Meeting Abstract

56.2  Tuesday, Jan. 6  Nudibranch diversity in the Ross Sea, Antarctica: Theyre cold, but are they old? SHIELDS*, C. C.*; MARKO, P. B.; WOODS, H. A.; MORAN, A. L.; Clemson Univ.; Clemson Univ.; Univ. of Montana; Clemson Univ. shields@clemson.edu

The Southern Ocean (SO) surrounding Antarctica is extremely cold and geographically isolated. The phylogenetic affinities of only a few SO taxa, e.g. the notothenioid fish, have been examined in detail; in these, a high degree of endemism and radiation within the SO has been established using molecular phylogenetic methods. We used Bayesian inference to construct a phylogenetic tree of nudibranch molluscs based on cytochrome-c oxidase (COI) mtDNA. Sequence data includes 56 specimens collected on SCUBA over two seasons in McMurdo Sound, Antarctica, 49 species collected in the NE Pacific and New Zealand, and 153 sequences from GenBank. We found surprisingly broad taxonomic diversity within the Nudibranchia of the Ross Sea. The tree topology shows 15 lineages (>22% divergent from the nearest sequence in the tree) of Antarctic nudibranchs. Nine of these lineages contain single taxa that split from their closest non-Antarctic relative in the phylogeny between 38 and 63 million years ago (using COI divergence rate of 1% per million years). Although our tree contains few non-Antarctic species from the southern hemisphere, these data are consistent with an old and phylogenetically diverse Antarctic nudibranch fauna that predates isolation of the SO by the Antarctic Circumpolar Current. The remaining Antarctic lineages form two monophyletic clades (split from temperate relatives 38 and 42 mya) that apparently diversified within the SO. In order to construct a more robust two-gene phylogenetic tree that gives better resolution at deeper nodes, we are in the process of combining 18S ribosomal DNA sequence data with the COI data.