For some marsupials, the process of mating is rigorous and wild enough to cause death when it is over, according to new Australia-based research.

Previous studies have attempted to figure out the phenomenon, AFP reported, but the new research claims to pinpoint the true reason. Marsupial males go to such extreme measures to ensure the safety of their sperm, because they only get one chance every year to mate with a female, that it kills them.

"There's always a cost to reproducing - it's an energy expensive thing that animals do," lead researcher Diana Fisher, a mammal ecologist at the University of Queensland, said. "But in this case they haven't spread out their effort over time, they do it all at once in a really short time. And they just die afterward."

Previous work has speculated the animals died due to fighting or to leave food for their offspring. The new study, published in the U.S.-based journal Proceedings of the National Academy of Sciences, suggests something else entirely.

It is extremely rare for mammals to mate once then die, but the occurrence is somewhat common among fish and plants. Of mammals to do so are small mouse-like marsupials like the antechinus and the phascogales, which resembles a possum.

Fisher said the actual cause of death is a heightened level of testosterone built up so much that stress hormones break down the animal's body tissue and cause the immune system to collapse. This "cascade effect" is triggered by the animal's dead-set intentions of mating. However, the males do not waste all that effort and testosterone on one female partner.

"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 said. "They just kill themselves mating in this extreme way."

For the study, the researchers analyzed 52 species of marsupials in in Australia, Papua New Guinea and South America, but not all took their own lives after sex. Fisher said the act is actually uncharacteristic of the animals and that they may not know it is going to happen.

"They have a nice temperament, they are very inquisitive little animals. They are quite interactive. It's a bit sad," she said. But they don't know it's coming I suppose, it's just something that happens to them."