Spiny, snooty, and strange, echidnas are among Australia’s wackiest animals. They’re mammals, which means they feed their young milk, but only after the puggle (that’s the word for a newborn echidna) hatches from an egg.
Now, biologists from the University of Adelaide in Australia have taken a closer look at what is going on inside the ‘pseudo-pouches’ of short-beaked echidnas (Tachyglossus aculeatus) while they rear their young.
The females of most other Australian marsupials have permanent pouches, kitted out with milk-dispensing nipples, to feed, protect, and carry their young in the early days.
Echidnas, however, do not have a true pouch. Instead, they form what’s called a pseudo-pouch by contracting their abdominal muscles, concealing their baby as it drinks its mother’s milk in a unique way.
“The puggle rubs its beak against a part of the pseudo-pouch called the milk patch, causing milk to come out of the skin, sort of like a sweat or oil gland,” explains biologist Isabella Wilson from the University of Adelaide.
As one of the two kinds of monotremes (the other being the platypus), echidnas lay a single egg instead of giving birth to live young. The mother echidna carries this egg in her pseudo-pouch for as little as 10 days before a tiny, pink, jellybean-like baby echidna hatches.
As you can see, it is very small and very helpless at this time. And the spines, thankfully, only come in once the puggle has grown much bigger (about the same time the mother kicks them out).
Like every other nook and cranny of an animal’s body, echidna pseudo-pouches have a specific microbiome made up of bacteria and other microbes. Because puggles hatch from eggs, they do not have the opportunity to pick up their mother’s microbiome from the vaginal canal, as other mammals do during birth.
This means the pseudo-pouch ecosystem is where puggles, without a functioning immune system, first encounter bacteria and other pathogens. But little is known about how it works.
To understand this better, biologists collected samples of pseudo-pouch microbiomes by swabbing 22 different echidnas at different stages of their reproductive cycle. Some were live animals at Taronga Zoo, and some were wild echidnas killed by traffic on Kangaroo Island and around the Adelaide Hills.
The biologists collected swabs from echidnas during and outside of breeding season, and others who were lactating.
“During lactation, pseudo-pouch microbial communities show significant differences in composition compared with samples taken outside of breeding season or during courtship and mating,” Wilson says.
“This suggests that the echidna pseudo-pouch environment changes during lactation to accommodate young that lack a functional adaptive immune system.”
The bacteria phylum Firmicutes became more dominant in the pseudo-pouches of lactating echidnas, while Bdellovibrionota and Verrucomicrobiota numbers dropped.
In lactating echidnas, the relative abundance of more than half the bacteria genera found in the echidna pseudo-pouch was reduced, suggesting something had killed them off.
Wilson and her team also found that in non-lactating echidnas, the pseudo-pouch microbiome was functionally the same regardless of whether it was breeding season or not, or whether they were wild or captive. This suggests it’s not a factor in the relatively low survival rate of captive-bred young.
“We were surprised to find no major difference in the pseudo-pouch between zoo-managed and wild animals, which suggests to us that the milk, rather than external environmental factors like captivity, is what primarily shapes the bacterial landscape of the pseudo-pouch,” Wilson says.
The next question is how echidna milk changes the pseudo-pouch microbiome on a molecular level, and how biologists, zoos, and wildlife carers can use all this information to better support echidna breeding.
This research was published in FEMS Microbiology Ecology.
