Tadpoles select ivermectin-free substrates

LÓPEZ, JAVIER A.; GHIRARDI, ROMINA; GUTIÉRREZ, MARÍA F.; ANTONIAZZI, CAROLINA E.; LIFSCHITZ, ADRIÁN; MESA, LETICIA M.

South American Journal of Herpetology

Sociedade Brasileira de Herpetologia

Año: 2022 vol. 25 p. 88 - 93

1808-9798

Ivermectin (IVM) is an antiparasitic widely used in veterinary medicine around the world, and cattle injection with IVM is a common practice in wetlands of the Middle Paraná River. Approximately 45% of administered IVM is eliminated in livestock feces. Immediately after injection, cattle enter wetland for feeding and drinking, incorporating feces with IVM into aquatic systems, where it accumulates in the substrate, especially in sediments rich in organic matter. Thus, our objective was to experimentally assess the habitat selection of nektonic (Boana pulchella) and benthic (Physalaemus albonotatus) tadpoles between patches of substrate with and without IVM. The experimental units consisted of quadrangular plastic trays with the bottom divided into four internal quadrants, two filled to 1 cm depth with IVM-free substrate and the other two with substrate containing IVM (nominal IVM concentrations were 3000 ng/g substrate fresh weight), filled to 3 cm depth with water. We placed one tadpole in the center of each tray (B. pulchella: n = 22; P. albonotatus: n = 50) and visually recorded its position (IVM-free or IVM quadrants) every 1 h during the first 10 h, with a final observation at 24 h. The recovery concentration of IVM in the IVM quadrant substrate was 73.95% (percentage of target concentration) and was not detectable in the IVM-free quadrant. The frequency of observations of tadpoles was significantly higher in IVM-free quadrants than in IVM quadrants (B. pulchella: 57%; P. albonotatus: 58%), and this pattern did not differ between nektonic and benthic tadpoles. Thus, tadpoles of both species selected the quadrants free of IVM. The response of tadpoles to IVM merits investigation in a wider spectrum of species and different concentrations to better understand the effects of this emergent pollutant on amphibians.