Global Patterns of the Fungal Pathogen Batrachochytrium dendrobatidis Support Conservation Urgency

Abstract

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) is a skin pathogen that can cause the emerging infectious disease chytridiomycosis in susceptible species. It has been considered one of the most severe threats to amphibian biodiversity. We aimed to provide an updated compilation of global Bd occurrences by host taxon and geography, and with the larger global Bd dataset we reanalyzed Bd associations with environmental metrics at the world and regional scales. We also compared our Bd data compilation with a recent independent assessment to provide a more comprehensive count of species and countries with Bd occurrences. Bd has been detected in 1,375 of 2,525 (55%) species sampled, more than doubling known species infections since 2013. Bd occurrence is known from 93 of 134 (69%) countries at this writing; this compares to known occurrences in 56 of 82 (68%) countries in 2013. Climate-niche space is highly associated with Bd detection, with different climate metrics emerging as key predictors of Bd occurrence at regional scales; this warrants further assessment relative to climate-change projections. The accretion of Bd occurrence reports points to the common aims of worldwide investigators to understand the conservation concerns for amphibian biodiversity in the face of potential disease threat. Renewed calls for better mitigation of amphibian disease threats resonate across continents with amphibians, especially outside Asia. As Bd appears to be able to infect about half of amphibian taxa and sites, there is considerable room for biosecurity actions to forestall its spread using both bottom-up community-run efforts and top-down national-to-international policies. Conservation safeguards for sensitive species and biodiversity refugia are continuing priorities.

Social Behavior, Community Composition, Pathogen Strain, and Host Symbionts Influence Fungal Disease Dynamics in Salamanders

“…An emerging infectious fungal disease, chytridiomycosis, has captured the attention of biologists and the general public because it has driven die-offs in hundreds of amphibian species around the world (3,(9)(10)(11)(12)(13). This disease is caused by the chytridiomycete fungi, Batrachochytrium dendrobatidis (Bd) (14) and Batrachochytrium salamandrivorans (Bsal) (15), which infect and disrupt skin function, including osmoregulation, and can lead to death (15)(16)(17)(18).…”

Tracking, Synthesizing, and Sharing Global Batrachochytrium Data at AmphibianDisease.org

“…Instead of a biological samples-based approach, Bd-Maps database compiles localitybased summaries by species as reported in diverse ways in the literature. Entries generally were not submitted by authors but compiled from literature queries or sent to the data manager as unpublished observations (21,22). We elucidate the transition with an important migration step: matching all Bd-Maps fields to the DarwinCore standard equivalent used in the Amphibian Disease Portal.…”

“…Fields for date, taxonomy, and geography such as latitude and longitude, for example, were relatively straightforward to map. Three Bd-Maps fields that tally counts of total positive Bd samples ("BdDet"), total samples ("Tested") and total number of samples with low zoospore levels which made them questionable ("BdQues" or "BdUnc") required different accommodations, and are important to Bd-Maps based analyses [e.g., (21,22)]. These fields were dependent on the "Location Number" field, which is matched to the portal field "locationID."…”

“…The chytridiomycosis research community soon turned to Bd-Maps as the main source for compiled global data on Bd (21). This has been a laborintensive aggregation of global Bd sampling efforts including >33,000 data records at >14,000 unique site coordinates to date (22). Based on both the Bd-Maps data and unique records recently summarized by Castro Monzon et al (23), Bd has been detected in 1,375 of 2,525 (55%) species (composed of 88% of frog families, 100% of salamander families, and 70% of caecilian families) and 93 of 134 (69%) countries sampled to date [see (22) for details].…”

“…In particular, it has become increasingly important to not only document known occurrences of Bd and Bsal, but also known instances of negative data (i.e., samples tested for Bd and/or Bsal that did not find evidence of infection), which by themselves may not be suitable for publication in many peer-reviewed journals. These data are critically important, however, in predictive distribution modeling [e.g., (22,24)], and in examining host species traits such as phylogeny, habitat use, or behavior that may explain host infection or disease susceptibility [e.g., (25,26)], and help understand the synergisms of co-occurring chytrid fungi [e.g., (27)]. If samples have linked genetic and genomic data, pathogenic fungal migration and evolution can be examined, revealing new insights on virulence, novel introductions, and origins of pathogens using phylodynamics [e.g., (11,(28)(29)(30)].…”