Physiological Mechanisms Of Dermacentor Silvarum In Response To Low Temperature Stress

As obligate blood sucking ecto-parasites,ticks are widely distributed in the world,and can transmit a great variety of pathogens,which bring severe damages to human health and livestock production.The harsh low temperature in winter is an important factor affecting the occurrence and dispersal of ticks,and further restricting the diffusion and dispersal of tickborne diseases.However,researches on cold tolerance and physiological response to low temperature of ticks are very limited.Therefore,investigations on overwinter physiology and ecology of ticks will be of great significance to help understand the adaptation mechanisms of arthropods against low temperatures.In this study,the physiological adaptation and cold hardiness of Dermacentor silvarum were systematically analyzed using biochemical and interdisciplinary methods including cold acclimation,supercooling point determination system,GC/MS and LC/MS.To further explore the relationships between cold tolerance and cryoprotectants of D.silvarum,changes on water content,glycerol content,fatty acids,protein content and total fat content were evaluated before and after cold acclimation.Results showed that the 50% lethal temperature and discriminating temperature of larvae were-16.9? and-18.5?,respectively.In nymphs,the 50% lethal temperature and discriminating temperature were-15.8? and-22.6?,respectively.For females,they were-20.1? and-22.6?,respectively,whereas for males,they were-20.0? and-22.7?,respectively.The survival rates of nymphs and adults were significantly increased after rapid cold acclimation,whereas the survival rate of larvae and nymphs decreased rapidly with lower temperature below the subzero temperature,and the survival rate of adult was significantly higher than that of larvae and nymphs.The supercooling points were lower than-19.0? in all developmental stages of D.silvarum,suggesting the great potential of supercooling ability in this tick sepcies,and the supercooling points of adults were the lowest.After rapid cold acclimation,the water content and total fat content were significantly increased in nymphal stage(P <0.05);whereas no significant changes were observed in adults.The content of glycerol and glycogen were increased with the decline of the temperatures.Significantly glycerol changes were observed in the nymphs(5? treatment)and in adult(0? and-3? treatment)(P <0.01),whereas glycogen changes were found in nymphal and female ticks(-3? treatment)(P <0.05).GC/MS results detected ten fatty acids with carbon chain lengths between 16 to 23,and among them,four fatty acids(C18: 2,C19: 2,C19: 3 and C23: 4)were found increased after rapid cold cold acclimation.After rapid cold acclimation,protein content in different developmental stages of D.silvarum were decreased with the decline of temperatures,whereas the diversity of the proteins expressed in active stage and winter preparation stage were obviously higher than that in winter stage.