Comparative phylogeography and connectivity of sibling species of the marine copepod Clausocalanus (Calanoida)

Connectivity of the marine epipelagic environment is subject to presence of subtle barriers that can be difficult to identify and to signals from the geological history of the oceans. This study examines the effects of species' geographical distribution on their population structure as mediated by differential effects of the recent geological history of the oceans. For this purpose, we studied the sequence variation of the mitochondrial cytochrome oxidase c subunit I (COI) gene in samples of two sibling species of the calanoid copepod genus Clausocalanus. Analyses included molecular population genetic, phylogeographic, and phylogenetic approaches. The cosmopolitan Clausocalanus arcuicornis is shown to have a single panmictic population across this species' extensive geographic range, with sufficient gene flow – despite vast distances and geological and oceanographic barriers – to maintain genetic cohesion. In contrast, the biantitropical Clausocalanus lividus exhibits clear differentiation between Atlantic and Pacific Ocean populations, suggesting a vicariance process that started after the rise of the Isthmus of Panama.

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► We compared a cosmopolitan (C. arcuicornis) to an antitropical (C. lividus) species.
► C. arcuicornis shows connectivity throughout its geographical range.
► C. lividus Atlantic and Pacific populations are genetically isolated.
► The Isthmus of Panama rise would have started the vicariance process in C. lividus.