Amazing stuff! Feeling itchy around your scalp? Gives the expression fellow travelers a whole new meaning.
"... Head lice (Pediculus humanus capitis) cling to hairs and feast on blood from the scalp. They are an old foe; people around the world have complained about lice for thousands of years. Because head lice can only spread between people—and not from, say, human to rat or rat to human—they’re a good proxy for tracking human migrations ...
[researchers] gathered 274 lice from around the world, including a few they collected themselves from schools in Mexico and Argentina. They sequenced the insects’ DNA and singled out short, repetitive segments known as microsatellites. Lice that share these segments inherited them from a common ancestor, giving the researchers a tool to sort the parasites into closely related families. One cluster of microsatellites pointed to a genetic link between lice in Asia and Central America, reflecting the initial migration of people from East Asia into the Americas ..."
From the abstract:
"The human louse, Pediculus humanus, is an obligate blood-sucking ectoparasite that has coevolved with humans for millennia. Given the intimate relationship between this parasite and the human host, the study of human lice has the potential to shed light on aspects of human evolution that are difficult to interpret using other biological evidence. In this study, we analyzed the genetic variation in 274 human lice from 25 geographic sites around the world by using nuclear microsatellite loci and female-inherited mitochondrial DNA sequences. Nuclear genetic diversity analysis revealed the presence of two distinct genetic clusters I and II, which are subdivided into subclusters: Ia-Ib and IIa-IIb, respectively. Among these samples, we observed the presence of the two most common louse mitochondrial haplogroups: A and B that were found in both nuclear Clusters I and II. Evidence of nuclear admixture was uncommon (12%) and was predominate in the New World potentially mirroring the history of colonization in the Americas. These findings were supported by novel DIYABC simulations that were built using both host and parasite data to define parameters and models suggesting that admixture between cI and cII was very recent. This pattern could also be the result of a reproductive barrier between these two nuclear genetic clusters. In addition to providing new evolutionary knowledge about this human parasite, our study could guide the development of new analyses in other host-parasite systems."
Nuclear genetic diversity of head lice sheds light on human dispersal around the world (open access)
Fig 1. Humans and lice.
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