Is the Chytrid Fungus Really Responsible for Amphibian Decline

Besides other pathogens, the chytrid fungus Batrachochytrium dendrobatidis has been considered the main etiologic agent that causes chytridiomycosis and associated with amphibian die-offs. Chytrid fungus was first described in a living specimen of a Physalaemus signifer population (Anura, Leiuperidae), a common frog in natural environment in Rio de Janeiro, Brazil. The P. signifier integument is formed by a poorly keratinized epidermis supported by a dermis, which is subdivided into a spongious and compact layers. The granular and mucous glands are located in the spongy dermis. Although P. signifer showed no macroscopic lesions, microscopic analysis revealed hyperkeratosis (epidermal disruptions associated with thickening of horny layer), and some oval to spherical sporangia in the horny layer. The occurrence of chytrid fungus indicates that this pathogen is still active in Brazilian anurans and can be spreading. Considering the few sporangia in the epidermis and the strong epidermal disruption, the results suggest that the integument lesion occurs before the colonization by the chytrid fungus. Thus, the chytrid may be an opportunist fungus and not the main cause of amphibian decline.