Geographic Differentiation And The Underlying Evolutionary Mechanisms On Larval Developmental Traits Among Four Populations Of Asiatic Toad(Bufo Gargarizans)

Population divergence and its underlying evolutionary mechanisms are among the main contents of population genetics and evolutionary biology.Phenotypic divergence as the external performance of population divergence,is affected by both genetic divergence and environmental differences among populations.The extent of genetic divergence among populations is affected by neutral processes(including mutations,gene flows and genetic drift),which are related to the geographical distance and the effective population size on the one hand.On the other hand,it is also affected by natural selection relating to environmental differences among populations.When the environmental differences are huge,the populations evolve in different directions under the actuation of natural selection,result in increased population divergence.When the environmental differences are small,the effect on population divergence correspondingly small such that population divergence is probably mainly affected by the neutral processes.Many studies have showed phenotypic divergence among populations,and some of them demonstrated the existence of genetic divergence through common garden or reciprocal transplant experiments.However,few studies assess the relative contributions of neutral processes and natural selection to the population divergence.The amphibian shows weak ability of dispersal and great sensitivity to environmental changes,so both geographic distances and environmental differences could affect the pattern of divergence among amphibian populations.Asiatic toad(Bufo gargarizans)is one of the most widely distributed amphibians such that it is suitable to study the issue of population divergence and the underlying evolutionary mechanisms.This paper studied on four Asiatic toad(Bufo gargarizans)populations from Hunan(SZ),Henan(XC),Hebei(GBD)and Heilongjiang(SHZ)respectively.We raised tadpoles through common garden experiments to eliminate the effects of environmental differences,recorded variable growth parameters of tadpoles,summarized the divergence pattern of the intrinsic developmental phenotypes relative to the latitude and environmental factors and estimated the phenotypic divergence(QST)using the growth parameters.Moveover,we estimated the neutral genetic divergence(FST)using microsatellites.By comparing the value of QST and-FST and making the correlation analysis between them,we assess the relative contributions of neutral processes and adaptive evolution to the population divergence.Finally,we determined the main driving factors that lead to adaptive evolution through the correlation analysis between the phenotypic divergence(QST)and the environmental differences.The measurement of phenotypic divergence(QST)ranged from 0.313 to 0.988,while the value of genetic divergence(FST)was 0.169,showing that the phenotypic divergence(QST)was greater than neutral genetic divergence(FST).The correlation analysis between QST and FST showed no significant correlation(0.325<P<0.687).These results suggested that phenotypic divergence was not significantly explained by neutral genetic divergence and adaptive evolution had played a crucial role in the population divergence.Subsequently,we analyzed the correlation between phenotypic divergence(QST)and environmental factors.The results showed that the annual mean temperature had a significant correlation with the phenotypic divergence(QST)(P=0.043).It indicated that temperature was the main ecological factors driving B.gargarizans larvae to adapt local environments through changing developmental traits.The study combined analyses of macro-and micro-evolution,showed both phenotypic and genetic divergence among four B.gargarizans populations,assessed the relative contributions of neutral evolutionary processes and natural selection to the population divergence,and finally found the main ecological factors driving local adaptation.This study supplements new data to studies on divergence among amphibian populations,and provides a foundation for the future research in our laboratory.