A queen bee stashes all the sperm she’ll need to make a lifetime’s worth of babies in a few days. Let’s just start there. This virgin queen flies out from her nest to mate with as many as 90 male drones mid-flight (though usually more like a dozen), then returns to her hive with a stash of up to 100 million sperm cells in her oviducts. Later she’ll pare that down to just five or six million to store in her spermatheca. The drones, meanwhile, die—their abdomens have literally been ripped open by the mating process, and they’ve served their only purpose to their species.
Lots of social insects follow basically the same routine, but honeybees are unique in that their queens can go on multiple mating flights. The goal: increasing genetic diversity. The queen bee will mother every worker in her hive until a daughter takes her place, so the more variation she can add to their pool of potential fathers before settling down, the better. A broad selection of sperm from diverse sources means more genes in the hive, which means a better chance of surviving should disease or environmental disaster knock some of them out. Some research suggests a hive is less likely to reject a young queen if she’s been inseminated by a bigger group of drones, and there’s some evidence that a queen will determine whether or not to expend energy on more flights before she starts laying eggs based on how successful her previous nuptial spree was.
But if you’re a drone who’s already mated with the flighty queen in question, you don’t want her to go out finding other dudes to add to her sperm collection. You want your sperm to get passed along. Every other male who mates with her decreases the fraction of offspring that will get your genes.
And so drones blind the queens to keep them hive-bound.
The toxin that makes vision go blurry is actually just one of some 300 proteins in bee seminal fluid that seem to have some effect on queens. Boris Baer, a professor of entomology at UC Riverside, and his team have been investigating what these peptides might do for the last decade. Previously they’d also found a protein that attacked sperm from other males, a tactic that’s common amongst insects, but this new toxin was a step up in the sexual arms race that is bee mating season. You can read about their results in the journal eLife.
The protein seems to work by changing the expression of genes responsible for vision inside the queen bees’ brains, though the exact mechanism isn’t yet clear. Baer and his team tested whether the peptide was actually influencing vision by artificially inseminating the bees, then attaching tiny electrodes to their brains to test the queens’ responses to a flickering light. Queens inseminated with actual seminal fluid, as opposed to a saline solution with no proteins, displayed signs of compromised vision within a few hours, though the effect wore off eventually.
Since vision is fairly crucial to the art of flying (at least if you’re a bee), the overall effect is that queens have a harder time navigating. But it’s not for lack of trying.
Baer and his team also attached tiny RFID tags to some of their study subjects to see whether the inseminated bees had any chance. Those with impaired vision actually left for subsequent mating flights sooner than those who’d only gotten saline. The researchers speculate that this might be an evolutionary response to one-ups-man-ship from the drones. You want to blind me? I’ll just try to go on even more mating flights.
The problem, of course, is that the vengeful queen is flying (somewhat) blind. Only about 40 percent of inseminated bees made it back to their hives, compared to 90 percent of the saline-injected study subjects. And as the peer reviewers of the paper pointed out, that raises something of a question about whether this really does benefit males.
If the queens don’t make it back to lay their eggs, then the drones they mated with (and consequently killed) don’t get to produce any offspring at all. The authors acknowledge in their paper that this is just a proof of concept. There’s plenty more to be done to truly confirm (or reject) the idea that honey bees are battling it out biologically.
Either way, there’s definitely something fascinating going on inside bee seminal fluid. We’re just not sure exactly what yet.