Instituto Gulbenkian de Ciência, Oeiras, Portugal.
Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK.
Mol Ecol. 2018 Oct;27(19):3935-3949. doi: 10.1111/mec.14482. Epub 2018 Feb 10.
In many diploid species, the sex chromosomes play a special role in mediating reproductive isolation. In haplodiploids, where females are diploid and males haploid, the whole genome behaves similarly to the X/Z chromosomes of diploids. Therefore, haplodiploid systems can serve as a model for the role of sex chromosomes in speciation and hybridization. A previously described population of Finnish Formica wood ants displays genome-wide signs of ploidally and sexually antagonistic selection resulting from hybridization. Here, hybrid females have increased survivorship but hybrid males are inviable. To understand how the unusual hybrid population may be maintained, we developed a mathematical model with hybrid incompatibility, female heterozygote advantage, recombination and assortative mating. The rugged fitness landscape resulting from the co-occurrence of heterozygote advantage and hybrid incompatibility results in a sexual conflict in haplodiploids, which is caused by the ploidy difference. Thus, whereas heterozygote advantage always promotes long-term polymorphism in diploids, we find various outcomes in haplodiploids in which the population stabilizes either in favour of males, females or via maximizing the number of introgressed individuals. We discuss these outcomes with respect to the potential long-term fate of the Finnish wood ant population and provide approximations for the extension of the model to multiple incompatibilities. Moreover, we highlight the general implications of our results for speciation and hybridization in haplodiploids versus diploids and how the described fitness relationships could contribute to the outstanding role of sex chromosomes as hotspots of sexual antagonism and genes involved in speciation.
在许多二倍体物种中，性染色体在介导生殖隔离方面起着特殊作用。在单倍二倍体中，雌性是二倍体，雄性是单倍体，整个基因组的行为类似于二倍体的 X/Z 染色体。因此，单倍二倍体系统可以作为性染色体在物种形成和杂交中作用的模型。先前描述的芬兰 Formica 木蚁种群表现出全基因组的多倍体和性拮抗选择的迹象，这些选择是由杂交引起的。在这里，杂交雌性的存活率增加，但杂交雄性则无法存活。为了了解不寻常的杂交种群如何得以维持，我们开发了一个带有杂交不亲和、雌性杂合子优势、重组和交配选择的数学模型。杂种优势和杂交不亲和的共同存在导致了单倍二倍体的性冲突，这是由倍性差异引起的。因此，虽然杂合子优势总是促进二倍体的长期多态性，但我们在单倍二倍体中发现了各种结果，其中种群要么有利于雄性，要么有利于雌性，要么通过最大化渗入个体的数量来稳定。我们根据芬兰木蚁种群的潜在长期命运以及将模型扩展到多个不兼容性的近似值来讨论这些结果。此外，我们强调了我们的结果对单倍二倍体与二倍体中的物种形成和杂交的普遍意义，以及描述的适合度关系如何有助于性染色体作为性拮抗和参与物种形成的基因热点的突出作用。
