干旱区生态环境知识资源中心

We compared rates of evaporative water loss and body temperatures between an ontogenetic series of green tree frogs (Hyla cinerea) and their water-saturated plaster models to identify the stage of development during which skin resistance to evaporative water loss first appears in this species. Rates of water loss and body temperatures of live frogs matched those of their models through Gosner stage 42 of development (emergence of the forelimbs), but water loss of live frogs was significantly lower and body temperatures significantly higher from stage 43 (beginning of tail resorption) through the adult stage. An index of cutaneous resistance to water loss (ICR) was formulated in this study to provide a relative measure of cutaneous resistance without requiring measurement of exposed surface area, with an ICR of 0 indicating a complete absence of skin resistance. Mean ICR was -0.006 prior to stage 42 and 1.61 after stage 42. These results indicate that skin resistance appears abruptly at stage 43, the stage during which metamorphosing individuals of Hyla cinerea emerge from the water. Examination of skin sections using light microscopy revealed that by stage 42 a distinct stratum corneum is present and that both serous and mucous glands are producing secretions. Thus, neither of two existing hypotheses which propose that these structures function in providing skin resistance can be refuted based on these results.