Scientists Identify Gene Associated with Butterfly Wing Coloration

Patterns on the wing of a Heliconius melpomene, or postman butterfly, composed of tiles of overlapping colored scales. Image credit: Nicola Nadeau, University of Sheffield

Researchers published two separate studies in the journal Nature today confirming the role of the cortex gene in the coloration and darkness of butterfly and moth wings.

In the early 1800s, peppered moths (Biston betularia) in the woods around Manchester, England were grayish white and covered in (pepper-like) black specks. By 1848, on the heels of the Industrial Revolution, naturalists had found a second, all-black variety. By the 1950s, the carbonaria type, as the black-clad moths were called, had taken over.

Animal coloration is about more than simple aesthetics. Such a drastic change in appearance could only mean one thing: the new look conferred some evolutionary advantage. Something in the moths’ world must have changed so drastically that black became the new white. Indeed something had changed: the trees. The smoke and soot produced by Manchester’s factories had darkened the forest. The once well-camouflaged white moths would stand out starkly against the trees’ now-dark bark, but black moths could stay hidden from predators—and thus survive to live and breed.

Black and white peppered moths mating. Image credit: University of Bristol

Fortunately for Britain’s forests but unfortunately for black moths, Manchester made something of an environmental recovery. By the late 1900s, the trees had lightened up once more. With that, Carbonaria moths were again at a disadvantage, and so their numbers dwindled.

The peppered moth’s bizarre-but-true story has become something of a morality tale, but one element was missing: just how the moths made their costume change. A single insect can’t change the color of its wings any more than a person can change his or her skin color. These changes happen over generations, as an individual with a beneficial genetic mutation survives and reproduces, passing the mutation along.

That mutation has now been identified. Researchers at the UK’s University of Liverpool and Wellcome Trust Sanger Institute say that around the year 1819, one moth’s genetic code was host to a change: the insertion of a chunk of DNA into a gene the researchers call cortex. That inserted DNA is made of copies and repetitions of code from white moths. The authors say the extra code may encourage cortex to make more of a protein that affects the development of wing scales.

At the same time, an international team of butterfly researchers found cortex at work in the genus Heliconius, also known as the passion-vine butterflies.

The red postman butterfly (Heliconius erato cyrbia). Image credit: Melanie Brien

Like the peppered moths, the wings of these butterflies have changed dramatically and rapidly in a relatively short amount of time.

The scientists used DNA and gene expression analysis to compare the genetic codes of different Heliconius variations. Their results led them, like the moth researchers, to cortex—a fact that suggests it might be responsible for patterning in other species, too.

“In parallel with findings in the peppered moth,” the authors write, “our results suggest that this mechanism is common within Lepidoptera and that cortex has become a major target for natural selection acting on color and pattern variation in this group of insects.”

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How Bats Protect Rare Books at This Portuguese Library
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Visit the Joanina Library at the University of Coimbra in Portugal at night and you might think the building has a bat problem. It's true that common pipistrelle bats live there, occupying the space behind the bookshelves by day and swooping beneath the arched ceilings and in and out of windows once the sun goes down, but they're not a problem. As Smithsonian reports, the bats play a vital role in preserving the institution's manuscripts, so librarians are in no hurry to get rid of them.

The bats that live in the library don't damage the books and, because they're nocturnal, they usually don't bother the human guests. The much bigger danger to the collection is the insect population. Many bug species are known to gnaw on paper, which could be disastrous for the library's rare items that date from before the 19th century. The bats act as a natural form of pest control: At night, they feast on the insects that would otherwise feast on library books.

The Joanina Library is famous for being one of the most architecturally stunning libraries on earth. It was constructed before 1725, but when exactly the bats arrived is unknown. Librarians can say for sure they've been flapping around the halls since at least the 1800s.

Though bats have no reason to go after the materials, there is one threat they pose to the interior: falling feces. Librarians protect against this by covering their 18th-century tables with fabric made from animal skin at night and cleaning the floors of guano every morning.

[h/t Smithsonian]

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Honey Bees Can Understand the Concept of Zero
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The concept of zero—less than one, nothing, nada—is deceptively complex. The first placeholder zero dates back to around 300 BCE, and the notion didn’t make its way to Western Europe until the 12th century. It takes children until preschool to wrap their brains around the concept. But scientists in Australia recently discovered a new animal capable of understanding zero: the honey bee. According to Vox, a new study finds that the insects can be taught the concept of nothing.

A few other animals can understand zero, according to current research. Dolphins, parrots, and monkeys can all understand the difference between something and nothing, but honey bees are the first insects proven to be able to do it.

The new study, published in the journal Science, finds that honey bees can rank quantities based on “greater than” and “less than,” and can understand that nothing is less than one.

Left: A photo of a bee choosing between images with black dots on them. Right: an illustration of a bee choosing the image with fewer dots
© Scarlett Howard & Aurore Avarguès-Weber

The researchers trained bees to identify images in the lab that showed the fewest number of elements (in this case, dots). If they chose the image with the fewest circles from a set, they received sweetened water, whereas if they chose another image, they received bitter quinine.

Once the insects got that concept down, the researchers introduced another challenge: The bees had to choose between a blank image and one with dots on it. More than 60 percent of the time, the insects were successfully able to extrapolate that if they needed to choose the fewest dots between an image with a few dots and an image with no dots at all, no dots was the correct answer. They could grasp the concept that nothing can still be a numerical quantity.

It’s not entirely surprising that bees are capable of such feats of intelligence. We already know that they can count, teach each other skills, communicate via the “waggle dance,” and think abstractly. This is just more evidence that bees are strikingly intelligent creatures, despite the fact that their insect brains look nothing like our own.

Considering how far apart bees and primates are on the evolutionary tree, and how different their brains are from ours—they have fewer than 1 million neurons, while we have about 86 billion—this finding raises a lot of new questions about the neural basis of understanding numbers, and will no doubt lead to further research on how the brain processes concepts like zero.

[h/t Vox]

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