Morbidity and mortality of the Critically Endangered Lake Oku clawed frog Xenopus longipes

Between 2006 and 2010, recurring morbidity and mortality of the endemic Lake Oku clawed frog Xenopus longipes was observed at its only known locality, Lake Oku, Cameroon. During repeated visits in 2006, 2008, 2009 and 2010, we found large numbers of dead frogs around the lake shore, as well as a higher than expected prevalence of diseased frogs. No significant relationships between disease occurrence and environmental parameters were found, with the exception of a significant but unexplained association between phosphate concentration and disease incidence. Tissue samples from X. longipes collected during 3 field seasons were negative for the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) using a Bd-specific real-time PCR test, although other species of sympatric amphibians were positive for this pathogen. Only 1 of 48 tissue samples from diseased frogs was positive for ranavirus infection using a ranavirus-specific PCR, suggesting that this pathogen is not necessarily the cause of this disease. No evidence of pathogens was found in tissues examined histologically from 10 X. longipes which had been collected and fixed when freshly dead. The cause(s) of the morbidities and mortalities remain(s) unknown, as does their consequence to the population of this Critically Endangered species. Identifying the causative factor(s) of the X. longipes mortality and its impact on the population is crucial for planning conservation actions.