Showing posts with label tadpoles. Show all posts
Showing posts with label tadpoles. 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.

Tuesday, April 5, 2011

Tadpoles and an Invasive Crustacean

After 30 years, the common frog can not activate their defenses against the American crayfish.

Iván Gómez Mestre and Carmen Díaz Paniagua, biologists from the Biodiversity Research Unit of the Principality of Asturias CSIC-Universidad de Oviedo and Station Biological relevance of Doñana (CSIC) respectively have confronted two groups of tadpoles with the American crayfish and have compared the degree of activation of their defenses. The researchers note that, despite the common frog tadpoles activated when they detect predators, are unable to perceive the American crayfish, which leaves no recourse for this invasive species.

"The common frog in the Doñana National Park has not yet adapted to the American red crayfish (Procambarus clarkii ) [photo]," said Iván Gómez Mestre. Both the common frog tadpoles in the wetlands of Donana, a town three decades has been in contact with this predator (between 10 and 15 generations), and tadpoles from populations that are faced by first time crab responded the same way: "The degree of activation of defenses is the same in both cases: null," says the biologist.

Tadpoles, explains, they have many defenses available to it, but when they detect the chemical signals (the smell dissolved in water) of a predator such as dragonfly larvae can morphological and behavioral changes.
"The changes in shape result in a wider tail and more pigmented, which attracts the predator to her leaving intact the vital organs and no tears or loss of tail have such serious consequences, since they can regenerate. And changes in behavior resulting in a reduction of activity that passed over unnoticed, "said Iván Gómez Mestre.

But these changes, despite improved survival in case of predators, have a price: "By reducing its activity, the tadpoles were fed less, grew more slowly and faced with the progress of your pond dry season, addition to give advantage to competitors for food, "says the researcher. Hence, the activation of defenses is not permanent and depend on the detection of the predator species by the tadpoles.
An evolutionary race

The results published today contribute to better understand the series of changes that occur in the Iberian ecosystems that invasive crab, native to the Southeastern U.S. and present from Doñana to Asturias. As indicated by Iván Gómez Mestre, among other effects "are known to be in areas that present the American crayfish is a proliferation of predatory birds, so that the pressure on amphibians increases even more."
"The question is whether common frog populations exposed to American crayfish have enough time before dying to adapt to the presence of an introduced predator so voracious. Can not venture a period in evolutionary terms, because each species responds differently, but a reference can be detected cases in the U.S. adaptation of bullfrog tadpoles by introduced fish against the man after 110 years of contact, "says researcher.

The species was detected 15 years ago in Asturian rivers. The American crayfish damage native ecosystems and particularly harmful to salmonids, small fish, amphibians, and vegetation waters. It has also displaced the native crayfish ( Austropotamobius pallipes lusitanicus) in almost all waterways.

This situation has led to initiatives such as the Crab Project:

Ivan Gomez-Mestre and Carmen Díaz-Paniagua. (2011)  Invasive predatory crayfish do not trigger inducible defences in tadpoles Proc. R. Soc. B published online 30 March 2011doi:10.1098/rspb.2010.2762

Wednesday, March 16, 2011

Tadpoles provide clues as to how Putrescine protects the brain from epileptic seizures

The neurochemical putrescine surges
in the brain after a seizure. By
studying putrescine in tadpoles,
researchers found that it exerts a
calming effect, protecting the brain
for a while against a second seizure.
Credit: Mike Cohea/Brown University
March 6, 2011 Brown University Press Release

The aftermath of an epileptic seizure has some mysterious characters, including the molecule putrescine. In new research on tadpoles, which share similar brain chemistry with humans, putrescine emerges as a calming influence that conveys resistance to subsequent seizures. In the long run, the discovery could aid in developing drugs for young children with epilepsy.

For years brain scientists have puzzled over the shadowy role played by the molecule putrescine, which always seems to be present in the brain following an epileptic seizure, but without a clear indication whether it was there to exacerbate brain damage that follows a seizure or protect the brain from it. A new Brown University study unmasks the molecule as squarely on the side of good: It seems to protect against seizures hours later.

Putrescine is one in a family of molecules called “polyamines” that are present throughout the body to mediate crucial functions such as cell division. Why they surge in the brain after seizures isn’t understood. In a lengthy set of experiments, Brown neuroscientists meticulously traced their activity in the brains of seizure-laden tadpoles. What they found is that putrescine ultimately converts into the neurotransmitter GABA, which is known to calm brain activity. When they caused a seizure in the tadpoles, they found that the putrescine produced in a first wave of seizures helped tadpoles hold out longer against a second wave of induced seizures.

Carlos Aizenman, assistant professor of neuroscience and senior author of a study published in the journal Nature Neuroscience, said further research could ultimately produce a drug that targets the process, potentially helping young children with epilepsy. Tadpoles and toddlers aren’t much alike, but this basic aspect of their brain chemistry is.

“Overall, the findings presented in this study may have important therapeutic implications,” Aizenman and co-authors wrote. “We describe a novel role for polyamine metabolism that results in a protective effect on seizures induced in developing animals.”

The result that “priming” the tadpoles with a seizure led to them being 25 percent more resistant to a subsequent seizure four hours later was “puzzling,” said Aizenman, who is affiliated with the Brown Institute for Brain Science. It took about a dozen more experiments before his team, led by graduate student Mark Bell, could solve the mystery.

First they hindered polyamine synthesis altogether and found that not only did the protection against seizures disappear, but it also left the tadpoles even more vulnerable to seizures. Then they interrupted the conversion of putrescine into other polyamines and found that this step enhanced the protection, indicating that putrescine was the beneficial member of the family.

Going with those results, they administered putrescine directly to the tadpoles and found that it took 65 percent longer to induce a seizure than in tadpoles that didn’t get a dose of putrescine.

Further experiments showed that the protective effect occurs after putrescine is metabolized, with at least one intermediary step, into GABA, and GABA receptors are activated in brain cells.

“Potentially by manipulating this pathway we may be able to harness an ongoing protective effect against seizures,” Aizenman said. “However I should caution that this is basic research and it is premature to predict how well this would translate into the clinic.”

In the meantime, the research may also help explain a bit more about young brains in general, Aizenman said.

“Our findings may also tell us how normal brains, especially developing brains, may regulate their overall levels of activity and maybe keep a type of regulatory check on brain activity levels,” he said.

In addition to Aizenman and Bell, the paper’s other authors are undergraduates James Belarde and Hannah Johnson. The American Heart Association and the National Institutes of Health funded the study, while individual researchers were supported by the National Science Foundation, the Klingenstein Fund, and the Brain Science Siravo Awards for Epilepsy Research.