Marsupial That Dies After 'Frantic' Sex: New Mouse-Like Species Discovered In Australia

By Ben Wolford on February 19, 2014 3:48 PM EST

The new species is a black-tailed variation of this antechinus. (Photo: Flickr/Alan Couch, CC BY 2.0)

The new species is a black-tailed variation of this antechinus. (Photo: Flickr/Alan Couch, CC BY 2.0)

The antechinus is a small, ordinary mouse-like marsupial, but do not underestimate him. He has large testes, and he goes into every mating season knowing he may not walk away from it alive.

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Biologists in Australia have discovered a 13th species of the genus Antechinus, all of which are famous for their kamikaze sexual tendencies. The discovery of the new black-tailed antechinus, officially designated Antechinus arktos and described in the journal Zootaxa, comes just months after biologists discovered once and for all why the males die en masse after each mating season.

Before last October, scientists speculated that suicidal mating — known as "semelparity" among biologists — was derived from evolutionary altruism. They thought maybe food scarcity encouraged fathers to off themselves for the benefit of their young. They kill themselves by what science bloggers have taken to calling "frantic mating" — reproductive acts with such frenzied haste that the stress causes their immune systems to collapse, leading to infections, internal bleeding, and death.

Researchers at the University of Queensland weren't convinced by the offspring altruism theory. If that were the case, antechinuses would likely demonstrate more spousal fealty, and they don't. They're incredibly promiscuous, as Queensland's Dr. Diana Fisher and her colleagues discovered. "Each mating can take 12 to 14 hours, and they do this over and over again," she told the ABC of Australia last year.

That's because males stop producing sperm right after they reach sexual maturity (at about 11 months old) and right before the mating season. "They shut down their testes," says Fisher, adding that this is why these are disproportionately large compared with their small bodies. They "rely on sperm stored in the epididymis for mating, which is also lost in their urine. This gives them some urgency to mate, so it is no wonder that the breeding season is so frantic. ... Even if they survived the breeding period, they would be infertile anyway."

And so, all at the same time, hundreds of antechinuses go out into the wilds of Oceania in search of mates, all of them cognizant of their limited sperm and the limited window of female ovulation. With resources so precious, the males have intense genetic pressure to compete amongst themselves. But they waste no energy on claw-to-claw combat. Instead, their sperm will do battle for them, a phenomenon known as competitive mating. Fisher published these findings in October in the journal Proceedings of the National Academy of Sciences. She told the ABC, "Our previous work showed that females benefit from sperm competition because the best males sire more of their offspring."

In the summary of the new research on the black-tailed antechinuses there's no mention of suicidal mating. But The Telegraph reported that the newly discovered species almost certainly adheres to the same reproductive rituals. The recent paper in Zootaxa did say, however, that there probably aren't that many black-tailed antechinuses in the world and that climate change isn't helping their numbers. The species "will be at further risk with increasing warming trends," the authors wrote.

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