Assessing the Threat of Amphibian Chytrid Fungus in the Albertine Rift: Past, Present and Future

Abstract

Batrachochytrium dendrobatidis (Bd), the cause of chytridiomycosis, is a pathogenic fungus that is found worldwide and is a major contributor to amphibian declines and extinctions. We report results of a comprehensive effort to assess the distribution and threat of Bd in one of the Earth’s most important biodiversity hotspots, the Albertine Rift in central Africa. In herpetological surveys conducted between 2010 and 2014, 1018 skin swabs from 17 amphibian genera in 39 sites across the Albertine Rift were tested for Bd by PCR. Overall, 19.5% of amphibians tested positive from all sites combined. Skin tissue samples from 163 amphibians were examined histologically; of these two had superficial epidermal intracorneal fungal colonization and lesions consistent with the disease chytridiomycosis. One amphibian was found dead during the surveys, and all others encountered appeared healthy. We found no evidence for Bd-induced mortality events, a finding consistent with other studies. To gain a historical perspective about Bd in the Albertine Rift, skin swabs from 232 museum-archived amphibians collected as voucher specimens from 1925–1994 were tested for Bd. Of these, one sample was positive; an Itombwe River frog (Phrynobatrachus asper) collected in 1950 in the Itombwe highlands. This finding represents the earliest record of Bd in the Democratic Republic of Congo. We modeled the distribution of Bd in the Albertine Rift using MaxEnt software, and trained our model for improved predictability. Our model predicts that Bd is currently widespread across the Albertine Rift, with moderate habitat suitability extending into the lowlands. Under climatic modeling scenarios our model predicts that optimal habitat suitability of Bd will decrease causing a major range contraction of the fungus by 2080. Our baseline data and modeling predictions are important for comparative studies, especially if significant changes in amphibian health status or climactic conditions are encountered in the future.

Long‐term monitoring of tropical alpine habitat change, Andean anurans, and chytrid fungus in the Cordillera Vilcanota, Peru: Results from a decade of study

“…Critical to understanding the long‐term conservation threat of Bd to Telmatobius and other threatened genera in South America is determining whether T. marmoratus and sympatric species such as P. marmoratum and R. spinulosa have the potential to develop, or have already developed, innate tolerance to Bd infection. This has been observed for several anuran species in Africa (Seimon, Ayebare, et al., ).…”

“…The ITS1‐5.8S region of the Bd genome is multicopy, and copy number varies considerably between strains. If we assume an average of 77 copies per zoospore (Seimon, Ayebare, et al., ), the zoospore range would be equivalent to 29–22,258 zoospores/sample. However, at the time of collection, the carcasses were desiccated, which may have impacted the quality of the DNA because of degradation, leading to an underestimation of copy number.…”

“…A second datalogger, installed and collected on the same dates, was placed in a ventilated and shaded rock cavity on a hill summit 150 m NE of D5 Pond at 5,250 m. bition controls in the PCR reactions. PCR amplification was run as previously described (Seimon, Ayebare, et al, 2015). Purified genomic Bd DNA or Bd plasmid carrying the ITS1-5.8S-ITS2 region was provided by Dr. Allan Pessier (San Diego Institute for Conservation Research, CA, USA) and was diluted to a range of concentrations to generate a standard curve.…”

“…The ITS1-5.8S region of the Bd genome is multicopy, and copy number varies considerably between strains. If we assume an average of 77 copies per zoospore (Seimon, Ayebare, et al, 2015), the zoospore range would be equivalent to 258…”

Evolutionary history of the river frog genus Amietia (Anura: Pyxicephalidae) reveals extensive diversification in Central African highlands

“…Given the high susceptibility of Amietia to chytrid infection, the limited distribution of many species within the declining pristine habitats of the AR (Fig. 1), and the suitability of the AR highlands for chytrid fungus (Seimon et al, 2015), it is likely that many additional Amietia populations are threatened by chytrid infections.…”