A multidisciplinary assessment of social structure and reproductive strategy of the range-restricted ant <i>Plagiolepis flavescens</i>

The ant genus Plagiolepis and its relatives, which include both invasive and native species, often exhibit life history traits typical of invasive ants, such as inbreeding and dependent colony foundation. Although key life history traits such as social structure and reproductive system are critical for understanding species distribution and invasiveness, they remain unknown for most species in this genus. This study aimed to elucidate the social structure and reproductive system of Plagiolepis flavescens, a species with a limited distribution on the Korean Peninsula and primarily on Tsushima Island, Japan, and compare these traits with its congeners. To achieve this, we collected P. flavescens nests and conducted population genetic analyses, inter-colonial aggression tests, and laboratory experiments on mating and colony foundation. Our results showed that this species is polydomous, with small nests averaging 55 individuals. Colonies were monogynous or facultatively polygynous. Workers from different colonies exhibited high levels of aggression, indicating that they do not form unicoloniality. Furthermore, new queens were inferred to perform nuptial flights, engage in outbreeding and dispersal, and perform independent colony foundation. This life history of P. flavescens is typical in native ant species but contrasts with that of other known Plagiolepis species. However, some results from the laboratory mating and foundation experiments suggested an alternative reproductive system. While this is likely an artefact of captive conditions, it also suggests that environmental changes or a loss of genetic diversity following a bottleneck could weaken nestmate recognition and lead to the emergence of unicoloniality.