Dust mites that live and breed on your face have anuses, genome study finds

Dust mites that live and breed on your face have anuses, genome study finds

An illustration of Demodex folliculorum.

An illustration of Demodex folliculorum.
Photo: Shutterstock (Shutterstock)

Scientists have finally unveiled the genetic secrets of humanity’s coziest housemates: Demodex folliculorum, also known as skin mite. Among other things, the results confirm that these mites do indeed have anuses, contrary to previous speculation. They also indicate that microscopic animals may not be as dangerous as commonly thought, and that they evolve into co-dependent, symbiotic creatures that could provide us with some additional benefits.

D.folliculorum is actually one of two mite species who call us home, with Demodex short. Both species are arachnids, closer to ticks than spiders, but D.folliculorum mites are the ones that usually reside (and mate) on our faces. These stocky, worm-like creatures live for two to three weeks, while embedded in our pores, clinging to our hair follicles and feeding primarily on our sebum, the oily substance supplied by our bodies to protect and moisturize the skin. .

Although virtually every person in the world has their own collection of mites, there is still a lot we don’t understand about them. But in a new study published On Tuesday, in the journal Molecular Biology and Evolution, European researchers claim to have now completely sequenced the genome of D.folliculorum– an achievement that could answer some lingering questions about their inner workings.

Some researchers have argued, for example, that these mites do not have an anus. Without an anus, the theory goes, their faecal waste simply builds up inside them over their brief lifespan and is released only once when they die. Some have also speculated that an overabundance of mites can cause a skin condition known as rosacea, possibly due to bacteria released by this explosion of poo when a mite dies. However, other research has cast doubt on this claim, and the researchers behind the new study claim to have confirmed that mites do indeed have an anus.

Study author Alejandra Perotti, a researcher at the University of Reading in the UK, notes that the greater presence of mites in people who develop rosacea and other skin conditions may very well be a consequence of the disease and not its actual cause. And if the mites don’t leave massive amounts of poo behind when they die, then there’s a less clear rationale for how they would make us sick in the first place. Other studies, for what it’s worth, have continued find a link between dust mites and rosacea, although it is only one of many triggers involved.

“It’s easier and faster to blame the mites,” she said in an email to Gizmodo.

The team’s other findings show that these mites have evolved to become incredibly lazy, genetically speaking, as a result of hitching their cart to humans. They have a very simple genome compared to other related species, and they seem to survive on the bare minimum of cells and proteins needed to function (their pairs of legs are even powered by a single muscle cell each). They’ve lost the ability to survive exposure to ultraviolet light, which is why they burrow deep into our pores and only move and mate at night, and they don’t even seem to produce their own melatonin anymore. , as many animals do… instead, they seem to mock us. They are also transmitted from mother to child, often through breastfeeding, which means populations have relatively low genetic diversity. And their lack of natural predators, host competition and a generally sheltered existence suggests the mites are only likely to lose more genes over time.

Researchers hypothesize that these trends could one day lead to the end of D.folliculorum mites as a separate entity – a process that has been observed with bacteria but never with an animal, they say. Eventually, the mites might no longer live outside of our skin as parasites, but become entirely internal symbionts. If so, then we could see this transition happening now, although this transformation will probably not be complete for a long time.

Regardless of the future fate of these mites, scientists say they may be doing us good now. They could help cleanse the skin of excess dead cells and other material, for example, at least when their populations are controlled. Perotti also hopes their research will provide people “with a good understanding of those lifelong companions, who have been blamed for too long for our skin problems.”

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