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现已被广泛认定为一类常见的进化过程，其演化后果涵盖从杂交衰败到适应性基因渐渗的多样情形。此前我们曾在红褐林蚁（Formica aquilonia）与多形木蚁（Formica polyctena）之间发现一个木蚁杂交种群，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呈现杂交优势，而携带同类等位基因的雄性个体则表现出杂交衰败。本研究旨在探究杂交是否为该蚁类物种对间的普遍现象，我们利用微卫星标记（microsatellite markers）与一段1200碱基对（bp，base pair）的线粒体序列（mitochondrial sequence），对芬兰16个采样点的647份工蚁样本开展了分析。研究结果显示，27个采样蚁巢携带类亲本基因库（其中6个推定属于多形木蚁，21个推定属于红褐林蚁），其余来自9个采样点的69个蚁巢均携带有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杂交事件，要么在不同程度上与亲本基因库发生了回交（backcross）。与预期相悖的是，亲本物种的线粒体单倍型（mitochondrial haplotypes）在杂交个体中并非随机分布。具体而言，在核标记（nuclear markers）上更接近类亲本红褐林蚁的蚁巢，其线粒体更多来自多形木蚁；反之亦然。这种系统性分布模式暗示，可能存在潜在的选择压力，倾向于维持核质不匹配（cytonuclear mismatch）并促进杂交过程。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差异，这与针对雌雄杂交个体的拮抗选择所预测的模式一致。未来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个体基因组的选择压力机制。