Rapid GIT transit time in volant vertebrates, with implications for convergence in microbiome composition.

Area of Science:

• Comparative physiology
• Microbiology
• Evolutionary biology

Background:

• Volant animals, including birds and bats, possess simplified gastrointestinal tracts (GITs) to aid flight.
• Previous research indicated reduced GIT transit times in birds, but this has not been comprehensively studied in bats.
• Bat gut microbiomes are distinct, dominated by Pseudomonadota (formerly Proteobacteria), similar to flying birds.

Purpose of the Study:

• To investigate and compare gastrointestinal transit times across vertebrates, focusing on volant species.
• To test the hypothesis that rapid GIT transit times contribute to the convergent microbiome composition in birds and bats.
• To explore the relationship between body mass, GIT transit time, and microbiome composition within the bat order.

Main Methods:

• A meta-analysis of published vertebrate gastrointestinal transit time data was performed.
• Transit times were statistically compared between volant (birds, bats) and nonvolant vertebrates.
• Intra-order analyses within Chiroptera (bats) examined the correlation between body mass and GIT transit time.

Main Results:

• Bats and flying birds demonstrated significantly faster GIT transit times compared to nonvolant vertebrates.
• Within bats, a negative correlation was observed between body mass and GIT transit time (larger bats had faster transit).
• This inverted mass-transit relationship in bats contrasts with patterns seen in other vertebrates, including birds.

Conclusions:

• Rapid GIT transit is a shared characteristic of volant vertebrates, potentially driving convergent gut microbiome evolution.
• The inverse relationship between body mass and transit time in bats may be diet-influenced, with larger fruit/nectar feeders exhibiting faster transit.
• These findings offer insights into the physiological adaptations for flight and their impact on gut ecology in bats and birds.