Thursday, 9 February 2017

Did Bd cause historic amphibian population declines in Brazil?

A new paper by Tamilie Carvalho et al. in the Proceedings of the Royal Society shows that there is a link between Bd infection in tadpoles and amphibian population declines in Brazil (primarily in the Atlantic forest). Thus, Bd may have caused population declines a long time ago and even before it was described (1979-1987). The authors argue that these results suggest that Brazil is not the origin of Bd.

The abstract of the paper:
The recent increase in emerging fungal diseases is causing unprecedented threats to biodiversity. The origin of spread of the frog-killing fungus Batrachochytrium dendrobatidis (Bd) is a matter of continued debate. To date, the historical amphibian declines in Brazil could not be attributed to chytridiomycosis; the high diversity of hosts coupled with the presence of several Bd lineages predating the reported declines raised the hypothesis that a hypervirulent Bd genotype spread from Brazil to other continents causing the recent global amphibian crisis. We tested for a spatio-temporal overlap between Bd and areas of historical amphibian population declines and extinctions in Brazil. A spatio-temporal convergence between Bd and declines would support the hypothesis that Brazilian amphibians were not adapted to Bd prior to the reported declines, thus weakening the hypothesis that Brazil was the global origin of Bd emergence. Alternatively, a lack of spatio-temporal association between Bd and frog declines would indicate an evolution of host resistance in Brazilian frogs predating Bd's global emergence, further supporting Brazil as the potential origin of the Bd panzootic. Here, we Bd-screened over 30 000 museum-preserved tadpoles collected in Brazil between 1930 and 2015 and overlaid spatio-temporal Bd data with areas of historical amphibian declines. We detected an increase in the proportion of Bd-infected tadpoles during the peak of amphibian declines (1979–1987). We also found that clusters of Bd-positive samples spatio-temporally overlapped with most records of amphibian declines in Brazil's Atlantic Forest. Our findings indicate that Brazil is post epizootic for chytridiomycosis and provide another piece to the puzzle to explain the origin of Bd globally.

Tuesday, 10 January 2017

Refugia, connectivity, and transmission

Connectivity is bad for Bd and good for frogs. Read more here:
https://parasiteecology.wordpress.com/2016/03/23/refugia-connectivity-and-transmission/











(The cartoon was taken from the parasite ecology blog.)

Thursday, 22 December 2016

"After the epidemic": New review paper on chytrid epidemics in Australian amphibians

Ben Scheele and coauthors review the effects of chytridiomycosis on amphibian populations in Australia in a new paper in Biological Conservation (http://www.sciencedirect.com/science/article/pii/S0006320716310126).
Some highlights from the abstract:
"Chytridiomycosis in amphibians (caused by the fungal pathogen Batrachochytrium dendrobatidis, Bd) is an exemplar, with impacts ranging from rapid population crashes and extinctions, to population declines and subsequent recoveries."
"Population trajectories of declined species are highly variable; six species are experiencing ongoing declines, eight species are apparently stable and 11 species are recovering."
"Our results highlight that while some species are expanding, Bd continues to threaten species long after its emergence."

Monday, 17 October 2016

Tackling emerging fungal threats to animal health, food security and ecosystem resilience

Watch out for the new issue of the Philosophical Transactions of the Royal Society on "Tackling emerging fungal threats to animal health, food security and ecosystem resilience". There will be several papers on chytrids.

Access the articles here: http://rstb.royalsocietypublishing.org/content/371/1709

Monday, 26 September 2016

Side effects of itraconazole on post-metamorphic Alytes obstetricans after a cold stress

A small but important study on limitations of the use of itraconazole.

Itraconazole is the most widely used treatment against Batrachochytrium dendrobatidis (Bd), the fungal pathogen causing chytridiomycosis, a proximate cause of amphibian declines. Several side effects of itraconazole treatment, ranging in severity from depigmentation to death have been reported in different amphibian species and life stages, and these side effects were observed at commonly used dosages of itraconazole. However, no studies have investigated side-effects of itraconazole in conjunction with environmental stress. Post-metamorphic midwife toads (Alytes obstetricans) that were treated with itraconazole and subsequently exposed to a cold stress (exposure to 4°C cold water) had higher mortality rates compared to untreated individuals. Moreover, adults of booroolong frogs (Litoria booroolongensis) treated with itraconazole had a higher probability to become infected when subsequently exposed to Bd. Our results suggest that a post-metamorphosis itraconazole treatment of infected midwife toads combined with a subsequent release into the wild may be an ineffective disease mitigation strategy, as the cold stress during hibernation and/or exposure to Bd in the wild may reduce the hibernation emergence rate of treated individuals in this species.

Study accepted in Amphibia Reptilia

The global amphibian trade flows through Europe: the need for enforcing and improving legislation

The global amphibian trade is suspected to have brought several species to the brink of extinction, and has led to the spread of amphibian pathogens. Moreover, international trade is not regulated for *98 % of species. Here we outline patterns and complexity underlying global amphibian trade, highlighting some loopholes that need to be addressed, focusing on the European Union. In spite of being one of the leading amphibian importers, the EU’s current legislation is insufficient to prevent overharvesting of those species in demand or the introduction and/or spread of amphibian pathogens into captive and wild populations. We suggest steps to improve the policy (implementation and enforcement) framework, including (i) an identifier specifically for amphibians in theWorld Customs Organisation’s harmonised system, (ii) Parties to CITES should strive to include more species in the CITES appendices, and (iii) restriction or suspension of trade of threatened species, restricted-range species, and species protected in their country of origin. Commercial trade should not put survival of amphibian species further at risk.

http://link.springer.com/article/10.1007/s10531-016-1193-8?view=classic

Thursday, 11 August 2016

Predicting the future distribution of Bd under climate change

Data from bd-maps.net was used to predict the global future distribution of Bd. The paper was published in PLoS ONE and is freely available. A key model prediction is "a broad expansion of areas environmentally suitable for establishment of Bd on amphibian hosts in the temperate zones of the Northern Hemisphere."



The figure shows the predicted change in the distribution of (figure taken from the paper).