Water Loss During Periodic Physiological Processes in a Desert Pitviper

Cardwell, Michael D.

Department of Biology

San Diego State University

San Diego, CA 92182 USA

Desert squamates are models for minimal water flux among terrestrial vertebrates. Water intake for carnivorous desert squamates is almost entirely satisfied by the body water of prey. Cutaneous and respiratory evaporation has been estimated to account for 75% and 25% of continuous water loss, respectively. Water loss resulting from periodic physiological processes is less well studied. I confined five recently captured Mohave Rattlesnakes, Crotalus scutulatus (4 males, initial SVL 262– 830 mm, and 1 non-reproductive female, 724 mm) for 354 days in glass terraria with screen tops and heat lamps at one end in a closed room maintained at ~ 25C. Temperature and humidity were recorded hourly. Study animals were kept on clean newsprint paper and massed ca. weekly. Adult animals were fed thawed and massed laboratory mice; juveniles were started on fresh lizards (Sceloporus). Drinking water was provided overnight on only two occasions. Masses were measured to 0.1 g with an Ohaus decigram balance (magnetic damper removed). New newsprint was heated to drive off moisture before being massed and placed in terraria. After ecdysis or defecation events, animals were immediately massed and the newsprint containing the exuvium or feces was heated until dry and massed, from which the amount of solid matter and water lost was calculated. Continuous evaporative water loss rates were calculated for each animal and used to refine calculated water loss during periodic events, if pre-event massing of the snake was separated from the event by more than a day. Water loss is reported for 14 ecdysis and 62 defecation events. During the study, body mass for males increased from 3% to 303% (initial SVL 830 and 321 mm, respectively). The female fasted for the first 252 d and lost 10% of its initial body mass during the study, but added ~ 23 mm SVL.