It’s no surprise that tardigrade sex is a little unconventional. And according to a study in the Zoological Journal, the world’s toughest animal engages in an awful lot of foreplay.
But how do tardigrades reproduce? Let’s take a closer look.
The reproductive mechanisms and behavior of tardigrades
When it comes to reproduction, tardigrades show incredible adaptability. Some species can switch between sexual and asexual reproduction, depending on environmental conditions.
Many species of tardigrade reproduce sexually, with males releasing sperm into the female’s body cavity, where fertilization occurs. The female then lays eggs, which hatch into tiny new tardigrades.
Some hermaphroditic species—those with both male and female reproductive organs—can self-fertilize. This is an ideal trait for life in extreme environments, such as the deep sea or sand dunes, where finding a mate is as rare as winning the lottery.
Both asexual and sexual reproduction occur in tardigrades. Parthenogenesis, the only confirmed asexual method, involves females producing offspring from unfertilized eggs, creating clones of themselves.
Studies in the Journal of Experimental Biology and Covich’s Freshwater Invertebrates reveal more about their superpowers, showing how these microscopic wonders thrive in extreme conditions and how invertebrates can reproduce with ease.
Mysterious water bears caught red-handed
Video footage captured by a team of researchers from the Senckenberg Museum of Natural Sciences in Görlitz, Germany, provides insight into how the act is carried out in a hermaphroditic species of tardigrade called Isohypsibius dastychi.
And while it may not seem like much to the untrained eye, researchers assure us that things could get strange.
The animals mate immediately after the female has molted, which happens several times a year. The researchers paired up 30 male-female pairs (judging the sex of a tardigrade is no easy task!) and filmed them doing their thing.
They found that after the female’s outer skin comes off, she lays eggs inside it. If for some reason no male waddles by after she lays her eggs, that’s no problem; she simply reabsorbs them into her body.
But if a male is nearby, he will wrap his body around her head and the two will engage in an hour-long marathon of mutual stimulation. During this marathon, he may ejaculate multiple times into the space between her old and new skin, fertilizing her eggs.
Witnessing this unusual sexual spectacle has raised almost as many questions for researchers as it has answered. For example, how does a man direct his sperm to the right place when he’s actually shooting it under her skin? And how does such a tiny creature survive so much foreplay?
Back Up — What exactly is a tardigrade?
Tardigrades, sometimes called water bears or moss pigs, are microscopic aquatic organisms known for their incredible resilience to extreme environmental conditions. These tiny creatures are typically 0.012 to 0.02 inches (0.3 to 0.5 millimeters) long.
They are one of the few species found on every continent, in a wide range of environments – from the deep ocean floor to the highest mountains to extreme conditions like hot springs and Antarctic ice.
For example, it is incredibly difficult to kill one of these microscopic creatures. You can dehydrate them, starve them, freeze them, burn them, irradiate them, poison them, or stick them in the deepest, most pressurized ocean trench and they will survive. You can even expose them to the vacuum of space (more on that later).
Anatomy of a water bear
Tardigrades have a plump, segmented body with eight legs, each equipped with small claws or suckers, which give them their characteristic appearance.
They have a simple digestive system, with a tubular mouth, pharynx, and intestines, but lack a circulatory or respiratory system, relying instead on diffusion for gas exchange. Their nervous system consists of a brain and a ventral nerve cord. Unique cells called Malpighian tubules function in excretion.
Water bears have specialized structures such as the buccal apparatus to feed on plant cells, algae and small invertebrates. Their remarkable adaptability is partly due to cryptobiosis, which allows them to survive extreme conditions by entering a state of dormancy.
Chilling in Cryptobiosis
In this state, the bears retract their limbs, lose almost all of their body water, and form a tun: a desiccated, lifeless form.
Tardigrades can remain inactive in cryptobiosis for years, even decades. During this period, their metabolic activity drops to almost undetectable levels. They can tolerate extreme temperatures, high radiation, vacuum conditions, and lack of oxygen.
Researchers discovered that tardigrades produce unique proteins that protect their cells by forming a glassy substance when they dehydrate, helping them survive in harsh conditions. This glassy material melts away upon rehydration, allowing tardigrades to return to their active state.
Even NASA has studied tardigrades, specifically their ability to survive in space. Tardigrades have been sent to the International Space Station to study how they adapt to microgravity.
4 Notable Classes of Tardigrade Species
These tiny titans of the microscopic world have a diversity that would make even the most diverse ecosystems jealous. With over 1,300 identified species, these resilient creatures belong to the phylum Tardigrada, divided into several classes, orders and families.
1. Eutardigrade
First of all, in the class Eutardigrada we have the order Parachela, home to the family Hypsibiidae and his star player, Hypsibius dujardini.
This little guy is a favorite at the lab, known for his ability to survive conditions that would make a cockroach blush. And then there’s Macrobiotus hufelandi of the family Macrobioticswhich you can often find in the moss and lichen, while enjoying the view of his little world.
2. Heterotardigrade
In the class Heterotardigrada the order Echiniscoidea brings us the family Echiniscidae of Echiniscus blumia lover of freshwater and terrestrial habitats. Meanwhile, Echiniscoides sigismundi of the family Echiniscoididae prefers the salty embrace of marine environments.
3. Arthrotardigrade
Not to be outdone, Arthrotardigrada introduces the order Blue butterfly of the family Batsa marine animal known for its claw-like structures, perfect for the tardigrade fashion show.
4. Mesotardigrade
Finally, the class Mesotardigrada concerns itself exclusively with a single known species: Thermozodium esakiiThis elusive tardigrade was discovered in a hot spring in Japan and is rarely studied due to the limited number of specimens, making it the unicorn of the tardigrade world.
This article has been updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.
Original article: How do tardigrades reproduce? Several ways, it turns out
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