The impact of salinity on early developmental stages in two sympatric spadefoot toads and implications for amphibian conservation in coastal areas

Abstract

Salinity tolerance is critical during the early ontogeny of amphibians, shaping future population size, health and dispersal in a certain area. We focused our research on two related anurans with similar ecological niches—Pelobates fuscus and P. syriacus—inhabiting the western Black Sea coast, at the limits of their ranges. We hypothesize that their differences in salinity tolerance are shaping the actual range limits in coastal areas, within the sympatry zone. We quantified experimentally the impact of salinity (range 0–9‰) during early ontogeny to ask if salinity can modulate their coexistence, by affecting differently reproductive success and fitness. Exposure to salinity from egg to developmental stage Gosner 25 caused mild to severe malformations and affected survival and size in both species, but the impact was lower in P. syriacus compared to P. fuscus when exposed to salt concentrations of 6‰. Embryos of either species did not survive the 9‰ salinity concentration. We expect that increases in salinization up to 6‰ could severely reduce the range of P. fuscus, but not P. syriacus, in coastal areas. These results are highly relevant for the conservation of P. fuscus, which is already declining across Europe.