The biogeographic history and contemporary origins of north american arctic marine macroalgae

Abstract

Arctic coastal communities are expected to change in response to warming climate trends, and yet basic information is lacking in these systems. Marine macroalgae provide an opportunity to examine historical migration pathways into the Arctic, and may serve as a model system for future changes. In this thesis, phylogeographic and population level biogeographic patterns were examined in Arctic marine macroalgae. Multiple markers were used to examine phylogeographic patterns in 14 trans-Arctic lineages of red marine macroalgae and determine what role the opening of the Bering Strait and Pleistocene glaciation had on contemporary biogeographic distributions. Results confirmed the opening of the Bering Strait resulted in a predominantly Pacificto- Arctic/Atlantic movement of species, while Pleistocene glaciation did not appear to play a significant role in promoting trans-Arctic speciation events. The Last Glacial Maximum, however, is hypothesized to have extirpated marine coastal populations in the Northwest Atlantic, with subsequent recolonization out of the Northeast Atlantic. DNA barcode data were used to determine if trans-Atlantic populations of brown and red macroalgae were consistent with this hypothesis. Contrary to the historical consensus, isolation times in 60% of the species examined suggested populations were not recently derived from Europe. Sequence data were also used to assess recolonization pathways of marine macroalgae into the Arctic following the Last Glacial Maximum. Of the 100 species with Arctic populations examined (including brown, green, and red macroalgae), 39 had uncertain origins, 46 had origins in the North Atlantic, five had origins in the Pacific and the Atlantic, while the remaining 10 had origins in the North Pacific. Pacific contributions to Arctic recolonization, however, were inferred in 9 of the 12 best sampled species. Surprisingly, 18 genetic groups and some Arctic haplotypes in 28 species were not assignable to Atlantic or Pacific populations. The results from this thesis indicated that the Pacific Ocean has played a major role in establishing Arctic and North Atlantic lineages/populations of marine macroalgae. In addition, some marine populations may have survived glaciation in the Arctic basin, reducing the role of recolonization pathways out of the Atlantic and/or Pacific.