| Simocephalus belongs to Crustacea, Cladocera, Daphniidae.67secies of Simocephalus were reported, but there were about25species were validly existing, and13species have been reported in China. As a kind of Cladocera, many species of Simocephalus live in freshwater. The reproduction of Simocephalus was fast and the cultivation of Simocephalus was relatively easy. They were used for fish food, the indicators of water quality monitoring and always used to be experimental material. The research on Simocephalus mainly focused on morphological taxonomy, growth, reproduction and development, population and distribution and so on. In recent years, the methods of molecular biology have been applied to the taxonomy and ecology. There is still a conflict in the understanding of the taxonomy of the genus. Researches on Simocephalus in China were relatively scattered, and the distribution of Simocephalus is unknown. Make certain the effectiveness of the recorded species and the distribution of Simocephalus in China in time have important scientific significance and potential application value on the promoting of research and application of Simocephalus in China.The aim of this work was to investigate the biodiversity and phylogeny of Simocephalus. The morphological characters of the three new species and ten recorded species in China were described, and the photos of whole body and partial of living animals were obtained using bright field microscopy. The basis for taxonomy and the key to species of Simocephalus were summarized, the relationship of species was analyzed, and the fauna and distribution of Simocephalus also were analyzed. The results indicating that all the15species of Simocephalus in China distributed in the Palaearctic region. The molecular system analysis based on mitochondria gene of CO I and ribosomal18S rDNA were studied. The phylogenetic analyses were performed using neighbor joining (NJ), maximum likelihood (ML) and Bayesian inferences (BI). The results indicated the two genes can be used as molecular markers in Simocephalus, and the results were in accordance with morphological taxonomy. The results were as follows:1. The morphological characteristic of part of Simocephalus species71collection sites from18provinces in China and one collection site from Norway were checked.13species of Simocephalus were identified, including ten known species and three new species. The ten known species were Simocephalus vetulus, Simocephalus vetuloides, Simocephalus mixtus, Simocephalus beianensis, Simocephalus serrulatus, Simocephalus heilongjiangensis, Simocephalus exspinosus, Simocephalus himalayensis microdus, Simocephalus sibiricus and Simocephalus himalayensis et al., and the three new species were Simocephalus jiangxiensis sp. nov., Simocephalus fuyangensis sp. nov. and Simocephalus norwayensis sp. nov. et al.. According to the morphological characters,13species of Simocephalus were classified into four subgenera, i.e., Simocephalus s. str., Simocephalus (Coroncephalus), S.(Echinocaudus), and Simocephalus (Aquipiculus). Simocephalus s. str. contains S. beianensis, S. vetuloides, S. mixtus, and S. vetulus; S.(Echinocaudus) contains S. exspinosus, S. sibiricus, S. himalayensis, S. himalayensis microdus, S. fuyangensis sp. nov., and S. norwayensis sp, nov.; Simocephalus (Coroncephalus) contains S. serrulatus and S. jiangxiensis sp. nov.; Simocephalus (Aquipiculus) contains S. heilongjiangensis.The features and species identification were reported, the identification key was drafted and some photos of living animals were taken. According to the morphology, some regulations to identify the species were summarized, i.e.,1). The features of frontal part of head, is rounded or sharp, with or without denticles;2). Rostrum, long or short;3). Dorso-posterior valve angle, round, with or without prominence;4) The shape of supra-anal angle;5). Basal pecten of postabdominal claw, with or without spines. Among the species with observably dorso-posterior valve angle, only Simocephalus jiangxiensis sp. nov. with spines on the basal pecten of postabdominal claw. Among the species with spines on the basal pecten of postabdominal claw, the dorso-posterior valve angle was round in Simocephalus norwayensis sp. nov., and the supra-anal angle is obviously protruding in Simocephalus fuyangensis sp. nov..2. The distribution of the Genus SimocephalusThe fauna of Simocephalus were analyzed, the results indicated all the13species distributed in Palaearctic region, specie not only distributed in Palaearctic region but also distributed in oriental region contained Simocephalus vetulus, Simocephalus vetuloides, Simocephalus mixtus, Simocephalus exspinosus, Simocephalus himalayensis, Simocephalus serrulatus, Simocephalus heilongjiangensis et al.. The species diversity of Simocephalus is the most in northeast of China and the second most is the Yangtze River basin. Species in northwest of China, the Tibetan area and Xinjiang area is not much. Since now, there was no report of Simocephalus in Ningxia province.According to the geographic distribution and the climatic characteristics, there were eurythermal species, cold water species and warm water species in Simocephalus. The eurythermal species included Simocephalus vetulus, Simocephalusvetuloides, Simocephalus exspinosus and Simocephalus serrulatus and so on. The cold water species included Simocephalus microdus and Simocephalus beianensis, and the warm water species included Simocephalus fujianensis, Simocephalus jiangxiensis and Simocephalus fuyangensis sp. nov.. And Simocephalus himalayensis was plateau species, Simocephalus acutirostratus was endemic species of Yunnan province. 3. Molecular system analysis based on mitochondrial CO I geneSequences of11species were blast and analyzed, the results showed the genetic distance between species were0.068-0.225. The nucleotide composition, conserved sites, variable sites, parsimony informative sites, transition/transversion ratio and average genetic distances between each pair of species were determined using MEGA5.1. The phylogenetic analyses were performed using neighbor joining (NT), maximum likelihood (ML) and Bayesian inferences (BI). The results showed sequences of the same species from different places were clustered together. Species of S. serrulatus, S. jiangxiensis and S. heilongjiangensis were different with other species, S. vetulus, S. vetuloides and S. beianensis were sister groups and the relationship of S. vetulus and S. vetuloides was closer than other species. S. norwayensis sp. nov., S. himalayensis, S. microdus, S. fuyangensis sp. nov. and S. sibiricus were sister groups, S. norwayensis sp. nov. was closely related to S. himalayensis with the genetic divergence of6.7%and S. microdus was closely related to S. fuyangensis sp. nov..The sequences of eleven species were aligned with the six species of Simocephalus in GeneBank, with outgroup of Daphnia similoides. The results showed species of morphological similar were clustered together, and species in the same subgenera were closely clustered together. All the branches were basically consistent with the morphological taxonomy and the four subgenera. In the subgenera of Simocephalus s. str., S. beianensis and S. vetulus were closely related to S. vetuloides, the relationship between S. vetulus and S. vetuloides were closer than other species. The relationship between S. mixtus with the three is relatively far. The subgenera of S.(Echinocaudus) contains S. exspinosus, S. sibiricus, S. himalayensis, S. himalayensis microdus, S. fuyangensis sp. nov., and S. norwayensis. S. norwayensis sp. nov. was closely related to S. himalayensis and S. fuyangensis sp. nov. was closely related to S. himalayensis microdus and S. sibiricus. And S. exspinosus were at the base of the five species. S. serrulatus belong to the subgenera of Simocephalus (Coroncephalus), and S. heilongjiangensis belong to the subgenera of Simocephalus (Aquipiculus). All the branches were basically consistent with the morphological taxonomy.4. Molecular system analysis based on ribosomal subunits18S rDNASequences of Ribosomal subunits18S rDNA of ten Simocephalus were analyzed, with sequences of Daphnia pulex and Daphnia magna were used as outgroups. The nucleotide composition, conserved sites, variable sites, parsimony informative sites, transition/transversion ratio and average genetic distances between each pair of species were determined using MEGA5.1. The phylogenetic analyses were performed using neighbor joining (NJ), maximum likelihood (ML) and Bayesian inferences (BI). The results showed sequences of the same species were clustered together. The genetic distances among ten species were0.003-0.051. The genetic distances between5. fuyangensis sp. nov. and S. sibiricus was0.003, which is smaller than the genetic distances between S. vetulus and S. vetuloides (0.006). The genetic distances between S. norwayensis sp. nov. and S. himalayensis was0.007, fall in between the genetic distances between species of S. vetulus and S. vetuloides and species of S. vetulus and S. beianensis (0.008). The branches of18S rDNA were basically the same as CO I and the the results were basically consistent with the morphological taxonomy. |
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