title: Multiple lines of evidence on the genetic relatedness of the parthenogenetic and bisexual Haemaphysalis longicornis (Acari: Ixodidae).
abstract: As an obligate hematophagous ectoparasite, the hard tick Haemaphysalis longicornis exhibits two reproductive strategies, bisexual reproduction, and obligate parthenogenesis, which have attracted a widespread attention. However, the speciation of parthenogenetic population remained ambiguous due to its similarity in morphology but the remarkable differences in cytogenetics as compared with those of the bisexual ones. In the present study, we explored several new lines of genetic evidence to resolve this controversial issue. The number of the chromosomes in two lineages was checked by classical methods and their total DNA levels were determined utilizing flowcytometry. In addition, the sequences of 12S rDNA, 16S rDNA, cytochrome c oxidase I and II (COI, COII) and internal transcribed spacer-2 (ITS-2) genes were used to assess their phylogenetic relationship. We observed that the chromosome ploidy of bisexual and parthenogenetic H. longicornis collected by our laboratory was diploid and triploid, respectively. Flowcytometry analysis indicated a ratio close to 2:3 in the DNA contents of bisexual to parthenogenetic H. longicornis. Although the chromosome ploidy is different, their gene sequences are extremely similar. Analogous to the intra-species genetic difference of other invertebrates, sequence differences of all loci examined are below 2%. Phylogenetic trees constructed from 12S rDNA, 16S rDNA, COI, and ITS-2 genes revealed that they were all in the same monophyletic clade instead of splitting independently into evolutional branches. Moreover, according to 4× Rule, the K/θ ratio of two reproductive populations calculated based on COI was much smaller than four, strongly supporting that they belong to the same species. Therefore, we conclude that the evolutionary process just disturbs the chromosome ploidy and the sexual determination of parthenogenetic population and that it would be better to consider parthenogenetic H. longicornis as a metapopulation rather than a cryptic species.
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.
authors: Xuejie
authors: X
authors: Chen
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China; College of Basic Medicine, Chengde Medical University, Chengde 067000, China.
authors: Shiqi
authors: S
authors: Xu
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.
authors: Zhijun
authors: Z
authors: Yu
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China; Department of Environment and Chemical Engineering, Hebei College of Industry and Technology, Shijiazhuang 050091, China.
authors: Lida
authors: L
authors: Guo
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.
authors: Shujie
authors: S
authors: Yang
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.
authors: Limeng
authors: L
authors: Liu
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China. Electronic address: yangxl@mail.hebtu.edu.cn.
authors: Xiaolong
authors: X
authors: Yang
authors: Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China. Electronic address: jzliu21@heinfo.net.
authors: Jingze
authors: J
authors: Liu
mesh_terms: D000818:Animals; D059006:Chromosomes, Insect; D004247:DNA / Q000032:analysis; D017344:Genes, Insect; D049810:Genetic Speciation; D026863:Ixodidae / Q000145:classification* / Q000235:genetics*; D059785:Karyotype; D010312:Parthenogenesis; D010802:Phylogeny; D011003:Ploidies
chemical_list: D004247:DNA
keywords: Bisexual; Chromosome; Haemaphysalis longicornis; Metapopulation; Parthenogenetic; Phylogeny