Cloacal Microbiome Structure in a Long-Distance Migratory Bird Assessed Using Deep 16sRNA Pyrosequencing

Abstract

Effects of vertebrate-associated microbiota on physiology and health are of significant interest in current biological research. Most previous studies have focused on host-microbiota interactions in captive-bred mammalian models. These interactions and their outcomes are still relatively understudied, however, in wild populations and non-mammalian taxa. Using deep pyrosequencing, we described the cloacal microbiome (CM) composition in free living barn swallows Hirundo rustica, a long-distance migratory passerine bird. Barn swallow CM was dominated by bacteria of the Actinobacteria, Proteobacteria and Firmicutes phyla. Bacteroidetes, which represent an important proportion of the digestive tract microbiome in many vertebrate species, was relatively rare in barn swallow CM (< 5%). CM composition did not differ between males and females. A significant correlation of CM within breeding pair members is consistent with the hypothesis that cloacal contact during within-pair copulation may promote transfer of bacterial assemblages. This effect on CM composition had a relatively low effect size, however, possibly due to the species’ high level of sexual promiscuity.

Cloacal microbiota of barn swallows from Northern Italy

“…The phyla Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes dominated barn swallow CMs, consistently with the results on populations from the Czech Republic, which are~580 km far from our study area, where a high abundance of the phylum Tenericutes was also reported (Kreisinger et al 2015(Kreisinger et al , 2017. Proteobacteria and Firmicutes are common in the gastrointestinal trait of birds (Godoy-Vitorino et al 2012;Waite et al 2012;Waite & Taylor 2015).…”

“…Proteobacteria and Firmicutes are common in the gastrointestinal trait of birds (Godoy-Vitorino et al 2012;Waite et al 2012;Waite & Taylor 2015). A more detailed description of the bacterial community at a lower taxonomic level showed that the most abundant genera differed from those observed in previous studies: the genera Ralstonia, Pseudomonas, Aeribacillus, and Arenimonas were abundant in our samples, while they were not found in the two previous studies in the Czech Republic (Kreisinger et al 2015(Kreisinger et al , 2017. Ralstonia spp.…”

“…Interestingly, the two studies by Kreisinger and colleagues also found some differences in the CM compositions even among barn swallow populations that bred at short distance from one another. Indeed, in one paper (Kreisinger et al 2015), the most abundant genera were Candidatus Hamiltonella, Corynebacterium, Acinetobacter, and Comamonas, while in the other one (Kreisinger et al 2017), the most abundant genera were Mycoplasma, Catellicoccus, Serratia, Lactobacillus, and Dysgonomonas, together with some members of the family Enterobacteriaceae that were not classified at genus level. These differences may be due, at least partly, to the different methods used in the two studies.…”

“…Studies on birds also suggest that nestlings acquire their microbiota from the nest environment immediately after hatching or through the bolus regurgitated by parents, providing an example of vertical transmission of bacteria through generations (Lucas & Heeb 2005;Van Dongen et al 2013). Bacteria can be transferred also between adult birds during copulation (White et al 2010;Kreisinger et al 2015). This horizontal transfer of gut bacteria is favoured by the anatomy of the reproductive system of birds.…”

“…To date, only two published studies from the Czech Republic have investigated barn swallow CM (Kreisinger et al 2015(Kreisinger et al , 2017. In light of the large variability in the microbiota of bird populations from different geographical areas (Colston & Jackson 2016), our aim was to provide a description of the CM of a geographically different population.…”