Biological Characteristics And Phylogeny Analysis Of Two Haemaphysalis Species

Ticks, as obligate blood-sucking ectoparasites, are transmitting a great variety ofpathogens to their hosts, causing severe harm to human health and the development of animalhusbandry. On the basis of the works that our laboratory had done, we investigated thebiological characteristics of two Haemaphysalis species and their phylogeny, which isbenefited to the study the relationship among of host-tick-pathogen.Firstly, biological characteristics of Haemaphysalis doenitzi have been carried out inecology, phylogeny and genetics under laboratory conditions. The results revealed that thereare four developmental steps of H. doenitzi, including eggs, larvae, nymphs and adults; andtheir complete life cycle requires a mean duration of109.6days. The mean weight ofengorged nymphs is a good index to predict tick sex, and the female and male of them is1.01:1. There is174.42-fold increase in their body weight after females engorged, and theweight is highly correlated with the number of egg masses laid (r=0.9360, p <0.001). Inaddition, multisequence alignments and phylogenetic tree constructed based on themitochondrial16S rDNA sequences suggest that H. doenitzi is genetically close to H.longicornis. The karyotype of H. doenitzi is2n=20+XO (♂)/20+XX (♀), sex determinationmechanism is XO: XX. All the statistics data would benefit to of deeply studies of H. doenitziand Haemaphysalis species.Secondly, the species delimitation of parthenogenetic H. longicornis ticks is alwaysambiguity and questioned. Two races of H. longicornis in our laboratory are isolated inreproduction, but analogous in morphology and life style. Due to the stable divergence oftheir chromosomal ploidy, we discuss this problem in this paper through compared the geneticmaterial between bisexual and parthenogenetic H. longicornis.(1) We investigated thegenome size use classical genetics and flow cytometry, and the ratio of two lineages is closeto2:3.(2) We conducted the nucleic acid diversity and phylogeny relationship and the resultswere analyzed as follows:(a) sequence diversity between two reproduction races is rangedfrom0.11%to1.34%. All of them lower than2%, which is similar to the intraspecies genetic diversity of most animals.(b) sequence diversity of all mitochondrial and ribosomal genes wehave performed between H. doenitzi and H. longicornis are beyond4times greater than thediversity of two reproduction races of H. longicornis, which demonstrated that thedelimitation of parthenogenetic H. longicornis is fit for4X Rule.(c) phylogenetic treesdeduced based on four different genes revealed that, two reproductive lineages are in the samemonophyletic clade instead of spliting into independently evolving branches, the geneticdistance between them is belong to a intraspecies level. We could draw a conclusion thatchromosome ploidy is not a crucial factor act on disturbing the tick’s evolutionary processexcept for sex determination, and the genetic mutation, selection, and random drift is notenough for their speciation. Therefore, we approve of the previous delimitation ofparthenogenetic H. longicornis ticks and considered them as a metapopulation.In addition, owing to the high oviposition ability, many researchers focus on tick’sreproduction mechanism. In this paper, we identified and characterized the17beta-hydroxysteroid dehydrogenase (17β-HSD) from H. longicornis, which is proved acton steroid hormone, for the purpose of seek for a new target about tick’s reproductive research.The17β-HSD sequence we obtained is1508bp, encoding347amino acids, belong to SDRfamily and homology with17β-HSD12. Protein function predicted by online softwareindicated that this enzyme is an oxidoreductase, and as a growth factor act in cell envelope.Moreover, we detected the special expression in different development stages andorganizations of H. longicornis by Real time PCR, found that midgut has the maximumquantity, following by spermatheca, haemolymph and ovary. We estimated that17β-HSD isnot only related to reproduction but also play an important role on tick’s blood-meal digestion.Intensive study would help us to understand the upstream regulation of tick hormone andreproduction mechanism.