Tracking Chytrid in Madagascar

Steven Allain

By Steve Allain

Until recently, Madagascar was thought to be free from the amphibian chytrid fungus (Batrachochytrium dendrobatidis; hereafter Bd), which has caused devastation worldwide. For those of you who aren’t aware of the threat the disease poses to amphibians, approximately 200 species have already undergone extinctions or extirpations due in some part to chytrid. Other amphibian populations around the world have declined drastically, with the most affected areas being Australia and Central/South America. A paper published in Scientific Reports in February 2015 by Molly Bletz and an international team of collaborators showed that frogs from five areas of Madagascar which had been monitored between 2010 and 2014 were infected with Bd.

 

The disease prevalence ranged from very few incidences in the populations being sampled at some sites to every individual being positive for the pathogenic fungus at others. Unfortunately, this indicates that Bd is now established and widespread on the island. As we’ve seen in other parts of the world, it is possible that some of Madagascar’s frogs could  be resistant to the disease. However, one worry is that as the frogs are thought to have evolved in isolation from Bd, the disease may be able to take the final blow to amphibian populations that are already pressured by habitat destruction and over-harvesting. One thing that we do not yet know is the lineage of Bd present on Madagascar; so far it seems to be very similar to BdGPL – the Global Panzootic Lineage. There is a chance that it may be a new endemic lineage to Madagascar given its evolutionary isolation, but further work is still needed.

Fortunately, teams of people have been continuing to collect swabs from the amphibian communities where Bd was first identified, as part of a long term monitoring project. This is where my role within the Fisher Lab comes in. I’m currently running qPCR analyses on the swabs collected in 2016 (and soon those from 2017) to track the further potential spread of Bd on Madagascar. Thankfully, a brilliant team of other scientists has already analysed swabs form 2015 and most of the swabs from 2016 – I’m just picking up where they left off and helping to create an image of the big picture. I’m hoping that my research project in the lab, working with the valuable samples, will help to inform amphibian conservation efforts on the ground in Madagascar form the potentially apocalyptic effects of Bd. 

 

There are still a number of unanswered questions which I’m trying to tackle. The first is in relation to Bd‘s lack of spread and virulence in Madagascar. We know that when the disease first appeared in Central America, it moved like a wave through the Isthmus of Panama and into Colombia over the course of a few decades. As it spread, species disappeared and mass die-offs were observed. Nothing like this has been seen in Madagascar so far and, from what the samples tell us, the disease has a very low prevalence. Why is this? Could the frogs have some form of immunity to the disease? Could the environmental variables be unfavourable to Bd? Are the microbiomes of the frogs and the environments they inhabit acting as a shield, with Bd having to fight off competition in order to get a hold? These are all questions that can be answered in part by long term monitoring of the pathogen and I hope that by running these analyses I can help contribute towards a definitive answer.

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