Bergmann's Rule Among Chinese Amphibians And Squamates

Bergmann's rule is an ecogeographic rule that concerns on body size variation of animals along environmental gradients, it predicts that endotherms are larger in colder climates than their congeners in warmer climates. The mechanism underlying this rule is based on a thermoregulatory context:lower surface-to-volume ratios resulting from larger bodies facilitate heat conservation under colder conditions.Since it was first proposed, the majority of studies about the rule were conducted in Europe and the western hemisphere, there are few studies concern on the Bergmann's rule among animals in China. To achieve a better insight of the rule, we first summarized the studies focus on the Bergmann's rule and the conclusions already made, then we concerned the rule among squamates and amphibians live in China, in an attempt to figure out if ectotherm vertebrates showed a body size variation along the environmental gradients.In the form of reviewing the preview studies focus on the rule, we found that the majority of endotherm vertebrates like birds and mammals showed a Bergmann's rule, but the ectotherm vertebrates like reptiles, amphibians and fishes showed a complicated pattern that some taxa showed a Bergmann's rule, some taxa showed a conversed Bergmann's rule and some taxa showed no cline. Invertebrates also showed a complicated pattern like ectotherm vertebrates. We inferred that the reason why different clades showed different patterns may arise from the different ecological traits that different clades have.Here, we concerned with the Bergmann's rule among snakes, lizards, anurans, and urodeles with different hierarchies living in China to see if ecological trait plays a role in determining the size variation of different animals.Comparisons conducted in interspecific and assemble levels indicated that the urodeles live in eastern Asia generally did not show a size variation along the thermal or moisture gradients, nor the aquatic taxa or the terrestrial taxa. Such a pattern may arise because aquatic urodeles mainly live in water featured a stable ambient environmental condition, and for them there is no need to suit the environment in the form of changing body size; the terrestrial urodeles also did not show size gradient along the thermal or moisture gradients, which may due to terrestrial urodeles usually live in the forest and mainly under logs and leaf litters. Such a micro habitat can greatly buffer the fluctuation of macro habitat, and thus under this relatively stable condition, similarly there is no need for terrestrial urodeles to suit the environment in the form of changing body size.Among Chinese anurans, comparison conducted in both interspecific in Chinese frogs and intraspecific worldwide showed that the body size of terrestrial anurans is bigger in the places where is colder. Because when facing a changing and unpredictable ambient environment, growing bigger helps to maintain body temperature; however, the body size of aquatic and arboreal anurans showed no size variation along the thermal or moisture gradients, because the aquatic species may spend the majority of their lifetime in water which is characterized as stable and predictable with less chance of experiencing harsh condition. There is no need to change body size for survival. As for the arboreal species, they did not show a size variation too. This may because those anurans are mainly live in southern China where is warm and wet, which means the environmental condition is stable and predictable. It is not necessary to suit the environment in the form of changing body size.Both the intraspecific and interspecific comparison indicated that neither all Chinese lizard species nor the nocturnal species or the diurnal species showed a body size variation along the environmental gradients. Such a pattern may arise because lizards have a strong thermoregulation ability that they can adjust body temperature in the form of physiological and behavioral strategies, and thus there is no need for them to suit the thermal and moisture in the form of changing body size.Across all snake species in China, we found that Bergmann's rule is not a valid generalization.However, trends different were found with regard to ecological traits within and among species:the fossorial species and aquatic species showed no size variation with the changing environmental predictors, probably because those species spend the majority of their lifetime underground or in water and seldom exposed to the ambient environment directly. There is no need for them to enlarge body size to suit the therm or moisture gradients; the surface active, diurnal species also showed no body size variation along the environmental gradients, probably because those snakes can maintain the body temperature in a proper range physiologically and behavioral-strategically. There is no need for them to maintain body temperature in the form of enlarging body size; but the surface active, nocturnal species showed a Bergmann's rule that a bigger body size in colder regions, such a pattern emerges probably because a bigger body size helps to store more energy to facilitate the behavior at night.In the form of summarizing the research history of Bergmann's rule and focusing on the Bergmann's rule of squamates and amphibians in China, we reemphasized the importance of the ecological trait in the pattern of Bergmann's rule and provided a new road in the study of Bergmann's rule.