Genetic variability of Botryllus schlosseri invasions to the east and west coasts of the USA

Biological invasions are an important threat to the health and composition of coastal marine communities. One of the most important challenges for conservation biologists and ecologists is to develop methods for historically reconstructing the invasion process in order to better understand the tempo and mode of the invasion as well as to evaluate the biological consequences. Genetic markers provide 1 approach for documenting the temporal and spatial dynamics of recent invasions through characterization of the genetic structure of introduced populations. Here, we used microsatellites to determine the geographic origins of populations of the colonial ascidian Botryllus schlosseri from the east and the west coast of the USA. Specifically, we tested the hypotheses that the source of California populations was the east coast of North America. Eight populations were sampled from the east coast and California. This hypothesis was not substantiated. Rather, results suggest that either European or Asian populations are the most likely source for the introduction(s) of B. schlosseri to California.