Cane toads are evolving into super-invaders

[klr]

The bastards!

http://news.bbc.co.uk/earth/hi/earth_ne ... 096795.stm

Scientists have demonstrated a "runaway evolutionary effect" that is speeding up Australia's cane toad invasion.

This explains why the invasive toads have increased their rate of spread so dramatically, the researchers say.

They found that toads living at the very edge of their range were "super-invaders" - able to move beyond the boundaries of this existing habitat.

And when toads at the frontiers bred, their offspring inherited this ability to move quickly into new territory.

This phenomenon, which scientists have termed the Olympic Village Effect, has been proposed before, since these same scientists observed that the toads at the edge of the range had bigger front legs and stronger back legs - all the better to jump and to invade new areas.

In this study, the researchers tested the effect, essentially setting up a cane toad race.

Dr Ben Phillips from James Cook University in Queensland, Australia collected cane toads from four different populations.

He captured ten toads from the core population in northern Queensland, and ten from each of three populations that were increasingly distant from this point.

He took the toads to a facility in the appropriately named Middle Point near Darwin, where he fitted them with radio tags and then released them. The tags enabled the scientists to follow the toads' progress.

As Dr Phillips expected, toads that were collected from the edge of the range were much faster movers.

All in the genes

To confirm that this increased strength and speed had a genetic basis and could be inherited, Dr Phillips studied a generation further.

He allowed toads from the same population to breed. Then he set up another radio-tagged toad race, this time between these captive-bred offspring.

Toads that had parents from the edge of the range won the dispersal race, revealing that they inherited their speed and strength from their parents.

"It's bad news," Dr Phillips told BBC News. "It means they're getting faster and better at invading new areas."

Even worse, the researchers say, all animal invasions are likely to follow this pattern.

He explained that the faster moving toads even reproduced more quickly. But this could point to a chink in their biological armour.

"They have to be trading something off to do that," he said. "And one of the things we suspect is that they're trading off their immune systems."

Since the bigger, faster toads spread and breed so quickly, they are likely to leave any endemic diseases and parasites behind them because toads that move so quickly are likely to be disease-free.

This could mean that they and their offspring have less natural immunity. If this is the case, it could help scientists develop some sort of biological defence against the toads.

"If you re-introduce [these] parasites at the edge of the range, perhaps you could slow down the invasion," said Dr Phillips.

He and his colleagues plan to study the creatures in more detail in the hope of pinpointing some of these biological weak spots.

Cane toads were introduced to Australia in 1935, to north tropical Queensland to control sugar cane pests. They failed to do this, but succeeded in becoming one of the International Union for the Conservation of Nature's (IUCN) top 100 invasive species.

Their range now extends through most of Queensland and into Australia's Northern Territory.

"They're certainly up there with the worst invasive species," said Dr Phillips. "They're doing well for themselves, you have to give them that."

The work was published in the Journal of Evolutionary Biology.

[Thinking Aloud]

Wouldn't it be ironic if by observing evolution in progress, that can be seen, measured and verified, led to a way to exterminate the entire population?

Future-Comfort: "Evolutionists claimed to have observed macro evolution in the cane toad, but the self-same scientists wiped out every last trace of them. Isn't that convenient?"

[Svartalf]

It's not truly evolution... just natural selection.
When border invader cane toads have grown into a separate species from central habitat cane toads, we can actually speak of evolution.

As it is, that study just rediscovered that water is wet, and that in a population, those that move better will settle farthe from arrival pointr than others, and that statistically, they will breed with other good movers, which may result in a super hopper breed.

[Thinking Aloud]

I was just taking things to their (theo)logical conclusion...

[Rob]

When border invader cane toads have grown into a separate species from central habitat cane toads, we can actually speak of evolution.

I know we are being general here, but that is wrong. Evolution is not defined by speciation. My personal favorite definition of evolution is:

evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next

Perhaps being somewhat pedantic but meh.

[Svartalf]

speciation is the most tangible marker of the working of evolution, that's why the species canis familiaris was struck down from the roster and redefined as a set of subvarieties withing canis lupus.

[Pappa]

Cane toads aren't quite the bad guys we thought
http://www.newscientist.com/article/mg2 ... ought.html

IT COULD be one of the world’s most unfairly maligned creatures. Despite its invasion of Australia, the cane toad has not triggered the overwhelming ecological disaster that some predicted.

Cane toads (Bufo marinus) were brought to Australia in the 1930s in an attempt to eradicate a beetle destroying sugar cane. They quickly spread (see map). Last year, the toads were found in Australia’s most western state for the first time. One downbeat local newspaper headline lamented: “Cane toad battle lost”.

Australia’s frog-eating predators, including snakes, crocodiles and the northern quoll – a type of marsupial – have been dying en masse after ingesting the poisonous invaders. The worry was that mushrooming toad populations would outcompete native frogs and birds too. With the elimination of these native species seemingly imminent, an ecological catastrophe looked on the cards.

“People saw these ugly creatures moving across tropical Australia and common sense said there was going to be a huge disaster,” says Richard Shine, an invasive species researcher at the University of Sydney, who has reviewed various studies on the impact of cane toads (The Quarterly Review of Biology, DOI: 10.1086/655116). “But it just hasn’t happened at the scale that we feared.”

“The system seems to be absorbing the toads,” agrees Ross Alford of James Cook University in Townsville, Queensland. “Toads are not an overwhelming environmental disaster.”

Populations of native frogs and birds do not appear to have changed significantly since the toads were introduced, and recent experimental studies reviewed by Shine show that while the toads do compete with frogs for food and egg-laying sites, they also help frogs by removing their predators. “There isn’t much overall effect,” says Shine.

Shine says there is also no noticeable change in populations of insects, despite both cane toads and native toads eating them. Other researchers, including Alford, believe there isn’t enough evidence to be so optimistic. But Alford concedes that since populations of insect-eating species such as frogs and birds appear stable, it is probable that insect numbers have remained stable too.

Populations of goannas (monitor lizards), freshwater crocodiles, king brown snakes and northern quolls have dropped in some regions colonised by toads. But Shine believes many of these populations are reviving because the animals learn to avoid the toads. How so? According to Shine, native creatures encountering newly arrived adult cane toads will eat them voraciously, having “not grown up with them”. The experience is usually fatal, but once the toads have reproduced, their predators will survive eating the immature toads – which are less toxic than adults – and so learn not to eat the species again.

In 2008, for example, a wave of crocodile deaths was reported in the Victoria river, Northern Territory, coinciding with the toads’ arrival. The following year, toad-induced deaths among the crocodiles fell. Likewise goannas are once again abundant in areas of northern Queensland, even though 96 per cent of the lizards died when they first encountered the toads. “Nothing has become extinct,” says Alford.

Evidence that northern quoll numbers are recovering is weaker. This week the Nature Conservancy, a US non-profit organisation, published a report by John Woinarski, a zoologist at Charles Darwin University, Northern Territory, blaming cane toads for the quoll’s decline. “Northern quolls in some areas have been extirpated,” Woinarksi says.

Still, he points out that quolls were in decline even before cane toads arrived, because of a greater incidence of summer bush fires in recent years and the introduction by humans of cattle and predators such as cats. More encouragingly, Shine has evidence that young quolls can be trained to avoid cane toads by feeding them baby toads laced with a nausea-inducing chemical.

Woinarski says there is cause for optimism overall. “Our ecology is more robust than we feared,” he says.