The thought of this will certainly not amuse many people very much. But our face and nipples are the habitat for countless tiny eight-legged animals that have settled there in the hair follicles: Hair follicle mites (Demodex folliculorum) are so closely interwoven with us that they could be on their way from parasite to true symbiont. This is suggested by a study by Alejandro Manzano Marín from the University of Vienna and his team in »Molecular Biology and Evolution«.
The research group had analyzed and sequenced the genome of the eight -legged friends. The result: As a result of inbreeding and isolation on our bodies over time, the only 0.3 millimeter mites have abolished more and more genes and cells and thus developed into an already significantly reduced organism. "They survive with a minimal repertoire of proteins - the slightest number that has ever been observed in this and related species," says Manzano Marín.
The hair follicle mites feed on sebum, which is released by the hair cells in the pores. Especially at night they are active; then they move between the follicles and look for mating partners. However, they cannot survive permanently outside the pores. The study also found out one reason for the nocturnal activity: Among other things, the microorganisms have lost their UV protection gene and the so-called timeless gene, which is responsible for other organisms waking up in daylight. Instead, they are awakened by melatonin, which is released by us at night.
Manzano Marín and Co also refute the assumption, which has been regularly put forward so far, that the mites do not have an anus. According to this, her body would fill with feces during her short life. If they then die, it would be released, which could lead to skin irritation. But in fact, the animals possess an excretory organ and regularly release their digestive products. With this, you may even ensure that the skin pores clog less often.
The reproduction of the species is also unique among mites: The penis of the males protrudes forward, which means that they have to position themselves under the female while mating and both hold on to human hair. However, they always mate in the same population with each other, which is why there are rarely or never genetic refreshment in the genetic material. "The inbreeding results in an accumulation of harmful mutations, after all, bad gene variants spread quickly," says Manzano Marín. "This evolutionary path has already been observed in bacteria living in cells, but has not yet been clearly demonstrated in an animal." The path of the mites could therefore not only lead to a real symbiosis, but also in an evolutionary dead end with fatal consequences: the species could Then die out.
