One night of passion and you’re filled with a lifetime full of sperm with no need to ever mate again. As sex lives go, it doesn’t sound very appealing, but it’s what many ants, bees, wasps and termites experience. The queens of these social insects mate in a single “nuptial flight” that lasts for a few hours or days. They store the sperm from their suitors and use it to slowly fertilise their eggs over the rest of their lives. Males have this one and only shot at joining the Mile High Club and they compete fiercely for their chance to inseminate the queen. But even for the victors, the war isn’t over. Inside the queen’s body, their sperm continue the battle.
If the queen mates with several males during her maiden flight, the sperm of each individual find themselves swimming among competitors, and that can’t be tolerated. Susanne den Boer from the University of Copenhagen has found that these insects have evolved seminal fluids that can incapacitate the sperm of rivals while leaving their own guys unharmed. And in some species, like leafcutter ants, the queen steps into the fray herself, secreting chemicals that pacify the warring sperm and ease their competition.
The amazing thing about this chemical warfare is that it has evolved independently several times. Social insects evolved from ancestors that observed strictly monogamous relationships. Even now, the queens from many species mate with just one male during their entire lives. With just one set of sperm in their bodies, they have no problem with sperm conflict. The trouble starts when species start mating with several males during their nuptial flights, as honeybees, social wasps, leafcutter ants, army ants, and others do today.
The success of termites and other social insects hinges on their complex social systems, where workers sacrifice the ability to raise their own young in order to serve the colony and its queen – the only individual who reproduces. But this social order can be thrown into chaos by knocking out a single gene, and one that originally had a role in that other characteristic termite ability – eating wood.
Judith Korb from the University of Osnabrueck in Germany found that the queen termite relies on a gene called Neofem2 to rule over her subjects. Korb worked with the termite Cryptotermes secundus, and searched for genes that were strongly activated in quens but not kings or workers. Her search singled out Neofem2 and she used a technique called RNA interference (RNAi) to deactivate the gene in the queens of eight colonies.
Cryptotermes workers all have the ability to become royalty, but only if the current monarchs die. Until then, they keep their reproductive rights at bay. If queens are physically removed, the remaining workers start a war of succession, headbutting each other to try and establish their dominance. Those that butt most frequently ascend to the head job. And that’s exactly the behaviour that Korb saw when she nullified Neofem2.
The queen herself was unaffected, but her subjects became unruly. The frequency of butting bouts tripled in the day after the gene was silenced, something that didn’t happen in 24 control colonies where the queen’s genes were left unaltered. Cutting out this single gene made the workers behave as though their colony was queenless.
Termite colonies are families – millions of individual workers all descended from one king and one queen. But the colony itself tends to outlast this initial royal couple. When they die, new kings and queens rise to take their place. These secondary royals are a common feature of some families of termites, and they will often mate with each other for many generations. But there is more to this system than meets the eye.
Kenji Matsuura from Okayama University has found that the secondary queens are all genetically identical clones of the original. There are many copies, and they have no father – they developed from unfertilised eggs laid by the first queen through a process called parthenogenesis. These clones then mate with the king to produce the rest of the colony through normal sexual means.
It’s a fiendishly clever strategy. The original queen’s legacy to the colony is… herself. She effectively splits herself into several different bodies and in doing so, greatly increases the number of offspring she has. And because each of these descendants mates with the king, who has no genes in common with them, the colony neatly skirts around the problems of inbreeding.