Vital Limits and Rates of Desiccation in Salamanders

Abstract

Adaptations of major importance in the evolution of life on dry land are those increasing the resistance of an organism to desiccation. Among vertebrates, modern amphibians represent a transitional stage since, in addition to truly amphibious members, the group contains both completely aquatic and completely terrestrial forms; yet, when exposed to air, all lose water through the skin. Some amphibians live in surprisingly dry habitats, but all must have access to water other than that obtained in food. Two special adaptations of amphibians to desiccation are apparent: (1) the ability of some amphibians to endure large losses of body water. Thorson and Svihla (1943) and Littleford et al. (1947) subjected various amphibians to desiccation under controlled conditions and found that the ability to endure loss of body water is in most instances correlated with the dryness of their habitats; (2) another adaptation may be the comparatively slow rate at which some amphibians lose body water-or the fast rate at which they regain it (Thorson and Svihla 1943; Littleford et al. 1947; Cohen 1952; Thorson 1955, 1956). The present paper supplements the work of these authors and discusses some modification of the methods over those used in previous studies of this type. The amphibians studied were salamanders of the following species: Batrachoseps attenuatits (7 individuals), Ensatina eschscholtzi xanthoptica (6), Aneides lugubris (5), A. Ferreus (3), A. flavipunctatus niger (6), Plethodon elongatus (2), P. dunni (1), and Rhyacotriton olyinpicus variegatus (5). Localities from which the study animals were obtained are indicated in figure 4.