Water Collection and Drinking in Phrynocephalus helioscopus: A Possible Condensation Mechanism

Abstract

The drinking behavior of nine captive Phrynocephalus helioscopus was observed. When wetted, animals assumed a stereotyped posture in which the head was depressed to within several mm of the substrate, the limbs splayed, and the hindquarters and tail elevated. Drinking involved repeated, slight tongue protrusion, but without lapping from the substrate. This behavior was elicited in no other context. Simple experiments showed that the interscalar channels transport water across the skin to the mouth by capillary action. This mechanism is compared with that reported for another agamid, Moloch horridus. We hypothesize that the drinking posture 1) facilitates drinking rain water and/or 2) facilitates drinking water condensed on the skin and moved to the mouth by capillary action. We conclude that derived features of water collection and transport shared by Phrynocephalus and Moloch are convergent. Recently, Gans et al. (1982) examined the water-collecting mechanism of Moloch hor- ridus, an Australian agamid squamate. They elaborated upon an earlier study (Bentley and Blumer, 1962) which found that the integument acts as a blotting paper, soaking up standing water through capil- lary action, ultimately moving it to the