ezRAD sequencing in vesicomyid clams

Deep-sea clams of the family Vesicomyidae harbor sulfide-oxidizing endosymbiotic bacteria that are inherited through the maternal germ line. Strictly vertical transmission usually results in co-evolution of host and symbiont lineages as mitochondrial and symbiont genomes become genetically linked. Although this pattern is seen in the clam-bacteria symbiosis, various instances of incongruent host-symbiont phylogenies have been found, which implies that vesicomyid clams acquire their symbionts occasionally from an environmental source. The potential pathways of horizontal transmission in clam symbionts remain largely unknown. In the present study we report a new case of untypical symbiont compositions in the two cold-seep species Archivesica gigas and Phreagena soyoae by showing that several A. gigas individuals harbor the P. soyoae specific 16S rRNA symbiont phylotype. Using restriction-site associated DNA sequencing we address the hypothesis that contemporary hybridization between the two host species caused a symbiont switch in A. gigas.