Exploring host specificity and species boundaries of beetle-associated mites using molecular and morphological analyses

Understanding the evolution of host specificity and the determinants of host range are fundamental challenges to the study of the evolutionary ecology of symbionts. The study of host specificity is constrained by how species are defined, which requires accurate taxonomic knowledge, including clear species boundaries and phylogenies. Morphological, mitochondrial and nuclear markers were used to explore the species boundaries, the extent of cryptic diversity, and the degree of coevolution of tortoise mites (Mesostigmata: Uropodoidea) associated with carrion-feeding beetles (Silphidae: Nicrophorus) and bark beetles (Curculionidae: Scolytinae). Tortoise mites are among the most common and diverse groups of arthropod associates of carrion-feeding beetles and bark beetles, but their taxonomy and host associations are largely unstudied. In both natural systems, morphologically delineated species were supported by the molecular datasets. Molecular and morphological analyses revealed that a widespread generalist uropodoid species associated with carrion-feeding beetles is actually a complex of cryptic species with varying degrees of host specificity. In addition, these mites may be coevolving with their silphid hosts rather than tracking ecologically similar species. On the other hand, morphological and molecular analyses indicated that generalist uropodoids associated with bark beetles are truly generalists, and not cryptic species complexes. There was little evidence of coevolution or ecological tracking in these mites; however, it is possible that the evolutionary history of these bark beetle associates reflects a blend of both factors. Overall, these findings further the understanding of species boundaries, cryptic diversity, and the evolution of host specificity in symbiotic taxa.