Chytridiomycosis in Woodhouse's Toad(Anaxyrus woodhousii) in Colorado

摘要

As scientists in the 1990s became aware that amphibian popu-lations were experiencing population declines on a number ofcontinents, the most perplexing mortalities were those observedin relatively pristine environments in which man-made habitatdestruction, introduction of invasive species, or direct applicationof toxicants were not evident. Mass mortalities of amphibians inthese relatively untouched environments, such as wilderness areasof the American West and tropical rainforests in Australia andCentral America, shared a number of similarities that suggested acommon proximate cause. These similarities were: 1) mass mor-talities were observed principally in metamorphosed amphibians;2) populations experienced severe declines in size, and, in somecases, total extinction; 3) only some of the amphibian species ina given locality experienced declines; and 4) population declineswere more pronounced at higher elevations or in cooler regions thanin lower/warmer areas (Lips 1998; Carey et al. 1999). Many of themass mortalities sharing this pattern have now been attributed to achytrid fungal pathogen, Batrachochytrium dendrobatidis (hereaf-ter Bd; Berger et al. 1998; Skerratt et al. 2007). The observationsthat Bd is more likely associated with mass mortalities of amphib-ians at higher elevations in mountain ranges than in the adjacentlowlands have been replicated on several continents. For instance,numerous mass mortalities have been noted above approximately400 m in Costa Rica and Panama (Lips 1998; Lips 1999; Young etal. 2001) but, even though Bd has been documented histologicallyon a number of species living at lower elevations in these countries,no mass mortalities have been observed (Puschendorf et al. 2006).Die-offs are most pronounced at elevations over 400 m in Australia(McDonald and Alford 1999 and above ca. 2000 m in Spain (Boschet al. 2001; Bosch and Martinez-Solano 2006).