If you think the giant pandas were sick, think about the tiny parasitic mites that live in the pores of the skin on our faces, which could be headed for an evolutionary dead end, according to a new analysis of their DNA.
More than 90% of us host the 0.3mm long mites in the oily folds of our face, most living in the pores near our nose and eyelashes.
It’s probably the closest relationship with another animal most of us never knew we had.
The Demodex follicularum mite spends its entire life living in the follicles of our skin. During the day they feed on the secretions of our oily skin, at night they come out of the pore to find mates and find new follicles to have sex and lay their eggs.
If the thought makes you want to wash your face, forget it. You’ve been carrying mites since birth – they’re passed from mother to baby during breastfeeding – and they live too deep in your pores to be washed out. Also, we need them, says Alejandra Perotti of the University of Reading, co-author of the study.
“We should love them because they are the only animals that live in our bodies our entire lives and we should appreciate them because they clean our pores.”
“Plus, they’re cute,” says Dr. Perotti.
Perhaps not everyone would agree. Mites have four pairs of stubby legs, each with a pair of claws. Also, a long worm-like body that, under the microscope, can sometimes be seen protruding from our hair follicles.
But this latest study, published in the journal Molecular Biology and Evolution, showed just how incredibly intimate their relationship with humans has become.
The researchers analyzed the mite genome and found that it has the fewest functional genes of any arthropod (insects, arachnids and crustaceans).
The animals have become so dependent on their human host that their genome is “eroded” – reduced to the bare minimum of genes needed to survive, the researchers conclude.
They found that the gene that normally regulates wakefulness and sleep in arthropods was lost. Instead, the body detects changes in the levels of the hormone melatonin in the secretions of our skin. It goes up when we sleep, telling the Demodex to get up, and it goes down when we wake up – leaves it to go back to our oily pores for dinner.
They’ve also lost the gene that protects the body from UV light – what’s the point when you only go out at night? Even his body plan is minimalist – each leg is powered by just a single muscle cell.
Its ecology becoming so closely synchronized with humans shows that the species is on its way from being a parasite to a symbiote – one organism entirely dependent on another for its survival. In this case, we.
As their genetic diversity dwindles, and with it their ability to leave their host and find new mates, they are also at possible risk of becoming extinct – either when humans do or as a result of some significant change in their environment.
In the past, Demodex was believed to be the cause of common skin conditions, but in healthy people the evidence is that Demodex actually helps prevent problems like acne by unblocking pores.
But that’s not the only reason we should be concerned about them, says Dr. Perotti:
“We are living in a world where we should protect biodiversity – and these are our own animals.”