Population Ecology And Physiological Adaptation Of Dermacentor Everestianus

The Qinghai-Tibet plateau is the highest biogeographic units in the world,with harsh natural environment and special animal populations.The tick Dermacentor everestianus mainly distributs in the mountainous region of the Qinghai-Tibet plateau in China and Nepal,only apperas in high-altitude area at 3500~4500 m.They have a wide distribution with large population in parts of Tibet.This species transmits zoonotic pathogens which can cause severe human and animal diseases including Tularemia,Anaplasma ovis and Tick-borne spotted fever.It is of important scientific significance for this research and has potential to formulate the development of strategies for effective tick control.The population ecology,life history strategy and physiological adaptation of D.everestianus systematically were investigated.The main results are as follows:1.During the two years of field ecology studies,we used flag dragging and body surface examination to investigate the habitat,host selection and seasonal dynamics of this species.The results of the study showed that the non-parasitic D.everestianus were mainly found in high-cold steppe habitat which the dominant species is Kobresia tibetica,and there is few distribution in alpine shrub and alpine desert.The adults and nymph D.everestianus were primarily found on the neck,abdomen and groin of the yak,and also found on the ears of the sheep.The main host of the larva is Ochotona curzoniae(Unique species of Qinghai-tibet plateau),and the parasitic part is the auricle.In Tibet,D.everestianus can only complete one generation per year with a sequential seasonal distribution.Adults started to appear in late February to late April with a major peak in the late March.The larvae were found from May to June with a peak in late May.Nymph were mainly observed from late May to middle July and had a peak in middle June.2.The life cycle and biological characteristics of D.everestianus were investigated under natural field conditions with a controlled sample and used Oryctolagus cuniculus domesticus as the host.The results showed that the durations of the life cycle from unfed adults to the next generation unfed adults of D.everestianus required an average of 122.4 days(range 105~148 days).The female prefeeding,preoviposition and oviposition were 6.1 days(range 5~7 days),17.9 days(range 17~19 days)and 21.2 days(range 17~31 days),respectively.The egg incubation period was 26 days(range 24~49 days).larva and nymph period were 17.1 days(range 14~20 days)and 31.2 days(range 26~38 days).The weight of female increased significantly after engorgement,which was 41.5 times than that of starvation.The spawning quantity of female ticks was 2237.5(range 1287~2975),the number of egg was positively correlated with the weight of engorged females(r = 0.81)and the reproductive efficiency index(REI)reached 7.3 and the egg hatching rate was 81.2%.The incubation period of the egg was the longest in the life cycle,with the most tolerant of adults,which could survive up to 9 months,and during the winter,the adults inhabited under the snow-cover or rodents' caves.3.The anti-cold system and antioxidant enzyme system of D.everestianus were analyzed.The results show that D.everestianus associated with cold system included the body fat content(14.91%),glycogen content(69.98 mg/g),glycerin content(32.74 ?g/ml)and protein(1.22 gprot/l)were significantly higher than D.silvarum which distributed in the low altitude area(corresponding to the content of 10.73%,62.54 mg/g,29.27 ?g/ml and 1.11 gprot/l respectively).It is indicated that the lipid,glycogen and glycerol in D.everestianus played an important role in the adaptation of the extreme environment,and meanwhile enhanced the cold resistance and drought resistance of this species.The activity of SOD,CAT,POD and GSTs(27.73 U/mgprot,22.39 U/mgprot,11.08 U/mgprot and 118.3 U/mgprot)of D.everestianus were significantly higher than D.silvarum(24.31 U/mgprot,17.82 U/mgprot,9.98 U/mgprot and 103.7 U/mgprot).Excessive ROS produced by the ROS under the stress of the hostile environment resulted in the activity of various antioxidant enzymes in D.everestianus,which was significantly higher than D.silvarum(P < 0.05),so that could avoid excessive damage to the body.There was no significant difference in MDA content between field population(19.22 nmol/mgprot)and laboratory population(19.31 nmol/mgprot)of D.everestianus,indicating that their lipid peroxidation were similar.But SOD,CAT and GST activity of antioxidant enzymes activity in laboratory population(21.15 U/mgprot,18.73 U/mgprot and 106.1 U/mgprot)was significantly lower than the field populations(27.73 U/mgprot,22.39 U/mgprot and 118.3 U/mgprot),this may be related to adaptation to a non-habitat environment of D.everestianus.