Biological invasions in international seaports: a case study of exotic rodents in Cotonou

Black rat (Rattus rattus), brown rat (Rattus norvegicus), and house mouse (Mus musculus) are known to be among the most common anthropophilic rodent species in cities worldwide. These species are responsible for the destruction of domestic and industrial materials, considerable damage to food stocks as well as zoonotic pathogens circulation and transmission to humans and animals. These invasive species have disseminated in all continents following human-mediated exchanges, especially maritime transports. In particular, seaports appear as privileged rats and mice's entry points into new regions, thus making them international regulations' priorities for rodent surveillance and management. Yet, studies on seaport rodents are rare; in particular, investigations on their genetic structure are almost inexistent, thus precluding science-guided interventions. In order to fill such a gap, our study focused on the population genetics of R. rattus, R. norvegicus and M. musculus in the Autonomous Port of Cotonou, Benin. Nine different sites were surveyed for three years. In total, 366 R. rattus, 188 R. norvegicus and 244 M. musculus were genotyped using 18 microsatellites, 16 microsatellites and 17 microsatellites, respectively. Our results show very well-structured genetic clusters in all three species as well as limited impacts of rodent control campaigns. Using comparisons with genotypes from other European, Asian and African countries, we suggest for the first time that settlement of newly introduced individuals may be a rare event. Implications in terms of management units and control and monitoring are discussed.