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 hybridisation. 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 (standardised 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.

专性社会寄生物（obligate social parasites）与其宿主的配对体系——其中部分寄生物近期通过种内社会寄生（intraspecific social parasitism）从宿主类群中分化而来——为研究物种形成（speciation）的模式与过程提供了极具研究价值的实验体系。这类大概率发生在同域环境中的物种形成事件，在红林蚁（Myrmica rubra）及其种内社会寄生物类群中也被提出过。该类蚂蚁的寄生现象与蚁后体型多态性（queen size dimorphism）相关，小型蚁后（microgyne）已演化为大型蚁后（macrogyne）的社会寄生物。本研究针对芬兰南部11个样地的宿主与寄生物蚁后形态型，利用蚁后与工蚁的核基因标记及线粒体基因标记开展了遗传分化（genetic divergence）分析。我们构建并检验了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。研究结果显示，两种蚁后形态型彼此间遗传分化显著，且杂交事件极少。在分层分子方差分析（Analysis of Molecular Variance, AMOVA）中，当样地嵌套于蚁后形态型之下时，39%的遗传变异（genetic variation）可由蚁后形态型解释（标准化F'CT = 0.63，未校正FCT = 0.39），而18%的遗传变异来自样地差异（F'SC = 0.39，FSC = 0.29）。该结果佐证了先进同域物种形成（advanced sympatric speciation）假说。相较之下，线粒体DNA（mitochondrial DNA）数据无法明确区分样地与蚁后形态型这两个分层水平，因此同等支持初期同域物种形成（incipient speciation）与先进同域物种形成两种假说。综上，本研究结果支持以下观点：小型蚁后寄生物类群已从其大型蚁后宿主中发生遗传分化，达到了初期物种（nascent species）的等级。