Study On Environmental Influencing Factors Of Growth And Development For The Red Knobby Newt Larvae

Most amphibians have a bi-phase life history trait of aquatic and terrestrial stage,which the larvae developed in aquatic environment through to accomplish metamorphosis.Changing of environmental factors including hydroperiod,food,and predation risk would influence the growth and development of amphibian larvae.Knowing the growth and development life history and phenotypic variation of amphibian larvae will help us to understand how amphibian larvae were adapted to the change of environmental factors.Meanwhile,it could provide useful informations for the protection of the amphibians.This research will explore the variations of growth rate,body length and body mass at metamorphosis,metamorphosis time of the Red Knobby Newt(Tylototriton shanjing),which was the typical caudated amphibian in Yunnan montane environment,under the changes of hydroperiod,food,and predation risks in laboratory experimental conditions,so as to ascertain the effects of environmental factors on the growth and development and metamorphosis of the newt larvae.The main results are:1.Hydroperiod has an important effect on the ontogeny and metamorphosis of newt larvae.Relative to the stable and high water level environment,the newt larvae in unstable water environment with fluctuation and continual decreasing of water level have much lower growth rate,and faster development.The newt larvae accomplish their metamorphosis at smaller body length and body masses,and at earlier time.Most death of the larvae took place in the gill resorption period,and the newt larvae in stable and low water level environment has a highest death rate.It may be attributed to its unable to reach the threshold of body size needed to fulfill metamorphosis under the stable and low water level,and could not be adapted to the continual low water level.2.There were different performance of growth and development for the newt larvae under different predation risk conditions.In the early stage of the development,the growths of the newt larvae of the four treatments were identical,but it accelerated significantly at the middle and late stages for the three predation risk treatments.Body size and body mass at metamorphosis of the newt larvae for the predation risk treatment was much longer and heavier than of the no predation risk treatment,indicating that there was a larger body size at metamorphosis under predation risks.Whereas,time at metamorphosis of the newt larvae were shorter for the predation risk treatments than that of the no predation risk treatment.The experiments suggested that the newt larvae be adapted to the high predation risk environment by speeding up growth rate at the late stage of the embryonic development and shortening development time,accomplishing metamorphosis as soon as possible,and leave the developmental water body earlier when they were faced with the increasing predation risks.3.Stability and richness of food resources can affect ontogeny and metamorphosis of the newt larvae.The more abundance of food in aquatic habitat was,the shorter of the time to metamorphosis of the newt larvae was,and the longer and heavier body size and body mass at metamorphosis of the newt larvae.The increasing food environment was most advantage to the newt larval ontogeny and metamorphosis,but in the continuous low and fluctuating food environment,the larvae's development stagnated,metamorphosis delayed,and the body length and mass at metamorphosis were reduced,even they could not fulfilled metamorphosis in the current year.Lack of adequate food resource was principal reason of metamorphic delay and diminished body size4.In the three environment factors of hydroperiod,food and predation risk,the most influence factor on the newt larval ontogeny was food.Food level was the most important factor which affect on the body size,body mass and time of metamorphosis of the newt larvae.