Peek AS, Feldman RA, Lutz RA, Vrijenhoek RC (1998) Cospeciation of chemoautotrophic bacteria and deep sea clams. Proceedings of the National Academy of Sciences, USA 95: 9962-9966

Vesicomyid clams depend entirely on sulfur-oxidizing endosymbiotic bacteria for their nutriment. Endosymbionts that are transmitted cytoplasmically through eggs, such as these, should exhibit a phylogenetic pattern that closely parallels the phylogeny of host mitochondrial genes. Such parallel patterns are rarely observed, however, because they are easily obscured by small amounts of horizontal symbiont transmission or occasional host-switching. The present symbiont genealogy, based on bacterial SSU (16S) rDNA sequences, was closely congruent with the host genealogy, based on clam mitochondrial COI and LSU (16S) rDNA sequences. This phylogenetic evidence clearly supports the hypothesis of tight coevolution between the participant in this symbiosis.