Survival in Glacial Refugia Versus Postglacial Dispersal in the North Atlantic: The Cases of Red Seaweeds
The past two decades have witnessed the North Atlantic used as a model system to explore how climate changes and environmental conditions shaped the spatiotemporal distributions and biogeographic processes of intertidal seaweed species. The tectonic reconfigurations of the Northwestern and Northeastern Atlantic shores caused by the Quaternary ice ages allow us to examine two evolutionarily contrasting scenarios: survival in local glacial refugia versus postglacial trans-Atlantic dispersal. In this chapter, we collected comparative data from the red algae Chondrus crispus, Mastocarpus stellatus, Palmaria palmata, and Porphyra umbilicalis across the North Atlantic to illustrate the effects of paleoclimatic oscillations on historical demography, lineage divergence, and genetic connectivity. The genetic signals detected in C. crispus and P. palmata are consistent with the hypothesis that they survived in situ on each side of the North Atlantic during the Quaternary glaciations, while the phylogeographic evidence for M. stellatus and P. umbilicalis indicates postglacial trans-Atlantic dispersals. Bayesian coalescent analysis detected signals of demographic expansions in the four algal species, during the late Pliocene to the middle Pleistocene. In addition, the dated genetic splits between lineages were compatible with the expansion times for each species. In summary, our comparative analysis revealed contrasting biogeographic processes in these seaweeds despite their similar contemporary distributional ranges in the North Atlantic. These results also highlight the importance of comparative phylogeographic surveys in exploring dynamic evolutionary patterns and phylogeographic histories of intertidal marine organisms.
KeywordsDemographic history Divergence time Genetic diversity Genealogical isolation The quaternary ice age Postglacial recolonization
We would like to thank Ceridwen Fraser and two anonymous reviewers for valuable comments on the early version of this chapter. This study was partially supported by National Natural Science Foundation of China (31370264) granted to Z.M. Hu.
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