Science-- there's something for everyone

Thursday, April 17, 2014

Why do Zebras have stripes?

Why do zebras have those flashy stripes? In a world where predators could be lurking anywhere, being so boldly conspicuous seems like a huge handicap. There must be some kind of evolutionary advantage to that distinctive coloring and biologists have come up with several ideas. The stripes might be courtship or other social cues, helping the animals mate or bond in groups. They might allow the animals to identify each other. They might confuse predators by making the zebras blend together. Perhaps they offer some type of temperature control. Nope. Tim Caro of the University of California, Davis and his colleagues ruled out those possibilities. It turns out that it’s all about the bugs.

That’s right, bugs. More specifically, biting insects like tsetse flies, stomoxys stable flies and tabanid biting flies. The researchers found that the ranges of animals with body stripes (zebras) exactly matched the ranges of these bloodsucking insects.

In the diagram below, you can see the different species of wild equine. Some have full body stripes, some leg stripes, some neck stripes and some are not striped at all. The blue dots show species not plagued by tabanid flies. Notice that those are the animals with no stripes. There was no such correlation with other factors like the presence of certain predators or temperature.

Striping and tabanid activity.
Phylogenetic tree of equid subspecies showing leg stripe intensity (inside circles) and proportion of geographic range overlap with 7 consecutive months of temperature lying between 15 and 30 C and humidity between 30 and 85% (outside circles).
Drawings by Rickesh Patel.
DOI: 10.1038/ncomms4535,

But aren't there plenty of other animals living in those same areas that are not striped? Yes, but zebras are covered with short hairs that biting insects can penetrate with their mouth parts. Non-striped mammals living in the same areas typically have longer, thicker fur that the flies can't get through.

How do stripes help animals avoid biting insects? Apparently, many insects, including tabanids and tsetses, don’t like to land on striped surfaces. And indeed, solid colored feral horses suffer much more harassment from flies than do their striped cousins.

The idea that insect parasites drove the evolution of stripes isn’t settled science yet, but it’s a fascinating hypothesis. I can’t wait to see if further studies confirm it.

Caro, T., Izzo, A., Reiner, R., Walker, H., & Stankowich, T. (2014). The function of zebra stripes Nature Communications, 5 DOI: 10.1038/ncomms4535,

Wednesday, April 16, 2014

Just for fun: X-ray art

Photographer Hugh Turvey uses x-rays to create works of art that he calls Xograms. Here's one example, an image he calls "Femme Fatale".

Picture of womans foot x-ray high heels 
You can read an interview with Turvey and see more of his work here.

Tuesday, April 15, 2014

First asteroid with rings

Artist’s impression of the rings around Chariklo
Artist's rendition of Chariklo, Courtesy of ESO
The Kuiper asteroid belt is full of objects that orbit the sun out beyond Neptune. Some of these objects have orbits that cross the paths of the gas giants, but they don’t generally get any closer than that.

This means that most of these objects are too far away for us to ever learn much about them if we can even detect them in the first place. But sometimes we get lucky. If one of these objects passes in front of (and consequently dims the light) of another star, we can use that information to determine how big the object is.

When astronomers observed an asteroid named Chariklo passing in front of a star (not the sun) last summer, they were able to calculate not only its size (250 kilometers in diameter), but something far more amazing. They found that Chariklo has rings. To be exact, it has two rings, one thin one and one thicker one. This makes the asteroid only the fifth object in our solar system to have rings, after Jupiter, Saturn, Uranus and Neptune.

How did the cosmologists come this conclusion? As Chariklo traveled across the path of that distant star, the light from that star was dimmed. But that slight fading didn’t happen just once, as it would if a single body were crossing in front of the star. Instead, there were five light dips: a small one (A), a bigger one (B), a much bigger one (C), then one exactly the same size as B, and finally one the exact same size as A. The regularity of the dips strongly suggests that A and B are rings.

It’s very likely that Chariklo is not the only asteroid with rings. After all, we once thought Saturn was the only planet with rings, and we now know that all the gas giants have them. It may be all the more amazing if relatively tiny asteroids can have rings since none of the rocky planets, which are far larger than asteroids, have rings. Even Mercury is nearly 20 times larger than Chariklo and it doesn't have rings.

You can read more about this at Bad Astronomy.

Camargo, J., Vieira-Martins, R., Assafin, M., Braga-Ribas, F., Sicardy, B., Desmars, J., Andrei, A., Benedetti-Rossi, G., & Dias-Oliveira, A. (2013). Candidate stellar occultations by Centaurs and trans-Neptunian objects up to 2014 Astronomy & Astrophysics, 561 DOI: 10.1051/0004-6361/201322579.

Monday, April 14, 2014

Get ready for a lunar eclipse

If you live in North America, you're going to have a chance to see a lunar eclipse tonight.

A lunar eclipse occurs when the moon passes through Earth's shadow. Phil Plait has an excellent description of this upcoming event over at Bad Astronomy, including this helpful diagram:

geometry of an eclipse
Note: objects are not to scale. Drawing by Shutterstock / fluidworkshop 

You can also see an explanation of how the eclipse will effect the Lunar Reconnaissance Orbiter (LRO), which is currently orbiting the moon, below:

When is the best viewing? The main event should take place between about 2- 5 am EDT. Plan accordingly.

Friday, April 11, 2014

What makes a Stradivarius violin so special?

PHOTO: In this March, 27, 2014 photo, three violinists play Stradivarius violins during a rehearsal at the Colburn School in Los Angeles.

The superiority of Old Italian violins like those made by Stradivari is legendary. For hundreds of years, people have tried to discover the source of that excellence. Was it the varnish? A property of the wood? The surprising answer may be that it's a trick question. Those old violins may not actually be any better than new violins. So say renowned violin soloists during blinded tests.

Claudia Fritz of Sorbonne Universit├ęs and her colleagues invited ten multiple award winning violin soloists to participate in their study. All of the musicians had experience playing Old Italian violins and some used them exclusively. While wearing welder’s goggles that made it impossible to identify violins by sight, the violinists were presented with six new violins (no more than two decades old, but antiqued to have the same worn edges as much older violins) and six old violins (made by 17th and 18th century masters like Guarneri del Gesu and Stradivari).

After playing their own violin as a reference, the subjects tried out the twelve violins and ranked them for preference, as if they were considering buying them. Once he had selected his four highest rated violins, each musician was presented with three violins: his own, his top pick out of the twelve, and his top pick from the opposite category. For example, if he liked an old violin the most, the third violin would be his top ranked new violin. Those three violins were then rated for a variety of musical attributes such as tone quality and projection.

The entire experiment was repeated twice, first in the practice room within the home of professional musicians and later in a 300 seat concert hall.

The two highest scoring violins were both new ones. Four of the six violins that had been ranked number one by at least one musician were new ones. All but one new violin was at least one person’s top pick, whereas four of the six old violins were no one’s top choice. For most criteria, the violinists preferred a top ranked new violin to their own violin. In contrast, they tended to prefer the qualities of their own violins to those of old violins.

No one is suggesting that the old Italian violin makers did not create masterpieces. It’s just that those instruments may not be as magical as they are given credit for. It also means that our modern violin manufacturers are doing an excellent job.

Fritz, C., Curtin, J., Poitevineau, J., Borsarello, H., Wollman, I., Tao, F., & Ghasarossian, T. (2014). Soloist evaluations of six Old Italian and six new violins Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1323367111.

Thursday, April 10, 2014

Sunset paintings are more than just art

If you wanted to study meteorological conditions before the advent of modern recording devices, what would you do? Well, if you’re like Christos Zerefos of the Academy of Athens or his colleagues, you’d look at old paintings. The researchers used paintings of sunsets made from the year 1500 to 2000 to estimate the amount of pollution in the air at those times.

First off, you may be wondering what could have produced enough pollution to blot the sky hundreds of years before the industrial revolution. The answer is volcanic eruption. Sure enough, paintings made within a few years of major eruptions have redder skies than paintings made at other times. This is because the ash and dust in the air after an eruption scatter the sunlight, shifting the ratio of red to green light.

To test how accurately a painting could be in predicting the clarity of the atmosphere, the researchers asked Panayiotis Tetsis, a colorist and landscape artist, to paint a series of sunset pictures from the island of Hydra. Unbeknownst to Tetsis, during the experiment there happened to be a Saharan dust storm blowing over Greece. You can see the results below:
Tetsis paintings
Greek landscape painter Panayiotis Tetsis created the top images on June 19 and 20, 2010, respectively. The photographs below them reflect the real sunsets on those evenings. There were more aerosols in the sky, and more red in Tetsis' painting, on June 19.
P. Tetsis (paintings) and C. Zerefos (photos).

The top two panels are of Tetsis’ paintings, the bottom panels are photographs taken while he was painting. The panels on the left were made during the dust storm, the panels on the right were made the next day. Notice how much redder the sky is during the dust storm in both the photographs and the paintings.

If earlier artists were equally good at capturing color differences, then paintings made hundreds of years ago could be useful for determining pollution levels.

Zerefos, C., Tetsis, P., Kazantzidis, A., Amiridis, V., Zerefos, S., Luterbacher, J., Eleftheratos, K., Gerasopoulos, E., Kazadzis, S., & Papayannis, A. (2013). Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters Atmospheric Chemistry and Physics Discussions, 13 (12), 33145-33176 DOI: 10.5194/acpd-13-33145-2013.

Wednesday, April 9, 2014

Just for fun: Cyborg drummer

Drummer Jason Barnes lost his right arm after being electrocuted two years ago. Thanks to help from Gil Weinberg’s lab at Georgia Tech, Barnes now has a robotic arm with which to make music.

Notice that the prosthesis holds two drumsticks, only one of which is controlled by Barnes’ bicep muscles. The second drumstick is an independent robotic device that can improvise, based on what Barnes is doing with the drumsticks he controls.