Genetic differentiation between the ant Myrmica rubra and its microgynous social parasite

Abstract

Hymenopteran inquiline species have been proposed to originate by sympatric speciation through intraspecific social parasitism. One such parasite, Myrmica microrubra, was recently synonymized with its Myrmica rubra host, because comparisons across Europe indicated insufficient genetic differentiation. Here, we use microsatellite markers to study genetic differentiation more precisely in a sample of Finnish M. rubra and its inquilines collected at two localities, supplemented with mitochondrial DNA sequences. The parasite had much lower genetic variation than the host at three of the four loci studied. Genetic differentiation between the host populations was moderate (F ST = 0.089), whereas the parasite populations were more strongly subdivided (F ST = 0.440). The host and parasite were highly genetically differentiated both across populations (F ST = 0.346) and in strict sympatry (0.327, 0.364), a result that remained robust both in a haplotype network and in PCA ordination. Individual assignments of genotypes indicated that gene flow between sympatric host and inquiline populations is reduced by about an order of magnitude relative to the gene flow within the morphs. Our results suggest that the parasitic morph of M. rubra may be an incipient species, but it remains unclear to what extent the observed genetic differentiation between host and inquiline is due to possible assortative mating and selection against hybrids or to recurrent bottlenecking and genetic drift. We conclude that an explicitly functional species concept would be unambiguous in treating this inquiline as a full species, as it begets its own kind and maintains its integrity in spite of occasional interbreeding with the host.

Phylogeny, divergence-time estimation, biogeography and social parasite–host relationships of the Holarctic ant genus Myrmica (Hymenoptera: Formicidae)

“…By testing the hypothesis that social parasites are the closest relatives of their respective hosts, it helps to clarify whether social parasitism evolved once or several times within a genus. Moreover, the validity of SFER has been used as evidence in favour of sympatric speciation (Buschinger, 1990;Bourke and Franks, 1991;Savolainen and Vepsäläinen, 2003;Vepsäläinen et al, 2009).…”

Acceptance of alien queens by the ruby ant Myrmica rubra (Hymenoptera: Formicidae): Gene flow by queen flow

“…The models were run using the backward elimination method, i.e., the least signifi cant interaction term was removed fi rst and the model was re-run until only fi xed variables remained. (Vepsäläinen et al, 2009;Radchenko & Elmes, 2010;Schar & Nash, 2014;Leppänen et al, 2015). On the one hand the opposite behaviour has also been suggested.…”

“…Interestingly, this species seems to have an intraspecifi c parasite, a microgyne queen that does not contribute to worker production (Radchenko & Elmes, 2010). The microgyne seems not to be closely related to the host colony (Vepsäläinen, et al, 2009;Schär & Nash, 2014;Leppänen, et al, 2015), which raises the question whether this species allows alien conspecifi c queens to join its colonies.…”

Myrmica ants host highly diverse parasitic communities: from social parasites to microbes

“…Owing to their well-defined morphological character set, Seifert (1993) described this microgyne morph as a separate species under the name M. microrubra. Later, studies based on molecular evidence demonstrated that M. microrubra has not evolved separately to M. rubra and although they are locally separated, they do not differentiate on the regional level and they share a common gene pool ( Steiner et al, 2006;Vepsäläinen et al, 2009;Leppänen et al, 2011). Therefore, the microgyne can be more readily considered an intraspecific parasitic morph of M. rubra (Steiner et al, 2006;Jansen et al, 2010).…”

“…Therefore, the microgyne can be more readily considered an intraspecific parasitic morph of M. rubra (Steiner et al, 2006;Jansen et al, 2010). Some studies suggest, due to its distinctive morphological and behavioral features, that it is an intriguing example of ongoing sympatric speciation (Vepsäläinen et al, 2009;Jansen et al, 2010;Leppänen et al, 2011). The microgyne forms occur also in M. ruginodis, but in contrast to M. microrubra they are free living and produce normal workers (Brian and Brian, 1955).…”