Males of many species “guard” females after they’ve mated, presumably to prevent them from mating with other males. But in the cricket Gryllus campestris, males have a more noble intent when they guard their mate: to save her from being eaten.
Researchers Rolando Rodriguez-Muñoz, Amanda Bretman, and Tom Tregenza in England observed crickets in their natural state. What they found was that, for males, there is a trade-off between living and having the most offspring. You can read about it in this week’s Current Biology (or, watch the video below to hear about it straight from Dr. Rodriguez-Muñoz). You can also check out other videos of crickets doing their thing (including doing it) here.
The authors found many types of evidence for the male being chivalrous, but as is probably the case with most “chivalrous” men as well, cricket males didn’t do it for free. If a female didn’t want to mate with him, he didn’t waste much time hanging around her or protecting her from bad guys.
But when she did mate with him, a male cricket would fight to the death for his mate. They also treated their ladies with respect. After watching thousands of hours of video, the authors so no indication that males forced females to stay in their burrow or were ever aggressive toward them at all. In fact, if the lady felt like going over to spend some time with the guy next door, the chivalrous dude was cool with that, too (but if the guy next door comes over, the fight is on! Females think this is pretty sexy, too; they mate with the winner).
This doesn’t seem quite right, though. Why wouldn’t he fight to keep her from leaving the burrow and potentially mating with other males? After all, he put a lot of energy into courting and mating, not to mention all the sperm. What’s in it for the male, exactly?
The authors found that males that guarded their mates were allowed to mate with that female more times than if they didn’t guard. Apparently, female crickets find near-death experiences sexy, because males that guarded were about 4 times more likely to die from a predator attack. Females being guarded were 6 times more likely to survive an attack, so I guess they really only like near-death experiences when they’re not the ones experiencing them.
The female benefits from this situation by, well, not dying. She can leave and find another mate any time she wants, but it’s in her best interest to stay with the guarding male and not risk getting eaten.
The benefit for the male? All those extra matings he’s getting, and the fact that the female is likely to survive any attack, means that she is going to be pumping out eggs fertilized with our hero’s sperm probably even after he’s dead. By checking the DNA of the guarding male and the female’s offspring, the researchers were able to confirm that guarding males had more offspring.
I guess if the trade-off is between living longer and getting more nookie, it’s really a no-brainer, right?
Rodríguez-Muñoz, R., Bretman, A., & Tregenza, T. (2011). Guarding Males Protect Females from Predation in a Wild Insect Current Biology DOI: 10.1016/j.cub.2011.08.053