Toxic Toad Invasion Threatens Madagascar Predators

This photo shows Duttaphrynus melanostictus, the toxic Asian toad invading Madagascar. (Wolfgang Wüster)

(CN) – Following the recent introduction of the common Asian toad to Madagascar, a new study suggests fears that the toxic amphibian will threaten the island’s animal populations are valid.

The report, published Monday in the journal Current Biology, shows nearly all predators native to Madagascar are highly sensitive to toad toxins.

Eating the new arrivals could be a fatal mistake.

“In Australia, the introduction of cane toads has caused profound perturbation to many ecosystems by removing key predators from local food webs with their toxins,” said co-author Wolfgang Wuster, a senior lecturer in zoology at Bangor University in the United Kingdom.

“Similar effects are likely to occur in Madagascar, where toads were never present before, as well; predators that frequently feed on toads and do not rapidly learn or evolve to avoid them are likely to become much rarer or possibly extinct.”

Bufonid toads secrete bufadienolides that kill certain predator species by inhibiting the sodium-potassium pump (Na+/K+-ATPase) – an enzyme that pumps sodium out of cells while pumping potassium in, both against their concentration gradients – a key aspect of animal cell membranes.

However, some species can develop a resistance to these toxins through multiple, predictable and mutations to specific points in the gene encoding this critical enzyme.

The significant threat the toxic and invasive Asian toads (Duttaphrynus melanostictus) pose to Madagascar’s ecosystem has prompted vigorous debate regarding their likely impact, and what can be done to control or eradicate them.

“A crucial knowledge gap has been whether native Malagasy predators are indeed sensitive to toad toxins: this has been widely assumed by conservationists, but without concrete evidence,” said co-author Andolalao Rakotoarison, co-chair of Madagascar’s IUCN Amphibian Specialist Group.

To fill this gap, the team analyzed the sequences of the sodium-potassium pump gene of 77 Malagasy species that might feed on toads. The species include 28 birds, 27 snakes, 12 frogs, eight mammals and two lizards. The results show only one native species – a rodent known as the white-tailed antsangy – displayed evidence of resistance to the toad’s toxin.

The findings show the importance of controlling the spread of this non-native species to avoid a worsening biodiversity crisis, according to the team.

“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, a senior lecturer at the Liverpool School of Tropical Medicine in the United Kingdom.

Malagasy amphibian specialist Frank Glow, co-author of the report and head of the herpetology section of the Bavarian Collection of Zoology, said the toad’s tadpoles might also threaten endemic fish in addition to invertebrate predators, including crustaceans, dragonfly larvae and water beetles. As such, further research is needed to evaluate the vulnerability of the island’s aquatic predators.

“This is another example of how species introduced from one part of the world to another can disrupt natural ecosystems,” said first author Ben Marshall, a master’s student at Bangor. “Preventing the introduction of alien invasive species must be a top priority for biodiversity conservation.”

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