The taxonomic position of Asian Holopedium (Crustacea: Cladocera) confirmed by morphological and genetic analyses
The cladoceran Holopedium gibberum Zaddach, 1855 (Ctenopoda: Holopediidae) was once thought to occur broadly in the northern hemisphere, but its cryptic sister species was recently separated from H. gibberum sensu stricto (s.s.) as a new species, Holopedium glacialis. In East Asia, although “H. gibberum” occurrence has been recorded in many water bodies, the identity of the surveyed populations has rarely been confirmed via molecular analyses. Thus, it is unclear whether it is actually H. gibberum s.s. or H. glacialis that is distributed in East Asia. We used DNA-barcoding techniques to check the taxonomic status of Holopedium samples collected in Japan. We sequenced mitochondrial cytochrome c oxidase subunit 1 (mtCOI) and nuclear 18S ribosomal DNA (nr18S) of Japanese Holopedium and compared the results with those of H. gibberum s.s. collected in Norway and H. glacialis collected in Canada. The mtCOI sequence divergences between Norwegian H. gibberum s.s. and Japanese Holopedium were at most 2.4%, which was within the degree of intraspecific differentiation in cladocerans. Norwegian H. gibberum s.s. and Japanese Holopedium shared identical nr18S haplotypes. Individuals of Canadian H. glacialis were genetically different from those of Japanese Holopedium. We therefore concluded that Japanese Holopedium can be identified as H. gibberum s.s.
KeywordsDNA barcoding Freshwater biodiversity Integrative taxonomy Zooplankton
Marcia Kyle (Norwegian University of Life Sciences) and Tom Andersen (University of Oslo) collected Norwegian Holopedium specimens, and Paul Frost, Andrea Conine, and Clay Prater (Trenton University) collected Canadian Holopedium specimens. We are truly grateful for their very kind support. The present study was also supported by grants from the Japan Society for the Promotion of Science (16770011, 19770010, 23570015, 15H02380, 15K07211, and 18K06407); by funds from the Ministry of the Environment, Japan (the Environment Research and Technology Development Fund, 4-1602); by funds from the Water Resources Environment Technology Center (2008-06, and 2018-03) to WM; and by grants from the Japan Society for the Promotion of Science (25291094 and 16H02522) and the Ministry of the Environment, Japan (the Environment Research and Technology Development Fund, D-1002) to JU.
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