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Some male marsupials are literally killing themselves with too much rigorous sex.  According to a new study, which compared 52 marsupial species, males of the antechinus and phascogales species expended so much energy and time frantically mating – sometimes for up to 14 hours a day - that they dropped dead as soon the deed is done.

Dying shortly after reproduction, known as semelparity, is more common in nature than one might think, especially with plants, insects and fish. Cicadas, butterflies, may flies and Pacific salmon are all examples of organisms that reproduce only once in their lifetime.  However, the act is extremely rare with mammals.  Up until now, scientists attributed sudden marsupial post-sex deaths to fighting or competition over other resources, but this study says otherwise.

So, why do they die?

Mating season is much shorter for these particular species – usually only a couple of weeks.  Prior to the start of mating season, the males’ testes also stop actively producing sperm, giving them little time to disperse their quickly disintegrating stores of sperm.  As a result, they engage in what is called extreme “sperm competition,” whereby they have to “get it on” with as many females as possible to successfully pass on their genes.  All this frenzied sex, along with their high testosterone, triggers an escalation in stress hormones, their bodies’ fat and muscle to break down and their immune systems to completely collapse.  The creatures hemorrhage and develop severe infections before they eventually die, usually well before the birth of their young.