Microbial composition of enigmatic bird parasites:WolbachiaandSpiroplasmaare the most important bacterial associates of quill mites (Acari: Syringophilidae)

Abstract

AbstractThe microbiome is an integral component of many animal species, potentially affecting behaviour, physiology, and other biological properties. Despite this importance, bacterial communities remain vastly understudied in many groups of invertebrates, including mites. Quill mites (Acariformes: Syringophilidae) are a poorly known group of permanent bird ectoparasites that occupy quills of feathers and feed on bird subcutaneous tissue and fluids. Most species have strongly female biased sex ratios and it was hypothesized that this is caused by endosymbiotic bacteria. Their peculiar lifestyle further makes them potential vectors for bird diseases. Previously,Anaplasma phagocytophilumand a high diversity ofWolbachiastrains were detected in quill mites via targeted PCR screens. Here, we use an unbiased 16S amplicon sequencing approach to determine other Bacteria that potentially impact quill mite biology.We performed 16S V4 amplicon sequencing of 126 quill mite individuals from eleven species parasitizing twelve bird species (four families) of passeriform birds. In addition toWolbachia, we foundSpiroplasmaas potential symbiont of quill mites. Interestingly, consistently highSpiroplasmatitres were only found in individuals of two mite species associated with finches of the genusCardfuelis, suggesting a history of horizontal transfers ofSpiroplasmavia the bird host. Furthermore, there was evidence forSpiroplasmanegatively affectingWolbachiatitres. We found no evidence for the previously reportedAnaplasmain quill mites, but detected the potential pathogensBrucellaandBartonellaat low abundances. Other amplicon sequence variants (ASVs) could be assigned to a diverse number of bacterial taxa, including several that were previously isolated from bird skin. We observed a relatively uniform distribution of these ASVs across mite taxa and bird hosts, i.e, there was a lack of host-specificity for most detected ASVs. Further, many frequently found ASVs were assigned to taxa that show a very broad distribution with no strong prior evidence for symbiotic association with animals. We interpret these findings as evidence for a scarcity or lack of resident microbial associates (other than inherited symbionts) in quill mites, or for abundances of these taxa below our detection threshold.