As we evolved from ape-like primates to bipedal apes to large-brained humans, we were accompanied by an extraordinarily loyal companion: Pediculus hunus (also known as the human louse).
And all the while, lice have recorded this journey in their genes.a new researchFor example, it turns out that some lice in the Americas are hybrids of lice brought by Native Americans and lice brought across the Atlantic Ocean by European settlers.
“We don’t live in a bubble,” says Marina Ascans, an evolutionary geneticist at the U.S. Department of Agriculture and author of the new study. “Lice are part of our lives and history.”
Lice commonly live on a person’s head, clinging to the hair shaft and penetrating the scalp to suck blood. Parasites cannot survive once they leave the human body, and can be passed from person to person. When people are crammed together in unsanitary conditions, such as in overcrowded prisons, lice can spread to clothing and feed on other parts of the body.
Other mammals and birds also have their own types of lice. Each type of parasite has exquisite adaptations to specific hosts, whether penguins or bats. This close relationship is ancient.Discovered by paleontologists in Germany Lice 44 million years ago Fragments of feathers are stored in the intestines.
Lice fossils are so rare that little can be learned about their history. But their DNA contains more clues. By analyzing a louse’s genetic material, entomologists can build a family tree and reveal which species are most closely related.
Often, a louse’s closest relatives live on its host’s closest relatives. For example, in the early 2000s, David Reid and colleagues at the University of Florida discovered that human lice are most closely related to lice that live on chimpanzees, and more distantly related to lice that live on monkeys. In other words, for about 25 million years, our lice have followed our evolutionary path.
That’s not to say that lice are completely loyal. Another species, Pthirus pubis (better known as the crab), lives exclusively in human pubic hair. Crabs are not closely related to head lice. Instead, Dr. Reed and his colleagues discovered that their closest relatives live in lice. gorilla. Early human ancestors may have picked up crabs while sleeping in old gorilla nests or ate gorilla carcasses.
In another exciting study, Dr. Reed and his colleagues compared human lice taken from different regions of the world. They focused on genetic material known as mitochondrial DNA, which is passed only from women to their offspring. Researchers have found that many lice belong to one of her two lineages. Remarkably, these lineages probably diverged from female lice that lived a million years ago.
Dr. Reed and his colleagues speculated that this deep division may have arisen when humans expanded out of Africa. In addition to their own lice, they also picked up lice from Neanderthals and other extinct human groups.
Recently, lice researchers have focused on the chromosomal DNA that lice inherit from both their mothers and fathers.
In 2010, Dr. Askans joined Dr. Reed’s team to lead efforts to collect such DNA from around the world.
In the new study, published Wednesday in the journal PLOS ONE, Askance and his colleagues analyzed the DNA of 274 lice taken from people in 25 locations around the world, including Honduras, France, Rwanda and Mongolia.
DNA revealed two geographic clusters of lice. One existed in Africa, Asia, and the Americas. Among these lice, researchers found a close genetic link between Honduras and Mongolia. They believe this relationship may be a sign that lice were introduced by Asians, who first spread to the Americas about 23,000 years ago.
The remaining lice formed a second cluster, which researchers found in Europe as well as the United States, Mexico and Argentina. The researchers also discovered 33 hybrids from two clusters, 25 of which were found in the Americas.
Dr. Askans and his colleagues see in these results a chronicle of modern history. That is, European colonists took lice with them when they sailed to the New World. In the Americas, a second cluster spread, sometimes landing on the heads of people who were already infected with lice from the first cluster.
But if these lice are truly colonial hybrids, Dr. Ascans and her colleagues are puzzled that no others have been discovered yet. The rarity of hybrids may be the result of some barrier to hybridization. It’s possible that the two louse populations were isolated from each other for so long that they acquired mutations that made them not work as well when they mixed again.
Askance said lice researchers are still in the early stages of their research. In the new study, she and her colleagues examined just 16 small regions of her DNA in lice. The next wave of research will examine the entire louse genome, and she hopes this new data will yield even more insights.
For example, we may be able to understand how human lice evolved the ability to travel from the head to the body, and why body lice are the only species that harbor microorganisms that can cause diseases such as typhus fever. . And researchers may be able to determine exactly how our ancestors picked up the lice that still plague us today.
“The genetic information found in modern human lice could still tell us about our past,” Dr Askans said.