Meeting Abstract
Most terrestrial vertebrates use lungs to breathe. The few exceptions include lungless amphibians (hundreds of species of salamanders, but only two other amphibians), which breathe entirely through the skin and buccal cavity. How lungless amphibians are able to meet metabolic demands is a topic of considerable speculation. Lunglessness places theoretical limits on thermal tolerance and body size, but lungless salamanders paradoxically live across diverse thermal environments and reach relatively large body sizes. Lungless salamanders display a slight increase in vascularization of extrapulmonary tissues (the skin and buccal cavity) compared to some lunged species, but morphological differences alone do not explain observed increased extrapulmonary respiratory capacity. Molecular differences between lungless and lunged species may account for greater extrapulmonary respiratory capacity. We have discovered a novel paralog of a lung-specific gene that likely evolved in salamanders and may serve a unique function in lungless species. This paralog is expressed solely in the lungs in lunged salamanders, resembling the expression pattern of its ancestral gene. However, the expression site of this paralog in a lungless salamander is dramatically divergent: in embryos and larvae of Desmognathus fuscus, the paralog is expressed throughout the skin. At metamorphosis, expression shifts to the buccal cavity. We propose that the salamander-specific paralog is neofunctionalized in lungless salamanders to facilitate cutaneous and buccal respiration. Neofunctionalization of this gene and its dynamic expression pattern may help lungless salamanders adapt to shifting life history-related demands for gas exchange and may help account for the remarkable adaptive radiation of lungless salamanders.
