Echidnas have sex while sleeping, study says

By Marina Kamenev 23 December 2010
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Little is known about the sex life of echidnas, but an AG society-sponsored study is making some surprising findings.

AUSTRALIAN ECHIDNAS CAN BE just as pushy as humans when it comes to sex: a 16-year study of Tasmanian echidnas reveals that males routinely sneak up on females hibernating in their burrows and mate with them while they are fast asleep.

“It’s very interesting and very unique,” comments Dr Greg Johnston, a zoologist from the University of South Australia in Adelaide. “The female is asleep and comfortable, and the male taps her on the shoulder, has a bit of rumpy-pumpy and leaves; meanwhile she goes back to sleep.”

Despite being among the most common mammals in Australia, little has been known about the reproductive practices of short-beaked echidnas (Tachyglossus aculeatus). However, an Australian Geographic Society-sponsored research project, at the University of Tasmania, Hobart, is unlocking the secrets of echidna sex.

Exploring the link

“We knew very little about how they mated,” says Professor Stewart Nicol, the zoologist leading the research. “I just knew there was a link between hibernation and reproduction, which is what I wanted to explore.”

To test the link further, Stewart has led a team of researchers who have tagged and monitored 280 wild echidnas over a 16-year period, monitoring 20 of them very closely.

Echidnas are only known to hibernate in the coldest parts of their range. In Tasmania, they hibernate for five to seven months of each year, when food is scarce. However, male and females enter hibernation at different times; males settle down as early as February, while females start later because they are recovering from feeding their young.

Males arise from their slumber mid June and within a few weeks they are ready to mate with the sleeping females, disturbing their rest but not fully awakening them. Stewart says that mating typically occurs from mid June to late September. Over the last two years of the study, a total of 71 instances of mating were recorded – often involving groups of males – and in two thirds of these instances the females were still in hibernation.

Cold storage

The researchers are yet to determine why the females remain in hibernation after mating, but Stewart speculates that it could be because they store the sperm of different males. Remaining asleep, with a low body temperature, allows her time to keep the eggs and sperm ‘on ice’ while she waits to see if a better mate comes along, he says.

“It may allow the female to keep some sperm or even a fertilised egg in cold storage in the hope that she might find a better quality male. We know that if she’s pregnant, hibernation can slow down the development of the egg.”

Female echidnas have to choose potential mates carefully, because having offspring is a big physical commitment. Following pregnancy the mother doesn’t leave the burrow, even to eat, for six weeks. She also lactates for a further five months, then hibernates and repeats the cycle, or takes a year off, Stewart explains. “After all that, you would want successful offspring.”

“There is obviously intense competition between males, which has selected for them to be ready to mate very early,” he adds. “While females may not have much choice about which male they mate with, by not fully arousing from hibernation and mating many times, they may be able to decide whose sperm they allow to fertilise their egg.”

“Echidnas are an egg-laying mammal [monotreme], which is so special and so interesting,” he says. “As they are so widespread you would think a lot more would be known about their biology, but so far it’s all been a big mystery.”

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