Every year, antechinus marsupials get it on until the males all drop dead.

Researchers classified two new species of Dusky Antechinus, mouse-like creatures that engage in suicidal reproduction, and published their findings last week in the peer-reviewed journal Memoirs of the Queensland Museum -- Nature. The Mainland Dusky Antechinus, found in southeastern Australia, has been elevated from sub-species to a distinct species. And the newly discovered Tasman Peninsula Dusky Antechinus, found in southeastern Tasmania, already faces the threat of extinction due in part to loss of habitat and feral pests, researchers said.

Their proclivity for ferocious, suicidal sex frenzies aren't helping them any.

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"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," lead author Andrew Baker of the Queensland University of Technology said in a release.

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All of that testosterone "triggers a malfunction in the stress hormone shut-off switch" for the males, Baker said. The males then get so stressed out that their immune systems fail, and they die before the females actually give birth.

Baker said the "yearly male suicide mission" cuts the population in half, leaving enough spiders and insects for the mothers to eat while raising the offspring.

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Suicidal reproduction -- or semelparity-- is rare in mammals, and has so far just been documented in these kinds of marsupials.

2013 study published in the Proceedings of the National Academy of Sciences looked into why the marsupials evolved to have such extreme sexual behaviors. They concluded that the males didn't die off as some kind of altruistic act to ensure the survival of their offspring. Rather, females may be synchronizing their mating to coincide with the availability of food while they're pregnant. That short mating time frame creates intense competition -- so intense that the males end up dying.

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Over the past three years, scientists have identified five new antechinus species. The two marsupial species discussed in this new research occupy just a few square kilometers on remote, misty mountaintops. Most of the Tasman Peninusla animal's "habitat falls within state forest, which is being logged," Baker said. "This species now apparently only lives in tiny, fragmented stands of intact forest that are under threat."

"It's a shame that mere moments after discovery, these little Tasmanian marsupials are threatened with extinction at human hands," Baker said.

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