Geographic genetic structure of human lice provides insights into human migrations around the globe and past ecological interactions among hominids

The extent to which modern humans and archaic hominids interacted directly is a key question in anthropology. Recently, host-specific parasites have been used to better understand the ecology and evolution of humans. For example, mitochondrial DNA (mtDNA) of the human louse (Pediculus humanus) revealed evidence of a population expansion that coincided with the out-of-Africa expansion of modern humans roughly 100,000 years ago. However, this is the case for only one of the three known louse mtDNA haplogroups. Previous studies suggest that the three louse haplogroups (A, B, C) evolved on different hominids as early as 2 million years ago and later switched to modern humans when they co-occurred with other hominids. Here we use both mtDNA sequences and nuclear markers in more than 200 lice from around the world to determine whether the nuclear genome supports the ancient patterns of divergence seen in the mitochondrial genome. Bayesian clustering analyses assigned lice to distinct genetic clusters that were geographically structured. We will discuss the association, or lack of, between each mtDNA haplogroups and nuclear genetic clusters in each continent. These data allow us to assess recombination at the nuclear level in each geographic region and can provide insights into when lice from each mtDNA clade came in contact, thus reflecting host ecological interactions.