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

Area of Science:

• Microbiology
• Ecology
• Zoology

Background:

• Host-microbiota interactions are crucial for vertebrate health.
• Research has primarily focused on captive mammals, leaving wild and non-mammalian taxa understudied.
• Understanding microbiomes in wild birds offers insights into ecological and evolutionary processes.

Purpose of the Study:

• To characterize the cloacal microbiome (CM) of free-living barn swallows (Hirundo rustica).
• To investigate potential influences of sex and social pairing on CM composition.
• To explore microbial transfer dynamics within breeding pairs.

Main Methods:

• Deep pyrosequencing was employed to analyze the bacterial composition of cloacal swabs.
• Barn swallows were sampled in their natural, free-living environment.
• Statistical analyses were performed to compare CM composition between sexes and breeding pairs.

Main Results:

• Barn swallow CM was primarily composed of Actinobacteria, Proteobacteria, and Firmicutes.
• The phylum Bacteroidetes was found in low abundance (<5%), contrasting with many other vertebrates.
• No significant differences in CM composition were observed between male and female barn swallows.
• A significant correlation in CM composition was found between members of breeding pairs.
• The effect size of pair-based CM correlation was relatively small.

Conclusions:

• The cloacal microbiome of barn swallows exhibits a distinct bacterial profile.
• Cloacal contact during copulation likely facilitates bacterial exchange between breeding partners.
• High levels of sexual promiscuity in barn swallows may mitigate the impact of pair-specific microbial transfer.
• Further research is needed to fully elucidate the functional implications of the barn swallow microbiome.