Scurrying along the dense brush of coastal woodlands and forests, the small, mouselike antechinus appears more unassuming than many of Australia’s marsupials. But for the three weeks of their breeding season, the males transform into absolute sex-obsessed lotharios.
“They have this super bizarre breeding system, which is quite common among flies and some fish, where the males live one year, have a single shot at securing all their reproductive success, and then they die,” said John Lesku, a zoologist at La Trobe University in Melbourne, Australia, who has spent a decade studying antechinuses.
So committed to the live fast, die young lifestyle, a male antechinus even forgoes one of the most essential biological needs: sleep. In a study published Thursday in the journal Current Biology, Dr. Lesku and his colleagues discovered these marsupials shave off, on average, three hours of sleep per night during their mating season, with some individuals forgoing even more.
Antechinuses engage in suicidal reproduction, a biological phenomenon called semelparity that has been observed in other marsupial species, like kalutas. Males are known to ramp up their physical activity during their mating season, but how their sleep quality changed — antechinuses typically sleep around 15 hours a day — remained elusive.
Trekking over to Great Otway National Park in the southwestern part of the state of Victoria, Dr. Lesku; a Ph.D. student, Erika Zaid; and other collaborators spent several years trapping two species of antechinus. In one study, the results of which were published in 2022, the researchers found that accelerometers tracking body movements were a good way to estimate sleep in antechinuses. They strapped the devices to the hefty necks of dusky antechinuses, which were housed in an enclosure within the park.
Agile antechinuses are far too small for an accelerometer. Instead, the researchers measured levels of oxalic acid, a metabolite associated with sleep loss, for some of the animals before, during and after the breeding season. Blood testosterone levels were also measured for both species.
“We kind of expected to see an increase in physical activity,” Ms. Zaid said, but she was excited to see how much that increase in physical activity and the steep dip in oxalic acid levels correlated with a loss of sleep.
Male antechinuses lost, on average, three hours a night during their mating season. Going to 12 hours from 15 may not sound like much, but “if you were to extend your waking day by three or four hours a night,” Dr. Lesku said, “your performance at simple hand-eye coordination tasks would be reduced to the level of someone legally intoxicated.”
Some males also went the extra mile in prioritizing sex, depriving themselves even more — as much as seven hours. Ms. Ziad said it appeared that the males with the highest testosterone levels were also the ones sleeping the least. It’s unknown, however, at least from this study, if those same males were more successful in fathering offspring.
Scientists also don’t know how the marsupials’ sleep quality changes during their mating season, a point for future study, the researchers say. But their findings highlight the enigmatic nature of sleep and how little is understood of its true function, said Vladyslav Vyazovskiy, a professor of sleep physiology at the University of Oxford who was not involved in the study.
“We spend a third of our life asleep, and we want to think that this has a purpose,” he said. But an alternative thought, some scientists believe, is that how much an animal sleeps may be less important than how much they are awake. “Animals sleep in very different ways, and even the same individuals can have very different sleep requirements under different conditions,” Dr. Vyazovskiy said. That’s why more studies in the wild of different species are needed, he added.
A question remains: Is this sleep deprivation a factor in the huge die-off so soon after the sowing of marsupial wild oats? It’s a hypothesis proposed based on dead male antechinuses appearing, at least superficially, like chronically sleep-deprived laboratory rats. Dr. Lesku isn’t too sure, especially now with these findings.
“Three hours of sleep loss is not lethal in any animal we know of,” he said. “So what’s killing these males after one year? These males are just programmed to die, to end their evolutionary longevity after one year.”