Larval Adaptation to Salinity Shock in Cane Toads (Rhinella marina) From Coastal French Guiana

Many habitats not only differ in mean conditions but also in the degree to which these conditions fluctuate through time. Therefore, local adaptation to both mean abiotic conditions and habitat variability can enhance organismal viability. Within their native range in French Guiana, cane toads (Rhinella marina) inhabit both coastal beach and inland rainforest habitats. We surveyed breeding pools to quantify abiotic conditions. Breeding pools in coastal habitats exhibited high salinity levels and intermittent seawater inflow with rapid increases in salinity. Breeding pools in inland habitats had low, stable salinity levels. Salinity shock only caused mortality within coastal environments. To determine whether larvae were locally adapted to salinity conditions, we raised the offspring of toads collected from 14 inland and coastal sites under a range of salinity levels. We also mimicked seawater inflow by exposing larvae from 15 clutches to sudden increases in salinity to measure their tolerance to salinity shock. Although coastal and inland tadpoles performed similarly under constant salinity, tadpoles from coastal habitats survived a rapid increase in salinity better than did conspecifics from inland habitats. The capacity to tolerate variable environments and adapt to local conditions may have contributed to the cane toad's translocation success.