Deformities in cane toad (Bufo marinus) populations in Bermuda: Part I. Frequencies and distribution of abnormalities

Abstract

Observations of abnormal adult cane toads ( Bufo marinus ) in Bermuda in 1998 prompted surveys of the island's mature and newly metamorphosed populations from 1999 to 2003. External examinations revealed eye and facial abnormalities, spinal and pelvic abnormalities, and a variety of limb malformations. Malformed toads were found in all nine of Bermuda's parishes and the incidence rate was high in both age classes. The annual abnormality frequencies were 19-30% for adults and juveniles, and 16-24% for metamorphs. Annual metamorph abnormality rates at particular ponds were as high as 58%, and abnormality rates for particular cohorts were as high as 81%. The frequency of hind limb abnormalities was significantly greater than that of forelimb abnormalities in both age classes. Most eye and limb abnormalities were unilateral. The most common limb malformation was brachydactyly, and few cutaneous fusions or examples of polymely were observed. Breeding sites that were natural or artificial ponds in parks or nature reserves, or lined ponds on golf courses, had significantly higher abnormality frequencies than lined or cement ponds in backyard settings. No encysted Ribeiroia metacercariae were found in 80 malformed metamorphs collected from four sites with high abnormality rates, suggesting that these parasites were not responsible for the malformations observed. Frog embryo teratogenesis assays demonstrated that water and sediment extracts from the same four breeding sites induced severe developmental malformations in B. marinus and three other amphibian species. These data suggested that many B. marinus breeding sites in Bermuda are potentially contaminated with developmental toxicants.