How it happens6:17Toads conquered the world with their poisonous bags – and people helped them
There is an invasion of toads underfoot. No, really. According to new research having analyzed the DNA of 124 toad species, they can now be found on six of the seven continents, with a colony most recently spreading rapidly across East Africa.
Some scientists believe that much of the toad conquest has to do with the way the warty, tough-skinned creatures are built.
“They're filled with poisons,” said Chris Raxworthy, co-author of the study and curator of herpetology at the American Museum of Natural History. How it happens host Neil Coxal.
“Many toads have huge glands on the back of their heads, which we call parotid glands, and they are full of toxins.”
Toxins that can mean death to any predator that tries to eat them.
Raxworthy say their research showed that the evolution of the toad's toxic parotid glands coincided with the species' rapid spread to new continents tens of millions of years ago, giving them an “advantage” and “the ability to continue to conquer the world.”
Studying, published in Proceedings of the Royal Society B. October 15 argues that the glands were an effective anti-predator strategy that helped give tiny amphibians a chance to survive.
Where their journey began
It all started 61 million years ago, says Raxworthy, and there is evidence that the species originated in South America. Approximately 30 million years Later, Raxworthy says toads have successfully invaded Africa.
It is still unclear exactly how these tiny amphibians crossed the great Atlantic Ocean.thisThe scientists who conducted the study have several hypotheses. First, they could use Antarctica as a springboard.
“Antarctica was much warmer about 30 million years ago than it is now,” Raxworthy said. “And the position of the continents was a little different, so the scattering distance wasn’t that great.”
Second postulation The fact is that the amphibians could swim across the pond directly through floating mats of vegetation – a method known as rafting. It may sound crazy, but Raxworthy says he saw it with his own eyes.
“When there are heavy rainfalls, especially in the tropics on large rivers, there is bank erosion and tree falls, and huge covers of vegetation are carried downstream and out to sea,” Raxworthy said.
“So it's not hard to imagine a bunch of toads being swept out to sea in one of these mats of vegetation. And if a few weeks later they're still alive and wash up on shore, they could actually give rise to a new founding population.”
The scientists behind these findings “have done a really good job of linking biogeography to the development of trade, which is not very common in the literature,” says Richard L. Essner, a professor of biological sciences at Southern Illinois University who was not involved in the study.
“The key to their success is these glands because any predator, including, unfortunately, many native marsupial predators that try to hunt them, ends up getting a mouthful of this venom, and it can make them sick or cause mortality,” Essner said.
Modern distribution of toads
There is a modern example of this happening right now in Africa. Until 2014, Madagascar was one of the last places in the world not affected by toad infestations.
This continued until the Asian common toad appeared in the largest seaport of the East African country.
“They probably arrived in a shipping container,” Raxworthy said. “They have since spread to a 30 or 40 kilometer radius around their original invasion point.”
The appearance of this invasive species immediately raised alarm among scientists, not only because of how quickly they were spreading, but also because of the risk they posed to Madagascar's unique biota.
Essner says this partly echoes what happened when cane toads were first introduced to Australia in the 1930s to control native cane beetles that were damaging sugarcane crops.
According to Queensland Government website, The toads were unable to control the beetles, but they spread very successfully.
“They practically captured the entire continent,” they sayWith Essner.
Raxworthy fears the same fate could befall Madagascar's native fauna. And he says that, as with the cane toads in Australia, humans unwittingly appear to be the toads' biggest allies in their quest for world domination, since the toads likely arrived on a cargo ship.
“It makes me sad… in Madagascar, especially where I've been working for many years, to see these toads come and invade,” Raxworthy said.
“We're at the point now where we don't really know how to control it. We just have to kind of let this biological experiment play out.”
