Complex genetic patterns in closely related colonizing invasive species


  • This work was supported by research grants from Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Aquatic Invasive Species Network (CAISN) to M. E. C. and H. J. M., a Discovery Accelerator Supplement grant to H. J. M., and an Ontario Ministry of Research and Innovation Early Researcher Award to M. E. C. A. L. R. was supported by scholarships from Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT), Québec-Océan and McGill University. The United States Environmental Protection Agency (EPA) through its Office of Research and Development partially funded and collaborated in the research described here.

Aibin Zhan, Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario, N9B 3P4, Canada. Tel: +519 2533000, ext. 3749; Fax: +519 9713616; E-mail:


Anthropogenic activities frequently result in both rapidly changing environments and translocation of species from their native ranges (i.e., biological invasions). Empirical studies suggest that many factors associated with these changes can lead to complex genetic patterns, particularly among invasive populations. However, genetic complexities and factors responsible for them remain uncharacterized in many cases. Here, we explore these issues in the vase tunicate Ciona intestinalis (Ascidiacea: Enterogona: Cionidae), a model species complex, of which spA and spB are rapidly spreading worldwide. We intensively sampled 26 sites (N= 873) from both coasts of North America, and performed phylogenetic and population genetics analyses based on one mitochondrial fragment (cytochrome c oxidase subunit 3–NADH dehydrogenase subunit I, COX3-ND1) and eight nuclear microsatellites. Our analyses revealed extremely complex genetic patterns in both species on both coasts. We detected a contrasting pattern based on the mitochondrial marker: two major genetic groups in C. intestinalis spA on the west coast versus no significant geographic structure in C. intestinalis spB on the east coast. For both species, geo-graphically distant populations often showed high microsatellite-based genetic affinities whereas neighboring ones often did not. In addition, mitochondrial and nuclear markers provided largely inconsistent genetic patterns. Multiple factors, including random genetic drift associated with demographic changes, rapid selection due to strong local adaptation, and varying propensity for human-mediated propagule dispersal could be responsible for the observed genetic complexities.