Microbiota changes in lactation in the short-beaked echidna ( <i>Tachyglossus aculeatus</i> )

Monotreme and marsupial development is characterized by a short gestation, with young exposed to the environment at an early developmental stage and supported by a long lactation in the pouch, pseudo-pouch, or burrow. The lack of a functional adaptive immune system in these altricial young raises questions about how they survive in a microbe-rich environment. Previous studies on marsupial pouches have revealed changes to pouch microbe composition during lactation, but no information is available in monotremes. We investigated changes in the echidna pseudo-pouch microbiota (n = 22) during different stages of the reproductive cycle and whether this differs between wild and zoo-managed animals. Metataxonomic profiling using 16S rRNA gene sequencing revealed that pseudo-pouch microbial communities undergo dramatic changes during lactation, with significant differences in taxonomic composition compared with samples taken outside of breeding season or during courtship and mating. This suggests that the echidna pseudo-pouch environment changes during lactation to accommodate young that lack a functional adaptive immune system. Furthermore, captivity was not found to have a significant effect on pseudo-pouch microbiota. This study pioneers pouch microbiota research in monotremes, provides new biological information on echidna reproduction, and may also provide information about the effects of captive management to inform breeding programmes in the future.