Basket clams of the genus Corbicula are native to Africa, Australia, Asia and the Middle East. These clams are also successful aquatic invaders in America since the 1920s and in Europe since 1980. Interestingly, the genus Corbicula exhibits various reproductive modes including sexual dioecious species and asexual hermaphrodites which reproduce through androgenesis1. Corbicula arrived in the Dutch sector of the River Meuse in the early 1990s and invaded this river further upstream, with a significant impact on the potamoplankton and possibly on other ecosystem components. Several issues quickly emerged, which are tackled in this study: Which species are present in the R. Meuse and in other European rivers? Which biological traits may explain the invasive success of Corbicula? What are the impacts of Corbicula on river ecosystems? We carried out a detailed study of the population of Corbicula spp. in the river Meuse through phylogeny and population genetics, and broadened our genetic analyses by including samples from both native and invaded areas. We investigated the phylogenetic relationships of Asian, American and European populations of Corbicula, by combining morphometrics, sperm morphology, mitochondrial genes sequencing and microsatellite analysis. Mitochondrial/nuclear mismatches were observed and indicate androgenesis between lineages. This phenomenon challenges species delimitation and highlights the need of combining mitochondrial and nuclear DNA analyses in androgenetic taxa. Androgenesis may explain the invasive success of this clam genus since only androgenetic taxa seem to be widespread, whereas their sexual relatives are mostly restricted to their native areas. A reduced genetic diversity within clam populations is observed in the invaded areas (America and Europe). This suggests the introduction and dispersal of few asexual lineages. In addition to these analyses, we also conducted a survey of the densities in the R. Meuse wherever possible, along with preliminary laboratory experiments to determine the filtration rates in order to assess the impact of these filter-feeders on the ecosystem. Even though further data collection is needed, a modelling approach using these data allowed a first assessment of the impact of Corbicula in the R. Meuse. 1 In this form of asexual reproduction in the genus Corbicula, the maternal nuclear chromosomes are extruded after fertilization and the offspring are thus (nuclear) clones of the father.
|Date of Award||19 Oct 2011|
|Supervisor||Jean-Pierre DESCY (Co-Supervisor), Karine Van Doninck (Supervisor), Eric Depiereux (President), Johan MICHAUX (Jury), T. BACKELJAU (Jury) & Jean-Nicolas BEISEL (Jury)|