| The hot spring genus(Thermophis)is the endemic genus in Qinghai-Tibet Plateau,among which only three kinds of snakes are known,the Tibetan hot springs snake(Thermophis baileyi),the Sichuan hot spring snake(Thermophis zhaoermii),and the Shangri-La hot spring snake(Thermophis shangrila),distributed in the east and west sides of Hengduan Mountains respectively.Thermophis baileyi is the only species living in the hinterland of the Qinghai-Tibet Plateau with an average elevation of more than 4000m.Because of its unique natural environment,Qinghai-Tibet Plateau is of great significance to the biodiversity conservation and researches on globally environmental change,and has been listed as one of the biodiversity hotspots over the world.Through a long process of evolution,Thermophis baileyi,as the only snake in the hinterland of the Qinghai-Tibet Plateau,has been highly adapted to low-temperature,intense ultraviolet and other extreme climates,which can be used as an irreplaceable model for the study of reptile plateau adaptability.The microstructure characteristics of different body parts of Thermophis baileyi are observed in detail by electron microscope,the microstructure characteristics of dorsal and ventral scales were measured by Image-Pro Plus software.14 indices such as length/width of scale,longitudinal ridges,pore density,pore diameter,longitudinal ridges distance,length/width of denticulation,base width of denticulation,tip distance of denticulation and width/length of cell and so on,are measured respectively.Statistical analysis is completed by SPSS v25.0.The related species of the same genus are compared,including Thermophis zhaoermii,Thermophis shangrila,the Tibetan Pseudoxenodon macrops,and the Western American Heterodon nasicus.The thesis systematically discussed the microstructure characteristics of various ecological types,revealing the mechanism of adaptation of scale microstructure to special plateau environment,and attempted to provide a new theoretical basis or hypothesis for the adaptability of plateau snakes.The results show that the microstructure of Thermophis baileyi is not only determined by hereditary factors,but also influenced by ecological needs.The evolution of microstructure can be reflected by the gradient change of microstructure from head to tail of the scales.Microstructure may constitute the most primitive conditional characteristics in the head area of scales,while the exposed parts in the center and tail area of scales constitute the most evolutionary microstructure characteristics.The three species of hot spring snake genus have very similar microstructure characteristics,such as longer dorsal scales,unconspicuous fossa,weak longitudinal ridges,pores between the horizontal stripes are reticulated and so on.However,according to the analysis of microstructure indicators,Thermophis baileyi has the widest smooth zone of dorsal scale(0.21 times the length of scale),the shortest ridge(less than 100?m),the widest cell(the width to length ratio is 8.76),the longest denticulation(0.60 times the length of cell)and the narrowest ventral scale cell(9.3 times the width to length ratio).The ventral scales of Thermophis baileyi have regular narrow and sharp denticulation,longitudinal continuous arrangement,tips of denticulation overlap with denticulation of adjoining ventral scale,the hump of the dorsal scale is relatively smooth.These characteristics reduce friction and the attachment of soil particles,which increase the longitudinally backward friction force,and support the moving efficiency on solid substrate,showing a high degree of adaptability to rock and soil.The dorsal scales have weak ridges longitudinally,which can effectively break the adhesion of water film that help the snake swim in water.The pores among the transverse striation interweave into net,which could increase the permeability of the epidermis and keep the surface of snake scales smooth and glossy.These characteristics are adapted to semi-aquatic life.The three-dimensional structure of clear layer microstructure of dorsal scales could reflect sunlight and scatter the solar radiation,and has the function of camouflage.Therefore,the microstructure of scales of Thermophis baileyi is mostly characterized by adaptation to terrestrial life,as well as semi-aquatic and burrowing habitat.This paper also studies the ecology of Thermophis baileyi.Taking the Jieba hot spring in Zhongsa Township of Gongbu Jiangda County,Yangbajing hot spring in Yangbajing Township of Dangxiong County and Dezhong hot spring in Menba Township of Mozhugongka County as field observation sites,the habitat characteristics of Thermophis baileyi are investigated.The utilization of Thermophis baileyi to different habitats is evaluated in spring and summer by using the quadrat method,and data of 12 related ecological factors are also collected at the same time,including body temperature of snake,topographic factors,related data of hot spring and variable data of microhabitat.Statistical analysis is completed by SPSS v25.0.The results have shown that all Thermophis baileyi choose the southern slope(100%)and downhill(100%)habitats in spring and summer.The highest encounter rate was found in sunny days(100%)in spring and in cloudy or sunny days(85.71%)in summer.In terms of concealment selection,in spring,the stones near hot springs are chosen(100%),while in summer,the slopes wetland(14.29%),the stones near hot springs(57.14%),stones of the riverside wetland(21.43%)and the grasses on hot springs slopes(7.14%)are chosen as concealments.In terms of vegetation types,all Thermophis baileyi choose shrubs and herbs symbiotic type in spring(100%).In summer,besides shrubs and herbs symbiotic type(71.43%),they also choose herbs type of vegetation(28.57%).Mann-Whitey U Test analysis have shown that there is no significant difference between spring water temperature and air temperature in spring and summer(P>0.05),but there is significant difference between spring distance and temperature(P<0.05).One-Way ANO VA is used to analyze the three variables of substrate surface temperature,snake body temperature and the earth's surface humidity.There were significant differences between the three variables in spring and summer(P<0.05).It can be concluded that hot spring water temperature and substrate surface temperature provide sufficient conditions for the body temperature regulation of Thermophis baileyi.Seasonal changes in environmental temperature in the plateau region have brought great challenges to the survival of ectotherm.Thermophis baileyi lives in the hinterland of Qinghai-Tibet Plateau,but its scale microstructre has many characteristics of semi-aquatic and pit dwelling,which couldn't meet its needs of adapting to the cold and dry climate of the plateau.Only by taking hot springs as the key to body temperature regulation,through habitat selection and utilization strategies,can the survival conditions be guaranteed.Therefore,the suitable microhabitat of Thermophis baileyi is not cold and dry,but the warm and humid semi-aquatic cavernous land life.In addition,the microstructure characteristics of the head of Thermophis baileyi scales are also consistent with the humid and watery subtropical environment before the Qinghai-Tibet Plateau uplift,conforming to the geomorphology theory before the Qinghai-Tibet Plateau uplift. |
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