Features

Owen Lewis of Oxford's Department of Zoology is investigating the decline of the Small Tortoiseshell butterfly (Aglais urticae).

Ahead of a report on his research project airing on BBC South's Inside Out [on 11 March], I asked Owen what might be behind the decline and how volunteers can help track the cuplrit...

OxSciBlog: How concerned should we be about the health of Britain's butterfly populations?
Owen Lewis: We should be very concerned. Butterfly populations respond rapidly to environmental changes and are a sensitive bellwether for what is happening to biodiversity more widely.

We have a fairly small butterfly fauna compared with mainland Europe – about 55 resident species – but many of these have declined dramatically over the last few decades. We know this because there is a long history of butterfly survey work in Britain, almost all of it done by amateurs (for example, the volunteers working for the charity Butterfly Conservation).

In general the specialised species have fared most badly: ones where the caterpillars have exacting requirements in terms of microclimate and food plants. Butterflies like the beautiful High Brown Fritillary used to occur in almost every wood in the southern half of Britain. Now they are confined to a few carefully managed localities in the south and west.

Fortunately, butterfly ecologists have worked out how to manage habitats to maintain the right conditions for these threatened species. Restoring them to their original distributions will be far more challenging: the modern agricultural landscape just isn’t suitable breeding habitat for most butterfly species, and the remaining islands of good habitat are scattered in a sea of hostile terrain.

OSB: Why is the Small Tortoiseshell decline a particular concern?
OL: Their caterpillars feed on stinging nettles and are (or at least were) one of the most widespread, abundant and widely-recognised butterfly species in the country. Most people will have seen the adult butterflies feeding on Buddleia bushes or Sedums in their gardens, or will remember keeping the spiky black caterpillars in a jar as children.

Unlike the habitat specialist species, we had thought that Small Tortoiseshell populations were holding up well. However, in the last 10 years there has been a huge slump in population sizes, particularly in the south of Britain. Overall, numbers in the south have been reduced by 50 per cent, but the situation is much worse in some areas, where a complete absence of sightings has been reported during the summers of 2007 and 2008.

The slump coincided with the arrival from the continent of a new species of parasitic fly called Sturmia bella in the late 1990s. The fly lays its eggs on nettle leaves, and the Small Tortoiseshell caterpillars consume the eggs unwittingly along with the leaves. The fly eggs hatch in the caterpillar’s gut, and the fly maggots then develop within the caterpillars, literally eating them alive and eventually killing them. The southern parts of Britain where Sturmia bella has been recorded are also the areas where the Small Tortoiseshell is faring most poorly. We want to work out if the parasite is to blame, or whether this is just a coincidence.

OSB: How can volunteers help in the study of this decline?
OL: We want to track the spread of Sturmia bella through the UK and establish how it is in affecting populations of the Small Tortoiseshell and its close relative the Peacock. We are asking volunteers to look out for the caterpillars on nettle plants this summer, and to collect some to grow up at home. Any butterflies that result can be released, and any flies or wasps that develop from them can be sent for us for identification, along with a complete datasheet with information on the numbers collected and where they were found. Full details on how to join in are available through Butterfly Conservation.

OSB: We seem to be seeing an increase in parasitism and disease across many insect populations, what factors may be to blame? Is climate change implicated?
OL: I’m not sure if parasitism and disease are on the rise in general, but climate change may certainly bring new threats. No-one knows how Sturmia bella got here from the continent, but many species are spreading northwards as the climate warms – and this includes new pests and diseases as well as their hosts.

Another theory about the decline in the Small Tortoiseshell is that it is linked directly to climatic changes: caterpillars seem to do less well in dry summers, like the ones experienced in the first few years of this century. It’ll be interesting to see if the wet summer of 2008 leads to a resurgence of Small Tortoiseshells in 2009. Let’s hope so!

Dr Owen Lewis is based at Oxford's Department of Zoology.

Image: Small Tortoiseshell butterfly. Credit: Jim Asher

Software that gives robots a sense of ‘déjà vu’ is the key to them operating effectively in unfamiliar environments, as New Scientist reports in an article on the work of Oxford engineers.

For decades engineers have wanted robots to do jobs that are too dangerous for humans – such as entering disaster zones or exploring other planets. Yet, all too often, once these robots leave the confines of the lab or factory floor they run into one big problem: they get lost.

‘To start with it’s just a small error, say turning 89 degrees instead of 90 degrees, but pretty soon this small error is compounded until the robot is nowhere near where it believes itself to be’ said Mark Cummins of the Oxford Mobile Robotics Group, who has been researching this navigation problem with Paul Newman, who leads the group.

‘Humans too can make these kind of errors but, unlike robots, we can spot when we have been somewhere before and readjust our mental map accordingly. We are giving robots this same sense of ‘déjà vu’ so that, just by taking cues from their environment, they can readjust their sense of where they are and correct their own ‘mental’ maps.’

It may sound a simple task but in fact this ‘where am I?’ question has proved one of the most intractable problems in robotics. At present many autonomous robots rely on pre-produced maps or GPS to find their way around, but GPS isn't available indoors, near tall buildings, under foliage, underwater, underground, or on other planets such a Mars – all places we might want a robot to operate.

Oxford engineers have spent years addressing a key part of the ‘where am I?’ question – figuring out when a vehicle has returned to a previously visited place (known as the "loop closing problem"). To tackle it they've created The FABMAP algorithm that, through a combination of machine learning and probabilistic inference, is able to compare a current view of a scene with impressions of all the places it has been before.

Crucially it does this with great precision and rapidly – fast enough for a robot to realise it is retracing its steps and adjust its route [see images above and below: the green and red circles show parts that were matched/unmatched between the two images].

‘At the moment it can recognise and label different elements of its surroundings – making distinctions between, for instance, gravel paths and roads, stone walls and doorways, even different building types,’ Paul tells us. ‘This sort of ‘semantic exploration’ is the first step towards not just mapping its surroundings but starting to understand them as a human would.’

Mark adds: ‘Another motivation is that this kind of vision research is building towards robots that have some richer understanding of their environment, rather than the bare position information you get from GPS.’

‘In the future we want people just to be thinking about the task they want a robot to perform, and how it can help, rather than worrying about how it finds its way around or gathers useful information about its surroundings. ‘Where am I?’ is an important question, and being able to answer it accurately is central to the future of robot technology.’

Dr Paul Newman and Mark Cummins are based at Oxford's Department of Engineering Science.

Stuart West, who recently joined Oxford's Department of Zoology, has just published in Current Biology about his research into how bacteria cells interact.

I asked Stuart about what bacteria working together or cheating each other means for infection in humans:

OxSciBlog: What are the social interactions that go on between bacterial cells?
Stuart West: Bacteria cooperate to perform a wide range of functions. They secrete a number of factors out of the cell that then provide benefits to the local group - for example to scavenge nutrients, aid movement, overcome their host, kill and degrade prey, kill competitors and degrade antibiotics. They join together to form 'slime cities' (biofilms). Many of these behaviours are controlled by a social signalling system that has been termed 'quorum sensing' and which appears to switch on cooperative behaviours when they are most beneficial, which is when population densities are high.

OSB: How do these interactions affect the overall virulence of an infection?
SW: Hugely. These cooperative behaviours are crucial to the growth of bacteria and the damage that they do to their host. Indeed, many of these traits are also termed 'virulence factors'.

OSB: What is 'quorum sensing' and why is it important to understand it?
SW: Quorum sensing (QS) is the process where bacteria use small molecules diffusable molecules as signals which control other behaviours. The signal molecules are secreted out of the cell, and can then be taken up by the same cell or other cells nearby. This uptake has two effects.

First, it stimulates the production of many products that are released out into the environment, and which are 'public goods' that benefit the local bacteria. Second, it leads to an increase in production of the signalling molecules themselves. At high cell densities this leads to a positive feedback that markedly increases the production of factors released by the cell. The idea here is that QS turns on the production of these extracellular public goods when it is most useful to do so: at high densities.

From a pure science perspective, QS is interesting, because signalling and communication can be hard to explain from an evolutionary perspective, because they are exploitable by individuals that lie and cheat. From an applied perspective, QS is fundamental to the success and virulence of pathogenic bacteria.

OSB: How might your findings help in the search for new ways to combat infection?
SW: One way is that cheats that do not perform cooperative behaviours such as QS could be introduced into hosts to outcompete wild-type cooperators. As well as directly reducing virulence, this could drive down the bacterial population size, which may benefit other intervention strategies such as treatment with antibiotics. Another way is that other beneficial traits, such as antibiotic susceptibility, could also be hitch-hiked into infections by such cheats who do not perform QS or other social behaviours.

Stuart West is Professor of Evolutionary Biology at Oxford's Department of Zoology.

I really enjoyed this article in New Scientist about Lagrangian points - 'dead zones' in the solar system where opposing forces cancel out gravity and all kinds of items from cosmic dust to asteroids may accumulate becalmed.

NASA's twin STEREO probes, that were launched in 2006 to observe the Sun, are now being tasked to spy on two of these enigmatic spaces on the way to their final destinations (one orbiting ahead of the Earth and the other in its wake).

It's a great example of the serendipitous component to a lot of science: as one of the STEREO lead researchers explains the probes were never designed to look for asteroids (they're actually looking for solar storms) but now they have a golden opportunity to go rock-spotting.

I think the role of serendipity, especially in areas such as space and big science facilities where project lead times are so long, is something that doesn't get talked about enough. It's part of the invisible web that joins up different areas of science and ensures that a new instrument or technical advance in one area can create spin-off benefits for research into something very different. 

There's a nice Oxford link to STEREO that I'll be blogging about in detail later in the year. 

Today saw the launch of Galaxy Zoo 2: the project that enables web users to contribute to research into galaxies and how they evolve.

This report from BBC Breakfast's Graham Satchell gives an excellent overview of the project and includes an interview with one of Galaxy Zoo's founders, Oxford's Chris Lintott as well as just a few of the galaxy-spotting volunteers [nicknamed 'Zooites'] who have helped make the project such a success.

First reports are that GZ2's servers are buzzing with ten times the traffic of the original GZ launch: no doubt helped by the fact that Graham's report is linked from the front page of the entire BBC website! Chris's appearance on The Today Programme this morning can't have hurt either. 

Galactic mergers - cosmic 'train wrecks' in which galaxies collide - are one of the things that the GZ2 team hope users visiting the site can help them describe in detail. One of the discussions we had whilst putting the release together was whether mergers could be described as 'odd' or 'unusual' - although there was agreement that they are rare. 

Interestingly, as part of looking into this, I stumbled across this New Scientist piece that reports on research into how, in less than two billion years, our own galaxy - the Milky Way - will in fact merge with our neighbour the Andromeda galaxy: these two galaxies are currently rushing towards each other at 120 kilometres per second.

New Scientist's Hazel Muir writes: 'The scientists watched how gravity choreographed the motions of the two galaxies up to 10 billion years into the future. The results suggest they will pass close to each other in less than 2 billion years, well within the Sun's lifetime. At this point, their mutual gravity would start to mess up their structures and tug out long tails of stars and gas.'

'The two galaxies would then overshoot and come together again for a second close passage before finally merging about 5 billion years from now. The merged galaxy, which [the researcher] dubs Milkomeda, will be a blobby elliptical galaxy, rather than a neat spiral like Andromeda or the Milky Way today.'

Perhaps we should all visit GZ2 to find out what a merger looks like, just in case we're around in two billion years' time to watch...