Examining genetic diversity and fusion abilities of an invasive colonial ascidian

A two-part study was carried out examining population genetics and fusion behavior of an invasive colonial ascidian, Didemnum vexillum. A barcoding mitochondrial gene, COI, was used in previous studies at global and regional levels to assess the native region (Japan) by comparing diversity and to begin to examine how fusion may affect invasions. The study here uses higher-resolution multi-locus genotyping to assess population differences within the western North American region. Results show that a small isolated population in Alaska was bottlenecked to a degree beyond the decreased diversity of western North America in comparison with native Japan, and that Tomales Bay, off Point Reyes National Seashore, in central California, is surprisingly more genetically diverse than the nearby invasion hotspot of San Francisco Bay. The study also paired live colonies in field fusion assays and analyzed the effect pairwise relatedness had on fusion probability. Results show a correlation between higher estimated relatedness between paired colonies and the likelihood that those colonies fused. The results of this study have implications regarding Didemnum vexillum’s possible transport vectors and establishment success, which could aid in future management policies that are compatible with aquaculture.