Toxic Toad Threatens Madagascar's Biodiversity


The Asian common toad (Duttaphrynus melanostictus) may look relatively benign and harmless but can devastate entire ecosystems of predators. Wikimedia/Creative Commons Attribution-Share Alike 4.0

Sometimes in the movies, a newcomer wanders into town and ends up bringing everybody together and saving Christmas. But when it comes to invasive species — organisms that belong in one ecosystem, but make their way into another where they basically go bananas without any of the native ecological checks and balances of their native land — it's more like a horror movie where the stranger is bad and kills everybody.

This is the case with the Asian common toad (Duttaphrynus melanostictus), which has made its way to the African island of Madagascar (you know — the one with the lemurs) by way of people. If you're not a toad expert, you might think, "Oh look! A toad!" no matter where in the world you are. But in 2014, an Asian common toad was spotted at a large seaport in Madagascar and the conservation biology world collectively freaked all the way out. Because when these toads are threatened by something that might eat them, they secrete a toxic slime that sends the potential predator into cardiac arrest. Madagascar is one of the most biodiverse places in the world, and according to a new study published June 4, 2018, in the journal Cell Biology, a lowly toad could obliterate Malagasy ecosystems.

Extravagant toxins aren't always a deterrent to predators, especially in ecosystems where the predators and prey have a few hundred thousands of years to evolve side by side. Specialized genetic mutations in predators on the toad's home turf might render that poisonous slime just a tasty breakfast condiment, but to another animal that evolved elsewhere — a lemur, for instance — even a little lick would mean certain death.

The research team set out to discover exactly how many of Madagascar's native fauna would be susceptible to the Asian common toad's toxins. Past research suggested that some animals on Madagascar might already have evolved some genetic mutations that would protect them from the toad. However, of the 88 native species studied by the research team — which included mammals, birds, snakes, frogs and lizards — only one rodent had the genetic makeup that would allow it to eat an Asian common toad and live to tell the tale.

The toads haven't made it inland yet — they've only been found on a 215 mile (350 kilometer) section of the island's northeastern coast. But they're spreading fast because females lay thousands of eggs at a time and Madagascar's landscape just suits the water-loving amphibians.

"Our findings confirm that the invasive toads are likely to have a significant impact on many Malagasy endemic species, adding to the country's existing conservation problems and potentially endangering many of Madagascar's most iconic endemic species, such as tenrecs and the enigmatic fossa, as well as a plethora of other species," said co-author Nicholas Casewell of the Liverpool School of Tropical Medicine, in a press release.



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