Effects of Salinity and Pesticide on Sperm Activity and Oviposition Site Selection in Green Treefrogs, Hyla cinerea

Increasing salinity in freshwater habitats is an emerging threat in both coastal and inland environments. In addition, pesticides can be harmful to aquatic organisms and have been detected worldwide in aquatic systems. Both of these changes can strongly affect amphibians, as they typically rely on aquatic environments. With external fertilization, the selection of an oviposition site can be crucial for ensuring fertilization success and for providing offspring with a hospitable environment for development. We examined the effects of increased salinity and a commonly applied insecticide, carbaryl, on sperm activity and oviposition site selection of the Green Treefrog (Hyla cinerea). Sperm motility and velocity both decreased as salinity concentration increased but showed no effect of carbaryl at concentrations at and above those expected in the environment. Artificial pools with weakly brackish water received less oviposition than did freshwater pools. Carbaryl also inhibited oviposition, but only when pools had been freshly dosed. These findings suggest that increased salinity may negatively affect reproductive success in H. cinerea through its effect on sperm function, but that individuals may be able to avoid these costs by selectively ovipositing in freshwater. Although carbaryl did not influence two measures of sperm movement, selective oviposition may help adults to avoid habitats that could be harmful to their developing offspring. Thus, selective oviposition may increase the ability of amphibian populations to persist in degraded habitats, as long as some suitable sites are still available.