Department of Ecology and Genetics-Animal Ecology, Uppsala University, Uppsala, Sweden.
Department of Biology, Duke University, Durham, NC, United States.
Evolution. 2024 Feb 1;78(2):267-283. doi: 10.1093/evolut/qpad204.
Hybrid inviability is an important post-zygotic reproductive barrier between species, but emerging signs of reduced viability can be difficult to study across the lifespan of natural hybrids. We use a combination of long-term monitoring, extra-pair paternity, and mitochondrial DNA identification in a natural hybrid zone of Ficedula flycatchers to detect emerging signs of intrinsic hybrid inviability across their entire lifespan. We evaluate possible evidence of Darwin's corollary to Haldane's rule, predicting asymmetries in inviability between hybrids resulting from reciprocal crosses, due to incompatible genetic factors with sex-specific inheritance patterns. We found higher hatching failure among mixed-species pairs, possibly indicating early developmental impairments associated with specific parental genetic combinations. Adult hybrids had a higher basal mortality rate than both parental species and different age-specific mortality trajectories. There were signs of differences in age-independent mortality rates between the reciprocal hybrid crosses: hybrids with a pied flycatcher mother experienced slightly increased mortality later in life. Using an exceptional dataset with many natural hybrids tracked across life stages, we provide evidence for several emerging signs of reduced hybrid viability. Incompatibilities between alleles located on autosomes and uniparentally inherited factors such as Z-linked and/or mitochondrial genes are strong candidates underlying intrinsic hybrid dysfunction in this system.
杂种不育性是物种间重要的合子后生殖障碍，但在自然杂种的整个生命周期中，对降低的生存力的新兴迹象进行研究可能具有挑战性。我们在红腹灰雀的自然杂种区内使用长期监测、额外配对的父权鉴定和线粒体 DNA 鉴定的组合来检测整个生命周期内内在杂种不育性的新兴迹象。我们评估了由于具有性别特异性遗传模式的不相容遗传因素，来自相互杂交的杂种中生存力不对称的哈代-达尔文推论的可能证据。我们发现混合种对的孵化失败率较高，这可能表明与特定亲代遗传组合相关的早期发育障碍。成年杂种的基础死亡率高于两个亲代物种，并且具有不同的年龄特异性死亡率轨迹。在相互杂种交叉之间存在与年龄无关的死亡率差异的迹象：具有 pied 雀母鸟的杂种在生命后期经历了略有增加的死亡率。利用具有许多自然杂种的特殊数据集跟踪整个生命阶段，我们为杂种生存力降低的几个新兴迹象提供了证据。位于常染色体上的等位基因与单亲遗传因子（如 Z 连锁和/或线粒体基因）之间的不兼容性是该系统中内在杂种功能障碍的重要候选因素。
