Elevational Variation In Body Size Of Bufo Gargarizans Minshanicus, A High-elevation Toad Native To The Tibetan Plateau

The body size of the organism has been the focus by biologists,because it is closely related to the physiological traits and ecological characteristics of the species,including the rate of metabolism,time of development,input of reproduce,capacity of fecundity,ability of migration and longevity.In addition,the body size has a significant effect on the relationship between species and the formation of the community pattern.Moreover,body size indicates the adaptability respond to local environmental conditions.In this study,we regard Bufo gargarizans minshanicus native to the Tibetan plateau as study object to investigate the relationship between the body size and the altitude and to reveal effect mechanism of elevational variation in body size of amphibians,so as to take effective measures to protect them.B.g.minshanicus,lives on the eastern edge of the Qinghai-Tibet Plateau where altitude varies from 1700 m to 3700 m.This animal usually began to breed in mid-March every year,belong to typical explosive breeder.The large difference between the altitudes results in significant differences in the ecological conditions,which will provide an opportunity for us to examine the relationship between ecological stress and the body size of B.g.minshanicus.High human disturbances often occur at below 3000 m result in few B.g.minshanicus were found in this investigation(e.g.,less than 5 individuals/spawning site),thus our selected 6 study sites,such as 3027 m,3221 m,3230 m,3443 m,3447 m and3448 m where the B.g.minshanicus lives,including five of six study sites in the Gahai-Zhecha National Nature Reserve,one site at Red Star Township in Ruoergai County,Sichuan.Based on the analysis the body size of B.g.minshanicus,our results showed that body size follows Bergman's law,where the body size increases with altitude.Additionally,body size of female are larger than male from same altitude because female are older than male.Our results also showed that the altitude influences the age sexual maturity of both sexes.Individual at the highest altitude is older than that living at the lowest altitude.In addition,the altitude affects longevity in each of population.The age of sexual maturity and longevity increase with altitude,which is related with the temperature and naturalenemies.Based on the growth model of von Bertalanffy,the body size of mature amphibians is controlled by the factors,including age,growth rate and metamorphosis size.Moreover,age,growth rate and metamorphosis size follow the certain law with environmental temperature and seasonal length.For most amphibians that follow Bergman's rule,the effect of age on body size exceeds growth rate,but the growth rate of the male and female significantly increases with altitude,which is inconsistent with previous studies.In this study,we suggested that low temperature resulted in higher growth rate which was first cause of elevational variation in body size of B.g.minshanicus.Second,low temperature resulted in larger sexual maturity age and life expectancy,which was also one important reason for larger body size from higher elevation.In addition,humidity and water may also affect the elevational variation in body size of B.g.minshanicus.