Effects of Salinity on Early Life Stages of the Gulf Coast Toad, Incilius nebulifer (Anura: Bufonidae)

Abstract

Anuran amphibian populations worldwide are in decline due to a variety of factors including habitat destruction, climate change, disease, introduction of non-native species, and environmental contamination. We conducted a laboratory trial with Incilius nebulifer (synonym: Bufo nebulifer) to determine at what level salinity negatively affects hatching and metamorphosis, and how exposure to salinity during development affects metamorph characteristics that influence adult fitness. Embryos exhibited 95.5–99.5% hatching success at salinities of 0, 2, and 4 parts per thousand (ppt); 74.4% success at 6 ppt; and no hatching at 8 or 10 ppt. Salinity affected hatching success and larval survival, and we found linear trends between higher salinity and lower fractions of hatched embryos and living larvae. The odds of hatching were about the same for 0, 2, and 4 ppt, significantly lower for 6 ppt, and zero for 8 and 10 ppt. The odds of survival to metamorphosis were significantly lower in 6 ppt relative to 0, 2, and 4 ppt combined. Time to metamorphosis, mass, and hind limb length of recent metamorphs showed significant differences among treatment groups, with salinity having large effects on these variables. Development time was longer, mass was lower, and hind limb length was shorter in the 0 and 2 ppt treatments compared to 4 or 6 ppt. We showed that salinity affected the survival of early life stages of Incilius nebulifer and characteristics that have been linked to adult fitness. Our study suggests that low levels of salinity may affect the survival and fitness of other anurans.