Pulmonary and cutaneous O₂gas exchange: a student laboratory exercise in the frog

Temperature and mass scaling affect cutaneous and pulmonary respiratory performance in a diving frog

Global climate change is altering patterns of temperature variation, with unpredictable consequences for species and ecosystems. The Metabolic Theory of Ecology (MTE) provides a powerful framework for predicting climate change impacts on ectotherm metabolic performance. MTE postulates that physiological and ecological processes are limited by organism metabolic rates, which scale predictably with body mass and temperature. The purpose of this study was to determine if different metabolic proxies generate different empirical estimates of key MTE model parameters for the aquatic frog Xenopus laevis when allowed to exhibit normal diving behavior. We used a novel methodological approach in combining a flow-through respirometry setup with the open-source Arduino platform to measure mass and temperature effects on 4 different proxies for whole-body metabolism (total O₂ consumption, cutaneous O₂ consumption, pulmonary O₂ consumption, and ventilation frequency), following thermal acclimation to one of 3 temperatures (8°C, 17°C, or 26°C). Different metabolic proxies generated different mass-scaling exponents (b) and activation energy (E_A ) estimates, highlighting the importance of metabolic proxy selection when parameterizing MTE-derived models. Animals acclimated to 17°C had higher O₂ consumption across all temperatures, but thermal acclimation did not influence estimates of key MTE parameters E_A and b. Cutaneous respiration generated lower MTE parameters than pulmonary respiration, consistent with temperature and mass constraints on dissolved oxygen availability, SA:V ratios, and diffusion distances across skin. Our results show that the choice of metabolic proxy can have a big impact on empirical estimates for key MTE model parameters.

Comparative Morphology of the Lungs and Skin of two Anura, Pelophylax nigromaculatus and Bufo gargarizans

The lungs and skin are important respiratory organs in Anura, but the pulmonary structure of amphibians remains unclear due to the lack of a suitable procedure. This study improved the procedure used for fixing lungs tissues and used light microscopy, transmission electron microscopy and scanning electron microscopy to reveal the differences in the lung and skin morphologies between Pelophylax nigromaculatus (P. nigromaculatus) and Bufo gargarizans (B. gargarizans). In P. nigromaculatus and B. gargarizans, the cystic lungs comprise a continuous outer pulmonary wall on which primary, secondary, and tertiary septa attach, and a number of regular lattices form from raised capillaries and the pulmonary epithelium on the surfaces of the pulmonary wall and septa. Each lattice in P. nigromaculatus consists of several elliptical sheets and flat bottom, and the septa are distributed with denser sheets and have a larger stretching range than the pulmonary wall. The lattice in B. gargarizans consists of thick folds and an uneven bottom with several thin folds, and the septa have more developed thick and thin folds than the pulmonary wall. However, the density of the pulmonary microvilli, the area of a single capillary, the thicknesses of the blood-air barrier, pulmonary wall and septum, and the lung/body weight percentage obtained for B. gargarizans were higher than those found for P. nigromaculatus. In P. nigromaculatus, the dorsal skin has dense capillaries and a ring surface structure with mucus layer on the stratum corneum, and the ventral skin is slightly keratinized. In B. gargarizans, the stratum corneum in both the dorsal and ventral skins is completely keratinized. A fine ultrastructure analysis of P. nigromaculatus and B. gargarizans revealed that the pulmonary septa are more developed than the pulmonary walls, which means that the septa have a stronger respiratory function. The more developed lungs are helpful for the adaptation of B. gargarizans to drought environments, whereas P. nigromaculatus has to rely on more vigorous skin respiration to adapt to a humid environment.

Proteomic analysis of the skin from Chinese fire-bellied newt and comparison to Chinese giant salamander

Animal skin that directly interfaces with the external environment has developed diverse adaptive functions to a variety of ecological conditions laden with pathogenic infection and physical harm. Amphibians exhibit various adaptations related to their "incomplete" shift from the aquatic to the terrestrial habitat. Therefore, it is very necessary to explore the molecular basis of skin function and adaptation in amphibians. Currently, the studies on the molecular mechanisms of skin functions in anuran amphibians have been reported, but in urodele amphibians are rare. This study identified the skin proteomes of Chinese fire-bellied newt Cynops orientalis by a proteomic method, and compared the results to the skin proteomes of Chinese giant salamander Andrias davidianus obtained previously. A total of 452 proteins were identified in the newt skin by MALDI-TOF/MS, and functional annotation results by DAVID analysis showed that special functions such as wound healing, immune response, defense and respiration, were significantly enriched. Comparison results showed that the two species had a great difference in the aspects of protein kinds and abundance, and the highly expressed proteins may tightly correlate with living conditions. Moreover, the newt skin might have stronger immunity, but weaker respiration than the giant salamander skin to adapt to various living environments. This research provides a molecular basis for further studies on amphibian skin function and adaptation.