Abstract
Deep-sea anglerfishes are relatively abundant and diverse, but their luminescent bacterial symbionts remain enigmatic. The genomes of two symbiont species have qualities common to vertically transmitted, host-dependent bacteria. However, a number of traits suggest that these symbionts may be environmentally acquired. To determine how anglerfish symbionts are transmitted, we analyzed bacteria-host codivergence across six diverse anglerfish genera. Most of the anglerfish species surveyed shared a common species of symbiont. Only one other symbiont species was found, which had a specific relationship with one anglerfish species, Cryptopsaras couesii. Host and symbiont phylogenies lacked congruence, and there was no statistical support for codivergence broadly. We also recovered symbiont-specific gene sequences from water collected near hosts, suggesting environmental persistence of symbionts. Based on these results we conclude that diverse anglerfishes share symbionts that are acquired from the environment, and that these bacteria have undergone extreme genome reduction although they are not vertically transmitted.
Highlights
Symbiosis between animals and bacteria can enable both organisms to adapt to harsh environments or expand into new habitats, which impacts the ecology and evolution of both bacterial and host lineages (McFall-Ngai et al, 2013; Moran, 2007; Moya et al, 2008)
Within a species there was greater than 99% average nucleotide identity (ANI) to the previously identified symbiont species (Hendry et al, 2018) and the between symbiont species ANI was less than 74%
Within the broad phylogenetic spectrum of ceratioid anglerfishes sampled in this study we identified only two symbiont species, E. luxaltus and E. escacola
Summary
Symbiosis between animals and bacteria can enable both organisms to adapt to harsh environments or expand into new habitats, which impacts the ecology and evolution of both bacterial and host lineages (McFall-Ngai et al, 2013; Moran, 2007; Moya et al, 2008). Symbiosis with luminescent bacteria has evolved independently multiple times in diverse squid and fish species (Davis et al, 2016; Dunlap and Urbanczyk, 2013) and has been correlated with host diversification (Davis et al, 2016; Ellis and Oakley, 2016). Four genera of bacteria in the family Vibrionaceae engage in luminescent symbiosis (Dunlap and Urbanczyk, 2013; Hendry et al, 2018; Schaechter, 2009), including the model species Aliivibrio fischeri, but comparatively little is known about the bioluminescent symbionts of deep-sea anglerfishes. The genera Cryptopsaras and Ceratias harbor bacterial symbionts in additional
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