The genetic population structure of the ant Plagiolepis xene-implications for genetic vulnerability of obligate social parasites
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Obligatory social parasites, such as ant species that need colonies of other ant species for reproduction, are rare and many of them are classified as vulnerable. This is especially the case with highly adapted permanent inquilines that are specialised on one or a few host species. Their rarity may be due to reduced dispersal abilities, as a result of reduced body size, altered wing morphology, and curtailed nuptial flight, eventually leading to inbreeding. Furthermore, the host populations may differ in their ability to resist the parasite, yet the conditions of successful parasite invasion are largely unknown. Here we investigated the population structure of the inquiline ant Plagiolepis xene and its host P. pygmaea, using microsatellite data. Genetic differentiation, inbreeding, the effective population size and nest kin structure were analysed. We found that populations of P. xene are established by a single or at most a few individuals, and that the populations were genetically highly differentiated. However, within individual host populations the parasite is able to maintain panmixia, although data on the host suggests that the local distribution of the parasite also follows patterns of substructuring in the host population. Altogether our results suggest that inquiline parasite populations are genetically highly vulnerable.
Key words:genetic vulnerability inquilinism Plagiolepis xene population structure social parasitism
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We wish to thank Luc Passera for sharing samples of P. xene and his expertise for the collections, Ludivine De Menten for her contribution to the collection in Bruniquel, Birgit Schlick-Steiner and Florian Steiner, and Alfred Buschinger for up-to-date information on the distribution of Plagiolepis inquilines, and the Spatial Ecology program of the University of Helsinki. This work was financed by Finnish Graduate School in Wildlife Biology, Conservation and Management (LUOVA) and Emil Aaltonen Foundation (to KT), Academy of Finland (grants no 42725, 206505 to LS, and the Spatial Ecology Programme), and the Belgian Fonds National pour la Recherche Scientifique (to␣SA).
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