Blind cavefish not so blind, Beetlemania and other tidbits…

Stories about cavefish are like buses – you get a seeming infinity of nothing and then loads turn up at once. Just 10 posts ago, I wrote about a study which found that you can restore sight to blind cavefish by cross-breeding individuals from different caves.

The different populations lost their eyes through changes to different sets of genes and in the hybrids, each faulty version was paired with a working one. As a result, the hybrids had fully formed and functional eyes despite having lived in darkness for a million years.

Now, a new study shows that the larvae of blind cavefish can detect light (or more accurately, shadows) too, even without working eyes. They can detect shadows and seek shelter in them, just like the sighted surface-dwelling versions of the same species. The key to the behaviour is their pineal gland, a small organ that regulates the body clock and, in some species, is sensitive to light.

I wrote up the research for Nature News; mosey on over for the full story and some possible explanations for why the fish’s pineal has retained the ability to detect light, even though its eyes have been lost.

Some other things to mention:

• The new edition of the Tangled Bank carnival is up at the Inoculated Mind.
• Nature picked up my David Attenborough interview for its Books and Arts section. My old lab colleagues from my PhD days would bust a gut laughing if they knew that I’d finally got my name into Nature…
• Nature Network’s published an interview I did with Alfried Vogler, who studies beetles at Imperial College. Last year, Vogler carried out the most comprehensive ever study on the evolutionary relationships between the beetles, the most successful group of animals on the planet.

Loss of big mammals breaks alliance between ants and trees

The natural world is full of alliances forged between different species, cooperating for mutual rewards. The relationship between ants and acacia trees was one of the first of these to be thoroughly studied. But new research suggests that this lasting partnership may be sundered by the unlikeliest of reasons – the decline of Africa’s large mammals.

Acacias are under constant attack from hungry animals, from tiny caterpillars to towering giraffes. In response, many species like the whistling-thorn tree (Acacia drepanolobium) recruit colonies of ants as bodyguards. Any hungry herbivores eager to chomp on the acacia’s leaves quickly get a mouthful of biting, stinging ants. The tree is a fair employer. In return for their services, its ant staff receive a sugary and nutritious nectar as food and hollow swollen thorns called ‘domatia’ as board.

But this pact is a fragile one. Todd Palmer from the University of Florida and colleagues from the USA, Canada and Kenya have found that it rapidly breaks down if the large animals that graze on the acacia disappear. Without the threat of chomping mouths, the trees reduce their investments in bodyguards to the detriment of both partners.

Palmer demonstrated this with plots of land in Kenya’s Laikipia Plateau, where fences have kept out large plant-eaters for over a decade. Since 1995, no herbivore larger than a small antelope has entered the four-hectare “exclosures” in an attempt to study the effect of these animals on the local ecology.

Within these 10 years, Palmer found that the majority of trees produced fewer domatia and less nectar and unexpectedly, the strongest alliances were hit the hardest. What were once happy partners quickly became selfish rivals.

Evolutionary arms race turns ants into babysitters for Alcon blue butterflies

In the meadows of Europe, colonies of industrious team-workers are being manipulated by a master slacker. The layabout in question is the Alcon blue butterfly (Maculinea alcon) a large and beautiful summer visitor and its victims are two species of red ants, Myrmica rubra and Myrmica ruginodis.

The Alcon blue is a ‘brood parasite’ – the insect world’s equivalent of the cuckoo. David Nash and European colleagues found that its caterpillars are coated in chemicals that smell very similar to those used by the two species it uses as hosts. To ants, these chemicals are badges of identity and so similar are the caterpillars that the ants adopt them and raise them as their own. The more exacting the caterpillar’s chemicals, the higher its chances of being adopted.

The alien larvae are bad news for the colony, for the ants fawn over them at the expense of their own young, which risk starvation. If a small nest takes in even a few caterpillars, it has more than a 50% chance of having no brood of its own. That puts pressure on the ants to fight back and Nash realised that the two species provide a marvellous case study for studying evolutionary arms races (which I’ve blogged about before here).

Theory predicts that if the parasites are common enough, they should be caught in an ongoing battle with their host, evolving to become more sophisticated mimics, while the ants evolve to become more discriminating carers. The two species make a particularly good model for this because their geographical ranges overlap in a fractured mosaic.

Assassin bugs deceive spiders with coat of many corpses

The animal world is full of charlatans. Some have bodies shaped by natural selection to fade into the background or resemble other harmful species. Yet others, like chameleons and octopuses, have the rare ability to actively change their colour or shape to actively hide themselves from view.

Many species disguise themselves through their behaviour rather than their bodies; like human soldiers in camouflage gear, they don special suits to remain inconspicuous.

Decorator crabs, for example, coat their shells with a collection of sea anemones, algae, corals and sponges, held on with Velcro-like bristles while other crabs actively carry these living masks with specially modified legs. These species have the cartoonish air of a man carrying a pot plant in front of him while sneaking past on tip-toes. But some charlatans are not so amusing.

Robert Jackson and Simon Pollard from the University of Canterbury have been studying a pretender with a much more gruesome disguise – the ant-snatching assassin bug Acanthaspis petax, which covers itself with the corpses of its own prey.

Ants spread collective immunity through contact

Imagine you get a bad cold, but you decide to put on a brave face and go into work anyway. Instead of jokingly covering their mouths and making jibes about staying away from you, your colleagues act perfectly normally and some even and start rubbing up against you. It’s a weird scenario, but not if you were an ant.

With their large colonies and intense co-operation, ants are some of the most successful animals on the plant. But like all social insects and animals, they large group sizes make them vulnerable breeding grounds for parasites and infections. A infectious disease in a tightly knit colony spells trouble and it’s no surprise that social insects have evolved ways of stopping the spread of infections.

Some are sticklers for hygiene and meticulously clean their peers while others quarantine infected individuals in colony sick chambers. Some termites even warn their peers to stay away through head-banging. And bees kill off a heat-resistant bacteria by gathering in an infected part of the colony and raising its temperature, effectively setting off a ‘colony fever’.

Now, scientists from the University of Copenhagen have found that some ants use a form of collective immunity, where infected individuals trigger resistance in those around them through contact.

Ants herd aphids with tranquilisers in their footsteps

In your garden, there’s a fair chance that a farmer is currently tranquilising her livestock with a chemical cocktail she secretes from her feet. Don’t believe me? Look closer…

Humans aren’t the only species that farms other animals for food – ants do it too and their herds consist of aphids. They feed on plant sap and excrete a sweet and nutritious liquid called honeydew, which the ants drink.

In return, the ants run a protection racket, defending the aphids from predators like ladybirds. It seems like a nice two-way partnership that suits both partners, and aphid colonies tended by ants tend to be larger than unattended ones. But new research from two London universities suggests that ants are manipulating their herds more than previously thought. 

Buzzing bees scare elephants away

It’s a myth that elephants are afraid of mice, but new research shows that they’re not too keen on bees. Even though they fearlessly stand up to lions, the mere buzzing of bees is enough to send a herd of elephants running off. Armed with this knowledge, African farmers may soon be able to use strategically placed hives or recordings to minimise conflicts with elephants.

Iain Douglas-Hamilton and Fritz Vollrath from Kenyan conservation charity Save the Elephants first suspected this elephantine phobia in 2002, when they noticed that elephants were less likely to damage acacia trees that contained beehives.

Animals as powerful as the African elephant can go largely untroubled by predators. Their bulk alone protects them from all but the most ambitious of lion prides.

But these defences do nothing against the African bees, which can sting them in their eyes, behind their ears and inside their trunks. Against these aggressive insects, the elephants are well justified in their caution and local people have reported swarms of bees chasing elephants for long distances.

Ancient plants manipulate insects for hot, smelly sex

For plants too, sex can be a hot and smelly affair. In most plant-insect partnerships, the pollinator seems to do most of the work by voluntarily transferring pollen from plant to plant in exchange for a meal.

But an ancient lineage of plants – the cycads – takes more active steps to ensure its future with a bizarre combination of heat and smells. In the afternoon, they use heat and a toxic stench to drive insects out of male cones only to lure them into female cones in the evening with a more alluring scent.

Paper wasps – caring mothers evolved into selfless workers

The workers of many social insect colonies give up their chance to reproduce in order to raise their sisters and their nieces. A new genetic study in paper wasps, which are halfway down the road to this extreme altruism, tells us that worker selflessness evolved from motherly care.

Imagine that one day, you make a pact with your brother or sister, vowing to never have children of your own and instead spend your life raising theirs. You’ll agree to do the grocery shopping, cook for them, clean their rooms and bathe them, until you die.

That seems like a crazy plan, but it’s one that some of the most successful animals in the world – the social insects – have adopted. It’s called ‘eusociality’ and it’s a puzzle for evolutionary biologists. Why should an animal forgo the chance to reproduce in order to help rear its siblings and their young?

The strategy makes sense if you share enough genes with your close relatives. In helping them, you indirectly ensure the transmission of your own genetic material. But even if this explains the existence of eusociality, it doesn’t explain how such an extreme form of co-operation evolved.

Now, Amy Toth and colleages at the University of Illinois have found a clue in the genes of the paper wasp, Polistes metricus, which suggests that their altruistic actions evolved from motherly behaviour.

Mobs of honeybees suffocate hornets to death

When Oriental hornets attack, Cyprian honeybees mob them in a huge ball that targets the breathing apparatus in the hornet’s abdomen. The hornets can’t breathe without expanding their abdomens and with sheer numbers, the bees strangle the hornets to death.

Hornets are giant wasps that pack a powerful sting. To most people, they can be a painful nuisance, but to honeybees, they’re killing machines. Hornets greatly outsize and overpower honeybees and a few individuals can decimate entire colonies.

Asian honeybees have developed a remarkable defence called ‘heat-balling’ against their local hornet, Vespa velutina. A giant ball of bees piles onto the predator, weighing it down while vibrating their wing muscles. The frenetic activity greatly increases the temperature inside the ball to about 45C – hot enough to cook the hornet alive, but five degrees under the bees’ maximum tolerated temperature.

Cyprian honeybees face a different predator, the Oriental hornet Vespa orientalis and unlike its wimpier cousin V.velutina, this species can take the heat. The Oriental hornet lives in hot, dry climates ranging from Central Asia to the Mediterrenean and it tolerates temperatures just as high as honeybees.

Heat-balling shouldn’t work on them. And yet, Cyprian bees still encase Oriental hornets in large balls. Surprisingly, the strategy works – despite their heat tolerance, the hornets still die. The bees’ stings are useless against the hornet’s tough cuticle and they barely use them. What could they be doing instead?

Is a virus responsible for the disappearing bees?

A group of scientists have found that a virus – IAPV – may be responsible for Colony Collapse Disorder, the mysterious condition that’s emptying the hives of European and American beekeepers.

In 2006, American and European beekeepers started noticing a strange and worrying trend – their bees were disappearing. Their hives, usually abuzz with activity, were emptying.

Like honeycombed Mary Celestes, there was no trace of the workers or their corpses either in or around the ghost hives, which still contained larvae and plentiful stores of food. It seemed that entire colonies of bees had apparently chosen not to be.

The cause of the aptly named ‘Colony Collapse Disorder’, or CCD, has been hotly debated over the last year. Fingers were pointed at a myriad of suspects including vampiric mites, pesticides, electromagnetic radiation, GM crops, climate change and poor beekeeping practices. And as usual, some people denied that there was a problem at all.

But a large team of US scientists led by Diana Cox-Foster and Ian Lipkin have used modern genomics to reveal the main villain in this entomological whodunnit – a virus called Israeli Acute Paralysis Virus or IAPV.

Foul-tasting ant parasitises the colonies of other species

An ant nest is sheltered, well defended and stocked with food, but one that takes time to build and protect. Which is why some species of ants don’t bother to do it themselves – they just squat in the nests of others.

These ants are ‘social parasites’ – they don’t feed off their hosts’ tissues, but instead steal their food, sleep in their homes and use their resources. They’re like six-legged cuckoos

An ant colony is too dangerous a target to victimise lightly and the social parasites use several tricks to stop their hosts from ripping them apart. Some escape reprisal by chemically camouflaging themselves, either by mimicking their hosts’ odour, or by acquiring it through contact.

This specialised strategy ties the parasite’s fates into those of its host. Both are caught in an evolutionary arms race, with the hosts becoming more discriminating and the parasites’ deception becoming more accurate. But Stephen Martin from the University of Sheffield has found one ant species with a completely different and more flexible strategy – it tastes really, really bad.