Lethal and Sublethal Effects of Salinity on Three Common Texas Amphibians

Abstract

Amphibian populations worldwide are experiencing declines and contaminants are hypothesized to be one of the leading contributors to these declines. In particular, the salinization of amphibian habitats is a global issue that has received relatively little attention. Of the recent studies that have emerged, the majority focus on single-species responses, and because these studies often vary in methodology, assessing tolerances across species can be challenging. Thus, one step toward a broader understanding of salt loading is to assess tolerances across multiple species using similar methodologies. Additionally, in nature, amphibians can face low, sublethal concentrations of increased salinity. Though not lethal, these low concentrations can have long-term impacts on amphibian traits such as mass or their responses to future stressors. To address these issues, we first compared relative salinity tolerances of three common frogs in central Texas (Incilius nebulifer, Gulf Coast Toad; Lithobates berlandieri, Rio Grande Leopard Frog; and Acris crepitans, Blanchard's Cricket Frogs). Next, we explored the effect of sublethal salinities on the mass of I. nebulifer. Finally, we investigated the potential for sublethal salinities to increase tolerance of I. nebulifer to a later exposure of lethal salinity concentrations (acclimation). We found that across the three amphibian species, A. crepitans tadpoles were the most tolerant, followed by L. berlandieri tadpoles, and then I. nebulifer tadpoles. Sublethal concentrations of salinity did not affect mass of I. nebulifer tadpoles. Finally, exposure to sublethal levels of salinity did not increase tolerance of I. nebulifer tadpoles to a later exposure of higher salinity concentrations. Instead, tadpoles exposed to sublethal concentrations of salinity died at a faster rate when exposed later to a higher salinity concentration. With the increasing potential for salt loading to amphibian habitats due to anthropogenic influences and global climate change, understanding the consequences of salinity across multiple species as well as the effects of sublethal concentrations has important implications for amphibian conservation.