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Abstract:
Symbiosis involving chemoautotrophic bacteria allowsvestimentiferan tubeworms to thrive in sulfidic marine en-vironments. This study examined genetic variation amongendosymbionts associated with three vestimentiferan spe-cies from the Gulf of California. Small subunit (16S) rRNAsequences identified two evolutionary lineages of-Pro-teobacteria in these worms. Phylotype-II bacteria associ-ated with the hydrothermal vent speciesRiftia pachyptilaexhibited no subtype variation upon examination of form II(cbbM) RuBisCO, whereas the phylotype-I bacteria associ-ated with two cold-seep species,Escarpia spicataandLa-mellibrachia barhami, were polymorphic. Bacterial sub-types distinguished by three RuBisCO alleles occurred atsimilar frequencies in both host species when sampled to-gether from tubeworm clusters, offering, therefore, no evi-dence for host-specificity. Instead, the frequencies of thesesubtypes varied significantly among patchily distributedtubeworm clusters. Subtype variation on small spatialscales is consistent with prior evidence that vestimentifer-ans acquire their symbionts locally from the environment inwhich they settle as larvae.
