Long-term salinity exposure reveals site-specific physiological and behavioral responses in coastal and inland toads.

Salinization is a global phenomenon affecting many coastal and inland water bodies at unprecedented rates, and having multiple consequences for wildlife, mostly due to the high metabolic cost of osmoregulation. Most research on salinity effects has focused on juvenile life stages and short-term exposures. In this study, we evaluated the impact of chronic exposure (7 months) to environmental salinity (0, 2 or 4 g.l-1) in adult individuals of a widespread amphibian species, the spined toad (Bufo spinosus), originating either from coastal (salt-exposed) or inland (naïve to salinity) environments. Coastal and inland individuals, irrespective of exposure to salinity, differed post-exposure in telomeres length, cutaneous permeability, defensiveness and foraging behaviors, but unexpectedly not in triiodothyronine and testosterone levels, and mass-specific metabolic rates. As pre-exposure data were unavailable for some of these traits (metaolic rate, cutaneous permeability, and behavior), these differences may reflect either intrinsic population-level variation or population-specific responses to treatment. Coastal individuals exhibited compensatory growth in freshwater, suggesting differential energy allocation. Chronic exposure to moderate salinity increased osmolality and triiodothyronine levels while reducing growth and preferred temperature. Interestingly, defensiveness and thermal preference were more affected by exposure to salinity in coastal individuals. Despite their saline environment, they also showed higher cutaneous evaporative water loss, potentially facilitating water uptake to counter salinity stress. Our study demonstrates that salinization can have negative effects on critical traits of adult anurans, and emphasizes the importance to increase research effort on the impact of salinity on wildlife including both experimental and long-term field studies.