Am Nat. 2022 Aug;200(2):264-274. doi: 10.1086/720207. Epub 2022 Jun 15.
AbstractHybridization often occurs at the parapatric range interface between closely related species, but fitness outcomes vary: hybrid offspring exhibit diverse rates of viability and reproduction compared with their parental species. The mobile hybrid zone between two chickadee congeners ( × ) has been well studied behaviorally and genetically, but the viability of hybrids and the underlying mechanisms contributing to hybrid fitness have remained unclear. To better characterize the fitness costs of hybridization in this system, we analyzed 21 years of data from four sites, including more than 1,400 breeding attempts by the two species, to show that rates of hatching success changed substantially as the zone of hybridization moved across the landscape. Admixture-associated declines in hatching success correlated with reduced proportions of heterogametic (female) offspring, as predicted by Haldane's rule. Our data support an underlying mechanism implicating genetic admixture of the homogametic (male) parent as the primary determinant of offspring sex ratio, via incompatibilities on the hemizygous Z chromosome. Our long-term study is the first to directly measure changes in fitness costs as a vertebrate hybrid zone moves, and it shows that changes in these costs are a way to track the distribution of a hybrid zone across the landscape.
摘要 杂交通常发生在亲缘关系密切的物种的邻域界面，但适应度结果却有所不同：与亲代物种相比，杂交后代的生存力和繁殖力存在不同的变化。两种山雀近缘种（×）之间的移动杂种区在行为和遗传上都得到了很好的研究，但杂交种的生存力以及导致其适应度的潜在机制仍不清楚。为了更好地描述该系统中杂交的适应成本，我们分析了四个地点 21 年的数据，包括两个物种的 1400 多次繁殖尝试，结果表明，随着杂交区在景观上的移动，孵化成功率的变化幅度很大。与哈代法则预测的一致，与混合相关的孵化成功率下降与异配子（雌性）后代比例的降低有关。我们的数据支持了一种潜在的机制，即通过在半合子 Z 染色体上的不兼容性，使同配子（雄性）亲代的遗传混合成为影响后代性别比例的主要决定因素。我们的长期研究首次直接测量了随着脊椎动物杂种区的移动而导致的适应成本的变化，并表明这些成本的变化是追踪杂种区在景观中的分布的一种方式。
