Male and female marsh harriers should be easy to tell apart: the males have grey wing-tips and tails, while the females are mostly brown with distinctive creamy heads. The males also tend to be around 30 percent smaller. But looks can be deceptive. In western France, many of the “female” harriers are actually cross-dressing males that permanently wear the plumage of the opposite sex. Audrey Sternalski has found that this unusual costume allows them to lead more peaceful lives.
Forty percent of male marsh harriers don female costumes, and they start wearing them from their second year of life. Their feathers have the same colours, and they’re smaller in size. Only their irises give them away – they are pale, rather than the ochre-brown of females or the yellow-white of males.
To test the effect of these colours, Sternalski created model harriers and placed them in the territories of real ones. He found that males attacked the male decoys twice as often as either the female or female-like ones. So, by looking like females, male harriers become the beneficiaries of a “non-aggression pact”. They can get access to resources and mates without incurring the wrath of other males. Indeed, Sternalski found that typical males were forced to nest twice as far from another male as the female-like males did.
Sternalski also found that the female-like males almost never attacked male decoys. Instead, they were more likely to attack other females (or female-like males), just as true females are. Not only did they look like females, they behaved like them too.
This raises several questions – are the female-like males simply doing a superficial impersonation, or are they “female” at a deeper physiological level? To find answers, Sternalski now plans to study the genetic basis of the harrier’s female mimicry.
The marsh harrier is one of only two birds whose males permanently don the colours of females. The other – the ostentatious ruff – also uses its disguise to avoid aggressive assaults. They sneak into the territories of more dominant males and surreptitiously mate with the resident females. Such strategies are fairly common in the animal kingdom – they’re found in ants, wasps, fish, and more. In most cases, the deceptive males get some sneaky sex, or avoid attacks from rivals.
But that’s not necessarily the case. In 1985, scientists discovered that some male red-sided garter snakes release a female pheromone that attracts big clusters of up to 17 amorous suitors. By luring these males to him, the female mimic more easily mates with an actual female. The goal seems obvious: distract other males. But the same group later showed that the female-mimics might simply benefit by drawing heat from the writhing balls of other duped males.
Reference: Sternalski, Mougeot & Bretagnolle. 2011. Adaptive significance of permanent female mimicry in a bird of prey. Biology Letters http://dx.doi.org/10.1098/rsbl.2011.0914
More on mimicry:
A group of computer gamers are making habit of outshining scientists at their own game. Most of them have no scientific background, but they have a track record of cracking tough scientific puzzles, including at least one that went unsolved for over a decade. They are the Foldit players, and for their latest trick, they’ve shown that they can not only solve hard problems, but also create problem-solving tools that outperform the best in the business.
Foldit is an online multiplayer game, created by Seth Cooper and Zoran Popovic at the University of Washington. It’s designed to tap the collecting problem-solving skills of thousands of people, by reframing scientific problems in a way that even a complete novice can tackle.
In the game, players work together to decipher the structures of proteins. These molecules are feats of biological origami; they consist of long chains of amino acids that scrunch up into complicated three-dimensional shapes. Scientists need to resolve these shapes to understand how the proteins work, and the usual methods involve bouncing X-rays off purified crystals (which is difficult) or using predictive software (which is imperfect). Cooper and Popovic went down a third route: they got gamers to play their way to a solution.
In July 2002, an Italian man named Mr Francioni found something strange. Francioni owns a marble-cutting company in the Tuscan town of Pietrasanta, and he had just acquired a block of Egyptian marbleized limestone. After slicing the block into six slabs, he discovered the fossilised bones of an animal within. Fossils weaken the strength of cut stone and many people discard them outright. But Francioni was excited: he thought he had found a dinosaur, and contacted the nearby University of Pisa.
He got through to Giovanni Bianucci. “As soon as I saw the slabs, I realized that the finding was even more important than a dinosaur, at least for me. I study marine mammals,” he says. Bianucci realised that the bones belonged to an archaeocete, one of the predecessors of modern whales and dolphins. The story might have ended there: Francioni already had an offer from a foreign private collector, who wanted to slabs for his living room. Thankfully, Pisa’s local government intervened. They bought the fossils for the University’s Natural History Museum, where they are now on permanent display.
The melody sounds like it comes from a single bird, but it is actually sung by two: one male and one female. The couple alternates their syllables with almost unbelievable precision, each one placing its notes in the gaps left by its partner. The result is one of nature’s finest duets. And the singers are a pair of (rather drably named) plain-tailed wrens.
By studying the singing wrens, Eric Fortune from Johns Hopkins University has found that each bird has brain circuits that encode the entire song. Rather than focusing on just their own contribution, they process the whole melody. Their duet is conceived as a whole in both their brains, but emerges as two distinct parts, one from each beak.
As we get older, many of the cells in our bodies go into retirement. Throughout our lives, they divided time and again, all in the face of radiation bombardments and chemical attacks. Slowly but surely, their DNA builds up damage to that threatens to turn them into tumours. Some repair the damage; others give up the ghost. But some cells opt for a third strategy – they shut down. No longer growing or dividing, they enter a state called senescence.
But they aren’t idle. Senescent cells still secrete chemicals into the body, and some scientists have suggested that they’re responsible for many of the health problems that accompany old age. And the strongest evidence for this claim comes from a new study by Darren Baker from the Mayo Clinic College of Medicine.
Baker has developed a way of killing all of a mouse’s senescent cells by feeding them with a specific drug. When he did that in middle age, he gave the mice many more healthy years. He delayed the arrival of cataracts in their eyes, put off the weakening of their muscles, and held back the loss of their body fat. He even managed to reverse some of these problems by removing senescent cells from mice that had already grown old. There is a lot of work to do before these results could be applied to humans, but for now, Baker has shown that senescent cells are important players in the ageing process.
Each of our eyes sees a slightly different view of the world, and our brain combines these signals into a single three-dimensional image. But this only works in one direction, because our eyes face straight ahead and their respective fields of vision only overlap in a narrow zone. But there was once a creature that had binocular vision in a massive arc around its body, not just in front but to the sides as well. It’s called Henningsmoenicaris scutula and it lived around half a billion years ago.
H.scutula lived in the Cambrian period, the part of Earth’s history when most of today’s major animal groups exploded into existence. It was a crustacean, one of the earliest members of the group that includes crabs, prawns and lobsters. It was just a millimetre long and almost totally encased within a bowl-shaped shield. From beneath the shield, weird spike-tipped legs propelled it along, while two stalked eyes, each just half a millimetre across, peered out at the Cambrian oceans.
These eyes are compound ones, made up of several units or ‘ommatidia’. They’ve also withstood the test of time. Their organic tissues have since been converted into the mineral apatite, and the resulting fossils perfectly retain the shape and angle of each ommatidium. The eyes are so well-preserved that Brigitte Schoenemann from the University of Bonn could use them to reconstruct how H.scotula saw the world to a “quite impressive degree”.
It’s time for October’s Science Writer Tip-Jar picks. For those new to this, here’s the low-down:
Throughout the blogosphere, people produce fantastic writing for free. That’s great, but I believe that good writers should get paid for good work. To set an example, I choose ten pieces every month that were written for free and I donate £3 to the author. There are no formal criteria other than I found them unusually interesting, enjoyable and/or important.
I also encourage readers to support these writers through two buttons on the sidebar. There are two ways to help. Any donations via “Support Science Writers” are evenly distributed to chosen ten at the end of the month. Donations via the “Support NERS” button go to me; I match a third of the total figure and send that to the chosen writers too.
So without further ado, and in no particular order, here are the picks: