Rapid decline and extinction of a montane frog population in southern Australia follows detection of the amphibian pathogen Batrachochytrium dendrobatidis

The amphibian pathogen Batrachochytrium dendrobatidis (Bd) has been implicated as a leading agent of amphibian declines. However, few studies have documented the real-time host/pathogen dynamics during the arrival of Bd and the decline of an amphibian population. Diagnosing population declines is difficult because multiple factors may be involved and data are often inadequate. However, identifying the relative impact among different threatening processes is critical to understanding population declines. We report the decline and extinction of a population of a threatened temperate montane frog species Litoria spenceri in south-eastern Australia. Unlike most threatened species at the time, its ecology and population demography were well understood, and a monitoring programme was in place, enabling prompt detection of the decline and evaluation of its cause. Histology for Bd on a unique series of phalange samples showed that the decline was strongly linked to the arrival and increased prevalence of Bd, estimated to have emerged in the population within 39 days of first detection. Our study provides the first real-time observation of a mass die-off and decline in a temperate Australian species and the first tight estimate of Bd arrival in a declining population in Australia. These findings not only provide further evidence that Bd has contributed to amphibian declines but also demonstrates how Bd may work in concert with other threatening processes, resulting in extinction