Features

Kit Yates from Oxford's Mathematical Institute recently published in PNAS on his work into the modelling of locust swarms: I asked him about how seemingly 'random' changes in direction by individuals can add up to better collective choreography...

OxSciBlog: Why do animals such as locusts and starlings make these sudden changes in direction?
Kit Yates: Directional switching is an intrinsic property of the motion of many animal groups. This behaviour is not just limited to locusts and starlings, but extends to shoals of fish, flocks of various different bird types and groups of herding/swarming animals.

An important concept which unifies our understanding of these groups is that of transfer of directional information. It is clearly to the advantage of all the members of a group if they can rapidly change direction away from an oncoming predator or towards a food source which has been detected by only a few members of the group.

Individuals which change their direction of travel in response to the direction taken by their near neighbours can quickly transfer information about the presence of a predatory threat or food source across the whole group.

It is thought that locusts sense their near neighbours using their eyes for the neighbours in front and to the sides their hind legs and abdomen for their neighbours behind. It has been found that locusts without the sensory perception in their abdomen (but still retaining the mechanical ability to move their legs) will often remain motionless while other locusts eat them alive! It is believed that this stimulus encourages the onward march of the locusts. A slightly weaker 'pull' towards the locusts in front is also thought to encourage onwards marching.

OSB: What are the challenges involved in modelling this kind of collective motion?
KY: One of the main challenges in modelling this type of behaviour is obtaining sufficient data to justify the model. Tracking animals in the wild over large distances or over long periods of time can be extremely difficult especially if we are trying to track large enough numbers of individuals to say something useful about the collective dynamics of the group.

For example, a typical locust swarm can contain as many as a quarter of a billion locusts. Fortunately a well thought out laboratory experiment was devised which allowed us to track up to 100 individual locusts for periods of up to 8 hours. Once the data was obtained finding a model which was well suited to the data was quite simple.

There are well known models which display directional switching behaviour like that found in the actual locust data. One of these models which we decided to use is commonly known as the Czirók model or One-Dimensional Vicsek model. In this model, known as a 'self-propelled particle' model, individual locusts are modelled as computer generated particles.

These particles are initialised with a position, direction and a set of rules for interaction with the other particles. The individuals are given a common interaction radius inside which they can sample the velocities of neighbouring individuals. They use the average of these sampled velocities to update their velocity and position at regular time intervals. Some random noise is added to their updated velocities to incorporate the fact that in reality the locusts will not be able to sample the velocities of their neighbours perfectly.

The choice of the magnitude of this noise term is something which previously has not been given much thought but when the computationally generated data is compared to the experimental data it turns out to be very important.

OSB: How did you attempt to create more accurate mathematical models of this behaviour?
KY: We compared certain characteristics of the model to those of the experimental data in order to ascertain how well the model replicated the experimental findings. One of these characteristics was the magnitude of the noise term applied to the locusts' velocity update which models the the randomness in the locusts' new velocities.

We found that the model replicated the data more realistically when the magnitude of the noise term given to individual locusts varied with how aligned that locust was to its near neighbours. We altered the noise term in the model so that the locusts become worse judges of the velocities of their near neighbours when they were not aligned to them. This allowed us to replicate qualitatively the behaviour we saw in the experimental locust data.

OSB: What did you discover about the seemingly 'random' direction changes of individuals?
KY: There are several reasons why a locust might increase the noise term when it finds itself to be unaligned. For example, when unaligned, a locust might want to try several random directions in quick succession in order to reorientate itself with the other locusts.

When a locust swarm changes direction most of the individual locusts will find themselves unaligned at some point. Increased individual noise allows individuals to find alignment with their neighbours (and consequently reorientate and realign the swarm) quickly in order to avoid predation or head towards a food source.

Although the advantage at the group level is palpable (and what is best for the swarm is best for the individual in the tasks of avoiding predation and finding food sources), what makes the individual want to reorientate itself so rapidly?

Previous studies have found that locusts are cannibalistic and, if allowed, will eat each other in their desperate search for salt and protein. It has also been found in studies on immobilised locusts that locusts which are most likely to be eaten are those which are side-on to the swarm, rather than aligned with the swarm.

It is thought that the reason for this is that even when immobilised a locust's hind legs, which it uses to sense other locusts, can be used to kick out at locusts trying to take a quick nibble whereas locusts which are sideways-on to the swarm have no such defence. It could be that an attempt to not be cannibalised is a motivating force for realignment of individual locusts to the rest of the swarm.

Another contributing factor could be that when a locust is not aligned it becomes more difficult for it to measure its neighbours' velocities accurately as its usual sensing mechanisms (eyes, hind legs and abdomen) are disorientated. In short our modelling approach to the data allowed us to propose the idea that an individual-level response to local lack of alignment allows locust swarms to turn more efficiently.

OSB: How might your research help us understand other examples of collective motion - such as traffic jams?
KY: Self-propelled particle models have been used to model collective motion in animals from fish to birds. It would be interesting to compare our findings to data from other animal groups and to see whether this 'increased individual noise in response to a loss of alignment' is a ubiquitous phenomenon.

Noise in response to lost alignment may be an example of a general property of organization of collective motion. Another example is found in traffic-jam models where one way of avoiding “phantom traffic jams” is to introduce additional noise to traffic motion (although there is no direct link between this research and traffic calming measures). 

The paper 'Inherent noise can facilitate coherence in collective swarm motion' is published online in PNAS.

If you were Chancellor of the Exchequer right now you might not think that investing in holes was a good idea but, according to Radio 4's Material World, you'd be wrong.

But of course we aren't talking budgetary holes but rather those tiny holes known as nanopores, specifically those being developed by Hagan Bayley of Oxford's Department of Chemistry.

The programme suggested that Hagan and the spinout he founded in 2005, Oxford Nanopore, represent the kind of ideas the Government should be investing its £750m innovation fund in.

Hagan is working with Oxford Nanopore on a way to detect the four DNA bases using nanopores, research which is tantalisingly close to turning the $1000 human genome into a reality.

Last night Hagan was named Entrepreneur of the Year by the Royal Society of Chemistry [RSC] and in the Material World interview [22:50 on iPlayer] he talks about almost two decades of research that led to the award, the process of spinning out a company and how he came to settle on DNA sequencing as the most interesting application of his work.

The elements of a new pathway likely to be involved in most body functions – from blood flow to metabolism and fertilisation of egg cells – have been identified by an international team in which researchers in the Department of Pharmacology took a leading role.

The discovery, reported in Nature, could provide new targets for drug development for diabetes, heart abnormalities, and many other conditions.

‘Calcium plays a vital role in the body,’ says Dr John Parrington. ‘And it’s not all about building healthy bones and teeth. Calcium is used to coordinate and control many different events, responses and reactions in the body.’

Bodily processes as diverse as heart contraction, nerve growth, control of appetite, regulation of the immune system, and insulin secretion by the pancreas are mediated by calcium. Each of these processes requires cells to have a coordinated, measured, and timed response. And cells use calcium to achieve this.

Calcium ions are released from stores within cells in response to signals from hormones or other chemicals in the blood, and the sudden increase in the amount of calcium present triggers the right physiological response – whether that’s contraction of a heart muscle cell or release of insulin by a cell in the pancreas. Of course, when this process gets disrupted, it can lead to a range of different conditions.

It’s in our basic understanding of how these chemical messages mediate important physiological events in the body at the molecular level, that Professor Antony Galione and John Parrington, along with researchers at the University of Edinburgh and colleagues in the US, have made a breakthrough.

The release of calcium from stores in the cell can be triggered by three different chemical signals or messengers. They are called IP3, cADPR and NAADP. The IP3 system is well known, and that involving cADPR is partially understood. What the Oxford team has done is reveal exactly how the chemical messenger NAADP has an effect. Previously this was entirely unknown.

The team identified a set of protein channels that sit in a compartment of the cell called the lysosome. (This is interesting in itself, as the lysosome was previously thought of pretty much as a dustbin in which unwanted substances were broken down.) They have shown that NAADP triggers the protein channels to release calcium held within the lysosome.

‘It's been a bit of a detective story. We knew that there was this chemical NAADP and we had proposed from our earlier studies that it released calcium from lysosomes. However, our discovery of a new class of calcium release channel opened by NAADP on the lysosome really has been the acid test,’ says Antony Galione, who is head of the Department of Pharmacology. ‘This opens an entirely new chapter in calcium signalling, which is important since most cellular activities are either directly or indirectly controlled by calcium.’

‘Now with the identity of the NAADP receptor uncovered, the possibility of designing new drugs to combat conditions such as diabetes, obesity and abnormalities of the heart and immune system, have been greatly advanced,’ adds John Parrington. They are already beginning to reveal the potential for human health, showing that the newly identified channel is critical.

‘”Knockout” mice, from which the gene for the protein channel has been deleted, show abnormal NAADP-induced calcium signals in the pancreatic cells that secrete insulin in response to blood sugar levels,’ explains John Parrington. ‘This finding could have great relevance for understanding conditions such as diabetes.’

The hope now is that drugs can be designed to target the protein channel in the appropriate way and restore its function where it is impaired.

How did you celebrate April 22 and its heroic alter ego Earth Day?

Our friends at the Said Business School organised a conference, Beyond Kyoto, focusing on green innovation and technology and how we can support entrepreneurship that solves the problems of the 21st Century.

Topics covered included climate change adaptation, clean energy, learning for sustainability and entrepreneurship in the Oxford area.

Amongst the speakers was Malcolm McCulloch from Oxford's Department of Engineering Science. Malcolm and his team are behind a range of exciting green innovations including a smart meter to help people manage their electricity use, research into novel refrigeration technology, not to mention working on the electrics for the stunning zero emission Lifecar.

If engineers can keep inventions like these coming then the future could be exciting as well as green. 

Today Oxford's Isobel Hook will be telling attendees at the JENAM astronomy meeting all about the European Extremely Large Telescope [E-ELT].

Sometimes scientists are guilty of hyperbole in the naming of instruments but in this case 'extremely' is entirely justified as, with a mirror 42m in diameter, the E-ELT would be four times bigger than the biggest optical telescopes in use today [the Southern African Large Telescope, for instance, has a 10m mirror].

Why is mirror size important? Because for optical astronomers the size of your mirror determines the sharpness of your image - roughly speaking a mirror four times the size gives four times the sharpness - making it possible to see much smaller objects.

This is especially important in the search for exoplanets, planetary bodies orbiting other stars. Massive instruments such as E-ELT would offer the first realistic chance of directly imaging 'normal' [ie non-massive, non-luminous] planets like the Earth.

The E-ELT would also enable us to do some very cool galactic navel-gazing, staring into the heart of our own Milky Way to see whether it harbours a supermassive black hole as part of an Active Galactic Nucleus [AGN].

Isobel Hook, of Oxford's Department of Physics, is leading the science case for E-ELT and tells me that the aim is to create a flexible instrument that could perform a wide variety of experiments.

The wide range of science such a telescope could do is a powerful incentive to overcome the many technical and logistical challenges in building a telescope quite this big.

In fact the E-ELT is only possible because of advances in the field of adaptive optics, making it possible to combine the light from hundreds of smaller mirrors into a single image (rather like an insect's compound eye).

Let's hope E-ELT is successful so we can see what we can see...