Study On Environment Adaptation Of Life History Trait And Organ Size In Black-spectacled Toad

Adaptive evolution is a process in which organisms change their morphology,physiological and biochemical characteristics to adapt to different environments during the long-term natural selection process.Life history traits and organ size has played an important role in the study of environmental adaptation in amphibians.In this paper,we studied variation on body size,age structure and organ size in the Black-spectacled toad(Duttaphrynus melanostictus)along an elevational gradient(Mouding,101°33?E,25°17?N,1771 m.a.s.l.;Midu,100°28?E,25°20?N,1673 m.a.s.l.;Pinbian,103°41?E,22°59?N,1043 m.a.s.l.;Pingjiang,108°23'E,25°58'N,276 m.a.s.l.;Yuanling,110°24'E,28°26'N,120 m.a.s.l.)of China.Research on variation in body size and age structure have indicated that body size was positively correlated with altitude and latitude.Considered that body size was significantly positively correlated with age(Male,r=0.424,P<0.001;Female,r=0.939,P<0.001).When correcting the influence of age,body size still positively correlated with altitude(Male,F_4,113=132.486,P<0.001;Female,F_3,35=3.974,P=0.028)and latitude(Male,F_4,113=104.882,P<0.001;Female,F_3,35=3.360,P=0.047).The result of our research exhibited that there is significant variation in body size among populations D.melanostictus,demonstrating that the species comply with Bergmann's Rule.The results suggest that the Black-spectacled toad,like many endotherms and amphibians,adapted by increasing its body size to cope with lower temperatures at high altitudes/latitudes.Organ size(heart;lung;gallbladder;liver;spleen;kidney;testis;digestive tract;brain)significantly differed among populations(F?3.460,P<0.005).LMMs was used to detect the variation of organ size in geographical gradient,but we found only the relative lung size(F=1.697,P=0.014)and relative testis size(F=1.719,P=0.032)were significantly positively correlated with altitude gradient.This result suggests that larger relative lung size may help individuals adapt to low oxygen at high altitudes/latitudes.Larger relative testis size may have been used to increase reproductive investment and thus reproductive success for males.Forelimb muscle mass and hindlimb muscle mass significantly differed among populations in male.When removing the influence of body size,variation in forelimb muscle mass and hindlimb muscle mass were significantly affected by body size(forelimb,F_1,116=31.865,P<0.001;hindlimb,F_1,116=71.040,P<0.001)or altitude(forelimb,F_4,113=26.465,P<0.001;hindlimb,F_4,113=8.094,P<0.001).However,limb muscles mass did not differ significantly across populations in female.The results imply that with the increase in altitude,altitudinal variation in muscle mass for male showed an increasing trend.Environmental changes at different altitudes prompted the adapation of D.melanostictus to fitness traits,the variation in environmental factors such as climate and food resource thus lead to the variation in muscles mass among populations.In addition,males have much more robust forelimbs than females.The results suggest that males with robust forelimbs presumably are better able to maintain their grasp of the female during amplexus and thus to resist attempted take-overs by competing males.In general,the results provided strong scientific support for substantial adaptive differentiation along latitudinal and altitudinal gradient in amphibians.