Genetic diversity of the freshwater clam Corbicula fluminea from its native range in the mainland Southeast Asia

Abstract Corbicula fluminea is native to Asia and is well known for its remarkable success as an invasive species across Europe and the Americas. In its invaded range, C. fluminea shows very low genetic diversity and exclusively androgenetic reproduction. In this study, we investigated the genetic relationships, genetic diversity, and reproductive modes of C. fluminea s.l. in its native range in mainland Southeast Asia. Specimens collected from Thailand, Laos PDR, and Vietnam were analyzed using mitochondrial COI gene sequences alongside eight polymorphic nuclear microsatellite loci to assess genetic diversity and construct phylogenetic tree and haplotype network. The results revealed a monophyletic clade of C. fluminea , with eight mitochondrial haplotypes identified across the study area. The haplotype network showed that the widespread FW5 haplotype was dominant, along with a complex network of additional haplotypes associated with previously reported haplotypes from East and Southeast Asia. Mitochondrial diversity was relatively high compared to that in the invaded range. However, microsatellite diversity was surprisingly low, with many samples exhibiting identical genotypes, which may be due to asexual androgenetic reproduction. This is further supported by the observation of biflagellate sperm in all sampling locations, clonal genotypes, and some triploid individuals.