If you think giant pandas have had a hard time, spare a thought for the tiny parasitic mites that live in the pores of the skin on our faces and may be doomed to an evolutionary dead end, according to a new analysis of their DNA.
Over 90% of us harbor the 0.3mm long mites in the oily folds of our face, with most living in the pores near our nose and eyelashes.
This is probably the closest relationship with another animal that most of us never knew we had.
The mite, Demodex follicularum, spends its entire life living in our skin follicles. During the day 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 carry the mites from birth – they are passed from mother to baby during breastfeeding – and live too deep in the pores to be eliminated. And besides, we need it, says Dr Alejandra Perotti of the University of Reading, co-author of the study.
“We should like them because they are the only animals that live on our bodies all our lives and we should like them because they clean our pores.”
“Plus, they’re cute,” says Dr. Perotti.
Maybe not everyone would agree. Mites have four pairs of stubby legs each with a pair of claws. Beyond that is a long worm like body that under a microscope can sometimes be seen protruding from our hair follicles.
But this latest study, published in the journal Molecular Biology and Evolution, showed how incredibly intimate their relationship with humans has become.
Researchers analyzed the genome of mites and found that it has the fewest number of functional genes of all arthropods (insects, arachnids and crustaceans).
The animals have become so dependent on their human host that their genome is “eroding” – reduced to the bare minimum of genes needed to survive, the researchers conclude.
They discovered that the gene that normally regulates waking and sleeping in arthropods has been lost. Instead, the body 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 get our oily pores back down for dinner.
They’ve also lost the gene that protects their bodies from UV rays – what’s the point of only going out at night? Even their body plan is minimalist – each leg is powered by a single muscle cell.
Their ecology becoming so tightly synchronized with humans shows that the species is on its way from being a parasite to a symbiont – one organism entirely dependent on another for its survival. In this case, we.
As their genetic diversity decreases, and with it their ability to leave their host and find new mates, they are also at risk of becoming extinct, either when humans do so or as a result of significant changes in their environment. .
Demodex was once believed to be a cause of common skin conditions, but in healthy people, Demodex is actually proven to help prevent problems like acne by unclogging pores.
But that’s not the only reason we should care about them, says Dr. Perotti:
“We live in a world where we should be protecting biodiversity – and those are our own animals.”