The Asian common toad, Duttaphrynus melanostictus, is a member of the Bufonidae family and can be found in tropical areas from Pakistan to Indonesia. Photo © L. Shyamal
The catastrophic invasion of cane toads (Rhinella marina) in Australia is a story we are all well aware of and hope we have learned many lessons from. However, in recent weeks worrying reports from Madagascar could mean a similar fate for the endemic species of this island. The first sighting of adults of Asian common toads (Duttaphrynus melanostictus) were reported in December 2013, later confirmed on March by a team of local and foreign researchers. On this occasion six adults were collected from Toamasina, six kilometres away from Madagascar’s largest port. The close proximity to the port suggests that they arrived via shipping vessels from Asia. These handsome looking toads produce a poison that reduces their predation risk in their native range. The fear is that endemic Madagascan species that haven’t previously been exposed to the toads will prey on them and subsequently die from the potent toxins. This is of particular concern for the snakes of this area that may see the large toads as an easy meal. It could even spell disaster for the local human population if the toads are attracted to fresh water wells for reproducing as they could poison the water supply, but also because they might poison domestic animals. Halting this potential invasion has jumped up the top of the ‘to do list’ for conservationists fighting to protect Madagascar’s unique biodiversity.
The Asian common toad could affect the local amphibians by bringing parasites and diseases to the island that were previously absent. This will be particularly worrying if the collected toads test positive for the fatal chytrid fungus Batrachochytrium dendrobatidis, or Bd for short, although at present no D. melanostictus has ever tested positive for Bd in its natural range. Bd can cause the disease chytridiomycosis, which thickens the skin of the infected amphibian. This results in electrolyte imbalances and ultimately leads to cardiac arrest. A recent study by Kolby has found Bd to be present in commercially exported amphibians from Madagascar to the USA; but as recently stressed by Weldon and colleagues, a national monitoring program for detection of chytrid in Madagascar is in place in order to early identify the presence of Bd in wild amphibian populations. It is currently unknown how the Madagascan amphibians will react to the parasite, but I think we can all agree that it is something we would rather not find out!
Madagascar provides the ideal habitat for the generalist toads, which could spread rapidly throughout the island and may displace many native amphibians. The toads’ home range stretches from Pakistan down through South East Asia to Indonesia. They inhabit tropical to subtropical land and can be found at elevations of up to 1800 m above sea level. Also due to deforestation, the island has many ideal locations where the toad could prosper. Madagascar is home to many unique amphibians such as the iconic Golden mantella (Mantella aurantiaca), which may struggle to compete with this alien species. To ensure that the Asian common toads do not spread throughout the island, to protect the native fauna from their poison and to make sure they are not a competitive threat to native amphibians, Malagasy authorities together with the IUCN SSC Amphibian Specialist Group (in this case represented by Christian Randrianantoandro) are currently coordinating the research activities aimed at identify the current delimitation of this invasive alien species. Obtaining this data is the first step needed to prepare a suitable feasibility study for an eradication that is already integrated within the most urgent actions that need to be taken under the ACSAM (A Conservation Strategy for the Amphibian of Madagascar umbrella.For a more detailed account of the action being taken and to learn how you can directly support this project please visit: http://www.amphibians.org/news/toad-invasion-madagascar.
Across the field of conservation biology there is a push to become more proactive and less reactive. Until recently conservation has worked on the basis of identifying an endangered species and then working to protect the remaining population and boost its numbers through several different techniques. The decline in biodiversity seen across the globe demands that we rapidly move away from this approach and towards a method that encompasses the protection of multiple species. Madagascar displays many of the typical symptoms seen when human populations expand; deforestation, loss of biodiversity and decline in water quality to name a few. However, it is refreshing to see a group of conservationists being enthusiastic about protecting the Madagascar’s biodiversity in a proactive manner. A preemptive strike against the toads is certainly what is needed if the island is to have a chance of evading this invasive force.
By: Nadia Jogee