Category Archives: Amphibians

PREY LEARN THE FUTURE

Predation has shaped the whole of the living world, as prey respond to evolutionary changes in predators, and vice versa. The earlier prey can detect a predator, the greater their possibility of surviving, either by fleeing or hiding. In many aquatic species, prey detection can occur from beyond the grave – for example, Daphnia (“water-fleas”) develop hard protective structures (“inducible defences” – see picture below) when in the presence of water that had contained fish that had eaten Daphnia. The predators have been chemically “labelled” by their prey, enabling other Daphnia to protect themselves.

daphnia

Daphnia lumholtzi – on the left, reared in the presence of fish, on the right, in the absence of fish

A study about to be published in Behavioural Ecology and Sociobiology shows that these kind of effects can also involve prey learning, even before they have hatched out of the egg. Maud Ferrari and Douglas Chivers investigated the behaviour of woodfrog (Rana sylvatica) tadpoles in response to a predator, the Tiger salamander. These tadpoles show no innate prey recognition, but if they are exposed to the smell of salamander before they hatch from they egg, they avoid predators when they have turned into tadpoles, by reducing their movement. [It may seem counter-intuitive to talk of "smell" in water, but many aquatic animals (including fish) have clearly distinct smell and taste pathways. I'll blog about this in the future.]

Wood frog tadpoles (image: http://www.vernalpool.org)

Ferrari and Chivers have taken this a step further, by seeing whether the tadpole embryos can actually learn the threat posed by a predator. To test this, they presented frogspawn with salamander odour coupled with cues from injured tadpoles, for two hours a day over five days, then tested the tadpoles for their responses to the predator.

They found that the amount of freezing shown by tadpoles was dependent on the concentration of the injured tadpole cues coupled with salamander smell, demonstrating that the embryos had learned to associate the two signals. There also seemed to be a time of day effect – the effect was stronger when learning took place in the afternoon, compared to the morning or early evening – although further experiments need to be done to confirm this.

In some species (especially insects), early experience can lead to the non-genetic transmission of preferences from one generation to another. This study shows that interactions between predator and prey can be extremely complex, involving innate responses, and learned changes in behaviour, which may even occur before birth.

Original article (open access).

BBC page, with quotes from Ferrari.

 

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Filed under Amphibians, Behaviour, Predation

TOADS BREAK THE RULES

November 2007

You all know the generally-accepted “biological” definition of a species – a population of interbreeding organisms. Toads don’t seem to be quite so clear about this. A new article in Science looks at inter-specific hybridisation, which in two species of toad appears to be linked to environmental conditions.

BBC summary, including videos of toads; original article in Science (you or your institution will need a subscription to get past the abstract).

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Filed under Amphibians, Videos

SOLUTION TO THE AMPHIBIAN FUNGUS PROBLEM?

November 2007

One of the factors that may account for the global decline of amphibian populations is a fungal infection. New Zealand scientists suggest that a readily-available antibiotic, chloramphenicol, may resolve the problem. No peer-reviewed article yet, but this from the BBC.

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Filed under Amphibians, Diseases

AMAZING REPTILE IMPRESSION

November 2007

Seeing fossilized trackways is always cool, but this unique fossil from Pennsylvania shows body impressions of 330-MY old amphibians. Is it one animal or two? How was the fossil made?

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Filed under Amphibians, Fossils, Images

FANTASTIC COLLECTION OF PHOTOS

October 2007

Andrew Johnson (First Year) has a website which includes some amazing photos of amphibians and reptiles, taken both on his travels (in particular in Bali) and at home – including one of a minxy gecko that escaped and appears to have lived under his bed for several weeks. It’s really worth looking at these terrific pictures.

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Filed under Amphibians, Images, Reptiles

LOCH NESS MONSTER FOUND!

May 2007

OK, so it’s a toad. But it’s still where it shouldn’t be – 100m down at the bottom of Loch Ness.

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MORE ON THE DECLINE OF AMPHIBIA

April 2007

Various hypotheses have been put forward to explain the catastrophic collapse in the number of frogs to be found in the tropics, from hormonal effects due to pollution, to a lethal fungus linked to global warming. Another factor has now been added: a decline in leaf litter. This study looks at 35-year decline in amphibians and reptiles in a rainforest in Costa Rica.

BBC summary, Guardian summary, PNAS article (open access), Nature article about fungus/global warning (abstract only).

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Filed under Amphibians, Diseases, Reptiles