Phylogenomics of palearctic Formica species suggests a single origin of temporary parasitism and gives insights to the evolutionary pathway toward slave-making behaviour

Abstract Background The ants of the Formica genus are classical model species in evolutionary biology. In particular, Darwin used Formica as model species to better understand the evolution of slave-making, a parasitic behaviour where workers of another species are stolen to exploit their workforce. In his book “On the Origin of Species” (1859), Darwin first hypothesized that slave-making behaviour in Formica evolved in incremental steps from a free-living ancestor. Methods The absence of a well-resolved phylogenetic tree of the genus prevent an assessment of whether relationships among Formica subgenera are compatible with this scenario. In this study, we resolve the relationships among the 4 palearctic Formica subgenera (Formica str. s., Coptoformica, Raptiformica and Serviformica) using a phylogenomic dataset of 945 genes for 16 species. Results We provide a reference tree resolving the relationships among the main Formica subgenera with high bootstrap supports. Discussion The branching order of our tree suggests that the free-living lifestyle is ancestral in the Formica genus and that parasitic colony founding could have evolved a single time, probably acting as a pre-adaptation to slave-making behaviour. Conclusion This phylogenetic tree provides a solid backbone for future evolutionary studies in the Formica genus and slave-making behaviour