Phylogeography of sugar kelp: Northern ice-age refugia in the Gulf of Alaska

Abstract

Many Northeast (NE) Pacific fishes and invertebrates survived Pleistocene glaciations in northern refugia, but the extent that kelps survived in northern areas is uncertain. Here, we test the hypothesis that populations of sugar kelp (Saccharina latissima) persisted in the Gulf of Alaska during ice-age maxima when the western margin of the Cordilleran ice sheet covered coastal areas around the NE Pacific Ocean. We estimated genetic diversities within and phylogeographical relationships among 14 populations along 2,800 km in the NE Pacific and Bering Sea with partial sequences of mitochondrial DNA 5′-cytochrome oxidase subunit I (COI, bp = 624, n = 543), chloroplast DNA ribulose-1,5-bisphosphate carboxylase large subunit-3′ (rbcL, bp = 735, n = 514), and 11 microsatellite loci. Concatenated sequences of rbcL and COI showed moderate levels of within-population genetic diversity (mean h = 0.200) but substantial differences among populations (ΦST = 0.834, p