Preliminary evidence of cryptic species among host-associated populations of Unionicola hoesei (Acari: Unionicolidae)

Abstract

Water mites of the genus Unionicola Haldeman, 1842 are common symbionts of freshwater mussels, living on the gills or mantle and foot of their hosts, and using these tissues as sites of oviposition. Cryptic species – two or more distinct species that have been designated as a single species – in this instance, genetically differentiated host-associated populations that are difficult to distinguish morphologically – have been reported for these mites; however, the extent to which they typify the genus is not well known. As part of an ongoing study characterizing cryptic biodiversity among Unionicola mussel-mites, we examined sequence divergence in the mitochondrial cytochrome oxidase subunit I (COI) gene among populations of Unionicola hoesei Vidrine, 1986, a gill mite that is known to occur in association with many species of host mussels, and compared these data to those reported for other Unionicola cryptic species complexes. Genetic distance data revealed that four populations of Unionicola hoesei exhibited p-distances that are consistent (; range = 0.08–0.17) with those reported for cryptic species of Unionicola. A phylogenetic hypothesis for the populations of Un. hoesei in relation to other cryptic species of mussel-mites was constructed using neighbour-joining analysis. The gene tree indicated that host-associated populations of Un. hoesei, like other cryptic species of the genus, formed a distinct clade, whose branches mainly reflect their association with different species of host mussels. The results of this study raise questions about the patterns of host utilization among other populations of Un. hoesei reported from additional species of North American mussels. Future studies will compare heterogeneity in DNA sequence data among populations of Un. hoesei from a large number of host species, both locally and over a broad geographic range, to determine the degree to which genetic variability exhibited by these mites is structured geographically and by patterns of host use.