Posted in: Discoveries

Dust Mites Can Evolve In Reverse

house dust mites evolved in reverse

Dust mites have evolved in reverse, allowing them to create havoc not just in our noses but in our theories of evolution. A team of researchers led by two University of Michigan biologists studied 700 species of mites to create an evolutionary tree to track how the creepy crawlies have evolved over time. They examined the DNA and then created a phylogenetic tree — a so-called tree of life — which showed how the different species developed and branched out over time.

According to lead researchers Pavel Klimov and Barry O’Connor, they examined the specimens of 64 biologists from 19 different countries. They soon noticed something odd about the evolution of house mites. Their family tree seemed to suggest that they evolved in reverse — from free-living mites to helpless parasites that couldn’t live on their own back to the free-living species we know and hate today. The DNA suggested that the story went something like this.

Early dust mites lived in the nests of both bird and mammals. They were free-living animals. However, over time, some mites developed digestive enzymes that allowed them to eat normally indigestible foods like skin, hair, and fingernails.

It’s these irritating digestive enzymes that cause dust mites to be able to trigger such powerful allergic reactions. According to the US Environmental Protection Agency, they can cause not just miserable allergies but also life-threatening asthma. A recent study showed that babies who were delivered by C-section may be especially at risk for developing the allergies, which demand life-long treatment.

However, the first mites of that kind, according to Klimov and O’Connor, were true parasites that could never leave the body of their host, various species of birds or mammals, depending on which type they studied. The closest relatives of today’s house dust mite included skin mites like one that causes mange in livestock. These mites can’t survive outside the host.

That created a problem for the scientists, who were working under a National Sciences Foundation grant going back to 2006.

Dollo’s Law is not so much a law as a theory that biologists use when they construct evolutionary trees. It says that evolution doesn’t go backward. Once a family line has lost an ability or another complex genetic trait, it can’t ever re-evolve that trait.

However, the University of Michigan biologists show that dust mites have broken Dollo’s Law, since they have rediscovered the ability to be free-living — which explains why they can survive on household items like bedding.

Ugh. I’m sure we’ll all sleep better tonight knowing that our households are filled with wily, backsward-evolving dust mites.

[dust mite photo courtesy Wikipedia Commons]

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