In A Nutshell
The antechinus is a small Australian marsupial that only mates once in its life. During that time, it goes into a sex frenzy for weeks until it literally disintegrates, many of its bodily functions shutting down in order to get the precious sperm into the gene pool.
The Whole Bushel
Native to the temperate rain forests of Australia, the antechinus is a small, mouselike marsupial (although females actually do not have a pouch) that only lives for about a year. Most of that time is spent foraging for insects and spiders and avoiding predators. It lives alone during the summer, and usually an individual antechinus will work exclusively inside its own territory, distant from any other member of its species. But this cute little critter is nothing more than a furry ticking time bomb. Once August rolls around, the antechinus undergoes a radical transformation that will force it to stop eating and focus on one thing only: sex.
Antechinuses are semelparous, which means they only mate once in their lives. Or rather, at one period in their lives. For 11 months, the antechinus doesn’t mate at all, but after it reaches a certain age, its body suddenly stops producing sperm. When that happens, it flicks a biological switch and the little guy is consumed by the urge to reproduce as soon and as many times as possible. Since its body will never make sperm again, it only has a matter of time to use up everything that’s stored before it will never have another chance to pass on its genes. Salmon undergo the same process, along with plenty of insects, but the antechinus is one of the only known semelparous mammals in the world.
Now the antechinus has sex. Just loads of sex. They’ve been known to go at it for 12 hours at a time, rarely stopping for more than a few hours to rest. They stop eating, stop grooming, and stop doing everything except looking for more mates. Their fur will eventually start to come out in patches, and their blood vessels will begin to hemorrhage, causing them to bleed internally. At this point, their bodies shut down virtually every process except for their metabolism and begins stripping proteins from their organs to divert as much energy as possible into breeding. Organs fail. The immune system shuts down, and the antechinus’ body is invaded by bacteria. Gangrene sets in, and their limbs begin to atrophy. They’re falling apart from the inside out. But as long as the little trooper is still alive, none of that matters.
After two to three weeks of this (it happens to all the males in a local population at the same time), the males have either already died or are so crippled and delirious that the females are no longer interested in anything they have to offer. And while this (often violent) frenzy might not sound like much fun for the ladies, their bodies are actually physically adapted to the cycle as well. Their ovaries have special pockets specifically designed to store sperm for several days. They won’t actually begin ovulating until near the very end of the breeding period, allowing those ovary pockets to become as full as possible to maximize the chances of fertilization.
Show Me The Proof
NatGeo: Why A Little Mammal Has So Much Sex That It Disintegrates
Proceedings of the Natural Academy of Sciences: Sperm competition drives the evolution of suicidal reproduction in mammals
Animal Diversity Web: Antechinus stuartii