When head lice are mentioned, many get itchy heads. Humans and other mammals are also plagued by numerous other species of lice. Presumably, the relationship began a long time ago in Africa.
Elephants, hyraxes and elephant-shrews may have been among the first mammals to be plagued by lice. The common ancestor of these animals, which belong to the Afrotheria group, probably caught the parasites from birds millions of years ago, reports an international team of researchers in the journal Nature Ecology
Many different types of lice are found on mammals, such as head, pubic and clothes lice on humans. Some species of lice feed on blood, others on skin or secretions. When and how the parasites conquered the mammals as hosts was not exactly known. To answer this question, the researchers led by Kevin Johnson from the University of Illinois now examined the genome and family trees of lice and their mammalian hosts.
In total, they analyzed the genomes of 33 species of lice, and resequenced the genome of 14 of them. Among them were the louse of an elephant-shrew—a small African mammal resembling a shrew—and that of a hyrax, a mammal related to the proboscidea that is also found almost exclusively in Africa. Together with the elephant louse, which had already been sequenced, the researchers now had three species of lice from the Afrotheria group. The members of this group sometimes differ greatly in appearance, their relationship is supported by the same genetic characteristics.
The investigations showed that these Afrotheria lice were the phylogenetically oldest lice of the mammals. "This shows that the mammalian lice first appeared in this strange group of African mammals and then spread to other mammals," Johnson said.
Lice probably developed 90 to 100 million years ago and initially plagued birds and dinosaurs. "And then, after the dinosaurs went extinct about 65 million years ago, and birds and mammals diversified a lot, the lice also started to seek out new hosts and diversify," Johnson said.
The change from birds to mammals was probably very rare in the course of evolution. But once the lice learned to feed on and off mammals, they could move more easily from one group to the next. If their hosts evolved apart - for example due to geographical separation - the lice also evolved with them.