Mating makes queen bees blind

In nature, when a female mates with multiple males, this introduces competition between the sperm and a conflict between the sexes: the males “want” to transmit their genes to the greatest number of offspring, while the females “want” to maximise the genetic diversity - and hence fitness - of their brood. And among insects, a range of tricks and techniques are used to load the odds in favour of one sex over the other. But honey bees have taken this to a whole new level, as Joanito Liberti has been finding…

Joanito - When a honeybee queen mates, chemicals found in the seminal fluid of males affect the vision of the queen. This is potentially a manipulation that the males are imposing on the female to reduce the possibility of mating with other males, because honeybee queens have to fly out of their hives and find congregations where the males are waiting for her to mate. So the vision is very important!

Chris - Tell us how the story began then? How did you actually embark on this journey?

Joanito - During my PhD, I was interested in the effects of the reproductive secretions of the sexes, and how they regulate the conflicts and cooperation within and between the sexes. As part of these, we looked at what are the specific effects of seminal fluid on the female vision. So we set out to do an experiment in which we artificially inseminated the queens, and specifically looked at what happened in the brain after these inseminations.

Chris - When a bee actually mates, tell us a bit about that process, about how the queen finds a mate, or mates, and what happens during that?

Joanito - All social insects have a very special mating biology, in which the queens fly out to mate only on a single day, early in their adult life. They mate with males in the air and then they come back to their hive or they find they have found a new nest - after that they will never ever have sex in their life. Sometimes the life of a social insect can extend for one or two decades. And they use the sperm that they collected on the single day to fertilise all the eggs throughout their lifetimes. So they have to keep this sperm alive for many, many years. Now, the honeybee is special in all of this because she conducts potentially multiple mating flights over a few days, and that's where the potential for sexual conflict arises. Because all the copulations happen one after the other, because she flies on multiple consecutive days, the sperm that have already inseminated the queen may not want the queen to fly out again and dilute the chances that this sperm will actually end up being stored.

Chris - How did you hit on the visual system as being the key to this then. How did you realise that that was what was potentially going on?

Joanito - I analysed gene expression data, where we compared queens that were inseminated with a saline solution - as a control - and other queens were given seminal fluid. What I realised is that there were some genes related to vision that were different in their expression.

Chris - How did you pursue that then, and how did you resolve that difference and work out that it is something in the seminal fluid that then affects the visual system of the female and how do you know it actually affects the visual system? In other words renders her to be less visionally able?

Joanito - So from these gene expression data, we predicted that there would be effects on vision because genes were altered. But, of course, gene expression is not enough to demonstrate that something is actually happening to the vision. So we performed another experiment where we put little electrodes on top of the eyes of the queens and then we stimulated the vision with flashes of light and recorded the electrical signal and basically found that queens that had received seminal fluid from male could respond less to stimuli which showed that something was truly happening to the visual perception of queens.

Chris - How do you know though that that change translates into a reduction in inclination on the part of that queen to go mate with more males?

Joanito - We could measure the cost of these effects, right; we put little tags on the queens and then monitor their flight activity after we again used the same artificial insemination. The queens that had received seminal fluid compared to the queens that only received a saline solution, were more likely to get lost. So we assume that impaired visual perception will reduce the possibility of the queen to actually find throne congregations and mate with them in the air.

Chris - Do you know yet what the chemicals are in the seminal fluid that are doing this, or do you just know that seminal fluid as a whole does this?

Joanito - We know what the composition of the seminal fluid of the honeybee is. So we know what proteins are present in the seminal fluid, but we do not know yet which ones are responsible. And it will be exciting in the future to try to identify the specific compounds mediating these effects.