Why Male Antechinuses Mate Themselves To Death

Animal copulation is an awesome topic, because you get to write about phalluses and balls and explicitly use the terms which would otherwise considered taboo (though I will not be using a lot of these terms today). 

One of the most fascinating topics in animal copulation is semelparity, or suicidal reproduction, whereby one (usually the male) or both of the parents die after reproducing. Both male and female Pacific salmon die after reproduction—the same goes with octopus. Female praying mantis and Black Widow spider kill and eat their mate after sex.

Image: biologybiozine.com

Despite its popularity among non-mammalian species, suicidal reproduction also occurs in the 12 species of antechinuses and a few close relatives, all of which are small, insect-eating, hedgehog-like marsupials. The males of these marsupials die after devoting all their resources and energy to mating, an effort that helps their sperm—and genes—win out. But unlike non-mammalian species that sacrifice themselves after sex to provide more resources (in the case of arachnids, turning themselves into food) for the females or offspring, the death of male antechinuses has no direct relationship with food.

Image: phenomena.nationalgeographic.com

These animals feed on insects, and the population of insects fluctuates with the passing of seasons. The females would have higher chances of raising their young if they gave birth just before the insect population explodes, so that they are well-fed enough to wean their joeys. This effectively shortens and synchronizes their mating season, limiting it into a tight window of time. With so little time (usually a couple of weeks) to do so many things, a male antechinuses must work fast (and extremely hard) to pass on his genes.

In fact the entire process of mating is quite entertaining, because the males become so sex-crazed during the mating season they can last up to 14 hours (the average man lasts about 14 pathetic minutes during intercourse). And the males don't fight for females. Instead they develop huge testicles to produce a large reservoir of sperm, and let their sperms do the fighting. They mate with as many females as they can with the hope of displacing the sperm of earlier suitors. The males work tirelessly until their body literally disintegrate. Their blood saturates with testosterone and stress hormones, and their immune system fails. Their fur falls off. The pitiful males suffer from internal bleeding and become riddled with gangrene. Even up to that point some males could still be seen running around frantically searching for one last mating opportunity.
You seriously need to applaud them for their determination. Or rather, desperation.

Male marsupial mice, Antechinus stuartii, are overtly preoccupied with copulation and die abruptly at the conclusion of the mating season. Image: www.siumed.edu

And death is not the animals' only woe. Prior to the mating season, males stop producing sperm and their testes disintegrate, making them ball-less eunuchs reliant on stored sperm. So that's all the sperm the males will ever have.
And as if losing their balls and having a restricted mating period were not miserable enough, their stored sperm gets diluted in their urine and will eventually lost if they're not used for sex. Now that explains the desperation.

Malcolm
Info: Diana O. Fisher, Christopher R. Dickman, Menna E. Jones, and Simon P. Blomberg, Sperm competition drives the evolution of suicidal reproduction in mammalsPNAS 2013 DOI: 1310691110v1-201310691.