Traces of evolution: Genetic, chemical and ecological differentiation in two sibling species of the genus Lasius (Hymenoptera: Formicidae)

Natural selection is regarded as a driving force for present-day biodiversity. This is, among other groups, particularly evident in ants, which represent a tremendously diverse fauna. Two species of ants, Lasius niger and Lasius platythorax, are morphologically very similar, hinting at recent divergence. The goal of this research was to study the footprint of speciation by characterizing the genetic relationships of colonies within and between species, the ecological niches of both species, and by comparing their chemical recognition cues to evaluate different scenarios of speciation. The genetic work utilized microsatellite markers, while chemical work entailed gas chromatography coupled with mass spectrometry. Niches were characterized by a 69-day field baiting experiment, activity observations, and trail analysis. The two species were clearly distinct in all measures (genetic, chemical, ecological), although to varying degree. Genetic differences were consistent with expectations under neutral evolution, i.e. large differences were detected between species, complimented by some substructure according to subpopulations. Furthermore, the two species showed clear ecological niche partitioning along diet and environmental preferences. Chemical recognition cues were significantly shifted apart between species, while subpopulations differed only slightly. This pattern can be best explained by the force of disruptive selection. When all these measures are taken together, the most parsimonious evolutionary scenario includes an extended period of sympatry during the speciation process.