Latitudinal Variation in the Prevalence and Intensity of Chytrid (Batrachochytrium dendrobatidis) Infection in Eastern Australia

Abstract

Chytridiomycosis is a recently emerged, infectious skin disease of amphibians that has been linked directly to mass mortalities, population declines, and species extinctions worldwide. An understanding of the factors that limit the distribution and abundance of Batrachochytrium dendrobatidis (the etiological agent of chytridiomycosis) is urgently required. We conducted disease surveys at 31 lowland sites distributed north-south along 2315 km of the Australian east coast that encompassed 20.8 degrees of latitude. A total of 863 adult male stony creek frogs (Litoria lesueuri complex) were sampled, and the overall prevalence of B. dendrobatidis infection was 26%. B. dendrobatidis was detected at 77% of the sites, including sites at the northern and southern limits of the latitudinal transect. Frogs from temperate regions, however, had significantly more intense infections than did their tropical counterparts, often carrying an order of magnitude more B. dendrobatidis zoospores, suggesting that at low elevations, temperate frogs are at higher risk of chytridiomycosis-induced mortality than are tropical frogs. The prevalence and intensity of B. dendrobatidis infections were significantly greater at sites with high rainfall (>33 mm in the 30 days prior to sampling) and cool temperatures (stream temperature 1 h after sunset < 23 degrees C). Although climatic variables explained much of the variation in the prevalence and intensity of B. dendrobatidis infections between infected and uninfected sites, frog snout-vent length was consistently the best predictor of infection levels across infected sites. Small frogs were more likely to be infected and carried more intense infections than larger frogs, suggesting either that frogs can outgrow their chytrid infections or that the disease induces developmental stress that limits growth. Our results will directly assist amphibian disease researchers and wildlife managers, whose conservation efforts should focus on those amphibian populations living within the B. dendrobatidis climatic envelope that we have described.

Host size influences the effects of four isolates of an amphibian chytrid fungus

“…In amphibians, conditions in the larval environment, such as density of conspecifics, can determine size at metamorphosis; larger amphibian body size is associated with increased overwinter survival, earlier time to first reproduction, and increased fecundity (Berven, 1990; Earl & Whiteman, 2015; Semlitsch & Wilbur, 1988). For some amphibian species, the size of individuals has been linked to higher likelihood of Bd infection (Kriger, Pereoglou, & Hero, 2007; Searle et al., 2011) and survival after infection (Carey et al., 2006; Garner et al., 2009). Hosts of larger sizes may be more likely to be infected because of their increased ability to mount immune responses and survive.…”

DROUGHT REDUCES CHYTRID FUNGUS (BATRACHOCHYTRIUM DENDROBATIDIS) INFECTION INTENSITY AND MORTALITY BUT NOT PREVALENCE IN ADULT CRAWFISH FROGS (LITHOBATES AREOLATUS)

“…Variations in natural history, life history, behavioral, and immunologic traits among species can strongly affect the development and outcome of Bd infection (Voyles et al 2011). In addition, intraspecific variation in ecology (e.g., Puschendorf et al 2009), geography (e.g., Kriger et al 2007), and season (e.g., Lannoo et al 2011) can also influence infection prevalence, infection intensity, and host mortality. Batrachochytrium dendrobatidis infections are generally thought to be most intense in cool, humid habitats (e.g., Woodhams et al 2005) and in species that aggregate when threatened by dehydration (Longo et al 2010).…”

Lack of Evidence for the Drought-linked Chytridiomycosis Hypothesis

“…Indeed, bioclimatic modeling predicts that the fungus is more likely to inhabit wetter regions (Ron, 2005), and recent field studies confirm this prediction. Kriger et al (2007) found that both the prevalence and intensity of B. dendrobatidis infections in eastern Australia increase significantly in regions with high rainfall. Whereas chytrid infections were detected at all 17 sites that had received over 33 mm of rainfall in the 30 days prior to sampling, infections were detected at only half of the 14 sites that received less than 33 mm of rainfall.…”

“…Whereas chytrid infections were detected at all 17 sites that had received over 33 mm of rainfall in the 30 days prior to sampling, infections were detected at only half of the 14 sites that received less than 33 mm of rainfall. Kriger and Hero (2007a) demonstrated that B. dendrobatidis is largely restricted to wet microhabitats. Whereas 38.8% of 402 frogs breeding in permanent water bodies were infected with B. dendrobatidis, only one of 117 frogs breeding in ephemeral water bodies or in leaf litter was infected.…”

“…Infection prevalence in their study was significantly lower in 2001 than in 2000, and though daily mean temperatures did not differ significantly between the 2 yr, 11 of the 12 mo in 2001 were drier than their corresponding month in 2000. Finally, droughts often coincide with higher-than-average temperatures, and it is widely recognized that high temperatures are unfavorable to the growth and development of B. dendrobatidis (Piotrowski et al, 2004;Kriger and Hero, 2007b;Kriger et al, 2007).…”