Outrageous Beetle Sperm is the Result of the Complicated Evolution of Sex

You know you're into some groovy science when an author of a paper says "something happens and evolution goes crazy" in a release. Dawn Higginson, Kelly Miller, Kari Segraves and Scott Pitnick, of the University of Arizona and Syracuse University, have found some of the craziest insect sperm ever, which are great examples of just how complicated and individualized a certain species’ sperm can be. It seems loony, sure, but it serves a purpose: In the complicated insect world, having incredibly specific sperm can help keep a male of one species accidentally fertilizing the wrong mate.

There are thousands of species in the common insect phylum called the diving beetle, or Dytiscidae. Higginson and her colleagues looked closely at a sample of 42 of them, and they all had one thing in common: outrageous sperm. Aside from looking like microscopic space aliens, the diverse little guys shed some light on the complex evolutionary dynamics that occur between sexes. And that "something" that happened is simply the ancient evolution of internal fertilization, which was a big departure from, say, external fish sex.

Here's a quick overview of a sample of these wily life-givers.

All photos and video credited to Dawn Higginson, University of Arizona

In one species, their sperm paired up, glued their heads together, and curled their tails into crazy spirals:

Others are mashed together in huge snaking sperm "conjugates," which sort of reminds me of those hordes of goofy flying machines in that really terrible final Matrix movie:

Some put their heads together (literally), so they could bushwhack through the hazardous female reproductive tract like a giant, living machete:

And here is a video of a massive congregation of randy sperm writhing together. It's like Medusa's hair if those boring snakes were replaced with freakish insect gametes:

So by now you're probably wondering why diving beetles' sperm would have evolved in such weird ways. The authors allude to the case of the male peacock, who shows off his tail plumage, hoping it is as large and pretty as possible in order to attract mates:

Females prefer males with flashy tails, and then females want bigger and flashier tails after that, setting up a co-evolutionary cycle. We are not positive that this is happening here, but is possible that all this diversity we see in the sperm is the equivalent of flashy peacock feathers, and females have evolved reproductive tracts that favor one kind of sperm over another.

Furthering this idea is the fact that female diving beetles (and many female insects) often store sperm from multiple males at a time, inciting fierce sperm warfare inside their reproductive tract. The evolutionary pressure to fertilize would force sperm to evolve traits that help them get to the egg first – traits that could resemble the wacky ones Higginson and her team saw under their microscopes.

Whatever the various causes may be, what's clear is that the sperm are responding to the serious trials and tribulations of the female diving beetle reproductive tract. As Higginson points out, "the females are driving the sexual evolution. The sperm cells just have to keep up."

Of course, you’d probably need to employ evolutionary magic too if the maze your sperm had to navigate looked like this: