Phylogenetic relationships of hydrothermal vent mussels (Bathymodiolinae) and their symbionts

Abstract

Deep-sea mussels of the subfamily Bathymodiolinae (Bivalvia, Pteriomorphia, Mytilidae) are dominant members of hydrothermal vent communities across the globe and have been found within every known hydrothermal vent biogeographic province. Thus, the apparent rarity of bathymodiolines at vents of the Juan de Fuca Ridge (JdF) is a notable exception. We examined mussels collected from the JdF over a span of 18 yr to clarify the classifications of mussel hosts and their symbiotic bacteria, and the relationships between sparsely distributed individuals. Several specimens, previously classified as Bathymodiolus and Adipicola, were reassigned as Adipicola sp. JdF based on new phylogenetic evidence and previous morphological studies. Adipicola sp. JdF are the most deeply branching members of Adipicola identified to date. Ultrastructural, molecular phylogenetic, and stable carbon isotope analyses indicated that Adipicola sp. JdF mussels harbor bacterial chemoautotrophic symbionts that appear to be extracellular and that are closely related to symbionts of other bathymodioline hosts. This study demonstrates that a sparsely distributed, yet cohesive, population of Adipicola has inhabited JdF vents for at least the past 18 yr. Moreover, the presence of extracellular symbionts in Adipicola sp. JdF at hydrothermal vents stands in contrast to the evolutionary patterns proposed for bathymodiolines in general. Adipicola sp. JdF represents an exception to the trend of bathymodiolines harboring extracellular symbionts living exclusively in shallow marine wood and bone habitats (<1000 m), indicating that bathymodiolines are more flexible with regard to habitat and symbiont characteristics than previously considered.

The contrasted evolutionary fates of deep‐sea chemosynthetic mussels (Bivalvia, Bathymodiolinae)

“…These mussels were first attributed to the genus Bathymodiolus and labeled B. sp JdF (McKiness et al 2005) and then to Adipicola (Adipicola MV in [Southward 2008;] and Adipicola sp. JdF [Fontanez and Cavanaugh 2013;]). Tissue samples of these mussels were provided by E. C. Southward.…”

Limitations in the Use of Archived Vent Mussel Samples to Assess Genetic Connectivity Among Seafloor Massive Sulfide Deposits: A Case Study with Implications for Environmental Management

“…However, there is no evidence to date for gender-biased mitochondria in G. gladius' closest relatives, Bathymodiolus spp. (Won et al, 2003;Jones et al, 2006), and mitochondrial sequences are commonly used in phylogenetic studies of this group (Smith et al, 2004;Jones et al, 2006;Fontanez and Cavanaugh, 2013). As such, we consider mitochondrial COI to be a suitable marker for connectivity assessment of G. gladius.…”

Evidence for horizontal transmission from multilocus phylogeny of deep‐sea mussel (Mytilidae) symbionts

“…The 16S symbiont phylogeny was topologically consistent with previously reported phylogenies of bathymodiolines, grouping symbionts according to their residence in Western Pacific, Eastern Pacific and Indian Oceans, as illustrated by the coloured boxes in Fig. (Won et al ., ; Fontanez and Cavanaugh, ). While some functional gene phylogenies grouped symbionts by ocean residence with strong support (e.g.…”

“…These findings are consistent with the 16S phylogeny (Fig. ) and with previously reported 16S phylogenies with larger taxon coverage (DeChaine et al ., ; Won et al ., ; Fontanez and Cavanaugh, ). However, the uncertainty evident in the symbiont supernetwork, our best estimate of the ‘species’ tree, indicates that additional symbiont genes are needed to fully resolve the bathymodioline symbiont phylogeny.…”