Divergent paths in the evolutionary history of maternally transmitted clam symbionts

Ma va Perez, Corinna Breusing, Bernard Angers, Roxanne A. Beinart, Yong Jin Won, C. Robert Young

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Vertical transmission of bacterial endosymbionts is accompanied by virtually irreversible gene loss that results in a progressive reduction in genome size. While the evolutionary processes of genome reduction have been well described in some terrestrial symbioses, they are less understood inmarine systems where vertical transmission is rarely observed. The association between deep-sea vesicomyid clams and chemosynthetic Gammaproteobacteria is one example of maternally inherited symbioses in the ocean. Here, we assessed the contributions of drift, recombination and selection to genome evolution in two extant vesicomyid symbiont clades by comparing 15 representative symbiont genomes (1.017-1.586 Mb) to those of closely related bacteria and the hosts' mitochondria. Our analyses suggest that drift is a significant force driving genome evolution in vesicomyid symbionts, though selection and interspecific recombination appear to be critical formaintaining symbiont functional integrity and creating divergent patterns of gene conservation. Notably, the two symbiont clades possess putative functional differences in sulfide physiology, anaerobic respiration and dependency on environmental vitamin B12, which probably reflect adaptations to different ecological habitats available to each symbiont group. Overall, these results contribute to our understanding of the eco-evolutionary processes shaping reductive genome evolution in vertically transmitted symbioses.

Original languageEnglish
Article number20212137
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1970
StatePublished - 2022

Bibliographical note

Publisher Copyright:
© 2022 The Author(s) Published by the Royal Society. All rights reserved.


  • deep-sea
  • niche partitioning
  • reductive genome evolution
  • selection
  • symbiosis


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