The calanoid copepod, Acartia tonsa Dana, 1849 is one of the most abundant and well-studied estuarian species with a worldwide distribution. In this research, we use the mitochondrial cytochrome oxidase subunit I gene to study the phylogeography of A. tonsa by analyzing sequences from specimens collected in the western Gulf of Mexico (GOM) along with all sequences from previous research. We reconstruct the phylogeny for the genus Acartia Dana, 1846 and highlight numerous potential misidentifications of Acartia species deposited in GenBank. The incorrect taxonomy assigned to some of these sequences results in apparently paraphyletic relationships. This study demonstrates that A. tonsa is a species complex with multiple, deeply diverging, lineages of varying geographic affinities. Multiple new lineages are found in the Texas GOM that is basal to northwestern Atlantic lineages with phylogenetic connectivity also observed between Brazil and the Texas GOM. Results show two major phylogeographic breaks in the North American continent, one at the border between the Gulf of Mexico and the Northwest Atlantic, and the other at about 35° N. One of the major clades in the A. tonsa species complex shows a clear pattern of divergence that follows the prevailing currents. Within this clade, older lineages are found in the western GOM while newer lineages are found in the eastern GOM and the southern coast of the northwest Atlantic, with the youngest lineages diversifying in the north. The results show that A. tonsa can be used as a model species for observing phylogeographical structuring of coastal plankton along the American continent.
Figueroa, NIcole J.; Figueroa, Diego F.; and Hicks, David, "Phylogeography of Acartia tonsa Dana, 1849 (Calanoida: Copepoda) and phylogenetic reconstruction of the genus Acartia Dana, 1846" (2020). Earth, Environmental, and Marine Sciences Faculty Publications and Presentations. 24.