Validation of the status of a species with high CO1 and low nuclear genetic divergences: the scab mite Caparinia ictonyctis stat. res. (Acariformes: Psoroptidae) parasitizing the African hedgehog Atelerix albiventris.

We report two host-specific lineages of scab mites of the genus Caparinia, parasitizing European and African hedgehogs. Based on morphology, these mite lineages are closely related sister groups. The morphological differences, however, are subtle and do not provide clear-cut evidence for the existence of separate species. CO1 divergence between these lineages was 7.4-7.8%, well above the CO1 barcoding gaps or thresholds commonly used to separate species, whereas divergence of five nuclear genes was very low, 0.06-0.53%, suggesting that these lineages could belong to a single species with gene flow between them. Thus, there is a conflict between the mitochondrial (CO1) gene and nuclear genes (i.e mito-nuclear discordance). We attribute this conflict to the 'gray zone' where species delimitation is ambiguous due to substantial gene flow. We also report another 'gray zone' species, Psoroptes ovis (a species of veterinary importance), whose within-species CO1 distances reached 6.0%. We provide a detailed morphological description and figures of C. ictonyctis stat. res. from the African hedgehog, using light and SEM microscopy and give morphometric data for this species and its sister species, Caparinia tripilis from Europe. For all known species of Caparinia, we document their host associations and give a key to species of the world based on results of our morphological and molecular analyses and a nearly exhaustive study of museum specimens.