Data from: Genetic divergence between the sympatric queen morphs of the ant Myrmica rubra

Pairs of obligate social parasites and their hosts, where some of the parasites have recently diverged from their host through intraspecific social parasitism, provide intriguing systems for studying the modes and processes of speciation. Such speciation, probably in sympatry, has also been propounded in the ant Myrmica rubra and its intraspecific social parasite. In this species, parasitism is associated with queen size dimorphism, and the small microgyne has become a social parasite of the large macrogyne. Here, we investigated the genetic divergence of the host and the parasite queen morphs in 11 localities in southern Finland, using nuclear and mitochondrial markers of queens and workers. We formulated and tested four speciation-related hypotheses that differed in the degree of genetic divergence between the morphs. The queen morphs were genetically distinct from each other with little hybridization. In the nuclear data, when localities were nested within queen morphs in the hierarchical amova, 39% of the genetic variation was explained by the queen morph (standardized F'CT = 0.63, uncorrected FCT = 0.39), whereas 18% was explained by the locality (F'SC = 0.39, FSC = 0.29). This result corroborated the hypothesis of advanced sympatric speciation. In contrast, the mitochondrial DNA could not settle between the hierarchical levels of locality and queen morph, thus substantiating equally the hypotheses of incipient and advanced sympatric speciation. Together, our results support the view that the microgynous parasite has genetically diverged from its macrogynous host to the level of a nascent species.

专性社会性寄生物（obligate social parasites）与其宿主（host）的配对体系——其中部分寄生物近期通过种内社会性寄生（intraspecific social parasitism）从宿主类群中分化而来——为研究物种形成的模式与过程提供了极具研究价值的实验系统。这类极可能属于同域物种形成（sympatric speciation）的事件，在红林蚁（Myrmica rubra）及其种内社会性寄生物类群中也被提出过。在该蚁类中，寄生特性与蚁后体型二态性（queen size dimorphism）相关联，小型微型蚁后（microgyne）已演变为大型巨型蚁后（macrogyne）的社会性寄生物。
本研究在芬兰南部11个采样点开展，利用蚁后与工蚁的核基因标记（nuclear markers）及线粒体标记（mitochondrial markers），对宿主与寄生物蚁后形态型的遗传分化进行了探究。我们提出并检验了4项与物种形成相关的假说，这些假说的差异在于不同形态型间的遗传分化程度。
结果显示，两种蚁后形态型彼此间存在显著遗传分化，且杂交事件极少发生。在分层分子方差分析（hierarchical amova）中，当将采样点嵌套于蚁后形态型层级下时，39%的遗传变异可由蚁后形态型解释（标准化分化系数F'CT = 0.63，未校正分化系数FCT = 0.39），另有18%的遗传变异可由采样位点解释（F'SC = 0.39，FSC = 0.29）。该结果佐证了同域物种形成已进入高级阶段的假说。
与之相反，线粒体DNA（mitochondrial DNA）的分析结果无法在采样位点与蚁后形态型这两个层级间作出明确区分，因此同时支持了同域物种形成处于初始阶段与高级阶段的两种假说。
综合来看，本研究结果支持这一观点：微型寄生物蚁后已从其巨型蚁后宿主类群中发生了遗传分化，达到了新生物种（nascent species）的形成水平。