Phylogeography and genetic diversity of some Sinocalanus species (Copepoda, Calanoida, Centropagidae) detected in inland and estuarine waters of China

In spite of the important ecological roles of copepods, their phylogeny and taxonomy remain largely unexplored in China. Here, we investigated the taxonomy and diversity of some Sinocalanus species (Copepoda, Calanoida, Centropagidae) in China. We observed two morphospecies (S. tenellus and S. doerrii) from this genus in 42 of 636 Chinese waterbodies examined. Molecular phylogenies inferred from a mitochondrial (mitochondrial cytochrome c oxidase subunit I; COI) and a nuclear marker (the nuclear 18S ribosomal RNA gene; 18S) verified the identities of these species and allowed us to amend previous misidentifications. Pronounced ecological separation between the two Sinocalanus species detected was found: S. doerrii inhabited freshwaters and was widely distributed across China, whereas S. tenellus was mainly found in brackish estuaries. One clade of S. doerrii had been misidentified (based on molecular data only) as S. tenellus in previous works, with consequent mislabeling of the sequences uploaded to GenBank. Additionally, we detected a new mitochondrial lineage of S. tenellus, most frequently in Jiaozhou Bay, China, whereas its sibling lineage was distributed in estuaries along the coasts of the East China Sea. Our study contributes to understanding the taxonomy and genetic diversity of the genus Sinocalanus in Chinese freshwater and brackish-water ecosystems.