Showing posts with label Rhinella marina. Show all posts
Showing posts with label Rhinella marina. Show all posts

Friday, August 19, 2011

Cane Toad Tadpole Cannibalism

Rhinella marina. JCM
Most tadpoles eat almost anything, they filter the substrate and water for organic mater taking in bacteria, decomposing matter, mud, and other kinds of molecules they can get energy from. The Marine Toad or Cane Toad as the Australians call them have tadpoles that have very flexible diets. A forthcoming article in Animal Behaviour reports Rhinella marina tadpoles will eat the eggs of their own species. The BBC is reporting on this article, and the original article can be found here.

Cane toad tadpoles cannibalise eggs to survive, and the behavior starts when they are just a few days old.It is a habit that reduces competition and provides the cannibals a nutritional boost.

"Toad tadpoles almost never encounter eggs that are closely related to them - so they can happily go ahead and munch any they find” says Professor Richard Shine, University of Sydney. Researchers from the University of Sydney and James Cook University, Queensland in Australia, wanted to find out why cane toad tadpoles ate the eggs of their own species.

Their study compared two groups of tadpoles, one group was allowed to eat toad eggs and the other was prevented.

The team found that cannibal tadpoles survived, grew and metamorphosed into toads more successfully than the tadpoles that did not eat the eggs.

Although the tadpoles benefited from the nutrition of the eggs, they also improved their chances for the future, according to Professor Richard Shine who lead the research.

"The most important benefit is not nutrition, but the reduction of competition from the tadpoles that otherwise would have hatched from those eggs," he said.

But the tadpoles' voracious appetites do not extend to their siblings, as Prof Shine explained.

"The tadpoles don't eat close kin eggs, because of the short incubation period and the long delay between successive clutches by a single female," he told BBC Nature.

"Thus, toad tadpoles almost never encounter eggs that are closely related to them - so they can happily go ahead and munch any they find, without the risk that they are eating their relatives."

Proffesor Shine's results build on his previous findings that cane toad tadpoles can detect eggs in a pond using their sense of smell.

"Toad tadpoles can use specific chemicals produced by toad eggs to locate those eggs and eat them," he explained.

"We were astonished to discover that these simple little creatures, with brains the size of a pinhead, can react in subtle ways to specific cues.

"The tadpoles have a secret chemical language that only they can detect and respond to."

Cane toads are native to South America but were introduced to Australia in 1935 to control sugar cane pests.

Original Article
Michael R. Crossland, Mark N. Hearnden, Ligia Pizzatto, Ross A. Alford and Richard Shine. 2011.Why be a cannibal? The benefits to cane toad, Rhinella marina [=Bufo marinus], tadpoles of consuming conspecific eggs. nimal Behaviour, In Press, Corrected Proof, Available online 9 August 2011.

Friday, January 21, 2011

Monitor Lizard Mortality Due to the Cane Toad?

ABC Western Queensland is carrying the following story that reports anecdotal evidence that the Cane Toad is the cause of increased mortality in Varanus populations of the Cooper drainage. This is unedited.

20 January, 2011 3:37PM AEST

Cane toads in the Cooper threaten predators

By Nicole Bond and Julia Harris

Cane toads first arrived at Noonbah station homestead near Stonehenge, in March last year, although they were seen at a neighbouring property, Lochern, about six months earlier. Now, with a boom season in the district, the toad numbers are increasing, and Angus Emmott, a grazier and naturalist said he's starting to see their impact on goannas. He said the cane toads are just breeding like crazy.

"There's young ones everywhere but there's also lots of big ones," he said.

The issue of concern to Mr Emmott is he's now noticing that the goannas in particular are starting to die at Noonbah.

"I'm seeing goanna bodies lying around and anything like mulga snakes, De Vis banded snakes; any of those animals that have frogs as a significant component of their diet are really going to be hammered," he explained.

Mr Emmott said he hasn't seen a dead goanna with a cane toad in its mouth but the evidence from northern Australia is overwhelming.

"When the cane toads first move in, you get a mass die off of these particular groups of animals."

The promising part for Mr Emmott seems to be that over a period of about 20 years, the few goannas that do survive gradually learn to live with the cane toads and leave them alone.

He's hoping that will occur in the Cooper system over time as well.

"But we've probably got 15 to 20 years to wait until the goanna populations come back up to any sort of numbers again," he explained.

He said the goannas and other frog eating animals have a major role in the balance of the ecosystem and that's going to change.

"But without close, intense study we're probably not even going to be aware of what exactly those impacts are."

A number of scientists are interested in the invasion of cane toads into the Lake Eyre Basin catchments, and Mr Emmott said it's because it wasn't something that was predicted.

"It was thought that this part of the world would be too arid for them.

"They seem to be adapting quite well to the aridity; although it's not very arid at the moment!

"Sydney Uni had a student working around the Longreach area last summer and I'm sure if they can get some more money together they'll be doing some more work," said Mr Emmott.