Phylogeography of an Estuarian Calanoid Copepod; Acartia tonsa in the Texas Gulf of Mexic

The calanoid copepod, Acartia tonsa is one of the most abundant and well-studied estuarian species. However, the idea that this cosmopolitan species has unrestricted dispersal and high gene flow has been challenged. In this study, a more holistic picture of the phylogeography of A. tonsa was developed using the mitchondrial gene cytochrome oxidase one (mtCOI). Multiple new lineages were found in the Texas Gulf of Mexico that are basal to Northeastern Atlantic lineages. Connectivity was also observed between Brazil and the Texas Gulf of Mexico. The revised phylogeny shows a clear pattern of cryptic speciation as the species made a northward expansion since the last glacial cycle during the Pleistocene epoch. These data show that A. tonsa is a model species for observing phylogeographical structuring along the American continent.