October 11, 2013
Some Marsupials Have Fast, Furious And Fatal Sex Lives
Some Australian marsupials — animals that carry their young in stomach pouches — have a very unusual sex life.
Males of the mouse-like Antechinus species can grow up very quickly, hitting puberty within a year. Once they mature, they have a short yet riotous mating period when they can mate for long durations, with individual “sessions” lasting up to 14 hours on average. However, once they start having sex, the males continue to do so until their fur falls off, they start bleeding internally, their bodies become infected, and they finally die.
This type of sexual “suicide,” where the parent dies after reproduction, is usually common in plants, fishes and insects such as spiders and butterflies. The Pacific salmon, for example, lives in the ocean for many years, then swims up to freshwater to produce eggs, and dies immediately afterward.
For these species, dying after reproduction makes sense, because the number of offspring they produce in one fatal sexual episode is a lot – more than what some animals can produce in their lifetime. If having sex once can spawn a thousand children, for instance, then it might be worth dying for, so to speak.
But mammals can produce only a few young at a time. Why literally kill yourself over sex if you can’t produce enough children to show for it?
Perhaps the males are being selfless, killing themselves so there is more food left for the soon-to-be-born young. Or perhaps, sex triggers mutations in their genes that cause infections and kill them.
It turns out that the reason is neither; it is the female that is to blame. Antechinus females can be very picky when it comes to choosing a partner. Having to fight with other males to make sure their genes get passed on is what drives the males to have frantic yet fatal sex, according to a study published in the journal Proceedings of the National Academy of Sciences.
Antechinus males mate only when there is plenty of food for their soon-to-be-born young. The mating season is timed to produce young just before insects – their food source — start coming out in summer. In some places, insects are abundant only for a short time in a year. The females’ breeding season is even shorter: a few days each year. This means that the males have only that narrow window to impregnate as many females as they can.
To add to the males’ woes, females can be very promiscuous, mating with multiple males at a time and having many children with different fathers. This creates competition even between the sperm from different males inside the female’s reproductive tract, to ensure that only the best sperms win and genes of the highest quality get passed on.
Faced with such uneven odds, the only way the males can make sure their seed is sown, so to speak, is to compete fiercely for the female.
This competition could also be a motivation for the males to keep going for so long; the longer they spend mating with the female, the less time the female has to spend with other males, the researchers believe.
To aid them in their suicidal mission, these animals are endowed with gigantic testes that help them stock up on large quantities of sperm. Once mating season starts, they stop producing sperm and divert all their body’s energy towards impregnating the female.
When their job is done, most males die, even before the young ones are born, and the ones that survive become infertile for life.
Image Credit: Hein Nouwens / Shutterstock