Almost every human’s face is home to mites that gorge on the sebum released by cells. They scuttle between our hair follicles for nocturnal mating marathons – and now new research has shone a light on the peculiar effect their humble lives have had on their genetics.
Face mites (Demodex folliculorum) are microscopic, but with the help of some serious zoom-in and genome sequencing, a paper published in Molecular Biology and Evolution reports quite how simplistic these animals have become. They live almost completely alone on our faces, rarely coming across competing parasites – and since they only mate with genetically-similar mites, their body plans aren’t much to shout about.
“We found these mites have a different arrangement of body part genes to other similar species due to them adapting to a sheltered life inside pores,” said Dr Alejandra Perotti in a statement, Associate Professor in Invertebrate Biology at the University of Reading, who co-led the research.
“These changes to their DNA have resulted in some unusual body features and behaviours.”
Each 0.3mm-long mite has little legs powered by just three single-celled muscles and they're made up of the lowest number of proteins of any known related species. Their genotype is so simple, in fact, that they have lost the gene which causes them to wake in response to daylight, which is why our face-feasters are nocturnal critters.
A good thing, too, since they lack any form of protection against ultraviolet light. D. folliculorum is able to steal some of what they lack from their human hosts, as despite not having the genes necessary to produce melatonin they're able to forage for it by nibbling on the melatonin that’s secreted by our skin every evening.
The mites’ sex lives have also taken a turn in the face of diminishing genetics, having forced the males’ penises into such a position (it points upwards from the front of their body, sort of like a rhino's horn) that the only way they can copulate is by standing underneath a female as they both cling onto a human hair.
Curiously, the mites actually have a greater diversity of cells in their bodies as young mites, but this number drops off as they get older. This could indicate that they are shuffling towards becoming symbionts – a form of mutualism in which something lives off another, but they both afford each other some benefit.
In the case of face mites, that benefit could be eating away at clogged pores.
Anuses were thought to be something else D. folliculorum lacked, instead simply eating and accumulating feces until they died and released it all, allegedly causing skin inflammation. However, this latest research found that they do, indeed, have anuses and therefore aren’t guilty of explosive-death-poop-induced inflammation.
“Mites have been blamed for a lot of things,” said Dr Henk Braig, co-lead author from Bangor University and the National University of San Juan. “The long association with humans might suggest that they also could have simple but important beneficial roles, for example, in keeping the pores in our face unplugged.”