The Blind Toads of Paradise
September 1, 2014
The local history says that a century ago a priest brought the Cururu toad Rhinella jimi to eat insects on the archipelago of Fernando de Naronha (FN) which is located about 200 miles off of the northeast coast of Brazil. In 2014, the toad is easily found around houses or even sleeping in the sand on beaches.
At San Diego Zoo Global, our interests are in preventing extinction of species, so at first glance studying the Cururu toad wouldn’t seem a likely subject for a Field Postdoctoral Fellowship. However, there are signs of trouble in paradise and what we learn from the toads of FN has the potential to help preserve an important island ecosystem.
In 2008, amphibian biologist Felipe Toledo from the University of Campinas, Brazil first noticed the abnormal Cururu toads on FN. In fact, almost half of the toads he encountered had some kind of malformation. Most commonly toads had short or missing toes, but many others had small or even missing eyes. Some toads were completely blind. The high percentage of malformed toads far exceeded the rates seen in amphibian populations in other parts of the world making FN a malformed amphibian “hot spot.”
Later, more detailed examination of the toads in our laboratory at the University of São Paulo revealed not just malformations, also but infectious diseases such as mycobacteriosis.
These findings were certainly unexpected for one of the world’s most beautiful and admired islands. FN is listed as a UNESCO World Heritage site because of its important marine environment that hosts the last remaining examples of insular Atlantic forest and oceanic mangrove habitat in the south Atlantic region.
Furthermore, the island is home to the largest concentration of tropical seabirds in the western Atlantic Ocean, myriad endangered sea turtles, and a large resident population of spinner dolphins, among many others. The juxtaposition of great natural beauty with striking malformations and disease begs for further investigation.
We’ve recently returned to FN to begin studies to determine why there are so many sick and malformed Cururu toads on this little piece of paradise. The first task is a thorough survey of toads from different locations on the island. The malformations will be carefully documented and biological samples collected for genetic testing and disease diagnosis.
In addition, we’ll collect environmental samples like water and soil to test for contaminants. Later, we’ll be able to combine all of this information with epidemiologic methods to compare different sites and hopefully, determine some likely risk factors contributing to problems in this species.
In future blogs we will keep you informed on the progress of the investigation. Potential causes of malformations could include inbreeding, predation, exposure to UV-B radiation and chemical contaminants. Diseases like mycobacteriosis are very rare in wild amphibians, but they have been observed in populations of marine fish that inhabit disturbed environments. If environmental factors are contributing to problems in Cururu toads it is likely that the same factors could eventually affect the endangered wildlife and unique habitats of FN.
By following the FN toads as an early warning system there is hope for saving paradise.
Catia DeJuste de Paula, D.M.V., Ph.D.
Wildlife Veterinarian and ICR Postdoctoral Associate
Allan Pessier, D.V.M., Dipl. A.C.V.P.
Wildlife Disease Laboratories