| The tick Haemaphysalis tibetensis Hoogstraal, 1965 is only distributed in Qinghai-Tibet plateau in Tibet and Gansu of China and it is an important pathogen vector endemic in the Qinghai-Tibet plateau. The population dynamic, life cycle and molecular phylogeny of this species have not been investigated.In this study, we investigated the life cycle of H. tibetensis under field conditions from March 2014 to March 2015 in Damxung County, north Lhasa City in Tibet(Autonomous Region in China). The results demonstrated that the tick H. tibetensis requires an average of 177.8 days(range 129? 202 days) to complete a life cycle,with rabbits supplied as hosts in the field plot. Under natural lighting and climate conditions, the feeding periods of females were 7.7 days, and the pre-oviposition periods were 9.4 days, followed by 28.2 days for oviposition. The premolting periods of nymphs lasted 52.7 days, which was the longest duration during the life cycle. The average weight ratio of the engorged females to unfed ones was 58.20.Additionally, there was a highly positive correlation between the weight of the engorged female and the number of the eggs that were laid(r = 0.8273, P<0.05). The reproductive efficiency index and reproductive fitness index in females were 4.7 and5.1, respectively. In current study, we investigated the seasonal dynamics of the parasitic and non-parasitic H. tibetensis over a two-year period from March 2014 to February 2016 in the Tibetan plateau. During the two-year period, questing ticks were collected weekly by flag-dragging in grassland and shrubs, and parasitic ticks were removed weekly from marked sheep. Plateaus pikas were captured using traps and examined for immature ticks between May to September 2014. Results suggested that questing H. tibetensis were mainly distributed in the grassland,whereas the parasitic adults and nymphs were mainly found on sheep. Larvae were usually found on plateau pikas. The tick H. tibetensis can complete one generation per year with a population overlap between stages. Adults were observed from March to July with the major peak occurring in mid-April. Nymphs were found from March to August and reached a peak in late June. Larvae were collected from Aprilto September and their numbers peaked in late May.In this study, the 16 S rDNA, CO?, CO?, 12 S rDNA and ITS-2 from the genomes of H. tibetensis were amplified by PCR and sequenced for homology analysis. Based on the principle of Neighbor-Joining(NJ) and maximum likelihood(ML), MEGA 7.0 software was used to construct the individual phylogenetic trees of the five gene sequences for phylogenetic analysis. The results showed that the length of 16 S rDNA, CO?, CO?, 12 S rDNA and ITS-2 were 436 bp, 709 bp, 249 bp, 386 bp, 1991 bp and the ratio of transition and transversion were 1.458, 1.841, 1.077,1.587, 3.077 respectively. The sequence of 16 S rDNA and CO ? genes had no insertion and flaw. However, G+C content of ITS-2 was higher than A+T content.A+T content of 16 S rDNA,CO?,CO?and 12 S rDNA were 75.2%, 67.1%, 69%,78.7% respectively. The phylogenetic relationships of H. tibetensis and other tick species based on the sequence datasets of 16 S rDNA, CO?, CO?, 12 S rDNA and ITS-2 using NJ, and ML analyses. The topological structures of two phylogenetic trees of same gene were similar. In the trees based on the nucleotide sequences of the16 S rDNA, CO?and ITS-2 gene showed that H. tibetensis was clustered together with partial Haemaphysalis ticks,but the genetic distance between them was long.However, In the trees based on CO ?showed that H. tibetensis formed a distinct branch and was not clustered together with other Haemaphysalis ticks. This indicated that there were no close relative species of H. tibetensis and the phylogenetic relationship of H. tibetensis was far with Haemaphysalis ticks. |
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