Fatal ejaculations, exploding penises and post-coital cannibalism - many male animals are dying after wild sex.
Australian researchers have examined reproductive suicide in some insect-eating marsupials, where males die after mating as stress hormone levels rise and immune systems collapse.
The team, led by University of Queensland's Diana Fisher, conclude it's an adaptive response to intensified male sexual competition for females.
Females accrue "fitness benefits" by timing peak energy demands of reproduction to coincide with maximum food abundance, the researchers say in a paper published on Tuesday in the science journal PNAS.
In short mating cycles, there is increased competition between males so they put more energy into copulating and this reduces their post-mating survival.
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But shorter cycles alone do not explain suicidal reproduction, the scientists say.
Bigger testes and promiscuity also play a role.
"Among species with low post-mating male survival, we show that those with suicidal reproduction have shorter mating seasons and larger testes relative to body size," they say.
"This indicates that lethal effort is adaptive in males because females escalate sperm competition by further shortening and synchronising the annual mating period and mating promiscuously."
The paper said die offs after sex occurred in all 12 species of Antechinus, which includes a little marsupial mouse, and three species of Phascogale and in the single specie of Dasykaluta.
Suicidal reproduction, known as semelparity, is not unique to the small marsupials investigated in the paper.
A praying mantis rips off her mate's head right after sex and a black widow spider eats her mate.
The honey bee drones die after mating with the queen thanks to an explosive ejaculation that tears his penis off, and pacific salmon swim upstream to spawn and die.
