Chytrid fighting work around the world is continuing its rapid pace in 2015 with lots of exciting studies advancing our understanding of how Batrachochytrium dendrobatidis (B.d.) and Batrachochytrium salamandrivorans (B.sal.) infect and interact with frogs in wild populations. Our whole lab decamped for a weekend from St Mary’s Hospital to Cambridge to go to the Amphibian Conservation Research Symposium 2015. The huge range of innovative amphibian research going on was fantastic, and some of the new monitoring ideas were truly inspired!
Here are some particularly recent, quality studies highlighting quirks, complexities and confusions of conservation when you’re fighting the froggy fungus, as well as some especially exciting and unusual talks from ACRS 2015.
1) Elevated Corticosterone Levels and Changes in Amphibian Behaviour Are Associated with Batrachochytrium dendrobatidis (Bd) Infection and Bd Lineage
Authors: Caitlin R. Gabor, Matthew C. Fisher, Jamie Bosch
This study looked at interactions between Bd infection intensity, elevation, and Corticosteroid (CORT) levels in tadpoles and metamorphs of Alytes spp. Bd is known to have variable infection outcomes depending on a wide range of environmental, host and pathogen factors. Altitude, for reasons not yet entirely clear, is known to often be associated with higher levels infection intensity and worse disease outcome. Many amphibian keepers will tell you that they have had seemingly healthy animals suddenly begin to develop symptoms of chytridiomycosis on being exposed to a stressful situation, such as being but in quarantine. What is not known is how or if these factors can interact, and whether the level of virulence of the infecting strain influences how important these elements are. The study used an innovative non-invasive sampling measure (something that is particularly important for a study looking at stress responses!) shown below.
The infecting lineage of BdGPL infection was found to result in significantly higher CORT release rates than BdCape infection. As well as this, there was a significant interaction between altitude Bd infection status, confirming previous studies and suspicions that altitude increases Bd susceptibility while CORT levels were also seen to increase with elevation. Interestingly, it was also found that CORT release rates were higher when metamorphs were infected with BdGPL as compared to infection with BdCape.
The results of this study indicate that CORT levels are associated with susceptibility to Bd infection, and that CORT is itself affected by the Bd lineage infection type and that altitude and stress levels may both have an impact on Bd infection outcome. All of this makes CORT a viable biomarker of amphibian stress levels, providing a new angle with which to assess Bd susceptibility.
2) Amphibian Symbiotic Bacteria Do Not Show Universal Ability to Inhibit Growth of the Global Pandemic Lineage of Batrachochytrium dendrobatidis
Authors: Rachael Antwis, Richard Preziosi, Xavier Harrison, Trenton Garner
The field of amphibian skin microbiome and probiotics research is really taking off – many people have their hopes pinned to augmenting the skin microbiome of amphibians to halt the scourge of Bd on susceptible amphibian populations. The problem is that even within lineages, Bd displays huge levels of genotypic diversity so it’s difficult to know whether a bacteria that inhibits the growth of one isolate of Bd will inhibit the growth of other isolates of Bd.
There are two issues addressed in this study:
1) Whether candidate probiotics exhibit broad-spectrum inhibition of multiple isolates of BdGPL
2) Whether it is possible to predict broad-spectrum candidate probiotics according to taxonomy
In fact, only a small proportion of the candidate bacteria inhibited growth of all three of the BdGPL isolates they were tested against. In addition, although some bacterial genera showed greater levels of inhibition than others, genus and species could not reliably be used to predict the capability of a probiotic to inhibit a wide range of BdGPL isolates. This work suggests that if we are to use probiotics to address the Bd threat, a cocktail of bacteria is more likely to be much more effective than a single innoculation. In short, the pathogen and host microbiome relationship is really complicated!
3) Composition of Symbiotic Bacteria Predicts Survival in Panamanian Golden Frogs Infected With a Lethal Fungus
Authors: Matthew Becker, Jenifer Walke, Shawna Cikanek, Anna Savage, Nichole Mattheus, Celina Santiago, Kevin Minbiole, Reid Harris, Lisa Belden, Brain Gatwicke
In a similar vein to the paper above, the composition of the bacterial community on an amphibian’s skin was found to be key to predicting survival of Bd infection. Panamaniam Golden Frogs (Atelopus zeteki) are classified as Critically Endangered by the IUCN, due to the impact of chytridiomycosis. They are extinct in the wild, only now existing as captive assurance populations.
Golden Frogs were innoculated with Bd-inhibitory bacteria from Bd-tolerant frogs also from Panama. Following infection with Bd, 30% of Golden Frogs survived, but what was surprising was that this effect was not associated with the probiotic treatment. Instead, the initial composition of the bacterial community and its associated metabolites on the Golden Frog’s skin was found to be the key factor related to survival. This backs up the call of the authors in the second paper, that it is the microbial community as a whole that will have to be investigated if we are to go down the probiotic route for disease mitigation.
3) Using Sniffer Dogs to Track Down Endangered Amphibians (and Chytrid?)
Esther Matthew, speaker at ACRS 2015
Esther Matthew, of Che Weldon’s research group at North-West University in South Africa has hit upon a truly novel new way of monitoring a highly cryptic and (in South Africa) vulnerable frog population. The Giant African Bullfrog aestivates below ground for up to 11 months at a time, only emerging for a few weeks at a time. They’re vulnerable to increasing levels of urbanisation and development as they’re difficult to detect when environmental impact surveys are carried out.
Jessie the border collie has been trained by Esther to find live bullfrogs living below the soil (she can detect a bullfrog scent diluted to a factor of up to 1:100000), and bullfrog scents over 5 months old as well as being capable of tracking live frogs over their cross-waterway movements. In the future she’ll be trained to detect other endangered amphibians, and there’s some murmurings about training her to sniff out which frogs are infected with Bd – could we see Jessie’s protégés sniffing out infected trade amphibians at airport security check points soon?
4) Turning a Frog into a Prince!
Arun Kanagavel, speaker at ACRS 2015
Arun Kanagavel, an EDGE fellowship holder working in the Western Ghatsin India, has been addressing a problem faced by all lovers of amphibians – how to convince people that amphibians can work as flagship species worthy of contributing time and money towards for their conservation?
As expected, aesthetics played a huge role in people, particularly the general public, being willing to donate time and money to the conservation of a particular species. However, there was light at the end of the tunnel! Cultural significance was important, particularly for indigenous communities, as was rarity. People were willing to donate time and money to frog conservation, particularly when it was linked to more wholistic forest conservation. Maybe a wider range people are more interested in the weird and wonderful world of amphibians than we think!
5) Amphibian Conservation From A Chytridiomycosis Perspective
Annemarieke Spitzen, Speaker at ACRS 2015
Annemarieke Sptizen, from Ghent University in the Netherlands described the sudden population collapse of the fire salamander (Salamandra salamandra) due to an outbreak of chytridiomycosis caused by the (then) novel pathogen Batrachochytrium salamandrivorans. Despite strong similarities between Bd and Bsal they differ in their ecological niches. The alarming potential consequence of this is that amphibians not affected by one, may be susceptible to the other. Combined with global trade and traffic that ease their global spread, these two pathogens could between them cause total collapse of amphibian populations, which would in turn disturb ecosystem stability globally.
A worrying thought, but somewhat alleviated knowing that such great research and management is being done worldwide to address the myriad of threats faced by amphibians. Leaving the conference there was certainly a strong sense of optimism – amphibian conservation is gathering pace, and showing no signs of stopping any time soon!