Running along the dense brush of coastal woodlands and forests, the little mouse-like antechino 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 extremely strange reproductive system, which is quite common among flies and some fish, where the males live a year, have a single chance to ensure all their reproductive success, and then they die,” he said. John Leskuzoologist at La Trobe University in Melbourne, Australia, who has spent a decade studying antichines.
So committed to the life fast, die new lifestyle, a male antichin even foregoes one of the most basic biological needs: sleep. In a study published Thursday in the journal Current Biology, Dr. Lesku and his colleagues found that these marsupials shave off an average of three hours of sleep a night during mating season, with some individuals giving up even more.
Antechinuses engage in suicidal reproduction, a biological phenomenon called semelparity that has been observed in other marsupial species, such as kalutas. Males are known to increase their physical activity during the mating season, but how the quality of their sleep changed – antechins typically sleep about 15 hours a day – remained unknown.
Hiking in the Great Otway National Park in the south-west of the state of Victoria, Dr. Lesku. a Ph.D. student, Erika Ziad; and other collaborators spent several years trapping two species of antechin. In one study, the results of which were published in 2022, the researchers found that accelerometers that track body movements were a good way to assess sleep in antichines. They strapped the devices to the heavy necks of the dark stalwarts, who were housed in an enclosure within the park.
Agile antichines are 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 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 sound like much, but “if you extended your waking day by three or four hours at night,” Dr. Lesku said, “your performance on simple hand-eye coordination tasks would decrease to the level of someone legally drunk.”
Some males also went the extra mile by prioritizing sex, depriving themselves even more – up to seven hours. Ms Ziad said it appeared that the men with the highest testosterone levels were also the ones who slept the least. It is unknown, however, at least from this study, whether the same males were more successful at producing offspring.
Scientists also don’t know how marsupials’ sleep quality changes during the mating season, a point for future study, the researchers say. But their findings highlight the enigmatic nature of sleep and how little is understood about its actual function, he said. Vladyslav Vyazovskiyprofessor of sleep physiology at the University of Oxford who was not involved in the study.
“We spend a third of our lives asleep, and we like to think there’s a purpose to that,” he said. But an alternative thought, some scientists believe, is that how much an animal sleeps may be less important than how much it’s 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 massive die-off so soon after seeding of marsupial wild oats? It’s a hypothesis proposed on the basis of dead male antichines that appear, at least superficially, like chronically sleep-deprived lab rats. Dr. Lesku isn’t too sure, especially now with these findings.
“Three hours of sleep loss is not lethal to 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 a year.”