Dynamics of chytridiomycosis in a Tasmanian frog community

Most previous studies of the prevalence of chytridiomycosis (Batrachochytrium dendrobatidis, Bd) in wild frog populations in Australia have been in tropical or subtropical environments, in areas with predominantly summer rainfall (Kriger and Hero 2007; Kriger et al. 2007; McDonald et al. 2005). As Tasmania is both more temperate and does not have a summer-dominated rainfall pattern, seasonal patterns in prevalence in Tasmania may not be the same as in other parts of Australia. In tropical and subtropical areas of Australia, Bd prevalence and clinical disease are both higher in the colder and drier winter months (Berger et al. 2004; Kriger and Hero 2006; Retallick et al. 2004). In a broad-scale latitudinal study of chytridiomycosis in the Litoria lesueuri complex in eastern Australia, Kriger el al. (2007) found that prevalence and intensity of Bd infection increased with latitude, with an order of magnitude increase in the intensity of infection (as measured by zoospore equivalents) from 17° to 37°C. This latitudinal variation appeared to be related to a negative association between infection intensity and temperature in the warmest quarter of the year and a positive association between infection intensity and rainfall in the driest quarter. They suggested that temperate frog populations might therefore be particularly susceptible to chytridiomycosis, especially as substantial population declines have occurred in at least 11 frog species in south-east Australia (Hero et al. 2006). However, the highest latitude they examined was 37.26°S, close to the Victoria-New South Wales border, which is still in a region of predominantly summer rainfall