Parasite and Host Discordance
Our results found that much of the genetic structure in lice was similar to that of their human hosts, a few notable differences deserve further exploration. The hierarchical structure analysis (AMOVA) found high amounts of variation (>20%) across multiple spatial levels. This differs significantly from human genetic diversity where ~13% of variation is among continents, ~1% is among regions within continents and ~85% is within-population among regions (Jorde et al. 2000). These differences point to lice maintaining higher isolation than their hosts even with the ability of horizontal transfer compared to the strict vertical transfer in the host. Additional research is needed to understand the evolutionary forces acting upon local louse populations, but not on the host, to achieve these levels of louse variation and continental population genetic structure (High FSTvalues between continents).
The host-mediated geographical structure of nuclear diversity in lice contrasts with the documented distribution of mitochondrial clades in lice. Three deeply divergent mitochondrial clades (A, B and C) that are not geographically well defined have been hypothesized to be associated with lice on now-extinct species of hominids (e.g., Neanderthals) that dispersed onto modern humans during periods of contemporaneity and survived to present day (Reed et al., 2004). In contrast, the more geographically structured nuclear clusters mirror the human host distribution following modern human dispersal out of Africa. This is consistent with Ascunce et al. (2013) where they found no relationship between the mitochondrial clade a given louse was assigned to and the nuclear genetic clusters in which the individual was found.