Genetic Differences Among Sibling Species of the Subgenus Dimockatax (Acari: Unionicolidae: Unionicola): Heterogeneity in Dna Sequence Data Supports Morphological Differentiation

Abstract

Water mites of the subgenus Dimockatax (Unionicolidae: Unionicola) are common inhabitants of anodontine bivalve molluses. Morphological differences among the five species that comprise the subgenus are minor and based primarily on subtle differences in one or two characters. The newly described species Unionicola ernstingi (Edwards et al., 2008) is distinguished from its sibling species U. tumida (Wolcott, 1898) by the number of clawlets on the tarsus of the pedipalps. These mites have been reported from the same locality, although they inhabit distinct species of host mussels. Unionicola ernstingi occurs with Anodontoides radiatus (Conrad, 1834), and U. tumida is found in association with Strophitus subvexus (Conrad, 1834). Taxonomic delineations among Unionicola mussel-mites parasitizing different species of hosts have, however, been challenged by the suggestion that morphological differences between mites may be influenced by the host species in which they metamorphosed. To test the validity of the species status for Dimockatax mites from A. radiatus and S. subvexus, heterogeneity in sequence data of the coxl gene was examined. A comparison of coxl sequences for U. tumida from S. subvexus and U. ernstingi from A. radiatus revealed a high degree of differentiation (12.7%). The genetic differences observed for U. ernstingi and U. tumida are consistent with those observed for other closely related, yet morphologically distinct species of Unionicola reported from different species of host mussel and thus complement morphological data recognizing them as valid species.