The phylogenetic relationships of whale-fall vesicomyid clams based on mitochondrial COI DNA sequences

Abstract

Whale skeletons on the deep-sea floor provide sulfide-rich habitats that may act as stepping stones for the dispersal of animals dependent on chemoautotrophic production. However, the phylogenetic relationships between the faunas of whale falls, hydrothermal vents and colds seeps are not fully evaluated. To examine vesicomyid phylogenetic relationships, we collected 10 vesicomyid clams from 2 whale falls on the California margin, one at 1240 m in the Santa Catalina Basin and one at 960 m on the slope west of San Nicolas Island. We then compared DNA sequences for a portion of the mitochondrial cytochrome c oxidase subunit I gene from the whale-skeleton clams to those from other clam populations in this taxonomically difficult family. Seven adult whale-fall vesicomyids clustered with clams identified as Vesicomya gigas, a species also found near hydrothermal vents in Guaymas Basin (Gulf of California) and Middle Valley (Juan de Fuca Ridge). A single small whale-fall individual clustered with clams identified as Calyptogena kilmeri, a species found at cold seeps in Guaymas Basin, Monterey Bay, and along the Oregon Subduction Zone. A single small whale-fall clam clustered with Calyptogena elongata, a species found in anoxic California basins. Finally, a single adult clam was difficult to assign to any previously examined species group and could represent a new species in the 'gigas/kilmeri' cryptic species complex. With the inclusion of these vesicomyids, whale falls are known to share a total of 16 species with the faunas of deep-sea hydrothermal vents and cold seeps.