Phylogeography of a marine acanthocephalan: lack of cryptic diversity in a cosmopolitan parasite of mole crabs

AbstractAimLittle is known about phylogeography and cryptic diversity of parasites in the marine environment. The acanthocephalan Profilicollis altmani parasitizes intermediate hosts that are broadly distributed around the Americas and final hosts that are highly motile. We investigated the spatial genetic structure of this acanthocephalan found in three species of Emerita crabs: (1) to test whether land masses serve as biogeographic barriers promoting ocean basin divergence among parasite lineages or species; and (2) to test whether the distribution of parasite species matches the distribution of different crab host species.LocationThe Pacific, Atlantic and Gulf coasts of the USA, and the Pacific coast of Panama and Chile.MethodsSequences of cytochrome c oxidase subunit I (COI) and ribosomal internal transcribed spacers (ITS) were obtained from 204 acanthocephalans. Parasites were sampled from crabs in 15 sampling localities. These sequences were analysed with coalescent‐based methods and other population genetic analyses to infer phylogeographic patterns.ResultsHaplotype diversity for COI sequences was high (0.96) among parasites sampled, but nucleotide diversity was low (0.071) and there was no distinct geographic pattern between regions. Pairwise genetic distances were generally low, although there was a degree of population structure between oceans. Sequence comparisons showing an excess of low divergence alleles and a bimodal mismatch distribution provide evidence of either past selective events or demographic expansions. No variation was observed in the ITS sequences.Main conclusionsThe lack of geographic patterning in haplotype diversity of this parasite indicates that gene flow is probably occurring between ocean basins. In addition, the low genetic diversity suggests that the acanthocephalan parasitizing E. analoga in Chile is conspecific to the species found parasitizing several Emerita species along the coasts of North America, and is thus a cosmopolitan parasite that is most likely dispersed long distances by marine birds that serve as definitive hosts.