It Turns Out That Single-Celled Organisms Are Having Sex Too

Gisela Giardino, Wikimedia Commons // CC BY-SA 2.0
Gisela Giardino, Wikimedia Commons // CC BY-SA 2.0

So much for the stereotype of the chaste, pious diatom. (Wait. Is that not a stereotype?) Scientists examining tiny single-celled organisms say we've been wrong to assume they* lead lives of quiet, sexless desperation. The researchers described their microscopically racy findings in the journal PLOS One.

The tiny specks called diatoms are neither plants nor animals but somewhere in between; they're algae. There are more than 200,000 species living in the water all over the world, each with its own unique and beautiful frustule, or hard silica scaffolding.

Microscope image of Stephanopyxis grunowii frustule fossil.
Anatoly Mikhaltsov, Wikimedia Commons // CC BY-SA 4.0

To date, scientists have sequenced the genetic code of only two diatoms: the peapod-shaped Phaeodactulum tricornutum and the round, or centric, Thalassiosira pseudonana. The genes of T. pseudonana contained some sex-related code, but researchers believed it was vestigial, like our wisdom teeth or the wings of a kiwi bird.

"Everybody said Thalassiosira pseudonana was asexual, because they'd never seen anything else," corresponding author Kimberly Halsey of Oregon State University said in a statement. "The general thinking was that it just lost the ability or need to go through sex."

Not for lack of trying on our part. Previous experimenters have tried all kinds of things to get the little specks to get busy, from turning off the lights to adding more salt to the water.

"Lab efforts to induce sex in centric diatoms have ranged from sweet talk to torture," Halsey said. These efforts weren't entirely fruitless; once in a while, the diatoms might show some interest. But it wasn't clear why, or if the tiny organisms would do it on their own.

Halsey and her colleagues decided to take another close look at T. pseudonana. They went back over its genome, studying any gene that could be related to sexual activity, then stared long and hard at the diatoms themselves.

What they found surprised them. The diatoms had genes that would allow them to differentiate—that is, to become one sex or another. Lead author Eric Moore says he was startled by this realization.

"In fact, I was convinced my cultures were contaminated before I realized what was actually going on," he said. 

Moore, Halsey, and their colleagues also discovered the secret to getting T. pseudonana in the mood: a little aphrodisiac known as ammonia.

While many of us know ammonia as an awful-smelling cleaning agent, it's not hard to find it in the wild, as a component of urine and other waste. Exposing the diatoms to ammonia was all it took to get the cells to start making eggs and sperm.

The authors say the diatoms may be regularly soaking in ammonia and, consequently, getting sexy.

"Our discoveries solve two persistent mysteries that have plagued diatom researchers," Halsey said. "Yes, they have sex, and yes, we can make them do it."

 

*The single-celled organisms, not the scientists. The sex lives of the latter are none of our business.

Lítla Dímun: The Smallest of the Faroe Islands Has Its Very Own Cloud

While some islands are known for their unusual geography or unique history, Lítla Dímun is notable for its weather. The island, which is the smallest of Denmark's Faroe Islands chain, is often capped by a lens-shaped cloud, making it resemble a scene from a fairytale.

According to Mental Floss's own Kerry Wolfe writing for Atlas Obscura, the cloud floating above Lítla Dímun is a lenticular cloud. This type of cloud forms when moist air flows over a protruding geological feature, like a mountain top. When the wind moving up the landmass hits the air current directly above it, a sort of wave is created on the downwind side of the mountain. The moist air falling down this wave evaporates and then condenses into a large, flying-saucer-shaped cloud atop the mountain peak as a result.

Another factor that makes Lítla Dímun distinct is that it's the only one of the 18 main Faroe Islands without human inhabitants. Visitors to the mystical location will instead find a thriving population of sheep. Originally, Lítla Dímun was home to a group of feral sheep likely dating back to the Neolithic era. But they were hunted to extinction in the 19th century. Domesticated sheep were introduced there around the same time, and today, farmers visit the island once a year to round up their flocks.

One of the few signs of human life are the ropes farmers use to scale the cliff faces bordering the island. Even if you have rock-climbing skills, Lítla Dímun may be dangerous to visit. A boat ride to the rocky shore is only possible when the surrounding sea is calm.

[h/t Atlas Obscura]

Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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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