Archive for October, 2010

Evolutionary arms race turns ants into babysitters for Alcon blue butterflies

By Ed Yong | October 16, 2010 9:00 am

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This is an old article, reposted from the original WordPress incarnation of Not Exactly Rocket Science. I’m travelling around at the moment so the next few weeks will have some classic pieces and a few new ones I prepared earlier.

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. 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 the caterpillars smell so familiar 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.

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Salmonella gets its host to arm its secret weapon

By Ed Yong | October 14, 2010 2:00 pm

SalmonellaBacteria wield all sorts of molecular weapons that allow them to infiltrate their hosts. But one microbe – Salmonella enterica – has a particularly devious trick. It uses weapons that arm themselves by manipulating the host’s own proteins. When this bacterium infects cells, it turns them into accomplices to their own downfall.

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MORE ABOUT: caspase, Salmonella, sipA

I’d like to thank the academies…

By Ed Yong | October 14, 2010 11:00 am

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For a few weeks now, I’ve been cryptically hinting at some good news and I can finally reveal what it is: I’ve won one of the 2010 National Academies Communication Awards.

These awards are jointly presented by the National Academy of Sciences, National Academy of Engineering, and Institute of Medicine. They consist for four $20,000 prizes (seriously) for “creative, original works that address issues and advances in science, engineering and/or medicine for the general public”, in the categories of book; magazine/newspaper; broadcast; and online. I won the online category for this blog (press release here).

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CATEGORIZED UNDER: Personal

Wine-scented flower draws in fruit flies with yeasty tones

By Ed Yong | October 13, 2010 9:00 am

In a German lab, Johannes Stokl is wafting a series of fruity and yeasty smells in front of a panel of restrained testers. As the chemical cocktail tickles their senses, electrodes and brain scanners record their every reaction. This bizarre wine-tasting event is all part of a study into the bizarre deception of a flower – the Solomon’s lily. And Stokl’s subjects aren’t humans – they’re fruit flies.

Solomon’s lily is one of the arum lilies, a group that specialises in manipulating flies. They attract these unusual pollinators by giving off odours of urine, dung and rotting meat, repugnant smells that seem completely at odds with their attractive appearance. Solomon’s lily is an exception – it smells rather pleasant, a bit like a fruity wine. But this fragrance, like the fouler ones of other arum lilies, is also a trick. Solomon’s lily uses it to draw in flies that eat decaying fruit.

The lilies grow in Israel, Syria and Lebanon and if you cut them open, you can find flies in their hundreds. Stokl counted more than 400 individuals in each of two different flowers. The trapped insects included 8 different drosophilids – the fruit-eating species that are such darlings of geneticists.

The lily’s aroma of fermenting fruit certainly seems like the type of scent that would draw in such insects, but Stokl wanted to be sure. He collected the plants’ fragrances and ran them through equipment that separated them into their constituent chemicals. Each of these components was individually wafted over tethered flies, whose antennae had been hooked up to electrodes. Through this clever design, Stokl could identify the exact chemicals in the lily’s milieu that roused the fly’s senses.

He found six. Each of these is mildly attractive to a fruit fly but in combination, mixed according to the flower’s own recipe, they were just as enticing as powerful commercially-available traps. Among flowers, these chemicals are rare; two of the set have only ever been detected once before within a floral scent. But you inhale them whenever you take a whiff of overripe or rotting fruit, wine, or vinegar. Balsamic vinegar is an exceptionally rich source. All of these chemicals are given off by yeasts during the process of fermentation.

Yeast is the staple food of fruit flies – it’s what they’re after when they seek out rotting fruit. And the lily’s chemical ruse is so exact that it’s unlikely that the fly can separate the flower’s smell from the real deal. To demonstrate that, Stokl also deconstructed the scents of several rotting fruits, balsamic vinegar and a bottle of red wine (a “fruity Lambrusco variety” apparently), and wafted these in front of his tethered flies. The recordings show that the fly perceives all of these odours in much the same way as it does the lily’s scent, with the wine and vinegar providing the closest matches.

This deception is a deep one, for the lily exploits a sense that the flies have been using for millions of years. Using detailed brain scans, Stokl found that the six critical chemicals tickle a set of proteins that are conserved throughout the drosophilid group. As the flies evolved and diverged, these stalwart proteins changed very little, retaining their ancestral role as yeast detectors. As a result, even drosophilid species that have been separated by 40 million years of evolution respond to the smell of the Solomon’s lily in virtually the same way.

Like a good wine-tasting, Stokl’s thorough experiments have revealed something that is far more subtle than a casual sniff would suggest. It would be say that a wine-scented lily attracts flies that like fermenting fruit and call it a day. But by bringing the tools of neuroscience and genetics to the table, Stokl showed that Solomon’s lily produces a smell that taps into a sense embedded in the evolutionary history of the entire drosophilid line. It has evolved an all-purpose lie that dupes all manner of drosophilid flies, drawing in pollinators in droves.

Reference: Current Biology http://dx.doi.org/10.1016/j.cub.2010.09.033

More on mimicry:

CATEGORIZED UNDER: Uncategorized

Across an ocean, round a continent – the epic 10,000km voyage of a humpback whale

By Ed Yong | October 12, 2010 7:00 pm

Humpback

On 7 August 1999, a lucky photographer snapped a female humpback whale frolicking off the east coast of Brazil. Two years later, on 21 September 2001, the same whale was caught on camera again, by a tourist on a whale-watching boat. But this time, she was a quarter of the world away, off the eastern coast of Madagascar. The two places where she was spotted are at least 9800 kilometres apart, making her voyage the longest of any mammal.

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Invasive shrub increases risk of human disease (via ticks, deer and bacteria)

By Ed Yong | October 11, 2010 3:00 pm

Honeysuckle_deer_tickThere are many ways of fighting disease, but Brian Allan from Washington University has suggested a most unusual one – a spot of weeding. Allan’s research shows that getting rid of a plant called the Amur honeysuckle might be one of the best ways of controlling an emerging human disease called ehrlichiosis. The plant, however, doesn’t cause the disease. The connection between the two is far more complicated than that.

The Amur honeysuckle is an Asian plant that’s naturally alien to American shores. But, like many species that are brought to new habitats, it has become an invader. It forms thick growths that deprive native plants of light, causing local diversity to plummet in the face of an expanding blanket of honeysuckle. This story has been repeated all over the world with different species cast as invasive villains, and different communities cast as suffering victims. But the true consequences of these invasions often go unnoticed.

The honeysuckle doesn’t just crowd out local plants; Allan has found that it also attracts white-tailed deer. Where the deer go, so do their parasites, and these include the lone star tick, the animal that spreads ehrlichiosis. Through their blood-sucking bites, the ticks spread five species of bacteria that infect and kill white blood cells. This weakens the immune systems of their hosts and causing the flu-like symptoms that accompany a bout of ehrlichiosis.

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Photo safari – hummingbird

By Ed Yong | October 10, 2010 3:00 pm
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There are few experiences better than watching hummingbirds fly over a vineyard while sitting outside in the sunshine eating waffles. My wife and I have just been travelling through California for some much-needed rest and relaxation. We spent the last two days in the incredible Seven Quails vineyard (if you’re looking for accommodation near Paso Robles, stay there) and each morning, we delighted to see hummingbirds flitter between the trees of their back garden, against panoramic vistas of vines and rolling hills.

I’m assuming all of these photos are of the black-chinned hummingbird but if anyone has any other identification ideas, let me know. These photos are of Anna’s hummingbird. The money shots of the bird in flight were taken by my wife. The ones in the tree were me.

CATEGORIZED UNDER: Uncategorized

Photo safari – lion's mane jellyfish (in an amusing case of tangled tentacles)

By Ed Yong | October 10, 2010 12:00 pm
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Have you ever been to an aquarium where large swarms of jellyfish swim around each other in a beautifully lit tank? Have you ever wondered how those drifting tentacles managed to stay untangled, when humans can’t even manage to put a set of headphones in our pocket without ending up with a series of mind-bending knots? Have you ever wondered what would happen if jellyfish did get their tentacles in a twist?

Well, thanks to Monterey Bay Aquarium’s jellyfish exhibit, I can tell you the answer to that last question: hilarity ensues. These are lion’s mane jellyfish. They have no brain or central nervous system, which is fortunate because otherwise, they would probably die of embarrassment.

I shot these photos/videos myself yesterday. The aquarium is incredible. More photos to come later today, and then tomorrow, some brand new science for you.

CATEGORIZED UNDER: Uncategorized

Sex runs hot and cold – why does temperature control the gender of Jacky dragons?

By Ed Yong | October 8, 2010 10:00 am

Jacky_dragon

This is an old article, reposted from the original WordPress incarnation of Not Exactly Rocket Science. I’m travelling around at the moment so the next few weeks will have some classic pieces and a few new ones I prepared earlier.

Among Jacky dragons, females are both hot and cool, while males are merely luke-warm. For this small Australian lizard, sex is a question of temperature. If its eggs are incubated at low temperatures (23-26ºC) or high ones (30-33ºC), they all hatch as females; anywhere in the middle, and both sexes are born.

This strategy – known as ‘temperature-dependent sex determination (TSD) – seems unusual to us, with our neat gender-assigning X and Y chromosomes, but it’s a fairly common one for reptiles. Crocodiles are all-male at high temperatures and all-female at low ones, while turtles flip the rules around and produce more males in cooler climes. Assigning gender based on temperature is not uncommon but it is nonetheless puzzling.

Gender seems like an incredibly fundamental physical trait to leave to something as variable as the temperature of your surroundings. How has such a system evolved? What possible benefits could a species receive by switching control of from chromosomes to the environment? Now, a thirty-year old explanation for this puzzling system has finally been confirmed.

The most widely accepted hypothesis was put forward by Eric Charnov and James Bull over thirty years ago. They suggested that TSD occurs when the temperature of the environment affects the success of males and females strongly but differently. Parents can then use local temperatures as a sort of crystal ball, producing more males in conditions that are suited to males, and more females in conditions where they have the edge.

The idea is sound, but testing it has been remarkably difficult. The ideal experiment would involve hatching both males and females at the entire range of incubation temperatures and comparing their success over the course of their lives. Obviously, the very nature of TSD rules out that approach; how do you hatch males at low temperatures if those same conditions, by definition, beget females?

If that weren’t enough, most species that use TSD are large and long-lived. Imagine following a turtle for its entire 60 year lifespan and you begin to see the problem. All that changed this decade when TSD was found in the small and short-lived Jacky dragon (Amphibolorus muricatus). With a lifespan of 3-4 years, here was an animal that could be reasonably studied in experimental conditions.

With one problem down, Daniel Warner and Rick Shine from the University of Sydney solved the other by using hormonal treatments to sunder the link between temperature and sex. Temperature may decide gender but it does so through hormones. The key event is the conversion of testosterone to oestradiol (a relation of oestrogen) by an enzyme called aromatase. This happens at low temperatures and tells developing dragons to become females.

Warner and Shine overrode this process with a chemical that blocks aromatase. With the enzyme disabled, the duo managed to hatch male babies at temperatures that are exclusively female. The hormonally nudged Jackies were physically similar to their male siblings who developed in the normal way; that was essential if they were going to be compared fairly. The duo raised the babies in enclosures that mimicked their natural environments, and waited.

After three consecutive breeding seasons, Warner and Shine found (as predicted) that males sired more offspring on average if they were hatched at an intermediate 27ºC, a normal temperature for them in natural conditions. Males hatched at temperatures that are usually the province of females produced almost three times fewer young. The reverse was true for females; they enjoyed greater reproductive triumphs if they were hatched at a cooler 23ºC or a warmer 33ºC.

Although these results don’t explain why males and females should fare better at different incubation temperatures, they do fully vindicate the Charnov-Bull model. Exactly as predicted, male Jacky dragons produce more young if they hatch at temperatures that usually produce males, and likewise for females.

Such careful fine-tuning has done the lizards well over the course of evolution but it may put them in danger as the globe continues to warm. Like crocodiles, turtles and other reptiles that use TSD, the Jacky dragon may become a casualty of climate change, as rising temperatures lead to an all-female population and no way of producing a new generation.

Reference: Warner, D.A., Shine, R. (2008). The adaptive significance of temperature-dependent sex determination in a reptile. Nature DOI: 10.1038/nature06519

More on sex determination:

Newborn babies have a preference for the way living things move

By Ed Yong | October 7, 2010 10:00 am

Running_rabbitThis is an old article, reposted from the original WordPress incarnation of Not Exactly Rocket Science. I’m travelling around at the moment so the next few weeks will have some classic pieces and a few new ones I prepared earlier.

From an animal’s point of view, the most important things in the world around it are arguably other animals. They provide mates, food, danger and companionship, so as an animal gazes upon its surroundings, it needs to be able to accurately discern the movements of other animals. Humans are no exception and new research shows that we are so attuned to biological motion that babies just two days old are drawn to extremely simple abstract animations of walking animals.

Animals move with a restrained fluidity that makes them stand out from inanimate objects. Compared to a speeding train or a falling pencil, animals show far greater flexibility of movement but most are nonetheless constrained by some form of rigid skeleton. That gives our visual system something to latch on to.

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