Sneaky Snakes and Scholarly Sticklebacks

22 June 2009
Presented by Ben Valsler.


On this NewsFlash, we find out how sneaky Tentacled snakes catch fish through cunning, how pieces of RNA could switch off cancer, and how schools of sticklebacks learn from other fish.  Plus, how a taxi disguised as a bee can help to highlight the plight of our buzzy friends.

In this episode

Extraordinary snakes

There's an old wives tale that snakes hypnotise their prey, but a new study has revealed even more amazing - but real - goings-on in the snake world. Tentacled snakes (Erpaton tentaculatum) have evolved an astonishing way of tricking small fish into swimming right into their mouths. Kenneth Catania from Vanderbilt University in Tennessee in the US has uncovered how the snakes confuse the fish into swimming towards instead of away from them. The fish's reaction is so predictable that the snake aims at the spot the fish will arrive at, instead of tracking the actual movement of the fish.

These are most peculiar snakes, a type of mud snake, that have a pair of moveable tentacles on the end of their noses, the only reptiles in the world to have such a structure. They live in freshwater rivers and streams and in brackish water in Southeast Asia and when they are hunting they lie in wait motionless curling their body into a characteristic J-shape with their heads bent around in a hook.

Tentacled SnakeWhen a fish approaches, the snake lunges into action, striking out ballistically in only 15-20 milliseconds. But the fish have evolved a specialised escape mechanism that is even quicker. They detect ripples of pressure in their ears on each side of their body. When one ear picks up a pressure wave an automatic reflex signal is sent to the muscles on one side of its body, which contract causing the fish up into a C shape: scientists have called this the C-start. With their heads turned round, the fish then swims extremely rapidly away from the source of the sound, in a movement that can't be reversed once it has begun.

In his paper in the journal PNAS, Catania describes how he began watching snakes hunting in slow motion (on high speed cameras of up to 2000 frames per second) and discovered that instead of swimming away, the fish (fathead minnows) kept on swimming right into the jaws of the predator. Out of 120 trials he recorded on camera with 4 different snakes, 78% of the time the fish turned towards instead of away from the snake.

He also noticed that before the snake moves its head, it twitches a point slightly further down its body. Using a hydrophone he picked up a sound wave this motion produced.

So the snakes have co-opted the fishes' reflex escape response, deliberately making a sound comes from the other side to their heads, triggering the C-start response in the wrong direction - the fish swim towards instead of away from the snake, and all in super-quick time that a human observer can barely detect.

Even more extraordinary is Catania's discovery that instead of aiming at the fish and tracking it's movement as it swims away - as most predators do - the tentacled snakes head directly for the spot where it expects the fish to end up if they initiated a C-start towards the head.

The next thing Catania wants to find out is whether the snakes' predictive ability is hard-wired or whether they learn it. He hopes to find some baby snakes just after they have hatched and carry out the same video analysis of their first attempts to catch their dinner.

RNA-away liver tumours

Scientists have used a genetic technique to successfully treat mice with liver tumours.

DNA fragmentWriting in the current edition of the journal Cell, Ohio State University researcher Jerry Mendell and his team describe how they have used short sequences of genetic material to block the growth of cancers.

The work was based on the finding in recent years that cells regulate the activity of their genes through the use of a family of small molecules called micro RNAs (miRs).  These work by shutting off the actions of certain genes, particularly those linked to cell growth and which are normally active only when cells need to divide or in a developing embryo.  But if the production of these micro RNAs goes awry then many of these growth-associated genes can be reactivated, which is what, scientists believe, might promote the growth of tumours.

Indeed, when researchers have studied a number of different cancers they have found that many of the micro RNAs that should be present are in fact missing in the malignant cells.  This led the Ohio team to ask what would happen if they put the micro RNAs back into cancerous cells?

To find out the researchers used experimental mice with a genetic tendency to develop liver cancers. Having identified one micro RNA that was frequently missing from the malignant cells in these mice, the team inserted the genetic sequence for that micro RNA - called miR-26a - into an adeno-associated virus vector (AAV), which is effectively a viral shell that lacks the ability to reproduce.

One group of mice were given injections into a blood vessel supplying the liver of a million million particles of the virus containing miR-26a.  A second group of mice received injections with a dummy virus and were used as controls.

Three weeks later the animals were studied for signs of liver tumours.  As expected, six out of eight of the control animals all had large liver tumours, but the team found that of the ten animals given the therapeutic virus eight had very few signs of disease.  In these animals tests showed that the virus had successfully penetrated 90% of the cells in the liver, and of the two animals that did not respond the treatment appeared to have failed because the viruses did not reach the liver successfully - in other words for technical rather than biological reasons.

Clearly it is early days, and the safety of this approach still needs to be confirmed, but this discovery, the first of its kind, shows that the future treatment of cancer most likely rests with genetics, rather than just toxic drugs.

Size does matter

Giant sperm have been found inside ancient fossil crustaceans, revealing just how long ago these enormous male sex cells evolved. The oceans 100 million years ago were full of males hotly competing with each other over who got the best mates.

OstracodPublishing in the journal Science, Renate Matzke-Karasz of the Ludwig Maximilians University in Germany lead a team of researchers who studied the internal organs of some 100 million year old ostracods - a relative of crabs and lobsters that look a little like mussels (a type of mollusc of course). They are sometimes called seed shrimp, for obvious reasons if you see one.

There are around 65,0000 species of ostracod which live in marine and freshwater.

Some of the modern-day male ostracods have extraordinarily big sperm that can be up to ten times longer than they are. Now for the first time the sperm of the ancient ostracods have been discovered using a complex imaging technique called synchrotron X-ray holotomography. This non-invasive technique, developed at the European Synchrotron Radiation Facility, allows researchers to see inside these tiny creatures that are only around 1mm in size, and compile images together on a computer into a 3D model.

The team found evidence that the ancient male ostracods has huge sperm ducts (Zenker organs) inside them, and the females - like modern ostracods - have huge internal cavities that receive the sperm after mating.

Ostracods aren't the only animals that have such enormous sperm. A more familiar creature, the fruit fly, also produce 6mm sperm - an impressive feat for a 1-2mm fly. It seems bizarre to spend so much energy making such huge sperm, but it all comes down to competition for mates.

For a male that has to compete with lots of other males to get a mate, and when females mate with many different males, one way of ensuring he passes on his genes to the next generation is by producing huge sperm. In animals like fruit flies and ostracods bigger sperm are more likely to fertilize eggs inside the female than smaller ones.

It's best not to think of an analogy of this in human beings, but this study does shed light onto the evolution is this peculiar male trait - which in ostracods probably evolved just once - and showing that is been the case that size really does matter for a very long time indeed.

Social Networking in Fish

UK scientists have discovered that some fish learn by watching the experiences of others.

3 spined sticklebackDurham University scientist Jeremy Kendal, writing in the journal Behavioural Ecology, caught 270 sticklebacks from a local river.  The fish were divided into groups.  The first group were placed in a tank with two feeders, one which dished out generous portions of blood worms and another which was more frugal.

A test revealed that the fish had learned the drill and at this point they were then confined within a 'viewing gallery' section of the tank whilst a second group of fish were introduced. 

But this time the scientists reversed the feeders so that the previously generous one was now more stingey and vice versa.  The confined 'educated' sticklebacks were then left to watch how the newly-introduced fish fared.  Afterwards they were released again and the team observed which of the two feeders they now favoured.

Incredibly, just by watching how the other fish had got on, over 75% of the observering fish had learned from the experiences of the other sticklebacks that the feeder situation had reversed.  Even more impressive was that, in a subsequent experiment, when the team adjusted the relative generosity of the feeders the observing fish only changed their behaviour if they saw the other fish doing better in the new situation than they had in the old.

This kind of learning approach, known as a 'hill climbing strategy' is probably key to helping these animals to escape from predators.

"These fish are too vulnerable to forage alone," explains Kendal, "so they have to move around in groups. They are therefore social, and by watching the outcomes of others and responding appropriately this is a sound strategy to avoid predation and maximise returns."

And regardless of the evolutionary benefits, any claims of fish having a  once-round-the-tank-memory is definitely a fish out of water, at least in the stickleback world.

16:21 - The Plight of the Bumblebees

We investigate why bee numbers are falling and what effect this will have on our agriculture.

The Plight of the Bumblebees
Bridget Nicholls, Pestival; Pat Goodwin, Wellcome Trust; Steve Benbow, the London Honey Factory

Helen -   Another issue that's been hitting the headlines lately, is that of the plight of our beloved bees.  So we sent Meera Senthilingam down to London, to The Wellcome Trust to find out what all the buzz is about.

Bee CabMeera -  This week saw the unveiling of a taxi dressed up as a bee, driving around the streets of London.  Now, why is a taxi dressed like a bee, you ask?  Well, this bee cab has been custom made to celebrate Pestival.  A festival that celebrates insect life which is taking place on London South Bank this coming September.  And the theme for this year's festival is a collapse of bee colonies around the world.  Bridget Nicholls is the festival director.

Bridget -  The key theme of this year's Pestival is bees - We're creating the Queen Elizabeth Hall we'll be turning into the Queen Bee hall and is going to be called, 'The Bee Social' and it's all about people coming together from different disciplines to discuss colony collapse and creating a critical mass.  I just think that it's very important to get urban people thinking about saving the bees because they've got balconies, they can plant flowers for urban bees.  I think we are in danger of loosing our bees and obviously, we should do something about it while we can.

Meera -  Festival Director and organizer Bridget Nicholls.  This plight of bees is a theme well-chosen as bee populations have been decreasing at an alarming rate in recent years, with bumble bees in the U.K. estimated to have fallen by 60% since 1970 and in some parts of the country, honey bees by up to 80%.  The repercussions of this disease are enormous with the bees pollination services, having a commercial and economic value of around 20 to 50 billion pounds worldwide, as bees don't just make honey, but they pollinate more than 90 of the flowering crops we rely on for our food sources.

Wellcome Trust Scientist, Pat Goodwin explained why these services are so valuable.

Pat -  Fruits won't ripen, we won't get flower seeds without having pollination which actually fertilizes the seeds so that they can grow into fruits.  Apples, pears and all the flowers that we love in our gardens, they depend on pollinators as well.

Group of feeding bumblebeesMeera -  So no more apples, pears or pretty flowers?  Pat told me more about why these decrease is thought to be happening.

Pat -  Nobody really knows the answer.  There are lots of theories.  One thing is climate change which is the warmer winters are affecting bee hibernation for example and upsetting their whole, sort of, life cycle.  There's new pathogens coming up, the Varroa mite, but it's not just the Varroa mite.  It carries viruses, so it lives on the bees, but it also transmits viruses between bees, then there's lots of issues around modern agriculture. Whereby you have vast fields which are then harvested, so there's nothing left for bees to pollinate and because they use the nectar and then take it to their hives and make it into honey.  Another thing I think, is probably in breeding, bees have been bred to be non-aggressive and to produce lots of honey, and that is probably meaning that they're loosing some genes which are important for their vitality.

Meera -  Now a buzz word at the moment, thought to be causing some of the big falls in population numbers is colony collapse disorder, where entire colonies are dying and disappearing for no known reason.  This has happened on a larger scale in the U.S. but is increasingly happening worldwide.  Bee keeper Steve Benbow has over 350 commercial hives nationwide.  So I ask how this plight in bee numbers has affected his trade and if his hives have experienced colony collapse.

Steve -  We don't really see that directly at the moment, but we do see trouble from say, Varroa, a parasitic mite that latches on to the bees and this brings in lots of other diseases such as cloudy wing virus.  It causes a deformity in the wings. The diseases we have to keep on top off and trying to sort of learn new techniques, things like icing sugar is a very good way of managing the Varroa which at the moment is being trialed where the bees do what we call a hygienic behavior, where they're cleaning themselves and hopefully, knocking off the mites and cleaning and grooming each other to help reduce this terrible infestation that can take place.

MVorroa miteeera -  So bee keepers like Steve Benbow are finding new ways to get around these problems.  But is getting around these diseases in honey bees, enough?  What about the other species being affected?  Well, April 2009 saw the launch of the Insect Pollinator's Initiative by 10 million pounds donated by many U.K. funders, including the Wellcome Trust and Natural Environment Research Council will be used to try and understand the decrease in bee populations.  Pat Goodwin told me how the initiative plans on doing this.

Pat -  What we hope to do is to bring together researchers in different fields to look at all these complex interactions and if we can understand what is underlying the issues facing bees, we might be able to do something about stopping it.

Meera -  So whilst researchers are trying to find out the causes and the cure to this problem, why not find out a bit more about it or even learn how to keep bees as a hobby, at this year's Pestival, taking place from the fourth to the sixth of September at the South Bank Center in London.


Add a comment