Running along the dense scrub of coastal woodlands and forests, the small, mouse-like antechinus appears more modest than many Australian marsupials. But during the three weeks of the breeding season, the males transform into veritable sex-obsessed lotharios.
“They have this bizarre breeding system, which is quite common among flies and some fish, where the males live a year, have one chance to secure all their reproductive success, and then they die,” said John Lesku, a University zoologist. La Trobe University in Melbourne, Australia, who spent a decade studying antechins.
So committed to the “live fast and 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 found that these marsupials take away, on average, three hours of sleep a night during the mating season, and some individuals give up even more.
Antechines engage in suicidal reproduction, a biological phenomenon called semelparity that has been observed in other marsupial species, such as the Kaluta. Males are known to intensify their physical activity during the mating season, but how the quality of their sleep has changed (antechins typically sleep about 15 hours a day) has remained elusive.
Trekking to Great Otway National Park in southwestern Victoria, Dr. Lesku; a PhD student, Erika Ziad; and other collaborators spent several years trapping two species of antechinus. In one study, the results of which were published in 2022, researchers found that accelerometers that track body movements were a good way to estimate sleep in antechins. They tied the devices to the sturdy necks of the antechini shutters, which were housed in an enclosure within the park.
Agile antechins are too small for an accelerometer. Instead, the researchers measured levels of oxalic acid, a metabolite associated with sleep loss, for some animals before, during and after the breeding season. Testosterone levels in the blood were also measured for both species.
“We expected to see an increase in physical activity,” Ms. Ziad said, but she was excited to see how much that increase in physical activity and the sharp drop in oxalic acid levels correlated with sleep loss.
Male antechins lost, on average, three hours a night during the mating season. Going to 12 hours from 15 may not seem like much, but “if you extended your waking day by three or four hours a night,” Dr. Lesku said, “your performance on simple hand-eye coordination tasks would be reduced to the level of someone legally intoxicated.
Some males also went the extra mile to prioritize sex, depriving themselves even further, for up to seven hours. Ms. Ziad said it appears that males with the highest testosterone levels are also the ones who sleep the least. It is not known, however, at least from this study, whether those same males were more successful at fathering offspring.
Scientists also don’t know how the marsupials’ sleep quality changes during mating season, a point for future studies, the researchers say. But their findings highlight the enigmatic nature of sleep and how little is understood about its true function, said Vladyslav Vyazovskiy, a professor of sleep physiology at Oxford University who was not involved in the study.
“We spend a third of our lives sleeping and we want to think that this has a purpose,” he said. But an alternative thought, according to some scientists, is that how much an animal sleeps may be less important than how much it stays awake. “Animals sleep in very different ways, and even the same individuals can have very different sleep needs under different conditions,” Dr. Vyazovskiy said. That’s why further studies in nature on different species are needed, he added.
One question remains: Is this sleep deprivation a factor in the massive die-off so soon after seeding of the marsupials? This is a proposed hypothesis based on dead male antechins appearing, at least superficially, as chronically sleep-deprived laboratory rats. Dr. Lesku isn’t too sure, especially now with these results.
“Three hours of sleep loss is not lethal in any animal that we know of,” he said. “So what kills these males after a year? These males are simply programmed to die, to end their evolutionary longevity after one year.”