Two newly classified species of marsupials in Australia apparently engage in sex sessions "to die for" — unfortunately, that's quite literal for the males, who drop dead at the end of multihour reproductive orgies.

The tiny mouse-size marsupials, known as Dusky Antechinus, have a tendency to engage in ferocious mating sessions that wipe out huge numbers of them, according to researchers.

"The breeding period is basically two to three weeks of speed-mating, with testosterone-fueled males coupling with as many females as possible, for up to 14 hours at a time," said lead study author Andrew Baker of the Queensland University of Technology.

All that raging testosterone disables a "shut-off" switch regulating stress hormones, causing the males to get so stressed out that their immune system fails and they die even before the females give birth, Baker explained. It's an evolutionary tactic that reduces the population by half, leaving sufficient food supplies for marsupial mothers and their offspring.

The females may be synchronizing their mating period to coincide with the availability of food while they're pregnant, the researchers suggest, with the males ending up as sacrificial victims.

Known scientifically as semelparity, this type of suicidal reproduction is rarely seen in mammals. In fact, the tiny marsupial species are the only ones in which it has been documented, the researchers noted.

One of the newly classified Antechinus species was discovered in remote regions of the island state of Tasmania.

Several species of Antechinus are already under threat from climate change, feral predators and loss of habitat — so their extreme mating habits aren't helping.

"In a country with the worst mammal extinction rate anywhere on earth, Australia is in the midst of unprecedented loss of its biological treasures," he said.

Baker has campaigned to have two previously discovered Antechinus species found in Queensland added to the state's endangered species list.

Living in remote mountaintops in the southeast of the state, these animals have what may be the smallest distribution of any Australian mammal, with their habitats down to just a few square kilometers.

Baker and his research colleagues also want to have the species added to Australia's federal threatened list, which would bring protections aimed at preserving existing populations of the tiny marsupials.

"Nine in 10 Australian mammal species are unique, yet they are vanishing before our very eyes," Baker warned.

This study was published in Memoirs of the Queensland Museum - Nature.

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