Skin resistance to water loss in colubrid snakes: Ecological and taxonomical correlations

Abstract

:Rates of cutaneous water loss (CWL) in terrestrial snakes may be affected by the temperature and humidity prevailing in the habitat, the activity pattern of the snake, and the taxonomic position of the species. To find out whether variation in snake CWL is mainly due to the physical conditions characterizing a particular habitat, or whether it is better attributed to taxonomic position, we measured CWL and skin resistance to water loss (Rs) in four species of colubrid snakes. These species inhabit different climatic regions (from mesic Mediterranean to dry and hot desert) and habitats (semi-aquatic and terrestrial), and have different daily activities (diurnal and crepuscular-nocturnal). CWL and Rs were correlated more with aridity of habitat rather than with taxonomy. CWL rates of the non-desert species were higher, and their Rs lower than those obtained from desert species. The highest rates of CWL (0.98 mg cm−2 h−1) and the lowest Rs (117 s cm−1) were found in the water snake Natrix tessellata, whereas the lowest CWL (0.13 mg cm−2 h−1) and the highest Rs (1088 s cm−1) were found in the stripeless form of Psammophis schokari, which inhabits desert biotopes. Intermediate values were found in Coluber rubriceps and the striped form of Psammophis, both inhabiting mesic Mediterranean areas. CWL and Rs of Spalerosophis diadema,a species inhabiting arid desert biotopes, were not significantly different from those of the semi-aquatic Natrix. The apparent discrepancy between the low Rs found in Spalerosophis and the high aridity of its habitat can be attributed to the crepuscular-nocturnal activity of this species. The environmental conditions to which Spalerosophis is exposed during its activity in the desert nights are milder and much more moderate than those encountered by diurnal snakes. CWL and Rs reflect, therefore, not the apparent aridity of the habitat but the real ecological niche of the species, i.e.,the actual climatic conditions prevailing during the activity time of the species.