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.

趋异谱系间的杂交与基因流，现已被广泛认可为一种常见的演化过程，其后果可从杂交衰退（hybrid breakdown）涵盖至适应性基因渐渗（adaptive introgression）。我们此前曾发现一个由木蚁属（Formica）的Formica aquilonia与F. polyctena形成的杂交种群，该种群表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优势（hybrid vigour），而携带相同等位基因的雄性个体则出现杂交衰退（hybrid breakdown）。本研究旨在探究杂交是否为该物种对间的普遍现象，我们利用微卫星标记（microsatellite markers）与一段1200 bp的线粒体序列，对芬兰16个采样点的647个工蚁样本进行了分析。分析结果显示，27个采样蚁巢呈现类亲本基因库（其中6个推定属于F. polyctena，21个推定属于F. aquilonia）；其余来自9个采样点的69个蚁巢，均包含不同杂交程度的个体。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。与预期相悖的是，亲本物种的线粒体单倍型（mitochondrial haplotypes）在杂交个体间并非随机分布。具体而言，核标记特征更贴近类亲本F. aquilonia的蚁巢，其线粒体基因组多为F. polyctena的类型；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，青睐核质不匹配（cytonuclear mismatch）与杂交事件。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的杂交个体雌雄基因组的选择压力。