Aetokthonos hydrillicola (Ah) is a newly described cyanobacteria that forms dense colonies on aquatic macrophytes, primarily invasive Hydrilla verticillata, and is associated with mortality of freshwater wildlife. Prior research shows that Ah growing on Hydrilla is potently toxic to waterbirds, turtles, and fish, suggesting potentially broad sensitivity among vertebrates. We tested whether amphibian tadpole species were affected by ingestion of Ah-positive Hydrilla, and whether season, host plant, or tadpole age/size affected tadpole vulnerability. For trials involving ranid tadpoles (Bullfrogs, Rana catesbeiana; Green frogs, R. clamitans; and Southern leopard frogs, R. sphenocephala), feeding on Ah-positive Hydrilla collected during October–November resulted in the development of lesions within brain tissue and significant mortality. Ranid tadpole sensitivity to Ah toxin did not vary with age or size, but vulnerability from ingestion of Ah-positive Hydrilla varied seasonally and between two syntopic host plants. An unexpected result of our study was the apparent insensitivity of Green treefrog tadpoles (Hyla cinerea) fed toxic, Ah-positive Hydrilla. In conjunction with other studies, our results confirm wide but variable sensitivity among major vertebrate lineages to the Ah toxin. Differential sensitivity among species means that the introduction of Ah could alter interactions and structure within aquatic communities.
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We thank Rebecca Boyd, Rebecca McInroe, and James Hunt for their significant contributions to the execution of this work, and Richard Chandler and James Martin for assistance in modeling tadpole survival. This research was supported by two U.S. Fish and Wildlife Service Aquatic Nuisance Species Task Force grants through the Southeastern Environmental Cooperative Universities Program to J. C. Maerz and S. B. Wilde (FWS-800-037-2014-UGA).
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