Water Permeability of the Skin of the Amphibious Snake, Agkistrodon piscivorus

Abstract

The cottonmouth (A. piscivorus) is a semi-aquatic fresh water snake which is closely related to the terrestrial copperhead (A. contortrix). Despite the differences in habitat preference, both species have similarly low integumentary water permeability in the summer. Influx and efflux of water measured between tritiated distilled water and a 1 M NaCl solution were about 20-50 gtmoles/cm2 h. These are fairly typical values for terrestrial snakes, but abnormally low for fresh water species. A. piscivorus were caught soon after emergence from hibernation, and successive shed skins tested under constant conditions over a five month period showed significant declines in water permeability with a minimum of about 20 pmoles/cm2-h in June-September. Newborn A. piscivorus placed in water for three weeks had significantly lower cutaneous water permeabilities than those dehydrated by about 27% of their initial body mass in air. Thus integumentary perme- ability may vary in response to the state of body fluid hydration. Skin water permeability appears to be controlled by lipids since their extraction causes an enormous increase in influx and efflux. The lipid extracted shed skin of A. piscivorus demonstrated a marked asymmetry in downhill water diffusion, with influx exceeding efflux.