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Water mites of the genus Hydrodroma are common and frequently abundant in freshwater habitats on all continents other than Antarctica. Despite the broad geographic distribution, morphological differences between named species are minor and refer usually to one or two traits. DNA diagnostics may therefore prove useful for species delimitation in addition to morphological analyses. In this study, we use multiple statistical approaches, including Automatic Barcode Gap Discovery (ABGD), K2P distances, Neighbor-Joining (NJ) clustering and statistical parsimony (SP) based on mitochondrial cytochrome c oxidase subunit I (COI), and morphology to explore diversity among Hydrodroma species from North America and Europe. The results of ABGD confirmed species status of Hydrodroma despiciens (Muller, 1776), Hydrodroma pilosa Besseling, 1940, Hydrodroma torrenticola (Walter, 1908) from Europe and identified three species-level taxa from Canada, here provisionally called Hydrodroma sp. A, Hydrodroma sp. B and Hydrodroma sp. C. This outcome is congruent with NJ analysis that yielded a tree in which individuals clearly clustered into well-supported groups that matched described and putative species. The genetic distances between named and putative species ranged from 12.79% to 22.15%. Moreover, ABGD and NJ analyses based on COI sequences from our study and additional sequences available in GenBank and BOLD (Barcode of Life Datasystem) revealed five more clusters among North American Hydrodroma that likely also represent undescribed species. The results imply that future studies of Hydrodroma from other geographical locations and different habitat types are likely to reveal many more species of the genus. Moreover, this study highlights the potential utility of DNA barcoding in estimating true species diversity of the water mites, which is of fundamental importance in freshwater ecological studies and biodiversity surveys. |
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