Sexual Suicide: Some Marsupials Have So Much Sex They Die

Extreme sessions of procreation are, ironically, killing off male species of some small, insect-eating marsupials, according to a new study published in the Proceedings of the National Academy of Sciences.

Dying after breeding is common in some species of insects, plants and fish, but the act is quite rare in mammals, and why certain species of marsupials seem to simply drop dead after sex has long puzzled interested researchers. Some speculation on the cause has led to suggestions that the creatures died from fighting or as a result of competition for other resources.

But it turns out that, at least for some marsupials, the deaths are a form of biologically programmed sexual suicide.

For the mouse-like antechinus and the phascogales, which resembles a possum, the males expend extraordinary amounts of energy procreating in just a short time, and once the mating is done, the creatures drop dead.

"Our investigations show that rather than altruism, individual sexual selection leads to apparent self-sacrifice in these mammals," said Diana Fisher a biologist at University of Queensland in Australia.

The way Fisher described the sexual saga of the creatures reads like the plot of a stage play.

"These species experience extreme sexual behavior, sexual conflict, female and male promiscuity, dramatic death, and synchronized suicide in males," she said.

Fisher likened the behavior of these marsupials to that of some male spider species, who advance their kind when the female stops seeking other mates after eating a successful male.

"Males compete by sperm competition," Fisher said. "Males with larger testes and better endurance succeed. Females benefit by promoting this extreme sperm competition, because the highest-quality males father their young."

The biological processes in place are as grim as the eventual outcome. All the sex causes an escalation in stress hormones throughout the breeding season, which leads to total immune system collapse, hemorrhaging, infections and, ultimately, death in most males after breeding.

"They mate for 12 or 14 hours at a time with lots of females, and they use up their muscle and their body tissues and they are using all of their energy to competitively mate, that's what they are doing. It's sexual selection," Fisher told the AFP. "They just kill themselves mating in this extreme way."