Dispersal Ability and Genetic Structure in Mytilid Mussels of Whale-Fall Communities

Abstract

Since organic falls are ephemeral and distributed sporadically, organisms in organic-fall communities must acquire high dispersal ability to migrate from one organic fall to another. However, the dispersal ability of obligate organic-fall organisms has not been investigated thoroughly and the stability of the genetic structure of their communities is unknown. In this study, in order to elucidate the dispersal ability and genetic structure in the organic-fall communities, we carried out po- pulation genetic analyses based on sequences of mitochondrial NADH dehydrogenase subunit 4 in two mytilid mussels. Adipicola pacifica was obtained from whale and cow bones artificially settled in Japanese waters off Cape Noma (CN) and in the Nansei-Shoto Trench (NS) and Sagami Bay (SB), and Benthomodiolus geikotsucola from natural whale bones in the Torishima Seamount (TS); both species are symbiotic with chemoautotrophic bacteria. Genetic differentiation (Fst) indicated almost no annual change in genetic structure between 2003, 2004, 2005, and 2007 collections of A. pacifica from CN (depth 225 - 229 m), although the 2010 collection had somewhat different genetic structure from the others. Similarly, there was not significant genetic differentiation between 1993 and 2005 collections of B. geikotsucola from TS (depth 4020 m). The Fst and gene bidirectional mean rate of gene flow (Nm) indicated high gene flow and no significant genetic differentiation between A. pacifica specimens collected from CN, NS, and SB. The results suggest that the genetic structure is stable and A. pacifica has high dispersal ability. The mismatch distribution suggests that A. pacifica expanded their distribution from SB to NS via CN, as expansion time (τ = 2ut) decreased from SB to CN and NS.