Water economy in two species of plethodontid salamander

I compared morphology, physiology, behavior, and habitat utilization of two species of plethodontid salamander to determine adaptations to a desiccating environment. Physiological and morphological measurements, and behavioral experiments were conducted at Humboldt State University's Energetics Laboratory, Arcata, California. Habitat variables were measured at Arcata Community Forest, and Simpson Timberlands, Humoldt County, California. Batrachoseps attenuatus had more surface area (standardized by body mass) than did Ensatina eschscholtzii (26.38 ± 0.28 cm2 and 16.72 ± 0.31 cm2, respectively; x ± SE; F1,7= 462.1, p 0.01), but there were no differences in water loss and water gain between species (water loss: F1,17 = 0.04, p 0.10; water gain: F1,17 = 0.83, p 0.10). Total resistance to water loss did not differ between B. attenuatus and E. eschscholtzii (t = 0.59, df = 8, p = 0.57), however resistance was twice as variable in B. attenuatus than in E. eschscholtzii. Both species had skin resistance greater than a free water surface (for B. attenuatus t = 2.31, df = 6, p 0.10; for E. eschscholtzii t = 3.81, df = 3, p 0.05). In a dry laboratory environment, B. attenuatus and E. eschscholtzii were curled up more than expected (X2 = 12.2, p = 0.0005, df = 1), and under leaf litter more often than expected (X2= 7.9, p = 0.0049, df = 1). In the field, there were no differences in ambient and microclimate characteristics at plots with only B. attenuatus, only E. eschscholtzii, both species, or neither species (Wilks' Lambda = 0.48,F30,121 = 1.13, p = 0.31). I found more E. eschscholtzii at the moister study area (32 E. eschscholtzii on 28 sites) than at the drier study area (8 E. eschscholtzii on 32 sites; Wilk's Lambda = 0.66, F1,51= 13.2, p 0.001), but there was no difference in the abundance of B. attenuatus between study areas. Batrachoseps attenuatus and E. eschscholtzii appeared to have several adaptive mechanism by which they lowered cutaneous water loss. Both species had an integument that retarded water loss. Both species altered their behavior in response to environmental changes. Although this study did not present conclusive evidence that B. attenuatus utilized drier microhabitats, B. attenuatus seemed to be better adapted to a dry environment given that individuals had more variable physiological responses to water loss than E. eschscholtzii, indicating a broader range of skin resistance. This adaptation coupled with the ability of B. attenuatus to reduce the amount of exposed surface area, may sufficiently reduce cutaneous water loss in an environment that would otherwise be too dry for E. eschscholtzii to persist.