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

Abstract

Between 2006 and 2010, recurring morbidity and mortality of the endemic Lake Oku\rclawed frog \rXenopus longipes\rwas observed at its only known locality, Lake Oku, Cameroon.\rDuring repeated visits in 2006, 2008, 2009 and 2010, we found large numbers of dead frogs around\rthe lake shore, as well as a higher than expected prevalence of diseased frogs. No significant rela-\rtionships between disease occurrence and environmental parameters were found, with the excep-\rtion of a significant but unexplained association between phosphate concentration and disease\rincidence. Tissue samples from \rX. longipes\rcollected during 3 field seasons were negative for the\ramphibian chytrid fungus \rBatrachochytrium dendrobatidis (Bd)\rusing a \rBd\r-specific real-time PCR\rtest, although other species of sympatric amphibians were positive for this pathogen. Only 1 of 48\rtissue samples from diseased frogs was positive for ranavirus infection using a ranavirus-specific\rPCR, suggesting that this pathogen is not necessarily the cause of this disease. No evidence of\rpathogens was found in tissues examined histologically from 10 \rX. longipes\rwhich had been col-\rlected and fixed when freshly dead. The cause(s) of the morbidities and mortalities remain(s)\runknown, as does their consequence to the population of this Critically Endangered species. Iden-\rtifying the causative factor(s) of the \rX. longipes\rmortality and its impact on the population is cru-\rcial for planning conservation actions.