For mites, the “hype” started in 2014 when a study (Thoemmes et al., Plus one) revealed that almost all of humanity is “inhabited” by these arthropods of the arachnid family — closer to spiders than to insects in the tree of relationships between living beings.
two types, Demodex Folliculorum and Demodex brevisin fact share the “territory” of our skin, each present at the base of our hair and protected by our sebaceous glands, from which they come out at night to reproduce.
These mites, invisible to the naked eye (about 0.3 mm long), feed on our sebum and are concentrated on our face – eyelashes, eyebrows and nostrils – but also on our nipples, transferring them from mother to child during breastfeeding can be transferred.
Wrongly accused of causing rosacea or “rosacea” (skin disease manifested by redness) on the pretext that they have no anus – which is false – and that they therefore shed all their excrement when they die, they turn themselves in actually considered one out safe for our health.
A new study published in the journal molecular biology and evolution (6/2022), further lifts the veil over their way of life. Researchers from the Universities of Bangor and Reading (UK), Vienna (Austria) and Valencia (Spain) have extracted several dozen specimens D. folliculorum a person’s skin to sequence their genome.
Genes “lost” during evolution
Thus, the authors discovered that this species of mite holds the record among arthropods for the fewest number of genes that code for proteins – molecules that are nonetheless essential for cell construction and function.
In fact, this mite would have “lost” a large part of its genes in the course of evolution. According to the researchers, this would manifest a transition from an initial state of a “parasite” to a status of a “symbiote” – “symbiosis”, which denotes the close and enduring bond between two organisms of different species.
“We found that these mites have a different arrangement of genes associated with body parts than other similar species due to their adaptation to the sheltered life within the pores.” says Dr. Alejandra Perotti, Professor of Invertebrate Biology at the University of Reading, is quoted in a press release.These changes in their DNA resulted in unusual body traits and behaviors.“
The “reduction” and “reorganization” of genes in this mite is reflected in a simplified morphology – its three pairs of motor legs are activated by only three muscle cells – and above all in an adaptation to its “living environment”. Thus, the male’s penis has “migrated” to the front of his body, allowing him to mate by laying underneath the female when the two are vertically hooked by a hair.
⋙ These animals performing oral sex
Even more surprising is that their circadian rhythm (day/night alternation) mimics ours in reverse. Having lost both the genes responsible for dawn-stimulated awakening and protection from UV rays, these arthropods recognize melatonin – or “sleep hormone” – which our organism releases when we fall asleep. For them, on the contrary, this substance acts like a signal of “waking up”.
A positive role for humans?
A symbiosis usually involves a mutual benefit for both organisms. But if the benefits to the mite are obvious – our skin provides it with protection and cover and avoids competition from other parasites – the gain we bipeds derive from this shared life remains dominant on the other hand.
“Dust mites’ long association with humans may suggest simple but important positive roles: keeping the pores on our face unclogged, for example‘ suggests Dr. Henk Braig, co-author of the study and researcher at Bangor University and National University of San Juan (Argentina).
However, to be selected, a trait must confer a breeding advantage. However, it is not certain that unclogged pores allowed our ancestors to have a greater number of descendants…
However, should this hypothesis prove correct, it would mean that dust mites are involved in removing sebum from our pores, avoiding the accumulation of oil, which is the source of impurities. This doesn’t stop you from maintaining good hygiene by washing your face daily!
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