In evolutionary biology, there is a deeply rooted supposition that you can't go home again: once an organism has evolved specialized traits, it can't return to the lifestyle of its ancestors.
There's even a name for this pervasive idea. Dollo's law states that evolution is unidirectional and irreversible. But this "law" is not universally accepted and is the topic of heated debate among biologists.
Now a research team led by two University of Michigan biologists has used a large-scale genetic study of the lowly house dust mite to uncover an example of reversible evolution that appears to violate Dollo's law.
The study shows that tiny free-living house dust mites, which thrive in the mattresses, sofas and carpets of even the cleanest homes, 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," according to Pavel Klimov, EEB and Museum of Zoology assistant research scientist, and EEB Professor Barry Oconnor, curator of insects and arachnids in the Museum of Zoology.
Their paper, "Is permanent parasitism reversible?—Critical evidence from early evolution of house dust mites," was published online March 8, 2013 in the journal Systematic Biology.
The U-M findings also have human-health implications, said OConnor. "Our study is an example of how asking a purely academic question may result in broad practical applications," he said. "Knowing phylogenetic relationships of house dust mites may provide insights into allergenic properties of their immune-response--triggering proteins and the evolution of genes encoding allergens."
U-M News Service press release
Caption: A scanning electron microscope image of an American house dust mite. Photo credit: G. Bauchan and R. Ochoa.