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Researchers find evidence of reverse evolution in house dust mites

Researchers from the University of Michigan have found evidence of reverse evolution in house dust mites. This discovery contradicts the belief that once an organism has evolved certain traits, it will never again act like its ancestors.

According to a paper published in the journal Proceedings of the National Academy of Science, Dollo’s law states that evolution is not reversible. However, Dollo’s law is still a topic of much discussion among the scientific community. U-M researchers have reinvigorated this debate by locating evidence of reverse evolution that seems to defy Dollo’s law.

The study reveals that free-living house dust mites evolved from parasites, which in turn evolved from free-living organisms millions of years ago.

“All our analyses conclusively demonstrated that house dust mites have abandoned a parasitic lifestyle, secondarily becoming free-living, and then speciated in several habitats, including human habitations,” wrote authors Pavel Klimov and Barry OConnor of the U-M Department of Ecology and Evolutionary Biology.

According to the University of Kentucky’s College of Agriculture, house dust mites are not parasitic nor are they capable of biting humans. They do, however, contain powerful allergens in their cast skins, fecal material and secretions. U-M researchers note that allergens from house dust mites impact up to 1.2 billion people worldwide.

House dust mites are only about 0.5 mm long and the young ones are even smaller. They are typically only visible with the aid of a microscope. The two common species in the U.S. are the North American house dust mite and the European house dust mite.

U-M researchers note that the evolutionary relationships between house douse mites are not very well understood. Klimov and OConnor point out that there are more than 60 different published hypotheses about the evolutionary origin of house dust mites.

The researchers used large-scale DNA sequencing, the construction of detailed evolutionary trees called phylogenies, and complex statistical analyses to test the hypotheses. Their analysis revealed that the immediate parasitic ancestors of house dust mites include skin mites.

According to researchers, this finding contradicts Dollo’s law because it disputes the idea that highly specialized parasites cannot return to the free-living lifestyle of their ancestors.

“Parasites can quickly evolve highly sophisticated mechanisms for host exploitation and can lose their ability to function away from the host body,” Klimov said. “Many researchers in the field perceive such specialization as evolutionarily irreversible.”

OConnor, a professor in the Department of Ecology and Evolutionary Biology, said that identifying the phylogenetic relationships of house dust mites could help scientists learn more about the allergenic properties of their immune-response-triggering proteins.

The researchers believe that a combination of several characteristics of their parasitic ancestors allowed them to shift from parasite to a free-living state, including tolerance of low humidity, development of powerful digestive enzymes that allowed them to feed on skin and keratinous and low host specificity with frequent shifts to unrelated hosts.

The study’s findings are described in detail in the journal Systematic Biology.