Shallow-water Osedax (Annelida, Siboglinidae) from Antarctic, Subantarctic, and Mediterranean waters

SERGI TABOADA; MIQUEL A. ARNEDO; MARIA BAS; ANA RIESGO; CONXITA AVILA; GREG W. ROUSE; JAVIER CRISTOBO

Conferencia; 12th International Polychaete Conference; 2016

Osedax represent a remarkable example of evolutionary adaptation to a specialized habitat, namely sunken vertebrate bones. Usually, females of these animals live anchored inside bone owing to a ramified root system from an ovisac, and obtain nutrition via symbiosis with Oceanospirillales gammaproteobacteria. Since their discovery, 26 Osedax OTUs have been reported from a wide bathymetric range in the Pacific, North Atlantic, and Southern Ocean. Using experimentally deployed and naturally occurring bones we reported the presence of O. deceptionensis at very shallow-waters in Deception Island (type locality; Antarctica) and at moderate depths near South Georgia Island (Subantarctic). We present molecular evidence in a phylogenetic analysis based on five concatenated genes (28S rDNA, Histone H3, 18S rDNA, 16S rDNA, and COI), supporting the placement of O. deceptionensis as a separate lineage, although its position remains uncertain. This phylogenetic analysis includes a new unnamed species (O. 'mediterranea') recently discovered in the shallow-water Mediterranean Sea belonging to Osedax Clade I. A timeframe of the diversification of Osedax inferred using a Bayesian framework further suggests that Osedax diverged from other siboglinids during Middle Cretaceous (ca. 108 Ma) and also indicates that the most recent common ancestor of Osedax extant lineages dates to the Late Cretaceous (ca. 74.8 Ma), concomitantly with large marine reptiles and teleost fishes. Molecular analysis for O. deceptionensis also includes a COI-based haplotype network indicating that individuals from Deception Island and the South Georgia Island (ca. 1600 km apart) are clearly the same species, confirming their well-developed dispersal capabilities.