This Tiny Marsupial Gives Up Sleep for Sex, Then Drops Dead

Dusky Antechinus marsupial on moss at Mount Wellington in Hobart, Tasmania, Australia.
Dusky Antechinus marsupial on moss at Mount Wellington in Hobart, Tasmania, Australia.

A frisky marsupial cuts its sleep to just three hours a night so it can cram in 14-hour sex sessions, new research shows. However, this intense sex binge ultimately leads to the male’s death.

Researchers from Australia discovered that these marsupials, known as the antechinus, a small mouse-like creature, significantly reduce their sleep time to accommodate extended mating periods.

“We showed that males lose sleep during the breeding season, with one male halving his sleep during this mating period,” says Erika Zaid, a PhD student at La Trobe University in Melbourne, in a media release. “In humans and other animals, restricting the normal amount of sleep leads to worse performance while awake, an effect that compounds night after night. And yet, the antechinus did just that: they slept three hours less per night, every night, for three weeks.”

“They stay awake to secure paternity before they die,” says Erika Zaid, a wildlife biologist at La Trobe University in Australia and the study’s lead author. “It’s a huge trade-off, but the most important thing for them is to pass on their genes.”

Prospective antechinus papas aren’t alone in dealing with such pressure. This kind of one-and-done reproductive strategy, known as semelparity, is used by species ranging from cicadas to Pacific salmon. Only a handful of mammal species—all marsupials—practice semelparity. In antechinus, males alone face fatal repercussions; females can live an additional year and can participate in a second breeding season. The mass die-off of males after breeding, known as the “mating syndrome,” can get downright gruesome: scientists recently discovered that some male antechinus snack on their deceased competitors before meeting their tragic fates.

This photograph shows a male dusky antechinus in a naturalistic enclosure located in Cape Otway
This photograph shows a male dusky antechinus in a naturalistic enclosure located in Cape Otway, Australia. (CREDIT: Erika Zaid)

To determine the toll of antechinus’ rare reproductive strategy, Zaid and her colleagues headed to southern Australia’s Great Otway National Park right before the mating season. The team baited traps with rolled oats, peanut butter, honey, and bacon to capture members of two antechinus species. They took blood samples from agile antechinus (Antechinus agilis) before releasing them and collected 15 dusky antechinus (Antechinus swainsonii), 10 of which were males, and housed them in individual enclosures. This allowed the researchers to track the activity of each one before and during the breeding season. The scientists implanted tiny electroencephalographic (EEG) devices into each furry marsupial to measure how long they slept.

The team found that during the breeding season, male antechinus slept an average of only 12 hours a day for three straight weeks. While 12 hours sounds like a lot, it’s more than three hours less per day than the 15 hours they spent snoozing daily before the breeding season. One male took it even further, slashing its usual sleeping hours by more than half once the breeding season started. The blood samples from agile antechinus males also revealed reduced levels of oxalic acid. The decline of oxalic acid is a common biomarker associated with sleep loss.

The researchers say their study offers the first evidence for this type of sustained sleep restriction in any terrestrial mammal during its breeding season. But Mathew Crowther, a wildlife biologist at the University of Sydney in Australia, who was not involved in the new research, thinks other marsupials may also lose sleep when pressured to reproduce. “Antechinus are the most extreme, but I would not be surprised if other semelparous [species] sleep less during their breeding season,” he says. “They are so focused on mating with as many females, for as long as they can.” Some species, including antechinus, even forgo eating.

Despite running on limited shut-eye each night, the antechinus managed to maintain their torrid pursuit of mates—and researchers have recorded these animals participating in marathon mating sessions lasting 14 straight hours. Other animals have also exhibited similar feats of wakefulness; scientists have observed male Pectoral Sandpipers, members of a migratory shorebird species, spending up to 95 percent of their time awake and active during their three-week breeding season. And that extra activity appears to pay off: the sandpipers that sleep the least sire the most offspring.

Compared with these sandpipers, antechinus might seem relatively well-rested. “We expected these animals to lose more sleep,” Zaid says. With their demise imminent, it would make sense for male antechinus to forgo sleep entirely to maximize the chances of passing on their genes.

According to Zaid, the fact that male antechinus does still need to doze off “actually underlines the importance of sleep.” Even when racing against the clock, these doomed marsupials still require at least some shut-eye.

The study, however, did not establish a direct link between the marsupials’ exhaustive mating rituals and their subsequent deaths. An earlier study by Associate Professor Andrew Baker from Queensland University of Technology, published in Australian Mammalogy, suggested that post-sexual fatalities might be linked to extreme testosterone levels.

The research is published in the journal Current Biology.

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