Dataset Information

Multiple origins of parasitism in lice.

ABSTRACT: A major fraction of the diversity of insects is parasitic, as herbivores, parasitoids or vertebrate ectopara sites. Understanding this diversity requires information on the origin of parasitism in various insect groups. Parasitic lice (Phthiraptera) are the only major group of insects in which all members are permanent parasites of birds or mammals. Lice are classified into a single order but are thought to be closely related to, or derived from, book lice and bark lice (Psocoptera). Here, we use sequences of the nuclear 18S rDNA gene to investigate the relationships among Phthiraptera and Psocoptera and to identify the origins of parasitism in this group (termed Psocodea). Maximum-likelihood (ML), Bayesian ML and parsimony analyses of these data indicate that lice are embedded within the psocopteran infraorder Nanopsocetae, making the order Psocoptera paraphyletic (i.e. does not contain all descendants of a single common ancestor). Furthermore, one family of Psocoptera, Liposcelididae, is identified as the sister taxon to the louse suborder Amblycera, making parasitic lice (Phthiraptera) a polyphyletic order (i.e. descended from two separate ancestors). We infer from these results that parasitism of vertebrates arose twice independently within Psocodea, once in the common ancestor of Amblycera and once in the common ancestor of all other parasitic lice.

SUBMITTER: Johnson KP

PROVIDER: S-EPMC1691793 | biostudies-literature | 2004 Sep

REPOSITORIES: biostudies-literature

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Multiple origins of parasitism in lice.

Johnson Kevin P KP Yoshizawa Kazunori K Smith Vincent S VS

Proceedings. Biological sciences 20040901 1550

A major fraction of the diversity of insects is parasitic, as herbivores, parasitoids or vertebrate ectopara sites. Understanding this diversity requires information on the origin of parasitism in various insect groups. Parasitic lice (Phthiraptera) are the only major group of insects in which all members are permanent parasites of birds or mammals. Lice are classified into a single order but are thought to be closely related to, or derived from, book lice and bark lice (Psocoptera). Here, we us ...[more]

PMID: 15315891

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Project description:BACKGROUND: Genetic analyses of human lice have shown that the current taxonomic classification of head lice (Pediculus humanus capitis) and body lice (Pediculus humanus humanus) does not reflect their phylogenetic organization. Three phylotypes of head lice A, B and C exist but body lice have been observed only in phylotype A. Head and body lice have different behaviours and only the latter have been involved in outbreaks of infectious diseases including epidemic typhus, trench fever and louse borne recurrent fever. Recent studies suggest that body lice arose several times from head louse populations. METHODS AND FINDINGS: By introducing a new genotyping technique, sequencing variable intergenic spacers which were selected from louse genomic sequence, we were able to evaluate the genotypic distribution of 207 human lice. Sequence variation of two intergenic spacers, S2 and S5, discriminated the 207 lice into 148 genotypes and sequence variation of another two intergenic spacers, PM1 and PM2, discriminated 174 lice into 77 genotypes. Concatenation of the four intergenic spacers discriminated a panel of 97 lice into 96 genotypes. These intergenic spacer sequence types were relatively specific geographically, and enabled us to identify two clusters in France, one cluster in Central Africa (where a large body louse outbreak has been observed) and one cluster in Russia. Interestingly, head and body lice were not genetically differentiated. CONCLUSIONS: We propose a hypothesis for the emergence of body lice, and suggest that humans with both low hygiene and head louse infestations provide an opportunity for head louse variants, able to ingest a larger blood meal (a required characteristic of body lice), to colonize clothing. If this hypothesis is ultimately supported, it would help to explain why poor human hygiene often coincides with outbreaks of body lice. Additionally, if head lice act as a reservoir for body lice, and that any social degradation in human populations may allow the formation of new populations of body lice, then head louse populations are potentially a greater threat to humans than previously assumed.

Dataset Information

Multiple origins of parasitism in lice.

Publications

Multiple origins of parasitism in lice.

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