Cutaneous gas exchange in snakes

Summary Cutaneous aquatic gas exchange and pulmonary gas exchange have been compared in an aquatic snakeAchrochordus javanicus and the terrestrial snakeConstrictor constrictor.Gas exchange was measured by closed respirometry with the snakes in air and in water with access to air. Frequency of air breathing, tidal volumes and total lung volumes were also compared in the two species. All measurements were done at 20–22 ° C.The aquaticAchrochordus showed long periods of apnea in submerged condition interrupted by short periods of breathing activity at the surface. Average frequency of air breathing activity was 2.6 times per hour. Breathing in constrictor was more frequent but irregular with an average frequency of 143 breaths per hour.Total lung volume was 66±31 ml/kg body weight and 72.5±59 ml/kg body weight inAchrochordus andConstrictor, respectively. Tidal volumes were 41.5±4.4 ml/kg body weight and 29.5±14.8 ml/kg body weight, largest inAchrochordus. Constrictor had the highest total O₂ uptake ( ) correlating with a higher activity. Total gas exchange ratio (R _E ) was 0.69 forConstrictor and 0.77 forAchrochordus. InConstrictor air breathing accounted for 97% of the total whereas 21% of the CO₂ exchange was aquatic. Corresponding figures forAchrochordus were 92% of total by air breathing with as much as 33% of the CO₂ elimination as aquatic gas exchange.The results demonstrate that the trend among early air breathing vertebrates (fishes and amphibians) of a conservative evolution of CO₂ elimination by air breathing also extends to snakes.Significantly the cutaneous exchange component was highest in the more aquatic species.The results are discussed in relation to recent reports of a higher than alleged role of the skin of reptiles in evaporative water loss.This study was supported by grant HE 12071 from the National Institutes of Health in the U. S. A.