Holdridge's toad

Species of amphibian

Holdridge's toad (Incilius holdridgei), formerly Bufo holdridgei, is a species of toad endemic to Costa Rica. In October 2008, it was declared extinct by the International Union for Conservation of Nature in its Red List since the species had not been seen since 1987, despite years of extensive searches. However, the species was rediscovered in 2010 by a Costa Rican herpetologist and is now classified as critically endangered.

Originally found on Barva Volcano in Cordillera Central, Costa Rica, the Holdridge's toad is still endemic to that particular small area of Costa Rica's rainforests. It is named after the research scientist Holdridge for its discovery. It can be distinguished in classification from other toads by its morphological differences. For example, Incilius holdridgei differs from Incilius fastidiosus because of the different cranial crests and from Incilius peripetates due to the different sizes at the adult age. Incilius holdridgei tadpoles are small in size with ovoid shaped bodies that are dark brown in color and feature a lighter venter surface. The tail and caudal fins are rounded. The mouth is directed ventrally and the oral disc has beaks and 2 to 3 rows of denticles which are bordered by a row of large papillae. Since 1987, the species has declined in numbers and currently exists in a critically endangered state. It acquired this title because it produced eggs in forest floor pools. This species is known to reproduce in big collections in pools in open pastures. The main threat to Holdridge's toad is thought to be chytridiomycosis, a fungal pathogen, Batrachochytrium dendrobatidis, that causes an infections disease in amphibians. The fungus keratinizes any keratin containing skin layers in both the tadpoles and adult frogs. High levels of this fungus were detected in the breeding grounds of Holdridge's toad before and after the species appeared to vanish. Juveniles were found, indicating relatively recent reproductive activity, but no large aggregations were seen; this species should be considered Critically Endangered. The entire known range of Incilius holdridgei falls within a protected area: Parque Nacional Braulio Carrillo. However, breeding ponds in Alto El Roble are near the main road and may be under threat from increasing tourism.

The toad was added to the Red List of Endangered Species in 2006. Much of the known range of this species is protected in Parque Nacional Braulio Carrillo, 20 km north east of the capital of San José. The two sites where the species is known to persist in 2010 are located in the Cerro Dantos and Jaguarundi Refuges, neither of which has the same protection status as a national park. Even with the lower protection status, the forest cover of these refuges remains intact and seemingly not threatened. Although one might think that the population of Incilius holdridgei is
recovering, information on the only known populations is still very limited; there needs to be more research on the population dynamics, environmental factors of the breeding sites, population health and genetics. It is believed that the major cause of the toad's decrease in population is chytridiomycosis, an infectious disease that affects amphibians caused by the chytrid fungus. The increase of the chytrid fungus has been connected to global warming.