Monitoring the prevalence and distribution of chytrid fungus
(Batrachochytrium dendrobatidis) in the Kihansi Spray Toad
(Nectophrynoides asperginis) population in the Kihansi Gorge spray
wetlands, Tanzania
Abstract
Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is a
fungal disease only fatal to some amphibian species. Among the
vulnerable species is the Nectophrynoides asperginis, endemic to the
Kihansi Gorge spray wetlands in Tanzania’s Udzungwa Mountains. By 2009,
chytridiomycosis had driven N. asperginis to extinction in the wild,
though it survives in captivity. Reintroduction efforts have faced
difficulties, underlining the importance of understanding Bd’s
prevalence in the wild to guide re-introduction programs. We assessed
Bd’s presence 20 years after its initial detection in Tanzania and
determined whether it was responsible for the 98% mortality of 1000
captive-bred N. asperginis released in Feb 2022. In December 2022,
time-constrained surveys were conducted across three spray wetlands
covering N. asperginis habitats. Amphibians were skin-swabbed following
a protocol developed by the University of California, resulting in two
sets of 44 samples from seven species. These samples were analyzed for
Bd presence using conventional and real-time quantitative polymerase
chain reaction, followed by nucleotide sequencing of PCR products. Bd
was detected in 32% of samples, affecting four species: Arthroleptides
yakusini (14%), N. asperginis (9%), Ptychadena anchietae (7%) and
Hyperolius substriatus (2%). Whereas N. asperginis was severely
affected, the other species were healthy carriers. Bd-CAPE was confirmed
as the cause of the mass deaths of the released toads. The continuing
presence of Bd-CAPE in the spray wetlands remains a barrier to the
successful re-introduction of N. asperginis, necessitating further
experimentation to develop strategies for coexistence.