Aspects of the osmotic and water balance of the New Zealand native frog Leiopelma hochstetteri fitzinger, and the Australian whistling frog Litoria ewingi dumeril and bibron : a thesis ... for the degree of Master of Science in Zoology

Abstract

Rates of dehydration and rates of water uptake when hydrated or dehydrated are described for two species of frogs of similar size from different habitats. No detectable differences in rates of water loss in frogs of both species of comparable size were noted. Considerable differences were seen in rates of water uptake. These uptake rates were lower in hydrated and dehydrated Le. hochstetteri than in hydrated Li. ewingi. Differences in rates of water uptake were reflected in measurements of skin permeability and blood plasma osmolality. Rates of water uptake in Li. ewingi were dramatically increased after dehydration, and it was proposed that this was due to hormonal mediation. The osmotic permeability of different skin regions in frogs of different species may vary in the presence or absence of oxytocin or vasopressin. This was not observed in Le. hochstetteri where the skin exhibited relatively uniform permeability, but was seen in Li. ewingi and Li. aurea. In these two species, the abdominal skin was more permeable and more readily stimulated by oxytocin or vasopressin than the dorsal skin. Oxytocin and vasopressin also increased the short circuit current (inward Na+transport) through both dorsal and ventral skin in Le. hochstetteri, but most noticeably through the ventral skin in Li. ewingi and Li. aurea. The skin was observed to be thinner in Li. ewingi than in Le. hochstetteri or Li. aurea. Thin areas in the ventral pelvic integument of Li. ewingi and Li. aurea and the presence of epidermal capillaries in these two species are thought to be of importance in water uptake. It has been suggested that water uptake mechanisms are a major factor determining the distribution of the three frog species.