Socio- and population-genetic analyses of two West-African ponerine species (Megaponera analis and Paltothyreus tarsatus) with winged and wingless queens (Hymenoptera: Formicidae)

Depending on the reproductive strategy of a species, the same environmental barrier can affect gene flow differently. In this study, we analyzed the effects of a river on the gene flow of two ant species, one with wingless queens (Megaponera analis) and one with winged queens (Paltothyreus tarsatus), both with winged males. Colonies were sampled in the Comoe National Park, Cote d'Ivoire, from April to June, in 2017 and 2019. A detailed sociogenetic analysis corroborated monogyny and monandry for M. analis (74 of 78 colonies), including 29 colonies with evidence of recent fission events. In contrast, the sociobiological structure of P. tarsatus was more heterogeneous. Nine colonies were monogynous and monandrous, 14 colonies were either polygynous and / or polyandrous, and worker genotypes in seven colonies can only be explained by polygyny. For both species, we quantified gene flow between four sympatric subpopulations that are separated by the Comoe river. Comparisons of the different populations using two mitochondrial genes showed a clear substructure in M. analis, separating the respective river sides, while no substructure was found in P. tarsatus. Microsatellites, as likely neutral nuclear markers, showed, in contrast to mitochondrial DNA analyses, no significant substructure between any of the four subpopulations for both species. Even though microsatellites have been mostly replaced in population genetics by large-scale single nucleotide polymorphism analyses (e.g., based on restriction site associated DNA or whole genome sequencing), they are still the most efficient way to determine the social structure of social insect colonies based on thousands of samples (in our case, approx. 2000) or revealing atypical reproductive systems like genetic caste determination. These microsatellite analyses allowed us to show that gene flow in M. analis through wingless queens is restricted but compensated for by male dispersal on the nuclear DNA level. This underlines the importance of having at least one winged sexual alate in the reproductive strategy of social insects to allow for suf-ficient gene flow across minor environmental barriers.