Some Like It Hot: Evolution and Ecology of Novel Endosymbionts in Bat Flies of Cave-Roosting Bats (Hippoboscoidea, Nycterophiliinae)

Abstract

We investigated previously unknown associations between bacterial endosymbionts and bat flies of the subfamily Nycterophiliinae (Diptera, Streblidae). Molecular analyses revealed a novel clade of Gammaproteobacteria in Nycterophilia bat flies. This clade was not closely related to Arsenophonus-like microbes found in its sister genus Phalconomus and other bat flies. High population infection rates in Nycterophilia across a wide geographic area, the presence of the symbionts in pupae, the general codivergence between hosts and symbionts, and high AT composition bias in symbiont genes together suggest that this host-symbiont association is obligate in nature and ancient in origin. Some Nycterophilia samples (14.8%) also contained Wolbachia supergroup F (Alphaproteobacteria), suggesting a facultative symbiosis. Likelihood-based ancestral character mapping revealed that, initially, obligate symbionts exhibited association with host-specific Nycterophilia bat flies that use a broad temperature range of cave environments for pupal development. As this mutualism evolved, the temperature range of bat flies narrowed to an exclusive use of hot caves, which was followed by a secondary broadening of the bat flies' host associations. These results suggest that the symbiosis has influenced the environmental tolerance of parasite life history stages. Furthermore, the contingent change to an expanded host range of Nycterophilia bat flies upon narrowing the ecological niche of their developmental stages suggests that altered environmental tolerance across life history stages may be a crucial factor in shaping parasite-host relationships.

The Bacteriome of Bat Flies (Nycteribiidae) from the Malagasy Region: a Community Shaped by Host Ecology, Bacterial Transmission Mode, and Host-Vector Specificity

“…It is thought that ALOs may play a role in the provisioning of B vitamins, which are deficient in vertebrate blood, the only food source for these flies (13). The ubiquity of ALOs in bat flies, in which infection is at fixation, corroborates the hypothesis of an obligate endosymbiont (12)(13)(14)(15). Such patterns have been found in other exclusive blood-feeding species like bedbugs (31) and tsetse flies (32), two insect groups which rely on a single food source throughout their developmental cycle and harbor beneficial microbes that provide nutrients absent from their restricted diets.…”

“…(8)(9)(10)(11) and Arsenophonus-like organisms (referred to here as ALOs) (12)(13)(14)(15). These bacterial genera offer contrasting model systems for investigating the biotic factors driving the structures of associated microbial communities.…”

“…The group making up the ALOs is a monophyletic lineage that includes different genera, such as Arsenophonus, Aschnera, Riesia, and other unnamed groups (ALO-1 to ALO-3) (12)(13)(14)(15). In bat flies, ALOs are primary and obligate endosymbionts that are vertically transmitted from infected mothers to offspring due to the presence of bacteriocytes in the milk glands of all nycteribiid species (12)(13)(14)(15). It is thought that ALOs may play a role in the provisioning of B vitamins, which are deficient in vertebrate blood, the only food source for these flies (13).…”

Evolution, Multiple Acquisition, and Localization of Endosymbionts in Bat Flies (Diptera: Hippoboscoidea: Streblidae and Nycteribiidae)

“…1 and 3 (46) and Nycterophilia bat flies overlap substantially in host distribution, mostly occurring on ambient temperature and hot-cave-roosting bats in the families Natalidae and Mormoopidae, as well as some Phyllostomidae. The relatively close phylogenetic relationship between symbionts in these two host clades is more likely due to ecological shifts by their bat fly hosts to specialize on bats roosting in hot caves (41) rather than to host phylogeny, as there is currently no evidence of shared ancestry between the T. caecus group of Trichobius and Nycterophiliinae.…”

“…Within each clade, endosymbiont sequences cluster by host species. Strong patterns of codivergence have been found in the Nycterophiliinae subclade (41).…”