The “lice tree” traces back to the first mammals infected with lice

A long-nosed cattle lice. Image credit: Dennis Kunkel Microscopy/SPL

Recently, Kevin Johnson, a biologist at the University of Illinois at Urbana-Champaign, and co-authors have conducted a genomic study of the “lice tree” in mammals and found that the lice parasitic on today’s mammals can be traced back to the extinction of the dinosaurs, and the lice parasitized on non-bird mammals are the same ancestor. The findings were published in Nature, Ecology and Evolution on July 4.

The story of the mammalian louse is rarely told, but in some ways it is as dramatic as the mammalian story. For example, tens of millions of years ago, when seals adapted to live in the ocean, their lice adapted to become the only true marine insects. Bret Boyd, a biologist at Virginia Commonwealth University in the United States, pointed out that lice can co-evolve with their hosts in a very complex way.

Lice also have an extraordinary ability to switch hosts when opportunities arise. It’s this skill that helps explain why seals, skunks, elephants, and lice in humans all seem to be descendants of the same ancestor. After examining genetic data from 33 species of lice from all major mammalian populations, Johnson’s team concluded that lice had switched between mammalian hosts at least 15 times since they first parasitized in mammals.

Part of the reason mammalian “lice trees” are difficult to put together is host switching, but that’s not the only reason. Therefore, fixing “lice tree” has a broader meaning. Vincent Smith, a biodiversity informatics researcher at the British Museum of Natural History, said that biologists in the early 20th century tested their ideas about coevolution with lice, and the new study may attract biologists’ interest in these broad evolutionary topics and look at lice in a new light.

“Lice trees” can also provide important insights into host transformation, as the origin of some diseases can be explained by the transfer of hosts from other animals to humans. Johnson believes that any information that provides a deeper understanding of the mechanisms of this process may help us minimize the chances of switching new disease hosts to humans.

But the process is complicated. Boyd says one reason vampire lice survive in mammals is that the symbiotic bacteria carried by parasitic insects provide them with B vitamins that are not readily available from mammalian blood. However, just as lice can switch between mammalian hosts, bacteria seem to be able to switch between lice hosts as well. A few years ago, while studying a seal lice, Boyd’s team discovered that their bacterial symbiosis relationship was only recently acquired.

Boyd argues that lice may have lost some ancestral symbiotes and replaced them with new ones, so this is a lot like a host transformation, which demonstrates the complexity of that level. (Source: China Science Daily Xin Yu)

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