Effect of hydric stress on locomotion and morphology of tadpoles from temporary ponds.

Many frog species reproduce in temporary ponds maintained exclusively by rainfall, thereby being exposed to drought and possibly mortality of eggs and tadpoles. Some tadpoles, however, can survive for up to 5 days out of water but few data are available regarding the effects of dehydration on their development. The aim of this study was to evaluate whether hydric stress affects the locomotor capacity and the morphology in tadpoles of two leptodactylid frog species showing different reproductive modes (Leptodactylus fuscus and Physalaemus nattereri), examining specifically: (a) difference in survival rate and body mass between tadpoles at different hydration levels, (b) the hydric stress effect on locomotor performance, (c) difference in external morphology, and (d) visceral volume among tadpoles suffering hydric stress. Tadpoles for both species were divided into two groups, one staying in 100 ml of water and the other maintained on absorbent paper with 4 ml of water for 12, 24, and 72 hr (n = 20 each). Significant differences in weight loss were found between the groups of both species, the treatment losing more weight in all stress levels. Almost half of P. nattereri tadpoles died within 36 hr of hydric stress. We found no difference in locomotor performance between groups of L. fuscus tadpoles, but significant differences in locomotor performance, tail morphometry, and visceral volume between groups of P. nattereri tadpoles. Our results suggest that hydric stress has a significant effect on locomotion and morphology of P. nattereri tadpoles but not in L. fuscus.