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ABSTRACT Symbiotic marine bacteria that are transmitted through the environment are susceptible to abiotic factors (salinity, temperature, physical barriers) that can influence their ability to colonize their specific hosts. Given that many symbioses are driven by host specificity, environmentally transmitted symbionts are more susceptible to extrinsic factors depending on conditions over space and time. In order to determine whether the population structure of environmentally transmitted symbionts reflects host specificity or biogeography, we analysed the genetic structure ofSepiola atlantica(Cephalopoda: Sepiolidae) and theirVibriosymbionts (V. fischeriandV. logei) in four Galician Rías (Spain). This geographical location is characterized by a jagged coastline with a deep‐sea entrance into the land, ideal for testing whether such population barriers exist due to genetic isolation. We used haplotype estimates combined with nested clade analysis to determine the genetic relatedness for bothS. atlanticaandVibriobacteria. Analyses of molecular variance (AMOVA) were used to estimate variation within and between populations for both host and symbiont genetic data. Our analyses reveal a low percentage of variation among and between host populations, suggesting that these populations are panmictic. In contrast,Vibriosymbiont populations show certain degree of genetic structure, demonstrating that the hydrology of the rías is driving bacterial distribution (and not host specificity). Thus, for environmentally transmitted symbioses such as the sepiolid squid‐Vibrioassociation, abiotic factors can be a major selective force for determining population structure for one of the partners.
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Geography, not lifestyle, explains the population structure of free-living and host-associated deep-sea hydrothermal vent snail symbionts
Abstract BackgroundMarine symbioses are predominantly established through horizontal acquisition of microbial symbionts from the environment. However, genetic and functional comparisons of free-living populations of symbionts to their host-associated counterparts are sparse. Here, we assembled the first genomes of the chemoautotrophic gammaproteobacterial symbionts affiliated with the deep-sea snailAlviniconcha hesslerifrom two separate hydrothermal vent fields of the Mariana Back-Arc Basin. We used phylogenomic and population genomic methods to assess sequence and gene content variation between free-living and host-associated symbionts. ResultsOur phylogenomic analyses show that the free-living and host-associated symbionts ofA. hesslerifrom both vent fields are populations of monophyletic strains from a single species. Furthermore, genetic structure and gene content analyses indicate that these symbiont populations are differentiated by vent field rather than by lifestyle. ConclusionTogether, this work suggests that, despite the potential influence of host-mediated acquisition and release processes on horizontally transmitted symbionts, geographic isolation and/or adaptation to local habitat conditions are important determinants of symbiont population structure and intra-host composition.
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- Award ID(s):
- 1736932
- PAR ID:
- 10413897
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Microbiome
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2049-2618
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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