title: Evidence of a Native Northwest Atlantic COI Haplotype Clade in the Cryptogenic Colonial Ascidian Botryllus schlosseri.
abstract: The colonial ascidian Botryllus schlosseri should be considered cryptogenic (i.e., not definitively classified as either native or introduced) in the Northwest Atlantic. Although all the evidence is quite circumstantial, over the last 15 years most research groups have accepted the scenario of human-mediated dispersal and classified B. schlosseri as introduced; others have continued to consider it native or cryptogenic. We address the invasion status of this species by adding 174 sequences to the growing worldwide database for the mitochondrial gene cytochrome c oxidase subunit I (COI) and analyzing 1077 sequences to compare genetic diversity of one clade of haplotypes in the Northwest Atlantic with two hypothesized source regions (the Northeast Atlantic and Mediterranean). Our results lead us to reject the prevailing view of the directionality of transport across the Atlantic. We argue that the genetic diversity patterns at COI are far more consistent with the existence of at least one haplotype clade in the Northwest Atlantic (and possibly a second) that substantially pre-dates human colonization from Europe, with this native North American clade subsequently introduced to three sites in Northeast Atlantic and Mediterranean waters. However, we agree with past researchers that some sites in the Northwest Atlantic have more recently been invaded by alien haplotypes, so that some populations are currently composed of a mixture of native and invader haplotypes.
authors.affiliation: The Downeast Institute, P.O. Box 83, Beals, Maine 04611; pyund@downeastinstitute.org.
authors.forename: Philip O
authors.initials: PO
authors.lastname: Yund
authors.affiliation: Department of Anatomy, University of Otago, PO Box 913, Dunedin, New Zealand; and.
authors.forename: Catherine
authors.initials: C
authors.lastname: Collins
authors.affiliation: Department of Anatomy, University of Otago, PO Box 913, Dunedin, New Zealand; and Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand.
authors.forename: Sheri L
authors.initials: SL
authors.lastname: Johnson
mesh_terms: D000818:Animals; D001267:Atlantic Ocean; D004272:DNA, Mitochondrial / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics*; D014644:Genetic Variation; D006239:Haplotypes; D058865:Introduced Species; D008522:Mediterranean Sea; D014561:Urochordata / Q000145:classification* / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial; D003576:Electron Transport Complex IV