Lice and mammals: a 100 million year story

There are about 5,000 species of lice, and many of them have settled on the skin and hair of mammals. This cohabitation goes back several tens of millions of years. How does it work? A team from the University of Illinois investigated and determined the origin of this parasitism. Birds and small animals are involved in the basis of one of the most original groups of mammals.

Afrotherians, the first parasites

Lice are divided into two clans based on their eating habits. Those equipped with grinding mouthpiece nibble on skin or secretions while blood-sucking lice biting-sucking mouthparts pierce the skin to consume the blood of their hosts. Both types parasitize mammals, but bloodsuckers are found exclusively in them. Recent genomic studies have shown that blood-sucking lice are closely related to two groups of biting lice.. Analyzes conducted by scientists on the genomes of this entire bestiary show that all lines of lice that infect placental mammals come from the same ancestor.

And this common ancestor of lice originally targeted the Afrotherians, a superorder of mammals that includes small animals such as proboscis shrews, golden moles, or hyraxes, as well as giant elephants, manatees, or dugongs. “These lice then colonized other large groups of mammals in a host-switching process,” Kevin P. Johnson, lead author of the study, said in a statement published in the journal. Ecology of nature and evolution.

Echinopthirius horridus, these lice parasitize marine mammals such as sea lions. Credit: Stephanie Virrueta Herrera.

dinosaur origin

Even more extensive genomic reconstructions done on mammals and bird lice show that these parasites probably appeared 90–100 million years ago and attacked the dinosaurs first. And probably their feathers, as evidenced by a fossil preserved in amber, found in 2019, with insect nymphs frozen on their plumage, similar to those of today’s bird lice. This proves that lice passed from birds/dinosaurs to mammals.

A very rare event even on the scale of evolution, which turned out to be a very fortunate choice: in this way, lice were able to survive the disappearance of their first hosts 66 million years ago, during the extinction at the end of the Cretaceous. . By adapting to the Afrotherians, they were able to more easily adapt to other mammals and diversify as that group expanded…until they got into our children’s hair.

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