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Mickey Samuni-Blank via Wikimedia Commons // CC BY-SA 3.0
Mickey Samuni-Blank via Wikimedia Commons // CC BY-SA 3.0

Spiny Mice Are First Known Rodents to Have Menstrual Periods

Mickey Samuni-Blank via Wikimedia Commons // CC BY-SA 3.0
Mickey Samuni-Blank via Wikimedia Commons // CC BY-SA 3.0

Periods are a strange phenomenon. We don’t know why humans have them, or, to look at it another way, why most other animals don’t. Scientists say only 1.5 percent of mammal species have periods, and most of those are primates like us. The ranks of the menstrually afflicted grew a little bit recently, as researchers learned that female spiny mice have periods, too. They shared their findings on the bioRxiv preprint server.

The spiny mouse (Acomys cahirinus, also known as the Egyptian spiny mouse) is a perculiar little animal. It has spines like a hedgehog and will indiscriminately devour just about anything in its path, including mummified bodies. When in danger, a spiny mouse can shed (and later regrow) large chunks of its fragile skin. Needless to say, the spiny mouse has got scientists’ attention.

Curious about the spiny mouse’s reproductive system, researchers decided to get up close and personal with their nether regions. They brought 14 young, never-pregnant female mice into the lab and, once a day for 18 days, administered tiny saline douches into the rodents’ vaginas, watching to see what, if anything, would be washed out.

They found blood. Once every nine days, for about three days, the mice shed the lining of their endometrium and expelled it, along with some blood, just like humans do. The mice spent between 20 to 40 percent of their nine-day cycle menstruating, which is approximately the same proportion seen in human women. These findings make the spiny mouse the first known rodent with a human-like menstrual period.

Reproductive biologist Francesco DeMayo of the U.S. National Institute of Environmental Health Sciences was not involved with the study, but was impressed by the results. “When you do science you’re not surprised at anything—but wow, this was a really interesting finding,” he told Scientific American.

The discovery has implications not only for the rest of the animal kingdom (how many other menstruating species have scientists overlooked?) but for us. At the moment, the most popular animals used in research—mice, rats, birds, and fish—are period-free, which means they can’t be used to study the menstrual cycle. Learning about mouse menstruation could one day help us understand our own.

Why did it take scientists so long to notice that these curious creatures were part of the period posse? “The answer, as with many discoveries in science, is that no one really looked,” said Hayley Dickinson, a reproductive physiologist and long-time spiny rat researcher at the University of Monash. “Everyone knew that rodents didn't menstruate.”

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Big Questions
What's the Difference Between Gophers and Groundhogs?
Gopher or groundhog? (If you chose gopher, you're correct.)
Gopher or groundhog? (If you chose gopher, you're correct.)
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Gophers and groundhogs. Groundhogs and gophers. They're both deceptively cuddly woodland rodents that scurry through underground tunnels and chow down on plants. But whether you're a nature nerd, a Golden Gophers football fan, or planning a pre-spring trip to Punxsutawney, Pennsylvania, you might want to know the difference between groundhogs and gophers.

Despite their similar appearances and burrowing habits, groundhogs and gophers don't have a whole lot in common—they don't even belong to the same family. For example, gophers belong to the family Geomyidae, a group that includes pocket gophers (sometimes referred to as "true" gophers), kangaroo rats, and pocket mice.

Groundhogs, meanwhile, are members of the Sciuridae (meaning shadow-tail) family and belong to the genus Marmota. Marmots are diurnal ground squirrels, Daniel Blumstein, a UCLA biologist and marmot expert, tells Mental Floss. "There are 15 species of marmot, and groundhogs are one of them," he explains.

Science aside, there are plenty of other visible differences between the two animals. Gophers, for example, have hairless tails, protruding yellow or brownish teeth, and fur-lined cheek pockets for storing food—all traits that make them different from groundhogs. The feet of gophers are often pink, while groundhogs have brown or black feet. And while the tiny gopher tends to weigh around two or so pounds, groundhogs can grow to around 13 pounds.

While both types of rodent eat mostly vegetation, gophers prefer roots and tubers (much to the dismay of gardeners trying to plant new specimens), while groundhogs like vegetation and fruits. This means that the former animals rarely emerge from their burrows, while the latter are more commonly seen out and about.

Groundhogs "have burrows underground they use for safety, and they hibernate in their burrows," Blumstein says. "They're active during the day above ground, eating a variety of plants and running back to their burrows to safety. If it's too hot, they'll go back into their burrow. If the weather gets crappy, they'll go back into their burrow during the day as well."

But that doesn't necessarily mean that gophers are the more reclusive of the two, as groundhogs famously hibernate during the winter. Gophers, on the other hand, remain active—and wreck lawns—year-round.

"What's really interesting is if you go to a place where there's gophers, in the spring, what you'll see are what is called eskers," or winding mounds of soil, Blumstein says [PDF]. "Basically, they dig all winter long through the earth, but then they tunnel through snow, and they leave dirt in these snow tunnels."

If all this rodent talk has you now thinking about woodchucks and other woodland creatures, know that groundhogs have plenty of nicknames, including "whistle-pig" and "woodchuck," while the only nicknames for gophers appear to be bitter monikers coined by Wisconsin Badgers fans.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Watch Christmas Island’s Annual Crab Migration on Google Street View
Google
Google

Every year, the 45 million or so red crabs on the remote Australian territory of Christmas Island migrate en masse from their forest burrows down to the ocean to mate, and so the female crabs can release their eggs into the sea to hatch. The migration starts during the fall, and the number of crabs on the beach often peaks in December. This year, you don’t have to be on Christmas Island to witness the spectacular crustacean event, as New Atlas reports. You can see it on Google Street View.

Watching the sheer density of crabs scuttling across roads, boardwalks, and beaches is a rare visual treat. According to the Google blog, this year’s crabtacular finale is forecasted for December 16, and Parks Australia crab expert Alasdair Grigg will be there with the Street View Trekker to capture it. That is likely to be the day when crab populations on the beaches will be at their peak, giving you the best view of the action.

Crabs scuttle across the forest floor while a man with a Google Street View Trekker walks behind them.
Google

Google Street View is already a repository for a number of armchair travel experiences. You can digitally explore remote locations in Antarctica, recreations of ancient cities, and even the International Space Station. You can essentially see the whole world without ever logging off your computer.

Sadly, because Street View isn’t live, you won’t be able to see the migration as it happens. The image collection won’t be available until sometime in early 2018. But it’ll be worth the wait, we promise. For a sneak preview, watch Parks Australia’s video of the 2012 event here.

[h/t New Atlas]

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