Determinants of digestive efficiency during reproduction in a highly vagile colonial bat

Digestive efficiency, a component of digestion, is important to extracting nutrients and energy from food sources. Digestive efficiency is potentially shaped by many factors including gut microbiome, dietary compositions, gut morphology, physiological response to energy demands across life stages, and host genetics. Relative to other mammals, bats experience unusually high energetic demands owing to the costs of powered flight, yet have considerably shortened digestive tracts relative to similarly sized mammals. Moreover, mammalian pregnancy and lactation are costly, and probably even more so in bats which support fetuses that may be a third of the mother’s body mass. Furthermore, compositional shifts to the gut microbiome may be expected given the immunological modulation associated with pregnancy, but at the same time maintenance of microbiome community stability is thought to be necessary for optimal functionality. Because of the unique characteristics of bats, microbiome function may be particularly important for bat reproductive success. In the current study the relative roles of host microbiome, diet, and reproductive stage on variation in digestive efficiency in Brazilian free-tailed bats, Tadarida brasiliensis, was investigated. Fecal samples were collected from female bats ranging from early pregnancy though post-lactation. 16s rDNA gene sequencing was used to characterize bacterial community composition, qPCR to estimate microbiome bacterial biomass, arthropod COI barcode sequencing to characterize diet, and digestive efficiency quantified using bomb calorimetry. Both digestive efficiency and microbiome diversity declined slightly in later reproductive stages. While microbiome composition and bacterial load were important in shaping differences in digestive efficiency, microbiomes of bats collected more closely in time across the reproductive season had more similar microbiomes. Findings suggest that while pregnancy effects may reduce microbiome diversity, microbiome dispersal via social interactions may work to counteract microbiome diversity declines. A sociality-mediated rescue effect on microbiome diversity represents a previously unrecognized benefit to colonial living.