The tiny mites that live on almost all humans and mate on our skin can evolve from parasites to organisms that share a symbiotic existence with us.
This is according to scientists researching the organisms, which are a fraction of a millimeter in length, and are found in hair follicles on the face and nipples.
Mites called Demodex folliculorum feed on sebum, a substance that coats the skin that is released naturally by the cells inside our pores.
At night, when we sleep, they leave their hiding places to caress our faces.
About 90 percent of humans have these mites, and they are passed on at birth. They are usually harmless and go unnoticed, but in large numbers they can irritate the skin, make it flaky, and cause redness and itching.
They are one of two types of follicular mite species living on humans along with Demodex brevis, a solitary species that lives in the sebaceous glands under the skin.
from parasite to symbiotic
Until now, they were thought to have a parasitic relationship with us, extracting nutrients at our expense.
However, new research suggests that they may be symbiotic, meaning that their existence provides a mutually beneficial relationship.
For example, it was previously thought that the mite did not have an anus and would therefore store its feces for the rest of its life before releasing it upon death and causing inflammation in the skin.
However, according to research conducted by scientists from the University of Reading, the University of Valencia, the University of Vienna and the National University of San Juan, this is not the case.
The new study, published in the journal Molecular Biology and Evolution, found that the mite actually has an anus, and has been wrongly blamed for many skin conditions.
They can also help keep our skin clear.
“Mites have been blamed for many things. The long association with humans may suggest that they may also have simple but important beneficial roles, for example, in keeping our facial pores closed,” says Bangor University and co-lead author Dr. Henk Brigg from the National University of San Juan.
‘Unusual physical features’
In the first genome sequencing study of mites, it was found that they have an isolated existence and that inbreeding causes them to lose redundant genes and cells and become more simple organisms that may soon unite with their human hosts. .
“We found that these moths have a different arrangement of body part genes from other similar species, as they have adapted to a sheltered life inside the holes,” said Dr Alejandra Perotti, associate professor in invertebrate biology at the University of Reading. Research.
“These changes in their DNA have resulted in some unusual body characteristics and behaviour”.
These include the development of short legs made up of only three single cell muscles.
The loss of the gene also means that they lack UV protection, have lost the gene that causes animals to wake up in daylight, and cannot produce melatonin on their own.
Instead, they fuel up on melatonin from human skin, in what the researchers call an “all-night mating session.”
This paper describes in detail the mating habits and sexual anatomy of the mite.
Specifically, males have a penis that extends upward from the front of their bodies, and they have to position themselves beneath females during mating, which is when they both cling to human hair. .
We can’t live with mites forever though. Research has found a lack of exposure to potential mates who may add new genes to offspring means they could be on course for extinction.