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The invasive cane hatchlings toad in Australia don’t stand a chance against their deadliest predator: cannibalistic tadpoles that gobble up hatchlings as if they were at an all-you-can-eat buffet. But now the newborns are fighting.
They grow faster, reducing the time hungry tadpoles have to gobble them up, according to a new study.
“If the cannibals are after you, the less time you spend as an egg or newborn, the better,” said Jayna DeVore, principal investigator of the study, who conducted the research as an associate of postdoctoral research at the University of Sydney and is now a biologist. for the Tetiaroa Society, a non-profit conservation organization in French Polynesia.
Growing quickly, however, has its pitfalls. Compared to typically growing newborns, those who grew faster did less well when they reached the tadpole stage of life, the researchers found. So it’s not “worth trying to defend yourself in this way, unless cannibals definitely come for you,” DeVore told Live Science.
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The cane toad (Rhinella Marina) is a poster for invasive species. The poisonous warty toad, known to swallow anything that fits in its wide mouth, is native to South America. In the 1930s, farmers in Queensland, Australia believed that the toad would be the perfect predator to gobble up beetles that were destroying sugarcane fields. But without natural predators, the toad population has grown from just 102 to over 200 million, according to WWF Australia.
Another reason for their peak population is that female toads can lay more than 10,000 eggs at a time in small ponds. “When these eggs first hatch, the young cannot swim or eat yet, so they can practically only stay there at the bottom of the pond until they develop into tadpoles,” said DeVore.
Hungry tadpoles strike during this vulnerable time of hatchlings. “Once the hatchlings turn into tadpoles, they are too large and mobile for other tadpoles to eat them, so the cannibals have to work quickly if they are to consume them all,” DeVore said.
The tadpoles that cannibalize the younger generation are doing themselves a great service; they obtain nutrients and eliminate subsequent competition for resources. “When I first saw this behavior in the wild, I was amazed at how voraciously toad tadpoles searched for and ate toad hatchlings,” DeVore said. To determine if this behavior was “normal” or if it was an adaptation to extreme competition between invasive cane toads, DeVore and his colleagues compared the invasive cane toads from Australia to those from the native range, or cane toads from their native regions.
Warty Toad Arms Race
Several experiments have revealed that invasive toads – both hatchlings and cannibalistic tadpoles – are evolving at breakneck speed.
In an experiment done more than 500 times with different individuals, DeVore and his colleagues placed a tadpole in a container with 10 hatchlings. Although tadpoles from the native range have engaged in some cannibalism, “we found that a hatchling was 2.6 times more likely to be cannibalized if that tadpole came from Australia than it did. it came from the native range, ”she said.
Additionally, invasive tadpoles were much more attracted to hatchlings than native tadpoles. In another experiment, the team placed tadpoles in a pool with two traps; one trap contained hatchlings and the other was empty. “In Australia, cannibalistic tadpoles were attracted to hatchlings; the chances of an Australian tadpole entering the trap containing hatchlings were about 30 times greater than that of entering the empty trap,” he said. declared DeVore.
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In contrast, “tadpoles were not attracted to hatchlings; they were just as likely to enter the empty trap as the hatchling trap, ”she said. “This demonstrated that this strong attraction to the vulnerable hatchling stage, which helps cannibalistic tadpoles detect and locate their victims in Australia, is not present in the original range.”
Defending oneself
To retaliate, the invading hatchlings have developed an escape strategy. When researchers compared the time spent developing eggs and hatchlings, they found that invasive toads grew faster than native toads.
In both groups, “we found that Australian toad clutches grew faster; they reached the invulnerable tadpole stage in about four days, while native broods took about five days, ”DeVore said.
Additionally, invasive hatchlings had a more “plastic” or flexible response than hatchlings living in the wild when a cannibalistic tadpole was present; hatchlings from Australia were “more likely to be able to sense when cannibals are present and speed up their development in response,” DeVore noted.
While these strategies helped newborns survive, they paid for it later. Researchers tested 1,190 tadpoles for survival, development, growth, and plasticity, and found that those that developed faster as eggs and hatchlings to escape cannibalism fared worse and developed more slowly in the tadpole stage than native tadpoles, the team found.
Could cannibalism lead to extinction?
Could Cane Toads Eat Each Other To Extinction? Probably not, DeVore said.
“Australian toads may be their worst enemy, but I wouldn’t expect them to disappear anytime soon,” she said. This is because cannibals profit too much from eating their own kind. After acquiring nutrients and limiting competition, cannibalistic tadpoles “turn into toads faster and larger,” she said. It is even possible that these “successful” toads are invading new places in Australia more quickly.
“The good news is that cannibalism can control population growth,” DeVore said. “So, while cane toads are unlikely to become extinct, these cannibalistic behaviors may help regulate their abundance after the invasion.”
The study was published in the August 31 issue of the journal Proceedings of the National Academy of Sciences.
Originally posted on Live Science.
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