Oleksii Voronin via Wikimedia Commons // CC BY-SA 3.0
Oleksii Voronin via Wikimedia Commons // CC BY-SA 3.0

How Chipmunks and Striped Mice Got Their Adorable Stripes

Oleksii Voronin via Wikimedia Commons // CC BY-SA 3.0
Oleksii Voronin via Wikimedia Commons // CC BY-SA 3.0

Scientists say they’ve found the genetic origin of stripes in chipmunks and other mice. They published their findings today in the journal Nature.

Cute though they may be, rodents’ stripes are hardly ornamental. Like a jaguar’s rosettes or a peppered moth’s sooty wings, stripes evolved to allow their bearers to vanish into their surroundings. On a large scale, we understand how these patterns came about: animals with camouflage markings survived and bred, while those without died out. On a smaller scale, we’ve still got a lot to learn.

To zoom in on the specific genetics of mammal stripes, an international team of scientists decided to take a very close look at the four-striped grass mouse (Rhabdomys pumilio), a resilient little rodent that spends its days munching seeds in southern Africa.

J. F. Broekhuis

The scientists first examined the individual hairs that form each mouse’s stripes. They found three distinct types: light hairs, with black bases and unpigmented hair shafts; black hairs, which were dark from base to tip; and banded hairs, with black bases and yellow shafts. All three hair types were found in both dark and light stripes, albeit in different proportions: dark stripes simply had a lot more black hairs, while light stripes were mostly light hairs.

Next, they bred baby grass mice in the lab, tracking the appearance of their skin and fur as they grew from embryos to pups. They found that just 19 days after fertilization, the length of the rodents’ fur began to vary over the areas that would one day be striped. Three days later, the embryos’ skin started to lighten in the same places that light-striped fur would later appear. At birth, the mouse pups’ coats showed variation in both hair length and skin color. Two days after that, their characteristic stripes were clearly visible.

To understand what was causing these shifts, the researchers scanned the rodents’ genomes at all four points in development. They found that, as early as day 19 of embryonic development, a gene called ALX3 was showing up on the embryos’ backs in the same sites where the light stripes would one day appear. 

The researchers learned that ALX3 was kind of a bully to a pigment cell–producing protein called microphthalmia-associated transcription factor (MITF). Wherever ALX3 appeared, pigment production was repressed, leading to very pale cells, which in turn led to light stripes.

Furthermore, the team found that the same mechanism—ALX3 smothering MITF activity—appears in similarly striped Eastern chipmunks (Tamias striatus). While mice and chipmunks are both members of the rodent family, their last common ancestor lived around 70 million years ago. The fact that two such distinct species share a similar stripe backstory suggests to the researchers that this useful genetic trick may have evolved a number of times across the mammal family tree—a phenomenon known as convergent evolution.

NOAA, Wikimedia Commons // Public Domain
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.

Joe Raedle, Getty Images
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.


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.


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.


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.


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.


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.


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.


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).


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.


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.


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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