Evidence of a Chytrid fungus infection involved in the decline of the common midwife toad in protected areas of Central Spain

Jaime Bosch

Iñigo Martínez-Solano and Mario García-París Museo Nacional de Ciencias Naturales, CSIC, c/ José Gutierrez Abascal 2 28006 Madrid, Spain

Jaime Bosch: bosch@mncn.csic.es

During the summers of 1997, 1998 and 1999 mass mortality episodes of post-metamorphic Alytes obstetricans occurred in Peñalara Natural Park. The park is an alpine area at about 2000 meters of elevation that has been protected for 70 years. Since the Park is very close to the city of Madrid, every year more than 100,000 visitors come here. A. obstetricans was one of the most common species in the past, keeping high larval densities in several ponds in the Park.

The population that suffered a sharp decline: tadpoles have disappeared from 97% of the ponds which were used by this species, and the lack of direct or indirect observations of adults suggest that just some individuals may remain alive. Scanning electron microscopy and histological techniques support chytridiomycosis as the most plausible cause of the decline of the species in the area. This is the first report of an amphibian decline caused by chytridium in Europe. Two mutually exclusive hypotheses are plausible in this case: environmental changes that can increase sensitivity of the host to parasites or produce fungus blooms, and a recent accidental introduction of the pathogen in the area. A pH increase in some ponds of the Park was detected in a limnological study performed in the summer of 1998 that supports the former. While evidence of amphibian species introductions in both relatively old and recent episodes in the Park support the latter, although the disease may have been carried by humans.