France.
Mol Biol Evol. 2023 Jul 5;40(7). doi: 10.1093/molbev/msad166.
Quantifying gene flow between lineages at different stages of the speciation continuum is central to understanding speciation. Heliconius butterflies have undergone an adaptive radiation in wing color patterns driven partly by natural selection for local mimicry. Color patterns are also known to be used as assortative mating cues. Therefore, wing pattern divergence is considered to play a role in speciation. A corollary is that mimicry between closely related species may be associated with hybridization and interfere with reproductive isolation. Here, we take a multifaceted approach to explore speciation history, species boundaries, and traits involved in species differentiation between the two closely related species, Heliconius hecale and Heliconius ismenius. We focus on geographic regions where the two species mimic each other and contrast this with geographic regions where they do not mimic each other. To examine population history and patterns of gene flow, we tested and compared a four-population model accounting for linked selection. This model suggests that the two species have remained isolated for a large part of their history, yet with a small amount of gene exchange. Accordingly, signatures of genomic introgression were small except at a major wing pattern allele and chemosensing genes and stronger in the mimetic populations compared with nonmimetic populations. Behavioral assays confirm that visual confusion exists but that short-range cues determine strong sexual isolation. Tests for chemical differentiation between species identified major differences in putative pheromones which likely mediate mate choice and the maintenance of species differences.
量化物种形成连续体中不同阶段谱系间基因流动的程度是理解物种形成的核心。凤蝶属蝴蝶在翅膀颜色图案上经历了适应性辐射，这部分是由于局部拟态的自然选择驱动的。颜色图案也被认为是作为交配选择的线索。因此，翅膀图案的分歧被认为在物种形成中起作用。一个推论是，密切相关的物种之间的拟态可能与杂交有关，并干扰生殖隔离。在这里，我们采用多方面的方法来探索两个密切相关的物种——凤蝶属 hecale 和凤蝶属 ismenius 的物种形成历史、物种边界以及涉及物种分化的特征。我们专注于两个物种相互模仿的地理区域，并将其与它们不相互模仿的地理区域进行对比。为了研究种群历史和基因流动模式，我们测试并比较了一个考虑连锁选择的四种群模型。该模型表明，这两个物种在其历史的大部分时间里一直保持隔离，但有少量的基因交换。因此，基因组渐渗的特征除了在主要的翅膀图案等位基因和化学感觉基因外很小，在模仿种群中比在非模仿种群中更强。行为测定证实存在视觉混淆，但短程线索决定了强烈的性隔离。对物种间化学分化的测试确定了主要差异，这些差异可能在介导配偶选择和维持物种差异的假定信息素中起作用。
