A legacy of contrasting spatial genetic structure on either side of the Atlantic-Mediterranean transition zone in a marine protist

摘要

The mechanisms that underpin the varied spatial genetic structuresexhibited by free-living marine microorganisms remaincontroversial, with most studies emphasizing a high dispersalcapability that should redistribute genetic diversity in contrast tomost macroorganisms whose populations often retain a geneticsignature of demographic response to historic climate fluctuations.We quantified the European phylogeographic structure of themarine flagellate Oxyrrhis marina and found a marked differencein spatial genetic structure, population demography, and geneticdiversity between the northwest Atlantic and Mediterranean Seathat reflects the persistent separation of these regions as well ascontext-dependent population responses to contrasting environments.We found similar geographic variation in the level of geneticdiversity in the sister species Oxyrrhis maritima. Because the capacityfor wide dispersal is not always realized, historic geneticfootprints of range expansion and contraction persist in contemporarypopulations of marine microbes, as they do in larger species.Indeed, the well-described genetic effects of climatic variation onmacroorganisms provide clear, testable hypotheses about the processesthat drive genetic divergence in marine microbes and thusabout the response to future environmental change.