A population genetics pilot study of Phoronis pallida in Washington’s Puget Sound
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Phoronida (Lophophorata) is the perplexing, small group of marine invertebrates that contains at least 10 species of lophophore-bearing horseshoe worms. One species, Phoronis pallida, is an inquiline commensal that aggregates in burrows made by the mud shrimp Upogebia pugettensis. Similar to other species of phoronids, there are questions surrounding the biogeography and reproductive habits of Phoronis pallida. The purpose of this study is to examine the P. pallida population level structure in Puget Sound, Washington, USA, and also infer from these data if the adults of this species are capable of reproducing asexually. Adult P. pallida specimens were collected from the shrimp burrows in the low intertidal mud flats of False Bay, Argyle Lagoon, and Padilla Bay in Washington’s Puget Sound region. Twenty-seven samples of this phoronid were collected from 16 burrows among all sites and successfully analyzed using the mitochondrial cytochrome c oxidase subunit one gene (COI). Statistical parsimony identified 24 distinct haplotypes sorted into two networks. The networks showed no geographic pattern among our sites but were separated by a large p-distance of 0.06 indicating either a sequence divergence. No evidence for asexual reproduction was found since only genetically distinct individuals were found from the same burrows. Further sampling at larger spatial scales is necessary to find the total number of haplotypes, determine if the networks correlate to larger geographic areas, and investigate the sequence divergence in P. pallida.