Interações entre estressores naturais e etinilestradiol no desenvolvimento larval de Physalaemus cuvieri (Anura: leiuperidae)

Abstract

There are amphibian populations declining in many parts of the world, due to environmental changes caused by humans. The aquatic contamination by endocrine disruptors, which act by interfering with the physiology of animals and alter the functions of the endocrine system may be one factor that is contributing to this decline. Among the disruptors, hormones pose a danger because it can act during larval development of amphibians, a critical period for survival and reproductive success of individuals. This risk may increase if there are interactions of the hormone with the stressors that maintain the natural balance of populations. The objective of this study was to assess the effects of contamination by the hormone 17α- ethinylestradiol and its interaction with natural stressors in tadpoles, using as model the specie Physalaemus cuvieri. For this, a factorial experiment was set up to evaluate the effects of ethinylestradiol in different concentrations (0, 0.005 or 2.5 µg/L) and their interactions with density (high or low) and predator (present or absent). To evaluate the effects of treatments were used, as response variables, survival to metamorphosis, survival of tadpoles not metamorphosed, malformations, size at metamorphosis, development time and sex ratio. It has been found to decrease survival in the higher concentration and at high density, being more evident in the first 30 days, indicating an acute effect of hormone and stress caused by a higher density. Most of the tadpoles that completed metamorphosis were exposed to concentrations of 0 and 0.005 µg/L on treatments with low density and absence of the predator, which reflects the action of ethinylestradiol at a concentration of 2.5 µg/L and at high density. Individuals were found with malformations (mainly located in the limbs), which have a higher occurrence in the treatments exposed to 0.005 µg/L of ethinylestradiol and low density, which is connected can lower rates of survival and selection of stronger individuals in treatments with higher concentration and density, and a possible chronic effect on the tadpoles exposed to lower concentration. There is the hypothesis that ethinylestradiol acts on the hormonal mechanisms regulating the metamorphosis by inhibiting the thyroid, which could explain the slower development of tadpoles in treatments with 0.005 and 2.5 µg/L and the predator, that can also decrease the metabolism of tadpoles. The size at metamorphosis was higher in treatments in the presence of 2.5 µg/L and predator, a fact associated to increased development time and possible stimulation of Prolactin and Growth Hormone by ethinylestradiol. There was no change in sex ratio of the treatments exposed to ethinylestradiol, when compared to control. This study indicates that exposure of tadpoles P. cuvieri to the estrogen 17α-ethinylestradiol together with stressors in natural communities, alters the normal development of different forms.