Abstract
Aim: Tapinoma melanocephalum is listed as one of the most important invasive pest species in China. Information regarding the patterns of invasion and effects of geographic isolation on the population genetics of this species is largely lacking. Location: South China. Methods: To address this problem, we genotyped 39 colonies (two colonies were collapsed due to genetic similarity) using microsatellite markers and mitochondrial DNA sequencing to compare colony genetic structure of T. melanocephalum on the mainland and islands of South China. Results: An analysis of the colony genotypes showed that the genetic diversity of the mainland population was slightly higher than that of the island populations but not significantly so. However, the observed heterozygosity on Shangchuan Island (SCD) was significantly lower than that of the other colonies. We also found six haplotypes in 111 mitochondrial DNA COI sequences. The relatedness (r) value between colonies of SCD was 0.410, higher than that of the other populations. The genetic clusters among colonies were not related to geographic locations and exhibited admixture likely due to frequent human-mediated dispersal associated with trade between the mainland population and the islands. Pairwise FSTs between populations showed differentiation among mainland populations, while SCD displayed high levels of divergence (FST > 0.15) from most mainland populations. There was no significant isolation by distance among colonies. Most populations showed signs of a bottleneck effect. Main conclusions: Our study suggests that there was no significant difference in the genetic diversity among the islands and the mainland; however, the lower genetic diversity, the higher degree of genetic divergence from other colonies, and the higher relatedness among nestmates made the SCD population stand out from all the others.