Many species of lice live on specific hosts, such as the head louse, Pediculus humanus, which lives on humans. This species is one of around 500 that belong to a group known as “sucking lice” or Anoplura. Anoplura only live on mammals and drink blood, in contrast to “chewing lice” which live on a variety of animals and eat skin, hair, or feathers. New research out of the University of Illinois has revealed the evolutionary origin of sucking lice and suggests that they likely evolved from chewing lice that jumped to mammals from birds.

Hyraxes are members of the mammal group Afrothesia. Afrothesia hosts the most ancient species of blood-sucking louse.

Using genomic data to construct a family tree of louse species relationships, researchers found that the branching pattern of the Anoplura family tree closely mirrors that of the mammal family tree. Just as chimps are the closest relatives to humans, chimp lice are the closest relatives to human lice. The family tree shows that the common ancestor of human lice and chimp lice was a descendant of the common ancestor of all sucking louse to infect primates, which itself was a descendant of the common ancestor of all sucking louse species. This pattern tells us that many sucking louse species have evolved alongside their hosts. The most ancient Anoplura species live on the mammal group, Afrothesia, made up of elephants, hyraxes, and their close relatives. It is likely that chewing lice jumped to the common ancestor of Afrothesia tens of millions of years ago. On the ancient Afrothesia, they then evolved the ability to suck blood. This novel blood-sucking ability allowed Anoplura to spread to other mammal hosts as mammals subsequently evolved and diversified.

The co-evolution of lice and mammals is an example of how broader knowledge of species relationships can improve our understanding of parasite-host evolution. In the case of human parasites, a better understanding of parasite-host evolution can help scientists and doctors develop more effective medicines and treatments.

About the researchers: Kevin P. Johnson is a principal research scientist and ornithologist at the Illinois Natural History Survey. Jorge Doña is a Marie Curie postdoctoral researcher at the University of Illinois Urbana-Champaign and the University of Granada, Spain. Conrad Matthee is a Professor in the Botany and Zoology department at Stellenbosch University, South Africa.

Managing Correspondent: Arianna Lord

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