Chromosomal characterization of human head and body lice

TOLOZA A.C.; PAPESCHI, A. G.; BRESSA, M. J.

Utah

Conferencia; 5th International Conference of Phthiraptera; 2014

The genus Pediculus that parasitize humans comprise two subspecies: the head lice Pediculus humanus capitis (P. h. capitis) and the body lice Pediculus humanus humanus (P. h. humanus). Despite the two hundred years of the first description of this two species, there is still a long debate about their taxonomic status. Some authors proposed that these organisms are separate species, while others suggest that are conspecifics. Head and body lice differ in their morphologies, feeding habitats and disease vectoring capacities. Strong evidences supported the hypothesis that body lice have evolved from head lice when humans started using cloths. The sequencing of both forms indicated that the difference between them is one gene absent in the head louse. However, their chromosomal number remains to be determined. In this study, we described the male and female karyotypes, and male meiosis  of head and body lice, and examined the chromatin structure by means of C-banding. In P. h. humanus and P. h. capitis, the diploid chromosome complement is 2n = 12 in both sexes. In oogonial prometaphase and metaphase and spermatogonial metaphase, it is evident that chromosomes lack a primary constriction, i.e. have no localized centromeres . No identifiable sex chromosomes or B chromosomes are observed in head and body lice. Neither chiasmata nor chromatin connections between homologous chromosomes are detected in male meiosis (so-called achiasmate meiosis). The kinetic behaviour of the chromosomes shows that they are holokinetic. C-banding reveals the absence of constitutive heterochromatin. Our results provide relevant information to be used in mapping studies of genes associated with sex determination and environmental sensing and response.