Efeito do estresse hídrico sobre a locomoção e morfologia de girinos de Leptodactylus fuscus e Physalaemus nattereri

Abstract

Several species of frogs (Leptodactylidae) breed in temporary pools maintained exclusively by rainfall. These pools easily dry out causing high mortality of eggs or tadpoles thereby possibly exerting strong selective pressure on the evolution of resistance mechanisms and survival in the early stages of development. However, the tadpoles of some species can survive up to five days in pools that are drying out, needing only a humid substrate for development which can provide an advantageous adaptation, because it enables the survival of tadpoles for a period that may be enough for the recurrence of new rains and restoration of the water body. Despite this ability to survive out of water, it is not known which possible damages dehydration stress causes in tadpoles during their ontogeny. The aim of this study was to evaluate the effect of hydric stress on: (1) the level of survival and weight loss; (2) locomotor performance; (3) external (linear morphometry) and internal morphology, analyzing the total volume and visceral volume (stereology); and (4) the time of development after stress. We used tadpoles of two species, Leptodactylus fuscus (Leptodactylinae) and Physalaemus nattereri (Leiuperinae), both species breed in temporary ponds in areas with welldefined dry season therefore these species are subject to the same selective pressure. In addition, the two species show different reproductive modes, and may possess different degrees of resistance to water stress. To this end, the tadpoles were divided into two groups, those who stayed in 100 ml of water (control group) and those that were subjected to hydric stress (treatment group) for three time periods (12, 24 and 72 hours). Significant differences for weight loss were found between the groups (control/treatment) in both species, with the treatment group losing more weight in all stress levels. Furthermore almost half of P. nattereri tadpoles died within 36 hours of stress. There was no significant difference for locomotor performance and total volume between control group and treatment group of L. fuscus tadpoles, but morphometric analyses indicated a significant difference in the components related to tail and visceral volume, with the gut of the treatment group was lower than the control. In P. nattereri tadpoles, there were significant differences between the groups tested for locomotor performance, total volume, tail morphometry and visceral volume, with the stomach of the treatment group being greater than in the control group. Our results suggest that hydric stress has a significant effect on locomotion and morphology of P. nattereri tadpoles, but not in L. fuscus.