In many fig wasp species, armored wingless males fight to the death for access to females inside figs. They use their jaws to inflict lethal injuries, sometimes tearing off the heads of their opponents. But until now, we weren’t certain who was fighting who: Are they males from the same species, and if so, are they related?
It generally goes against kin selection for males to kill their brothers. After all, they carry some of the same genes, and the reproductive success of one offers (indirect) genetic benefits for the other. In nature, siblicide can be avoided if brothers don’t occur in the same figs. But siblicide could happen if mate competition is overwhelmingly intense or if brothers simply don’t recognize each other. Of course it’s also possible that different but closely related wasp species are occupying the same fig; after all, up to 100 wasps might be roaming in the same fig.
“We do find severed heads quite often,” University of Reading’s James Cook told New Scientist. So, Cook’s team conducted the first ever genetic analysis of fighting in fig wasps, and then they tested alternative fighting scenarios for three Sycoscapter wasp species in Ficus rubiginosa fig fruits.
The team found that approximately 80% of fights were between males from the same species – but a surprising 20% were between males of different species. That’s unexpected because only males of the same species are actual rivals for females. It’s possible that the wasps can’t recognize their opponents, or perhaps it was simply better to strike first. It’s difficult to properly judge your enemy within a crowded, dark fruit, and while you’re measuring them up, they may have already killed you, Cook told New Scientist.
The researchers also found that few figs contained brothers. That means females are likely laying just one son per fig. The work was published in Ecological Entomology this month.
Fighting to the death isn’t typical behavior in the animal kingdom. Even violent combat between male elephant seals and stags, for example, are rarely lethal. But these wasps might live for just a couple days once they’ve matured, and non-pollinating species might never even emerge from the fig, ever. “Although they’re risking their life, the future value of their life is actually quite small,” Cook said. With just three or so females they could successfully mate with inside each fig, every chance could be his last.