Differences in susceptibility of various life stages of amphibians to pesticide exposure.

Pesticide exposure is discussed as one of the adverse factor that causes impairment of amphibian larval development. Susceptibility of tadpoles to pesticide exposure differs depending on the developmental stages at which individuals are contaminated. This study focused on the influence of the pyrethroid insecticide cypermethrin on the hatching success, mortality and deformities in further development, duration of metamorphosis, and growth of Rana arvalis tadpoles exposed at various life stages. Eggs were harmed significantly by exposure to different concentrations of alpha-cypermethrin dependent on exposure time. Amphibian embryos hatched with apparent abnormalities indicate insufficient protection by the jelly coat surrounding the embryo. Exposed individuals exhibited typical signs of cyano pyrethroid poisoning (twisting, writhing, abnormal swimming). During the life-stage treatments the observed morphological deformities and behavioral abnormalities lead mostly to death of the tadpoles in later development. Individuals exposed to alpha-cypermethrin in early life stages (as eggs or newly hatched tadpoles) metamorphosed earlier than in the corresponding control. However, exposure of the tadpoles throughout their whole development prolonged the metamorphosis. These metamorphs were distinguished by a much more compact physique (significant reduction in length and significant increase in weight compared to the corresponding control) so as to resist the adverse conditions. Observed effects of alpha-cypermethrin exposure on various life stages of R. arvalis tadpoles refer to the danger potential of this insecticide for amphibian development. Any kind of deformation influences the physiological fitness of the individuals (e.g. increased vulnerability to predation). Diminished hatching success, delays in metamorphosis and body growth impact negatively on the viability of amphibian populations in the long term. In combination with other anthropogenic influences (destruction or dissipation of habitats), these effects can cause the local extinction of amphibian species.