Rapid Emergence of an Amphibian Pathogen Coincided With Historic Amphibian Declines in the Neotropics

Abstract

Aim

The emergence of the fungal pathogen Batrachochytrium dendrobatidis (Bd) in South America has been attributed to multiple introductions and subsequent spread in a bidirectional latitudinal wave along the primary Andean cordilleras. This is supported for Ecuador by anecdotal evidence of declines in Bd-susceptible genera such as Telmatobius and Atelopus around the mid-1980s. We tested this hypothesis by combining published records of Bd with retrospective screenings of museum specimens (1950–2010) and surveys of contemporary populations to characterise the spatiotemporal and host-specific emergence of Bd in Ecuador.

Location

Ecuador.

Methods

We assembled a database of Bd records in Ecuadorian anurans (> 7000 samples) and assessed its spatiotemporal emergence using generalised linear mixed models and spatial clustering approaches. Data were also used to identify Bd prevalence within four representative genera of Ecuadorian anurans (Atelopus, Telmatobius, Gastrotheca and Pristimantis). We also used Bayesian approaches to test the probability of the presence of Bd in Ecuador prior to the first positive record.

Results

Our results overturn the prevailing narrative of Bd emergence in the Neotropics and provide a rare, long-term view of an invasive pathogen's trajectory from introduction to persistence. We found that: (1) Bd likely represents a novel pathogen to Ecuador; (2) Bd was first detected in 1974 and had become widespread by 1980; (3) there is no evidence supporting a bidirectional wave of spread; and (4) the genera Atelopus, Telmatobius and Gastrotheca experienced epizootic disease dynamics, with declines peaking in the 1990s.

Main Conclusions

We found that Bd is likely a novel pathogen that was introduced in the early 1970s and peaked in prevalence during the late 1980s and 1990s. The available evidence supports the conclusion that an outbreak of chytridiomycosis may have led to catastrophic declines in Ecuadorian amphibians. Disease dynamics have since subsided to enzootic coexistence in extant amphibian communities.