Haplotype Diversity in Endosymbiotic Bacteria Following A Host Switch by Parasitic Lice

The sucking lice (Anoplura: Psocodea: Insecta) parasitize mammals, exclusively consuming blood, which does not contain sufficient quantities of B vitamins to support louse development. Lice are dependent on maternally inherited endosymbiotic bacteria, which can synthesize B vitamins and make them available to the louse. Although most louse species parasitize 1 mammal species, lice occasionally colonize a different mammal species. Despite endosymbiotic bacteria being essential for louse development, little is known about the impact, if any, of a louse colonizing a new mammal species on the louse's endosymbiotic bacteria. To address this knowledge gap, we sought to examine genomic diversity in maternally inherited and host-beneficial endosymbiotic bacteria in sucking lice following the likely colonization of a new host. Here, we examined the genomes of endosymbiotic bacteria, Candidatus Riesia pediculicola, from the human head louse, Pediculus humanus. Pediculus humanus (and their endosymbiotic bacteria) are found on humans and South American primate species. The association of P. humanus with humans predates the appearance of modern humans; however, P. humanus appears to have colonized South American primates more recently (likely following the arrival of humans in South America). We examined the genome of Candidatus Riesia from P. humanus isolated from humans (Homo sapiens) and South American black howler monkeys (Alouatta caraya). Here, we find that endosymbiont diversity in lice collected from black howler monkeys included one-half of all known haplogroups described from lice collected from humans. Furthermore, the endosymbiont haplotypes identified from lice on the black howler monkeys reflect the haplotype diversity of endosymbionts present in lice parasitizing humans in the same geographic region. It is not known if the genetic diversity in the endosymbionts of P. humanus parasitizing the black howler monkey is the result of the ongoing movement of lice from humans to black howler monkeys or from a single host switch involving a genetically diverse population of endosymbionts.