Fungal pathogen causes competitive and developmental stress in larval amphibian communities


Ecologists increasingly recognize pathogens as playing significant roles in community dynamics, yet few experimental studies have documented patterns of disease impacts on natural systems. We studied the effects of a pathogenic fungus (Batrachochytrium dendrobatidis) on community interactions between two sympatric North American anurans: Fowler's toad, Bufo fowleri, and the gray treefrog, Hyla chrysoscelis. Recent studies have identified chytridiomycosis as an emerging infectious disease, whose widespread occurrence poses a significant risk for amphibian populations. We manipulated the presence of B. dendrobatidis in replicated experimental tanks and examined if exposure to this fungus during development could influence recruitment and competitive interactions between larval Bufo and Hyla. Tanks were followed throughout larval development, and we recorded survival, time to metamorphosis, and body mass at metamorphosis. We also tested the effects of competitive and pathogen-mediated stress on developmental stability by measuring fluctuating asymmetry (FA) of surviving metamorphs. B. dendrobatidis had no significant effect on larval survival, but the pathogen reduced metamorphic body mass and increased larval-period length. B. dendrobatidis had different effects on larval growth depending on the community structure; in the presence of the pathogen, both Bufo and Hyla metamorphosed at smaller body masses when reared together compared to when reared separately. Bufo also had strong negative effects on Hyla development, but only in the presence of B. dendrobatidis. FA of hind-limb length was significantly higher for metamorphs from pathogen tanks, but was not associated with density or competitive environment. Our results suggest that chytridiomycosis may impact Bufo and Hyla directly by reducing life-history performance and increasing developmental instability, and indirectly by inducing interspecific competitive effects in mixed-species environments.

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