A molecular investigation of the systematic relationships of Sirodotia species (Batrachospermales, Rhodophyta) in North America
1999
Vis, Morgan L. | Sheath, Robert G.
Six collections of the freshwater red algal genus Sirodotia from North America were sampled as follows: S. tenuissima (Collins) Skuja ex Flint from Rhode Island, S. suecica Kylin from Rhode Island and Labrador, and S. huillensis (Welwitsch ex West et G.S. West) Skuja from Texas, Mexico, and Costa Rica. To investigate relationships among these taxa, a fragment of the rbcL gene was sequenced. The ITS1–5.8S rDNA–ITS2 region, the rbcL–S spacer, and part of the rbcS gene were sequenced for all taxa and all but one collection. The rbcL gene sequence analysis showed S. suecica and S. tenuissima to be paraphyletic. The S. huillensis samples formed a monophyletic clade, with the Texas and Mexico collections being most closely related. The rbcL–S spacer and partial rbcS gene sequence data showed the same trend as the rbcL gene data, with S. suecica and S. tenuissima having identical sequence and S. huillensis samples forming a distinct, monophyletic clade. The rbcL–S spacer region may provide evidence for a closer phylogenetic relationship between Sirodotia and Batrachospermum gelatinosum (Linnaeus) DeCandolle than with the Lemaneaceae. In comparing the ITS1–5.8S rDNA–ITS2 region from S. suecica and S. tenuissima, little sequence divergence (~2%) was observed. Previous work on these two taxa revealed little morphological differentiation. Therefore, we conclude that S. suecica and S. tenuissima should be synonymized; S. suecica has priority. Based on the sequence variation among S. huillensis collections, further phylogeographic studies are recommended. The utility of ITS1–5.8S rDNA–ITS2 region data for phylogenetic and phylogeographic studies is discussed.
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