Echidna mothers change their pouch microbiome to protect tiny ‘pink jelly bean' puggles, new research finds

The Guardian

15-05-2025

When echidna mothers nurse their young, known as puggles, the microbiome of their pouch changes to protect their babies in their first weeks of life, new research has found.
These first few weeks are critical for puggles. At this early developmental stage, they are tiny – roughly the size of a 5-cent coin – and vulnerable.
'They can't see and they don't have a functional immune system,' said Isabella Wilson, lead author of the study published in FEMS Microbiology Ecology.
Echidnas lay their eggs into a temporary pouch, which they create by contracting their abdominal muscles. After about 10 days, puggles hatch from their eggs looking like, in Wilson's words, 'little pink jelly beans'.
During lactation, probiotic bacteria in the echidna's pouch increases, which the University of Adelaide researchers suggested offers protection to puggles and their developing immune systems.
The reproductive biology of the echidna is unique in many respects, Wilson said.
Monotremes – echidnas and platypus – share a lot of 'weird features', she said. As well as laying eggs, they lack nipples. So instead of suckling, puggles rub their beaks against a part of the pseudo-pouch called the milk patch, causing milk to come out of the mother's skin.
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This milk, which is sometimes pink, has barely any lactose compared to that of most other animals.
'The young hang out there [in the pseudo-pouch] for a few months, drink up a lot of milk,' Wilson said.
'Then, when they start to grow spines, they get turfed out of the pouch into the nursery burrow – where they continue to feed off mum for about 200 days.'
An echidna's pouch is only temporary – it is there while a puggle is inside. Healesville Sanctuary echidna keeper Craig McQueen, who was not involved in the research, agreed puggles generally stayed there for six to seven weeks, until their spines became 'too prickly' for mum.
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He said echidnas were curious animals that invested a lot of time into raising their young.
When they hatch out of their grape-sized egg, puggles are furless, blind and 'basically looked like they shouldn't have been born yet', he said – which is why they need the 'extra developmental time' in the pouch.
The paper explains that the reproductive microbiome, 'which includes vaginal, milk, and mammary microbiota, is increasingly being recognised for its contributions to infant health'. And in monotremes and marsupials, this extends to the pouch.
Researchers analysed bacteria present on swabs from both captive animals at Taronga Zoo and wild echidnas on Kangaroo Island. They found that the pouch's microbiome underwent significant changes during lactation, with an increase in lactic acid bacteria typically thought of as probiotic.
They found no major difference between the microbiomes of the zoo-managed and wild animals. Wilson said this suggested that milk, rather than any external factors, is the primary element shaping the pouch environment.