Abstract
Enigmatic amphibian declines were first reported in southern and southeastern Brazil in the late 1980s and included several species of stream-dwelling anurans (families Hylodidae and Cycloramphidae). At that time, we were unaware of the amphibian-killing fungus Batrachochytrium dendrobatidis (Bd); therefore, pollution, habitat loss, fragmentation and unusual climatic events were hypothesized as primary causes of these declines. We now know that multiple lineages of Bd have infected amphibians of the Brazilian Atlantic forest for over a century, yet declines have not been associated specifically with Bd outbreaks. Because stream-dwelling anurans occupy an environmental hotspot ideal for disease transmission, we investigated temporal variation in population and infection dynamics of three stream-adapted species (Hylodes asper, H. phyllodes, and Cycloramphus boraceiensis) on the northern coast of São Paulo state, Brazil. We surveyed standardized transects along streams for four years, and show that fluctuations in the number of frogs correlate with specific climatic variables that also increase the likelihood of Bd infections. In addition, we found that Bd infection probability in C. boraceiensis, a nocturnal species, was significantly higher than in Hylodes spp., which are diurnal, suggesting that the nocturnal activity may either facilitate Bd zoospore transmission or increase susceptibility of hosts. Our findings indicate that, despite long-term persistence of Bd in Brazil, some hosts persist with seasonally variable infections, and thus future persistence in the face of climate change will depend on the relative effect of those changes on frog recruitment and pathogen proliferation.
Highlights
Enigmatic amphibian declines were first reported in Brazil in the late 1980s and were attributed to unusual climatic events, pollution, habitat loss, and fragmentation [1,2,3,4]
In this study we investigated population dynamics and seasonal changes in Batrachochytrium dendrobatidis (Bd) prevalence in three species of stream-dwelling frogs in the Cycloramphidae and Hylodidae families (Hylodes asper, H. phyllodes, and Cycloramphus boraceiensis) on the northern coast of São Paulo state, southeastern Brazil
Understanding the effects of pathogens on wildlife requires long-term datasets to identify potential changes in natural population dynamics [37,38]
Summary
Enigmatic amphibian declines were first reported in Brazil in the late 1980s and were attributed to unusual climatic events, pollution, habitat loss, and fragmentation [1,2,3,4]. Reported declines included populations of obligate stream-dwelling frogs in the genera Hylodes, Crossodactylus (Hylodidae), and Cycloramphus (Cycloramphidae) throughout the mountainous regions of the Atlantic coastal forest of southern and southeastern Brazil [1,2,3]. The pathogenic chytrid fungus Batrachochytrium dendrobatidis (hereafter Bd) has been implicated in declines of wild amphibian populations worldwide [5,6,7,8], including in pristine areas with high natural vegetation cover [9]. Atlantic forest anurans have experienced long-term co-existence with this pathogen, which might explain high infection tolerance in many current anuran populations [19,20]
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