If you think giant pandas had it bad, spare a thought for the tiny parasitic mites that live in the pores of the skin on our faces which may be destined 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 on our faces, most living in the pores near our noses and eyelashes.
It is probably the closest relationship to another animal most of us never knew we had.
The mite, Demodex follicularum, spends its entire lifetime living in our skin follicles. In the daytime they feed on our oily skin secretions, at night they leave the pore to find mates, and find new follicles in which to have sex and lay their eggs.
If the thought makes you want to wash your face, forget it. You’ve been carrying the mites since you were born – they’re passed from mother to baby during breast feeding – and live too deep in the pores to be washed out. And besides, we need them, says Dr Alejandra Perotti of the University of Reading, who co-authored the study.
“We should love them because they’re the only animals that live on our bodies our entire life and we should appreciate them because they clean our pores.”
“Besides, they’re cute,” says Dr Perotti.
Perhaps not everyone would agree. The mites have four pairs of stubby legs each with a pair of claws. Beyond that a long worm-like body which, under the microscope, can sometimes be seen protruding from our hair follicles.
But this latest study, published in the journal Molecular Biology and Evolution, has shown just how incredibly intimate their relationship with humans has become.
The researchers analysed the genome of the mites and found it has the smallest number of functional genes of any arthropod (insects, arachnids and crustaceans).
The animals have become so dependent on their human host that their genome is “eroding” — stripped down to the bare minimum of genes needed to survive, the researchers conclude.
They found that the gene which normally regulates waking and sleeping in arthropods has been lost. Instead, the organism detects changes in levels of the hormone melatonin in our skin secretions. It goes up when we sleep, telling Demodex to get up, and goes down when we wake up – their cue to head back down our oily pores for dinner.
They’ve also lost the gene that protects their bodies from UV light – what’s the point when you only come out at night? Even their body plan is minimalist – each leg is powered by just a single muscle cell.
Their ecology becoming so closely synchronised with humans shows the species is on its way from being an external parasite to an internal symbiont – an organism entirely dependent on us for its existence.
As their genetic diversity shrinks, and with it their ability to leave their host and find new mates, they are also at possible risk of eventually going extinct – either when humans do or as a result of some significant change to their environment.
It was once believed Demodex were a cause of common skin conditions, but in healthy people the evidence is Demodex actually help prevent problems like acne by unblocking pores.
But that’s not the only reason we should care about them, says Dr Perotti:
“We are living in a world where we should be protecting biodiversity — and these are our very own animal.”