Phylogeography of the rock-pool copepod Tigriopus brevicornis (Harpacticoida) in the northern North Atlantic, and its relationship to other species of the genus

We investigated relationships among North Atlantic Tigriopus brevicornis populations and their relationships to Mediterranean T. fulvus and North American T. californicus, using crossing experiments and mitochondrial DNA sequencing. All T. brevicornis populations tested were interfertile, while interspecific crosses produced either no offspring or offspring that did not survive past the larval stage, with the exception of a few T. brevicornis × T. californicus crosses that produced mature adults. DNA sequencing of a fragment of mitochondrial cytochrome oxidase I (COI) showed that samples of T. brevicornis from Iceland, the Faroes, Ireland, Scotland and Nova Scotia formed a single shallow clade. In contrast, T. brevicornis from more southern populations in France and Portugal formed a clade with substantially greater branch lengths. Tigriopus brevicornis was monophyletic, and T. brevicornis plus Mediterranean T. fulvus were together also monophyletic. The phylogeography of T. brevicornis closely mirrored that found in T. californicus, with substantially reduced interpopulation divergence at northern latitudes. The known distribution of T. brevicornis in Iceland and the Faroes is shown and dispersal mechanisms and habitat selection briefly discussed.