Echidnas as egg-laying monotremes give birth to highly underdeveloped young known as puggles who hatch without a functioning immune system.

The reproductive microbiome plays a key role in infant health including in humans but its role in egg-laying monotremes remains largely unknown explains Isabella Wilson from the University of Adelaide whose research was published in FEMS Microbiology Ecology.

Unlike other mammals that acquire vaginal microbiota during birth puggles are protected by the eggshell and don’t come into direct contact with the mother’s cloaca.

The first few weeks after hatching are especially critical as puggles remain in the pseudo-pouch a temporary structure formed by the mother's abdominal muscle contractions which disappears once lactation ends.

We examined how the microbiota in the echidna’s pseudo-pouch changes throughout the reproductive cycle and found that during lactation the microbial composition differs markedly from that seen outside the breeding season or during courtship and mating says Wilson.

This indicates that the pseudo-pouch environment adapts during lactation to support the vulnerable puggles which lack a developed adaptive immune system.

Interestingly the way puggles nurse may also influence these microbial shifts.

Another distinctive feature of echidna biology is their lack of nipples. instead of suckling in the traditional sense the puggle stimulates milk flow by rubbing its beak against a specialized area in the pseudo-pouch called the milk patch. Milk is secreted directly through the skin similar to how sweat or oil glands function explains Wilson.

She notes that compounds present in both the milk and the skin likely play a role in shaping the microbial communities observed in the pseudo-pouch during lactation.

Although echidnas are commonly housed in zoos across Australia and globally earlier studies by the same research group revealed stark differences in the gut microbiomes of zoo-held versus wild echidnas. However this pattern didn’t hold for the pseudo-pouch.

We were surprised to find minimal differences in the pseudo-pouch microbiota between captive and wild echidnas Wilson says. This suggests that milk composition rather than environmental exposure is the primary driver of microbial changes in the pouch during lactation.

Understanding the bacteria within the echidna pseudo-pouch is crucial not only for advancing knowledge of monotreme biology but also for informing conservation strategies and improving breeding success both in captivity and in the wild.

Source: https://www.adelaide.edu.au/newsroom/news/list/2025/05/13/echidna-microbiome-changes-while-mums-nurse-puggle