Understanding the evolution of parasites is important to both basic and applied evolutionary biology. Knowledge of the genetic structure of parasite populations is critical for our ability to predict how an infection can spread through a host population and for the design of effective control methods. However, very little is known about the genetic structure of most human parasites, including the human louse (Pediculus humanus). This species is composed of two ecotypes: the head louse (Pediculus humanus capitis De Geer), and the clothing (body) louse (Pediculus humanus humanus Linnaeus). Hundreds of millions of head louse infestations affect children every year, and this number is on the rise, in part because of increased resistance to insecticides. Clothing lice affect mostly homeless and refugee-camp populations and although they are less prevalent than head lice, the medical consequences are more severe because they vector deadly bacterial pathogens. In this study we present the first assessment of the genetic structure of human louse populations by analyzing the nuclear genetic variation at 15 newly developed microsatellite loci in 93 human lice from 11 sites in four world regions. Both ecotypes showed heterozygote deficits relative to Hardy–Weinberg equilibrium and high inbreeding values, an expected pattern given their parasitic life history. Bayesian clustering analyses assigned lice to four distinct genetic clusters that were geographically structured. The low levels of gene flow among louse populations suggested that the evolution of insecticide resistance in lice would most likely be affected by local selection pressures, underscoring the importance of tailoring control strategies to population-specific genetic makeup and evolutionary history. Our panel of microsatellite markers provides powerful data to investigate not only ecological and evolutionary processes in lice, but also those in their human hosts because of the long-term coevolutionary association between lice and humans.
Anthropological studies suggest that the genetic makeup of human populations in the Americas is the result of diverse processes including the initial colonization of the continent by the first people plus post-1492 European migrations. Because of the recent nature of some of these events, understanding the geographical origin of American human diversity is challenging. However, human parasites have faster evolutionary rates and larger population sizes allowing them to maintain greater levels of genetic diversity than their hosts. Thus, we can use human parasites to provide insights into some aspects of human evolution that may be unclear from direct evidence. In this study, we analyzed mitochondrial DNA (mtDNA) sequences from 450 head lice in the Americas. Haplotypes clustered into two well-supported haplogroups, known as A and B. Haplogroup frequencies differ significantly among North, Central and South America. Within each haplogroup, we found evidence of demographic expansions around 16,000 and 20,000 years ago, which correspond broadly with those estimated for Native Americans. The parallel timing of demographic expansions of human lice and Native Americans plus the contrasting pattern between the distribution of haplogroups A and B through the Americas suggests that human lice can provide additional evidence about the human colonization of the New World.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.