Skin Mites That Mate on Our Faces at Night Are Slowly Merging With Humans

Skin Mites That Mate on Our Faces at Night Are Slowly Merging With Humans

If you are reading this, you are probably not alone.

Most people on Earth are habitats for mites that spend most of their brief lives buried, headfirst, in our hair follicles, mostly on the face. In fact, humans are the only habitat for follicular demodex. They are born from us, they feed on us, they mate with us, and they die with us.

Their entire life cycle revolves around chewing on dead skin cells before kicking the tiny bucket.

So dependent is D follicular on humans for their survival, new research suggests, that microscopic mites are in the process of evolving from an ectoparasite to an internal symbiont, and one that shares a mutually beneficial relationship with its hosts (that’s us).

In other words, these mites are gradually merging with our bodies so that they now permanently live inside us.

Scientists have now sequenced the genomes of these ubiquitous little beasts, and the results show that their human-centric existence could be causing changes not seen in other mite species.

“We found that these mites have a different arrangement of body part genes than other similar species because they are adapted to a protected life within the pores,” explained invertebrate biologist Alejandra Perotti of the University of Reading in the United Kingdom.

“These changes to their DNA have resulted in some unusual bodily characteristics and behaviors.”

D follicular seen in a potassium hydroxide preparation of human skin. (KV Santosh/Flickr, CC BY 2.0)

D follicular is actually a fascinating little creature. Detritus from human skin is their only food source and they spend most of their two weeks of life chasing after it.

Individuals emerge only at night, under cover of darkness, to laboriously crawl slowly over the skin to find a mate and hopefully copulate before returning to the safe darkness of a follicle.

Their tiny bodies are only a third of a millimeter long, with a set of tiny legs and a mouth at one end of a long sausage-shaped body, just right for slipping down human hair follicles to reach the tasty noms in they.

The work on the mite genome, co-led by Marin and geneticist Gilbert Smith of Bangor University in the UK, revealed some of the fascinating genetic characteristics that drive this lifestyle.

Because their lives are so complicated, with no natural predators, no competition, and no exposure to other mites, their genome has been stripped down to the bare essentials.

Their legs are powered by three single-celled muscles, and their bodies have the absolute minimum amount of protein, just what is needed to survive. It is the smallest number ever seen in its largest group of related species.

This reduced genome is the reason for some of D follicularThere are also other strange peccadilloes. For example, the reason why he only goes out at night. Among the lost genes are those responsible for protection against ultraviolet radiation and those that wake animals up in daylight.

They also cannot produce the hormone melatonin, which is found in most living organisms, with variable functions; in humans, melatonin is important in regulating the sleep cycle, but in small invertebrates it induces mobility and reproduction.

This does not seem to have prevented D follicular, nevertheless; it can collect melatonin secreted by its host’s skin at dusk.

follicular dorsal penis demodexThis is not convenient. (Smith et al., mole biol evolve., 2022)

Unlike other mites, their reproductive organs D follicular they have moved to the front of their bodies, with the penises of the male mites pointing forward and up from the back. This means he has to snuggle under the female as they perch precariously on a hair to mate, which they do all night, AC/DC-style (presumably).

But although mating is quite important, the potential gene pool is very small: there are very few opportunities to expand genetic diversity. This could mean that mites are headed for an evolutionary dead end.

Interestingly, the team also found that the nymphal stage of development, between larva and adult, is when the mites have the most cells in their bodies. When they transition to the adult stage, they lose cells, the first evolutionary step, the researchers said, in an arthropod species’ march toward a symbiotic lifestyle.

One might wonder what possible benefits humans can derive from these peculiar animals; something else the researchers found could partially hint at the answer. For years, scientists have thought that D follicular It does not have an anus, but instead accumulates waste in its body to explode when the mite dies, thus causing skin conditions.

demodex follicular anusThe arrow points to the mite’s anus, and now you’re probably on some kind of watch list. (University of Reading)

The team found that this is simply not the case. In fact, mites have little holes in their asses; Your face probably isn’t covered in posthumously expelled mite poop.

“Mites have been blamed for a lot of things,” said zoologist Henk Braig of Bangor University and the National University of San Juan in Argentina. “The long association with humans might suggest that they might also have simple but important beneficial roles, for example in keeping the pores on our face unclogged.”

The research has been published in Molecular Biology and Evolution.

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