An enigmatic mortality event in the only population of the Critically Endangered Cameroonian frog Xenopus longipes

Contemporary global declines and mortality events in amphibian populations have been often attributed to infectious disease and climate change, separately and in combination. We report on an enigmatic mortality event in the only known population of the Critically Endangered frog species Xenopus longipes. This aquatic and biologically distinctive species is restricted to Lake Oku, a high-elevation crater lake on Mt. Oku in Cameroon. Neither a quantitative PCR-based screen nor histopathological analysis revealed the presence of the chytrid fungus Batrachochytrium dendrobatidis, which is believed to be responsible for many declines and mortality events in amphibian populations around the world. Histopathology revealed widespread epidermal hyperplasia and multifocal saprolegniasis suggesting that the animals have been exposed to a source of skin irritation. These sources might include acidified surface waters, perhaps derived from inorganic fertilisers or other human-related pollutants, or to local geological processes distinctive of the Cameroonian Volcanic Line. Currently, the causes underlying this mortality event remain obscure.