Comparison of genomes and family trees for lice and their mammalian hosts

Comparison of genomes and family trees for lice and their mammalian hosts

According to a new study, the first lice began to live on a mammalian host, probably as a bird parasite. This host jumping event tens of millions of years ago began the long connection between mammals and lice, which set the stage for their co-development and provided more opportunities for lice to spread to other mammals.

Reported in the journal Nature Ecology and Evolution, the study compared the genome and family trees of lice and their mammalian hosts. The effort showed that the two trees share many parallel branches and twigs. These branch points – where a group of mammals began to diverge into new forms – were often reproduced in the genome of lice that parasitized these mammals, the researchers reported.

“In this article, we use data from genome sequencing to show that a large newly recognized group of mammalian lice, including human lice, originated in the common ancestor of Afrotheria, a group of mammals that are predominantly African in size, including elephants, hyraxes. and among other elephant fists, ”he said Kevin P. Johnsona leading researcher and ornithologist at Illinois Natural History Survey who led the study Jorge Doña, a Marie Curie Postdoctoral Fellow at the University of Illinois Urbana-Champaign and the University of Granada, Spain. “These lice then continued to colonize other large groups of mammals through the process of changing hosts.”

INHS is a division of Prairie Research Institute at U. by I.

Lice are divided into two groups based on their eating habits. Chewing lice munch on skin or secretions, while sucking lice penetrate the skin to consume the blood from their hosts, Johnson said. Both types feed on mammals, but sucking lice are exclusive to mammals.

Recent studies have revealed that sucking lice are closely related to two groups of chewing lice that also feed on mammals, and “each of the main groups in this newly identified lineage occurs in at least one member of Afrotheria,” the researchers wrote. Afrotheria is an ancient lineage of mammals that includes elephants, elephant dirt, hyraxes, golden moles, earthworms and others.

That research suggested that members of Afrotheria were the original mammalian hosts for lice. Johnson and Doña expanded the genomic sampling of mammalian lice genomes to include more lice associated with Afrotheria and compared the evolutionary history of mammals and their lice. More specifically, they included lice from elephant droppings and hyraxes.

Their analysis indicated that lice from elephants, hyraxes and elephant snails were the oldest in the group of chewing and sucking lice that fed on mammals.

“This shows that these mammalian lice started in this strange group of African mammals and switched to other mammals after that,” Johnson said.

The change of host from birds to mammals was very rare, Johnson said. The team found evidence that this only happened a few times – for example for Malagasy lemurs, South American rodents and some marsupials. But once lice learned to feed on mammals, they could more easily jump from one mammal species to another and probably had more opportunities to do so. And when certain groups of mammals were separated – for example geographically – they diverged and so did their lice, the analysis found.

While more work needs to be done to track the evolutionary history of lice and their hosts, Johnson said that lice probably go back 90 million to 100 million years and are probably the first parasitized dinosaurs or birds.

“And then, after dinosaurs became extinct about 65 million years ago and birds and mammals really diversified, lice also started jumping to new hosts and diversifying,” he said.

The National Science Foundation and the European Commission supported this research.

Reference: Johnson KP, Matthee C, Doña J. Phylogenomics reveal the origin of Afrotheria mammalian lice. Nat Ecol Evol. 2022. doi: 10.1038 / s41559-022-01803-1

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