Microscopic mites that live in human pores and mate on our faces at night are becoming such simplified organisms, due to their unusual lifestyles, that they could soon become one with humans, new research has found.
The mites are transmitted during birth and are carried by almost all humans, peaking in adults as the pores enlarge. They are about 0.3mm long, are found in hair follicles on the face and nipples, including eyelashes, and eat the sebum naturally released by pore cells. They are activated at night and move between the follicles looking to mate.
The first genome sequencing study of the D. folliculorum mite found that its isolated existence and resulting inbreeding are causing it to shed unneeded genes and cells and move toward a transition from external parasites to internal symbionts.
Dr Alejandra Perotti, Associate Professor of Invertebrate Biology at the University of Reading, who co-led the research, said: “We found that these mites have a different arrangement of body part genes to other similar species because they are “They adapt to a protected life inside the pores. These changes in their DNA have resulted in some unusual body characteristics and behaviors.”
In-depth study of the DNA of Demodex folliculorum revealed:
- Due to their isolated existence, no exposure to external threats, no competition to infest hosts, and no encounters with other mites with different genes, genetic reduction has turned them into extremely simple organisms with tiny legs powered by just 3 single-celled muscles. They survive with the minimum repertoire of proteins, the lowest number ever seen in this and related species.
- This gene reduction is also the reason for their nocturnal behavior. The mites lack UV protection and have lost the gene that makes animals wake up in daylight. They also haven’t been able to produce melatonin, a compound that makes small invertebrates active at night; however, they can fuel their mating sessions throughout the night using the melatonin secreted by human skin at dusk.
- Their unique genetic make-up also results in the mites’ unusual mating habits. Their reproductive organs have moved earlier, and males have a penis that protrudes upwards from the front of their body, meaning they have to get under the female when they mate and copulate while both hold on to human hair.
- One of their genes has been inverted, giving them a particular arrangement of mouthparts that protrude especially for gathering food. This helps their survival at a young age.
- Mites have many more cells at a young age compared to their adult stage. This contradicts the earlier assumption that parasitic animals reduce their cell numbers early in development. The researchers argue that this is the first step for mites to become symbionts.
- The lack of exposure to potential mates who could add new genes to their offspring may have put the mites on the path to an evolutionary dead end and possible extinction. This has been seen before in bacteria that live inside cells, but never in an animal.
- Some researchers had assumed that mites do not have an anus and therefore must accumulate all of their feces throughout their lives before releasing it when they die, causing skin inflammation. However, the new study confirmed that they do have anus and thus have been unfairly blamed for many skin conditions.
The research was led by Bangor University and the University of Reading, in collaboration with the University of Valencia, the University of Vienna and the National University of San Juan. It is published in the magazine Molecular Biology and Evolution.
Dr Henk Braig, co-senior author from Bangor University and St John’s National University, said: “Mites have been blamed for many things. The long association with humans might suggest they might also have simple but beneficial functions. important, for example, in keeping the pores on our face unclogged”.
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Gilbert Smith et al, Human follicular mites: Ectoparasites become symbionts, Molecular Biology and Evolution (2022). DOI: 10.1093/molbev/msac125
Provided by the University of Reading
Citation: The Secret Life of Mites on the Skin of Our Faces (June 21, 2022) Retrieved June 22, 2022 from https://phys.org/news/2022-06-secret-mites-skin.html
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