Parasite species drives microbiome composition
Our results suggest that the bat fly families Streblidae and
Nycteribiidae may have different primary symbionts in Brazil (Figure 2).Arsenophonus has been previously identified as a primary symbiont
of bat flies (Morse, Dick, et al., 2012; Morse et al., 2013; Trowbridge
et al., 2006; Wilkinson et al., 2016). The high relative abundance and
prevalence of Arsenophonus in all streblid bat flies sampled in
our study is consistent with the hypothesis that Arsenophonusacts as the primary symbiont in the family Streblidae. However, it is
unlikely that Arsenophonus is acting as the primary symbiont of
the nycteribiid species that we sampled, given its absence or low
relative abundance. Only one previous study which examinedArsenophonus as the primary symbiont of bat flies included
representatives of New World Nycteribiidae (Morse et al., 2013). Using
cloning and Sanger sequencing, those authors detected anArsenophonus variant in two individuals of Basilia
boardmani (Nycteribiinae), which is restricted to North America. The
strain detected was distantly related to the Arsenophonussymbionts found in all other examined members of the subfamily
Nycteribiinae and similar to those found in triatomine bugs. In
combination with the evidence presented here, these findings suggest
that Brazilian Basilia spp. rely on a different endosymbiont than
both the Streblidae and North American and Old World members of
Nycteribiidae.
In contrast to what we found in streblids, nycteribiid species were
dominated by Wolbachia and Bartonella (Figure 2), both of
which have been previously detected in bat flies (Morse, et al., 2012;
Wilkinson et al., 2016). Wolbachia is a primary symbiont in some
insects (Dedeine et al., 2005; Hosokawa et al., 2010; Nikoh et al.,
2014), but acts facultatively in others (Pontes & Dale, 2006), and also
sometimes functions as a reproductive parasite, causing mitochondrial
DNA sweeps as it increases its own prevalence in a population (Cariou et
al., 2017; Jiggins, 2003; Lack et al., 2011; Speer et al., 2019).Bartonella is an intracellular pathogen found in many mammalian
groups, including humans (Breitschwerdt & Kordick, 2000).Bartonella is common in bats and bat flies (Stuckey et al.,
2017), with bat flies potentially acting as a vector to bats (Morse, et
al., 2012). It may be that Wolbachia and Bartonella both
have high relative abundance in nycteribiid bat flies because they are
acting as primary or facultative symbionts, or because they are acting
as a reproductive parasite and pathogen, respectively. If the latter is
true, it may be that one of the less abundant bacteria, likeCandidatus Phlomobacter11Standard nomenclature for a
candidate genus., Mycoplasma , or Rickettsia , is the
primary symbiont or another microbe not detected by 16S rRNA sequencing
(e.g. fungi; (Gibson & Hunter, 2010).
In addition to family-level differences between bat flies, microbiome
composition was parasite species-specific (Table 2; Figure 3).
Host-specificity of arthropod microbiomes has been found previously in
tsetse flies (Glossinidae; Aksoy et al., 2014), which are also members
of the Hippoboscoidea. That microbiome composition shows such a strong
signal of parasite species identity indicates that even non-maternally
inherited bacteria may be maintained through life history traits (e.g.,
host bat associations, microclimatic preference). The impact of bat
species identity on the parasite microbiome is difficult to parse given
the hierarchical nature of the association of bat fly species with
specific bats species. Where bat species and bat sex seem to have a
large impact on the bat fly microbiome when considered as individual
variables (Table 2), these effects disappear when the interaction
between parasite species and each host bat variable is taken into
account (Table 3). We did not have information on bat roosts, but this
has been previously shown to have a large impact on bat fly abundance
and prevalence (Hiller et al., 2020). As indicated by our network
analyses of landscape variables, it may be that PERMANOVA is good at
identifying variables that have a strong impact on variation (i.e.,
parasite species), but is not the right approach for teasing apart the
impact of variables of small effect in this type of complex system
(i.e., host bat and landscape).