Data from: Widespread hybridization within mound-building wood ants in Southern Finland results in cytonuclear mismatches and potential for sex-specific hybrid breakdown

Hybridization and gene flow between diverging lineages is increasingly recognized as a common evolutionary process and its consequences can vary from hybrid breakdown to adaptive introgression. We have previously found a population of wood ant hybrids between Formica aquilonia and F. polyctena that shows antagonistic effects of hybridization: females with introgressed alleles show hybrid vigour, whereas males with the same alleles show hybrid breakdown. Here we investigate whether hybridization is a general phenomenon in this species pair, and analyze 647 worker samples from 16 localities in Finland using microsatellite markers and a 1200 bp mitochondrial sequence. Our results show that 27 sampled nests contained parental-like gene pools (six putative F. polyctena and 21 putative F. aquilonia) and all remaining nests (69), from nine localities, contained hybrids of varying degrees. Patterns of genetic variation suggest these hybrids arise from several hybridization events or, instead, have backcrossed to the parental gene pools to varying extents. In contrast to expectations, the mitochondrial haplotypes of the parental species were not randomly distributed among the hybrids. Instead, nests that were closer to parental-like F. aquilonia for nuclear markers preferentially had F. polyctena’s mitochondria and vice versa. This systematic pattern suggests there may be underlying selection favoring cytonuclear mismatch and hybridization. We also found a new hybrid locality with strong genetic differences between the sexes similar to those predicted under antagonistic selection on male and female hybrids. Further studies are needed to determine the selective forces that act on male and female genomes in these newly discovered hybrids.

分化谱系间的杂交与基因流日益被认为是一种常见的进化过程，其演化后果可从杂交衰退到适应性渐渗不等。我们此前曾发现一个木蚁（wood ant）杂交种群，涉及红褐林蚁（Formica aquilonia）与黑褐林蚁（Formica polyctena），该种群展现出杂交的拮抗效应：携带渐渗等位基因的雌性个体表现出杂交活力，而携带相同等位基因的雄性个体则出现杂交衰退。本研究旨在探究杂交是否为该物种对间的普遍现象，并利用微卫星标记与1200 bp线粒体序列，对芬兰16个采样点的647份工蚁样本进行了遗传分析。研究结果显示，27个蚁巢呈现亲本样基因库特征（其中6个推定属于黑褐林蚁，21个推定属于红褐林蚁），其余来自9个采样点的69个蚁巢均携带不同程度的杂交个体。遗传变异模式表明，这些杂交个体要么起源于多次独立的杂交事件，要么在不同程度上与亲本基因库发生了回交。与理论预期相悖的是，亲本物种的线粒体单倍型并未在杂交个体中随机分布。与之相反，在核遗传标记上更接近亲本样红褐林蚁的蚁巢，其线粒体更多携带黑褐林蚁的单倍型，反之亦然。这种系统性分布模式提示，可能存在支持核质不匹配与杂交的潜在选择机制。我们还发现了一个新的杂交采样点，其雌雄个体间存在显著的遗传分化，这与雌雄杂交个体受拮抗选择作用的理论预测相符。后续仍需开展进一步研究，以明确作用于这些新发现杂交种群雌雄基因组的选择压力。