Discussion
The results of the combined genomic and amplicon analyses which we
present here, illustrate a positive relationship between the dynamics of
louse microbiomes and the observed high diversity of symbiotic bacteria
in lice (Allen et al., 2016; Boyd et al., 2016; Boyd et al., 2014;
Fukatsu et al., 2009; Hypsa & Krizek, 2007). The twoNeisseria -related symbionts, which are the primary focus of this
study, represent a novel lineage, extending the known phylogenetic span
of louse symbionts. Considering their genomic characteristics together
with their distribution across the lice populations, we hypothesize that
they are bacteria in an early/intermediate stage of evolution towards
obligate symbiosis, which established their symbiosis independently
within two different genera of lice. Consistent with this view, FISH
analysis highlighted their localization within putative bacteriocytes
(Figure 4 & SupplementaryInformation/SupplementaryFigure4), and
amplicon screening showed that they are part of a rich microbiomes
diversity (Figures 2 & 3), in which some of the other dominant taxa are
closely related to the other known obligate symbionts in insects (the
most degenerated ones may even be disappearing ancient P-symbionts).
This complex picture suggests dynamic turnover of the symbiotic
bacteria, their frequent acquisitions, losses and replacements even
within local louse populations and young phylogenetic lineages.