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Slipping through grease and protected by our pores, tiny Demodex folliculorum mites lead a secret life in our skin, only emerging at night to mate on our foreheads, noses and nipples. As successful as these sexual encounters are, their days as independent parasites may be numbered.

The very first genome sequencing study of these mites appears to have caught them in the process of transitioning into internal symbionts, entirely dependent on us for their existence. Eventually, this process may even lead to their extinction.

Measuring just 0.3mm long, D folliculorum are worn by about 90% of people and are most abundant in the sides of the nose, forehead, ear canal and nipples. They lead a harmless life, feasting on the sebum naturally secreted by the cells in the pores, and have probably been present from an early age, having been transferred from our mothers during childbirth or breastfeeding.

“The long association with humans might suggest that they may have simple but important beneficial roles, for example, in keeping our facial pores unplugged,” said Dr Henk Braig of Bangor University and the National University of San Juan in Argentina, who conducted the research.

To better understand this relationship, Braig and his colleagues sequenced the genomes of D folliculorum mites, collected from a person’s nose and forehead using a blackhead remover – each collection producing about 40 mites.

Their findings, published in Molecular Biology and Evolution, revealed that mites survive on the minimum protein repertoire – the lowest observed in an insect, arachnid or crustacean so far.

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This gene loss resulted in an extreme reduction in cell numbers in adult mites – a likely first evolutionary step on their journey to adopting a fully symbiotic lifestyle within our tissues.

The more they adapt to us, the more likely they are to lose genes, until eventually they become entirely dependent on us. And with no possibility of obtaining additional genes from less closely related mites – they do not appear to transfer between adult humans during close physical contact – their isolated existence and resulting inbreeding may have ultimately put the mites on the path of an evolutionary impasse, and potential extinction.

If this happens, it could also be bad news for us. “They’re associated with healthy skin, so if we lose them you could have skin problems,” co-author Dr Alejandra Perotti from the University of Reading told the BBC.


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