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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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NOAA, Wikimedia Commons // Public Domain
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Animals
Watch the First-Ever Footage of a Baby Dumbo Octopus
NOAA, Wikimedia Commons // Public Domain
NOAA, Wikimedia Commons // Public Domain

Dumbo octopuses are named for the elephant-ear-like fins they use to navigate the deep sea, but until recently, when and how they developed those floppy appendages were a mystery. Now, for the first time, researchers have caught a newborn Dumbo octopus on tape. As reported in the journal Current Biology, they discovered that the creatures are equipped with the fins from the moment they hatch.

Study co-author Tim Shank, a researcher at the Woods Hole Oceanographic Institution in Massachusetts, spotted the octopus in 2005. During a research expedition in the North Atlantic, one of the remotely operated vehicles he was working with collected several coral branches with something strange attached to them. It looked like a bunch of sandy-colored golf balls at first, but then he realized it was an egg sac.

He and his fellow researchers eventually classified the hatchling that emerged as a member of the genus Grimpoteuthis. In other words, it was a Dumbo octopus, though they couldn't determine the exact species. But you wouldn't need a biology degree to spot its resemblance to Disney's famous elephant, as you can see in the video below.

The octopus hatched with a set of functional fins that allowed it to swim around and hunt right away, and an MRI scan revealed fully-developed internal organs and a complex nervous system. As the researchers wrote in their study, Dumbo octopuses enter the world as "competent juveniles" ready to jump straight into adult life.

Grimpoteuthis spends its life in the deep ocean, which makes it difficult to study. Scientists hope the newly-reported findings will make it easier to identify Grimpoteuthis eggs and hatchlings for future research.

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Joe Raedle, Getty Images
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Animals
10 Things You Might Not Know About Grizzly Bears
Joe Raedle, Getty Images
Joe Raedle, Getty Images

Ursus arctos horribilis is better known by the more casual term of grizzly bear. These massive, brown-haired predators have a reputation as one of nature’s most formidable killing machines. Standing up to 8 feet tall and weighing 800 pounds, these fierce mammals have captivated—and frightened—humans for centuries. Keep your distance and read up on these facts about their love for munching moths, eating smaller bears, and being polar-curious.

1. THEY’RE ACTUALLY PRETTY LIGHT EATERS.

Grizzlies—more accurately, North American brown bears—are strong enough to make a meal out of whatever they like, including moose, elk, and bison. Despite their reputation for having carnivorous appetites, their diet also consists of nuts, berries, fruits, and leaves. They’ll even eat mice. The gluttony doesn’t kick in until they begin to exhibit hyperphagia, preparing for winter hibernation by chomping down enough food to gain up to three pounds a day.

2. THEY USE “CPR” TO GET AT YOUR FOOD.

A grizzly bear eats fruit in Madrid, Spain
Dani Pozo, AFP/Getty Images

More than 700 grizzlies live in or near Yellowstone National Park, which forces officials to constantly monitor how park visitors and the bears can peacefully co-exist. Because bears rummaging in food containers can lead to unwanted encounters, the park’s Grizzly & Wolf Discovery Center tests trash cans and coolers to see if they’re bear-resistant. (Nothing is truly bear-proof.) Often, a bear will use “CPR,” or jumping on a canister with its front legs, in order to make the lid pop off. Containers that can last at least 60 minutes before being opened can be advertised by their manufacturers as being appropriate for bear-inhabited environments.

3. THEY CAN CLIMB TREES.

It's a myth that grizzlies can't climb trees. Though their weight and long claws make climbing difficult [PDF], and they need support from evenly-spaced branches, grizzlies can travel vertically if they choose to.

4. THEY’LL EAT OTHER BEARS.

Two grizzly bears play in a pool at a zoo in France
Jean-Francois Monier, AFP/Getty Images

In addition to being omnivorous, grizzlies can also be classified as cannibals. They’ve been spotted eating the carcasses of black bears in Canada. Calling it a “bear-eat-bear world,” officials at Banff National Park in Alberta said the grizzlies are “opportunistic” and more than willing to devour black bears—sometimes just one-fifth their size—if the occasion calls for it. And it’s not just black bears: One study on bear eating habits published in 2017 recorded a 10-year-old male eating a 6-year-old female brown bear.

5. THEY LOVE MOTHS.

Although grizzlies enjoy eating many insects, moths are at the top of the menu. Researchers have observed that bears are willing to climb to alpine heights at Montana’s Glacier National Park in order to feast on the flying appetizers. Grizzlies will turn over rocks and spend up to 14 hours in a day devouring in excess of 40,000 moths.

6. A PAIR OF THEM ONCE LIVED ON WHITE HOUSE GROUNDS.

A grizzly bear appears at the Wild Animal Sanctuary in Keenseburg, Colorado
John Moore, Getty Images

In what would be considered an ill-advised decision, explorer Zebulon Pike decided to gift his friend President Thomas Jefferson with two grizzly cubs in 1807. Jefferson reluctantly accepted them and kept them in a cage near the north entrance to the White House, and later re-gifted the cubs to museum operator Charles Willson Peale. Sadly, one of them got shot after getting too aggressive with Peale’s family.

7. THEY CAN RUN FASTER THAN USAIN BOLT.

The bears we see in fiction or lazing about in the wild tend to look cumbersome and slow, as most anything weighing nearly a half-ton would. But in a land race, even Olympic champions would be on the losing end. Grizzlies can reportedly run 35 mph, and sustain speeds of up to 28 mph for two miles, faster than Usain Bolt’s 27.78 miles per hour stride (which he can only sustain for a few seconds).

8. THEY MATE WITH POLAR BEARS.

A grizzly bear is shown swimming at a pool in an Illinois zoo
Scott Olson, Getty Images

In parts of Alaska and Canada where grizzlies and polar bears converge, there are sometimes rare sightings of what observers call “grolar bears” or “pizzlies.” With large heads and light-colored fur, they’re a hybrid superbear birthed from some interspecies mating. Typically, it’s male grizzlies who roam into those territories, finding female polar bears to cozy up with. Researchers believe climate change is one reason the two are getting together.

9. THEY KNOW HOW TO COVER THEIR TRACKS.

When it comes to intellect, grizzlies may not get all the same publicity that birds and whales do, but they’re still pretty clever. The bears can remember hotspots for food even if it’s been 10 years since they last visited the area; some have been observed covering tracks or obscuring themselves with rocks and trees to avoid detection by hunters.

10. THEY’RE NOT OUT OF THE WOODS YET.

A grizzly bear and her cub walk in Yellowstone National Park
Karen Bleier, AFP/Getty Images

For 42 years, grizzlies at Yellowstone occupied the endangered species list. That ended in 2017, when the U.S. Fish and Wildlife Service declared that a rise in numbers—from 150 in the 1970s to more than 700 today—meant that conservation efforts had been successful. But overall, the grizzly population is still struggling: Fewer than 2000 remain in the lower 48 states, down from 50,000 two centuries ago.

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