Several deep-sea mussels and their associated symbionts are able to live both on wood and on whale falls

Abstract

Bathymodiolin mussels occur at hydrothermal vents and cold seeps, where they thrive thanks to symbiotic associations with chemotrophic bacteria. Closely related genera Idas and Adipicola are associated with organic falls, ecosystems that have been suggested as potential evolutionary 'stepping stones' in the colonization of deeper and more sulphide-rich environments. Such a scenario should result from specializations to given environments from species with larger ecological niches. This study provides molecular-based evidence for the existence of two mussel species found both on sunken wood and bones. Each species specifically harbours one bacterial phylotype corresponding to thioautotrophic bacteria related to other bathymodiolin symbionts. Phylogenetic patterns between hosts and symbionts are partially congruent. However, active endocytosis and occurrences of minor symbiont lineages within species which are not their usual host suggest an environmental or horizontal rather than strictly vertical transmission of symbionts. Although the bacteria are close relatives, their localization is intracellular in one mussel species and extracellular in the other, suggesting that habitat choice is independent of the symbiont localization. The variation of bacterial densities in host tissues is related to the substrate on which specimens were sampled and could explain the abilities of host species to adapt to various substrates.

Deep, diverse and definitely different: unique attributes of the world's largest ecosystem

“…Even though these food-rich habitats are often small in area, extremely isolated and ephemeral at the seafloor (e.g., spanning 10s of meters, separated by 100 s of kilometres and lasting for years to decades in the case of vents and whale falls), they all support remarkable communities highly distinct from those of the background deep sea. Substantial adaptive radiations leading to extraordinary evolutionary novelty and contributing fundamentally to biodiversity (Van Dover, 2000;Smith and Baco, 2003;Smith, 2006;Fujiwara et al, 2007;Samedi et al, 2007;Lorion et al, 2009) have sustained many of these habitat types, including vents, seeps, whale falls and wood falls. In contrast, at shelf depths where in situ photosynthesis leads to much greater background levels of productivity, some of these same habitat islands (e.g.…”

Wood-based diet and gut microflora of a galatheid crab associated with Pacific deep-sea wood falls

“…The group has received a careful attention since the 1980s in the description of the animal communities (e.g. Marshall 1985Marshall , 1988Kiel and Goedert 2006a, b;Pailleret et al 2006), as well as in the study of the impressive taxonomic diversity of mussels (Samadi et al 2007;Lorion et al 2009). Moreover, the phylogenetic relationships among wood-, bone-, vent-, and seep-associated mussels led to propose the "stepping stones" hypothesis for the colonization of the deep-sea reducing environments (see Smith et al 1989;Distel et al 2000).…”

Rapid colonisation by nematodes on organic and inorganic substrata deployed at the deep-sea Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge)

“…Two types of organic substrata (wood and bone) and one type of inorganic substratum (slate) were deployed at the Eiffel Tower hydrothermal edifice on the Lucky Strike vent field on the Mid-Atlantic Ridge (MAR) for 9 months, at varying distances from visible hydrothermal activity. Wood and bone were chosen due to their organic nature, their wide distribution in the oceans (Smith and Baco 2003;Schwabe et al in press) and their potential as evolutionary stepping stones for hydrothermal vent colonization (Distel et al 2000;Lorion et al 2009). As inorganic substratum, slate was chosen due to its basalt-like smoothness and inert characteristics.…”