Behaviour of Australian rainforest stream frogs may affect the transmission of chytridiomycosis

Abstract

The amphibian disease chytridiomycosis, caused by the pathogen Batrachochytrium dendrobatidis, has been implicated in mass mortalities, population declines and extinctions of amphibians around the world. In almost all cases, amphibian species that have disappeared or declined due to chytridiomycosis coexist with non-declining species. One reason why some species decline from chytridiomycosis and others do not may be interspecific differences in behaviour. Host behaviour could either facilitate or hinder pathogen transmission, and transmission rates in the field are likely to vary among species according the frequency of factors such as physical contact between frogs, contact with infected water and contact with environmental substrates containing B. dendrobatidis. We tracked 117 frogs (28 Litoria nannotis, 27 L. genimaculata and 62 L. lesueuri) at 5 sites where B. dendrobatidis is endemic in the rainforest of tropical northern Queensland and recorded the frequency of frog-to-frog contact and the frequency of contact with stream water and environmental substrates. Frequency of contact with other frogs and with water were highest in L. nannotis, intermediate in L. genimaculata and lowest in L. lesueueri. Environmental substrate use also differed among species. These species-specific opportunities for disease transmission were correlated with conservation status: L. nannotis is the species most susceptible to chytridiomycosis-related declines and L. lesueuri is the least susceptible. Interspecific variation in transmission probability may, therefore, play a large role in determining why chytridiomycosis drives some populations to extinction and not others.

Batrachochytriumdendrobatidisinfection patterns among Panamanian amphibian species, habitats and elevations during epizootic and enzootic stages

“…Woodhams et al 2006), population connectivity (e.g. Robertson et al 2008), or behavior (Rowley & Alford 2007). Pool species tend to be generalists with broad geographic and elevational ranges, traits that have been associated with high mobility, and with immune systems adapted to deal with a wider range of pathogens (Altizer et al 2003 Haydon et al 2002).…”

“…Stable or coevolved host -pathogen systems typically involve enzootic pathogens, which are characterized by generally avirulent infections or a very low number of new infections per unit time (incidence), and a relatively constant proportion of infected individuals (prevalence). With enzootic pathogens, host extinction risk can be minimized in several ways: density of infected hosts is generally low, infection may be avirulent, hosts may have immunity or resistance (Swinton et al 2002), host behavior may reduce exposure to disease (Rowley & Alford 2007), or the pathogen may have low transmissibility (Anderson & May 1992).…”

Host species determines whether infection load increases beyond disease‐causing thresholds following exposure to the amphibian chytrid fungus

“…Batrachochytrium dendrobatidis has a broad host range but does not cause disease or death in every species that it infects. The survival rate of individuals exposed to B. dendrobatidis differ with host species (Parker et al, 2002;Davidson et al, 2003;Daszak, 2004;Blaustein et al, 2005;Woodhams et al, 2007) and lifehistory stage at exposure (Lamirande & Nichols, 2002;Carey et al, 2006) and research has focused on identifying the host traits causing these differences (Rollins-Smith et al, 2002b;Harris et al, 2006;Rowley & Alford, 2007;Woodhams et al, 2007). However, the effects of host species and life stage on the steps leading from exposure to disease have not been investigated.…”

Canopy cover and drought influence the landscape epidemiology of an amphibian chytrid fungus

“…Infection intensity, or Bd load, is the number of Bd zoospores on an individual. Interspecific variation in infection prevalence and intensity of Bd has been attributed to differences in behavior and life-history traits (Rowley andAlford 2007, Bancroft et al 2011). For instance, amphibians that are mostly aquatic tend to have higher Bd prevalence than more terrestrial species (Pearl et al 2007).…”