Abstract
BackgroundThe disjunct distribution of several Palearctic species has been widely shaped by the changes in climatic conditions during the Quaternary. The observed genetic differentiation or reproductive isolation between extant populations may be the outcome of their contemporary geographic separation or reproductive incompatibility due to differences in phenotypic traits which have evolved in isolated refugia. In the boreal ant Leptothorax acervorum, colonies from central and peripheral populations differ in social structure: colonies from Central and Northern Europe may contain several equally reproductive queens (facultative polygyny), while in colonies from peripheral populations in Spain only one the most dominant of several queens lays eggs (functional monogyny). By reconstructing the specie’s evolutionary and demographic history in Southwestern Europe we examine whether variation in social organization is associated with restricted gene flow between the two social forms.ResultsWe show that multi-queen colonies from all so far known inner Iberian populations of L. acervorum are functionally monogynous, whereas multi-queen colonies from all Pyrenean populations are polygynous, like those from other previously studied areas in Europe. Our analyses revealed complex spatial-genetic structure, but no association between spatial-genetic structure and social organization in SW-Europe. The population in the western Pyrenees diverged most strongly from other Iberian populations. Moreover, microsatellite data suggest the occurrence of recent bottlenecks in Pyrenean and inner Iberian populations.ConclusionsOur study shows a lack of reproductive isolation between the two social forms in SW-Europe. This in turn suggests that demographic and spatial patterns in genetic variation as well as the distribution of social phenotypes are better explained by co-variation with climatic, ecological, and historical factors. Moreover, we for the first time show the existence of substantial spatial-genetic structure in L. acervorum, suggesting the existence of multiple refugia in SW-Europe, including two extra-Mediterranean refugia in France. While gene flow among inner Iberian refugia may have been larger during the late glacial, extra-Mediterranean refugia in southern France may have contributed to the post-glacial recolonization of W-Europe.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0711-3) contains supplementary material, which is available to authorized users.
Highlights
The disjunct distribution of several Palearctic species has been widely shaped by the changes in climatic conditions during the Quaternary
Eighty percent of the inner Iberian colonies (43 out of 54) were functionally monogynous, i.e. only one of several queens that co-occurred in a single nest had elongated ovarioles with traces of previous reproduction
In accordance with previous studies documenting facultative polygyny in the Pyrenees and other parts of Central and Northern Europe [e.g. [7, 8]) we consider the Pyrenean populations of L. acervorum as facultatively polygynous and the inner Iberian populations Sierra de Albarracin (SA) and Sierra de Gúdar (SG) as functionally monogynous (Table 2; [8, 11, 20])
Summary
In the boreal ant Leptothorax acervorum, colonies from central and peripheral populations differ in social structure: colonies from Central and Northern Europe may contain several reproductive queens (facultative polygyny), while in colonies from peripheral populations in Spain only one the most dominant of several queens lays eggs (functional monogyny). Trettin et al BMC Evolutionary Biology (2016) 16:137 and accumulate unique genotypes and specific adaptations [5, 6] This is evident in the boreomontane ant Leptothorax acervorum (Fabricius, 1793) (Hymenoptera, Formicidae). Queens in colonies from the range margin (e.g. Central Spain and Hokkaido, Japan) form social and reproductive hierarchies and only the top-ranking queen reproduces (high skew, “functional monogyny”, [8, 10, 11]). Mating behaviour differs between populations from Central Spain and Central Europe [8]
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