Podcast Transcript

Cooperating Bats

A new study has shown that Bats might stay quiet and listen to each other when they are out hunting for their dinner.

That’s according to Cynthia Moss and her colleagues from the University of Maryland in the states who have been studying big brown bats in captivity, and tracking how their ultrasonic signals changes when the group pursues their flying insect prey.

Nocturnal bats use echolocation to forage for prey and safely navigate around in the pitch dark. They emit very high pitched squeaks and measure how long it takes to bounce back to them, and from that they can work out where objects are around them.

And of course most of the sounds bats make are inaudible to human ears – we can only pick up sounds of between around 20 hertz and 20 kilhertz, while bats can chirp at over 100 kilhertz.

What Moss and her team discovered was that at certain times some of the bats turned off their sonar and went totally quiet for a while – only for around 800 milliseconds, which might not sound like much but is in fact a long time in the fast-paced life of a bat.

For now we can’t be sure why the bats are going quiet like this, but it is possible that one bat stops making sounds and eavesdrops on the sounds of another bat, perhaps to help prevent crossed signals. You can imagine when they were lots of bats feeding in a similar area it would be very easy for all their signals to get mixed up and confused. If that is what the bats are doing then this would be evidence of a type of cooperation that has long been suspected but never proven in these flying mammals.

7th Sep 2008

The Genetic Key to a Happy Marriage!

Polygamy - of mice and men, or voles at least - Scientists have shown that a gene variant carried by some men could be the cause of marital dysharmony. The research builds on previous work carried out in rodents showing that prairie voles, which are highly monogamous, carry a different form of a gene called avpr1a compared with their fast and loose cousins the montane or meadow voles, which favour multiple matings. Researchers had
also shown that adding the gene from the faithful voles to the brains of the polygamous animals could convert them into model monogamous partners.

Now a similar finding has emerged amongst humans. Paul Lichtenstein and his colleagues at the Karolinska institute in Sweden studied the sequence of the human version of the avpr1a gene region in 552 married or co-habiting couples and compared the sequences with measures of relationship strength. Eleven different forms of the gene region were identified but, intriguingly, one of them - allele 334 - which was carried by 40% of the participants, was strongly linked to poorer "Partner Bonding Scores" (PBS). Men with two copies of the gene (one from their father and one from their mother) were also half as likely to be married (favouring co-habitation) and twice as likely to have faced marital crisis or the threat of a divorce in the previous 12 months (34%) compared with the men with one or no copies of the 334 allele, only 16% of whom reported marriage difficulties. This suggests that what goes for the voles also goes for humans, but may also have relevance to our understanding of certain other aspects of human social behaviour and development including altruism and autism, both of which have been linked to changes in this same gene.

7th Sep 2008

An Ancient Taste for Shellfish

It’s a myth that if a scuba diver spies a glimmering pearl inside a giant clam and reaches in to steal it his or her arm will be grabbed by the slamming jaws of the twin-shelled mollusc. Giant clams can grow to over a metre long and they do make pearls but it is virtually impossible to get yourself trapped inside one.

But giant clams have hit the science headlines recently, with the discovery a new species living in the Red Sea. This is the first giant clam discovery in twenty years, bringing the total number of species in the world to eight, thanks to an international team of researchers led by Claudio Richter of the Alfred-Wegener-Institute for Polar and Marine Research in Germany.

And what’s more, this new clam has uncovered some of the oldest evidence yet of mankind’s plundering of the oceans.

The new species, tridacna costata, is incredibly rare today, one reason why it had been overlooked for so long, but it has now been shown to be a separate species from studies of its shape and also its genetics.

Researchers have also looked back in time at the fossil record and discovered that this species used to be incredibly abundant. Around 125 thousand years ago, Tridacna costata made up around 80% of the species of giant clam living in the Red Sea. Now it makes up less than 1%.

And it seems that possible culprits for the clam’s massive decline could be ancient hunter-gatherers, who may well have taking a liking to these large, nutritious shellfish, which are extremely easy to harvest because they don’t run away! The timing of the demise of these giant clams coincides rather suspiciously with when it is thought early Homo sapiens began migrating out of Africa. Not just that, but the clams used to be much larger than they are today, pointing an even stronger finger of blame at mankind because is suggests that big specimens were wiped out a long time ago by our ancient ancestors.

7th Sep 2008

New Method to Vaccinate against the Flu

New approach to battling flu - Scientists have developed a new class of flu vaccines that might help to contain a future pandemic. Writing in this weeks PNAS New York-based researcher David Ho and his team have used DNA coding for part of the surface coat of flu viruses to protect mice against a lethal dose of the infection. Previously the best way to protect against the flu was to grow the virus in hens' eggs before chemically inactivating and purifying it to turn it into material that could safely be injected. But a major problem with this approach is that it takes a long time to produce the vaccine and, when injected, it tends to trigger a highly focused immune response against just that one form of the flu. As a result the vaccine regularly needs updating to ensure that it protects against new strains produced when the virus mutates, which it does continuously. To get around this problem the US team, who are based at Rockefeller University, first built a genetic family tree from 467 different strains of the H5N1 flu virus. This enabled them to home in on a part of the flu genome at the root of the family tree that was the same amongst the majority of the different viral strains. The team then produced a DNA sequence coding for this part of the viral genome, which was from the main surface protein called HA. Mice injected with this DNA sequence produced large amounts of antibody and white blood cells that could neutralise a range of H5N1 strains. Most encouragingly, when mice were infected with lethal doses of virus that killed control animals those previously given the new vaccine all survived. According to the researchers, their vaccine strategy offers a fast and affordable way to combat H5N1, viewed by many as the best contender to cause the next pandemic.

7th Sep 2008

Push-Pull - Using Plants as Natural Pesticides

Chris - Tony: You’re working at Rothamstead as well. You’re looking at how plants actually produce chemicals which themselves can repel pests.

Tony - Yes, that’s right. As James was talking about just a minute ago, plants themselves produce 2-300 compounds which are volatile chemicals on the surface of the plant. It’s what gives them the smell to us but it’s also what gives them the smell to the insects which try to colonise that crop and cause damage to it.

Chris - So the insects are sniffing out lunch by following the odour of the plant?

Tony - Yes.

Chris - And can the reverse also be true because James was saying that you can get humans that are naturally repellent to mosquitoes? Are there plants that are naturally repellent to plant pests?

Tony - Well, in this country aphids are, in particular, a nuisance pest for our crops. They’ve designed their olfactory system to go to the crop and find the specific one that they want to have for lunch., as it were. So there are compounds given out by that crop which that particular aphid really wants to go for. In the same way it’s not going to waste time going around trying to find crops where they’re not there. So there are some chemicals given off by none-host plants that the aphid doesn’t want to go to. They can repel the aphid.

Chris - So by planting those near to a plant which you want to have as a crop you could mask the smell of the attractive with the nasty one and then you repel the pest?

Tony - Yes, we have a project going on at the moment in Kenya in East Africa and in that region the people there are subsistence farmers. They want to grow maize. Maize is a very important crop there. It’s subsistence farmed but the maize is attacked by a stem borer pest. That’s a moth which lays eggs on the maize and the eggs hatch, create caterpillars, the caterpillars eat out the centre of the maize plants and they fall over and die so there’s no food. We put together a push-pull system in that part of the world where we’re using plants to control what those moths are doing. Round the outside of the field we have a plant which is very attractive to the moths so the moths will want to go there rather than go to where the maize is. The maize is protected from those moths. At the same time, in between the maize which is growing in the field, there are some plants planted which give off a chemical signal to the moth that would come in that says these plants are already damaged. The volatile chemicals that they give off simulate or are the same chemicals as what would be produced by a maize plant if it was damaged. Any insects that are inside the field looking for a good place to lay their eggs, they’re going to think that’s not a good place for me.

Chris - Because it’s already been half damaged? They think someone else has got there first and eaten all the food?

Tony - That’s right the signals tell them that this is not a good place.

Chris - Ok, so it sounds good on paper but does it work? If you do objective studies on this and count numbers does it work?

Tony - Yes. It works beautifully in East Africa at the moment. Because there is such a lot of damage caused by these stem borer pests and the expense of having pesticides in there is just not possible for subsistence farmers. While their yields are quite low because they haven’t got chemical inputs like we have in Europe the yields are very low. If you can increase those by using this push-pull approach where you’re pulling the insects out in to those trap crops, pushing them away with the inter-crops away from that maize then you get significantly more yield with it. 2-4 times the yield is common in these areas.

Chris - What about other kinds of pests because it’s not just insects which are a pest. Elephants are as well in Africa and I don’t expect you to do anything about that but plants themselves can be a pest. I’ve got bindweed galore in my garden at home and I know there are certain forms of that which can be a real nuisance. Is there any way of dealing with the plants themselves?

Tony - Plants themselves are also producing chemicals through the roots. We’ve talked about volatile chemicals that insects locate or avoid their host plant. Plants also produce materials in the soil. That’s a battleground as well so they’ll be trying to compete with other plants.

Chris - So they can literally fend off another plant?

Tony - Yes.

Chris - If they decide they don’t like it by secreting something into the soil?

Tony - That’s right.

Chris - And how can you use that?

Tony - It can be from the roots or the folia or material above the ground which then falls to the earth.

Chris - And how can you use that? Do you have plants that are friendly to crops but unfriendly to weeds then?

Tony - Well, this project in Africa that I was talking about just now. One of the crops that we put in between the maize to repel the insects: when that was used in the field situations we found that it completely stopped a parasitic weed which normally attacks maize as well. This weed’s called Striga hermonthica. It’s a Striga plant, it’s a witch weed and causes massive damage. We found that the intercropping that we use – the intercrop that we use in particular is called Desmodium (silverleaf is the common name). This was producing chemicals in the roots, naturally occurring chemicals in the roots which it uses in its own ecology. This was affecting the Striga seeds and preventing them from germinating in the soil and then attacking the maize plant.

May 2008

Mosquitoes - Why do they find you so attractive?

Chris - James, let’s talk abut your work on mosquitoes. It sounds a bit frivolous talking about mosquito bites but in the grand scheme of things mosquitoes are probably the most dangerous animals, aren’t they?

James - Quite possibly, yes. It’s not actually the mosquitoes that cause the problem although they bite and people react differently to their bites. You can have quite a severe allergic reaction to the bites. It’s actually the pathogens that they carry; the diseases they carry such as malaria, dengue fever, filariasis. There’s a whole number of diseases that they carry and, of course, those are the diseases that cause the problem.

Chris - There’s something like 300,000,000 cases of malaria every year, 3,000,000 deaths. It’s a huge number.

James - That’s right. Exactly, almost 2,000,000 people die every year.

Chris - So understanding what lures them to us is crucial in being able to tackle that problem head-on because we know that just spraying them doesn’t work.

James - Yes, the more we understand about finding them in the first place the better we can develop control methods to stop that from happening.

Chris - Those few hundred chemicals that you were telling Ben ooze out of our skin and that mosquitoes are sensitive to (at least to some of them): what actually are those chemicals and what are they doing?

James - Well, there’s a whole range of chemicals that mosquitoes respond to. The main chemical they respond to is carbon dioxide which is mainly given off by our breath but is also released through our body as well. Other chemicals such as 1-octen-3-ol which is also given off as an alcohol, it’s given off in our breath, and certain acids as well which are found in quite high amounts on your feet. These types of chemicals are very attractive to mosquitoes. Ammonia is another one as well.

Chris - Are they just naturally produced by cells in the skin and the mosquitoes have learned that this equals lunch so they home in on them?

James - Absolutely, yeah. The mosquitoes have learned that some chemicals are released through the skin. Other chemicals are actually produced by the bacteria on the skin. So bacteria do play a very big role and they sort of convert the chemicals into more volatile chemicals that the mosquitoes find attractive.

Chris - How do you do the research where you take a person and then look at what’s coming out of them to work out how they’re attractive, whether they’re attractive or not and also what those chemicals are that are doing that?

James - We use quite a bizarre technique. We place people inside large silver bags, thermal survival bags that are commonly used for mountaineering. They lie in there for two hours and we extract their body odours from the bag.

Chris - Could be bad!

James - Yeah. We trap the chemicals onto a filter and strip the chemicals off the filter which then gives us a liquid extract that we can analyse. We have all sorts of weird techniques whereby we can actually look at the response of the receptors on the antenna of the mosquito, which is its nose, to detect which chemicals the mosquito responds to in this complex mixture.

Chris - So, the chemicals that mosquitoes respond to: are they only attracted to us because some of the people that were in Kitchen Science with Ben were not attractive. You were very attractive, he wasn’t attractive. Is it just that he’s got less of these chemicals or is he making something else that’s in fact making mosquitoes go away?

James - It might be quite logical to assume that if you weren’t attractive to mosquitoes then you just simply lack the attractive chemicals but of course we all breathe. We all release carbon dioxide and these other very attractive chemicals.  There is something special about people who seemingly never get bitten and what we’ve found is that those people are producing certain chemicals in much higher concentration. When tested those chemicals have a repellent effect so it’s almost as if your body’s got a natural defence systems against these insects.

Chris - If you test people who live in areas where there are more mosquitoes that spread diseases (I’m thinking of places like Africa where malaria’s endemic and other diseases like that) do you find that the population naturally make more of these chemicals?

James - That’s a really good question and you probably would expect that in a place such as Africa where the selection pressure would be quite high. At the moment we don’t actually know. There was a study that was done fairly recently that showed 20% of the population in a township were most susceptible to contracting malaria. The other 80% seemed to be fairly protected. The authors suggested that this could be to do with those people producing repellent chemicals but nobody actually knows. We haven’t done a big enough study to be able to tell that.

Chris - There was a paper, I think it was published in Plos a couple of years ago. It was very interesting because they took children from the local school that had malaria and they put them at one end of a piece of apparatus and they had children who were malaria-free and put them at the other end of the apparatus. Then they put the mosquitoes in the middle and counted where the mosquitoes went. When the child was highly infectious for malaria all the mosquitoes flocked towards the malaria-ridden child. When they repeated the experiment with mosquitoes that were themselves malaria positive they avoided the child with malaria and went to the people that didn’t have malaria. How are they doing that?

James - Again that was a really interesting study. What it showed was that it wasn’t to do with things like body temperature and things like that. We know that mosquitoes are attracted to heat and to moisture. When you have malaria you do have a fever and so you’re very hot. Some people might think that’s the reason. These scientists actually showed that it was all to do with body odours.  So your body odour was changing and the point at which the parasite was most transmissible between the human and the mosquito was the point at which they were most attractive. Quite incredible.

Chris - It is incredible.

May 2008