Phylogeography of Macroalgal Species Distributed in Brackish Water: Ulva prolifera (Ulvophyceae) and Pyropia tenera (Bangiophyceae)

Comparative studies of closely related species or populations in contrasting environments can potentially provide insights into adaptive mechanisms. We review the phylogeography and population diversity of brackish water species derived from marine species, Ulva prolifera Muller (Ulvophyceae) and Pyropia tenera (Kjellman) N. Kikuchi, M. Miyata, M.S. Hwang & H.G. Choi (Bangiophyceae). Brackish U. prolifera and marine Ulva linza L. have been resolved as closely related species based on phylogenetic analysis of moleclar markers, with U. linza apparently parental to U. prolifera. Our analyses of 5S rDNA spacer region in samples from an Ulvalean bloom in Qingdao, China, indicate that the species appear to be derived from Japanese U. prolifera. Hybridization tests suggest that U. linza and the Qingdao bloom samples are probably distinct species, but gene flow is possible between them. The threatened brackish water species, P. tenera, is morphologically and phylogenetically related to the coastal species, Pyropia yezoensis (Ueda) M.S. Hwang & H.G. Choi. One form, P. yezoensis Ueda f. narawaensis Miura (new combination “Pyropia yezoensis f. narawaensis” has not yet been proposed), is the largest aquaculture source of “Nori” in Japan. Hybridization between these species has been reported, especially between male P. tenera and female P. yezoensis. Sequences of the nrITS1 region and rbcL gene, and PCR-RFLP (ARP4 gene) analyses suggested that P. tenera is distributed across 15 prefectures from Kyushu to Tohoku in Japan; but is restricted to estuarine and brackish water habitats. Based on SSR analysis on the genetically identified P. tenera samples, we conclude that this species spread from Kyushu to Tohoku through the Kanto region.