The crowd roars. A triumphant gladiator stands over the body of his enemy and is about to slay his second assailant.
The women in the crowd give him the sign - with their thumbs down, they let him know that they want him to kill again.
For most of us, this is a description of a painting by Jean-Léon Gérôme depicting a gruesome spectacle. Entitled Thumbs Down, it was painted in 1872. But for QEII Fellow Dr Boris Baer from the Collaborative Initiative for Bee Research (CIBER) , the scene is used as a possible analogy to his latest research, recently published in Science.
With colleagues at The University of Copenhagen, Dr Baer studied the seminal fluid of two species of bees - the multiple-mating honeybee and the single-mating bumble bee - and three species of Panamanian leaf-cutting ants, of which two are multiple-mating.
The researchers found first evidence that it is seminal fluid - rather than sperm - that may harm other males' sperm in the female, until a substance in the female can prevent further sperm damage.
"The painting is a good depiction of what we currently believe is happening in reproduction in multiple-mating insects, but we need further research to finally prove it," Dr Baer said. "The arena is the females' sexual tract, the gladiators are the ejaculates and the females have the power. Our findings now provide first empirical support for this idea, and our work at UWA has started to identify those components within seminal fluid that are responsible for the effects," Dr Baer said.
While there have been recent dramatic decreases in the quality of human sperm, the process of natural selection maintains very high sperm variability in social insect males because the sperm will only be used for fertilisation long after the males' death, which occurs during or shortly after mating.
"These social insects are amazingly efficient at keeping sperm alive but it is still too early to extrapolate any of our results into human fertility," Dr Baer said.
"The queens of ants and bees mate only once, as young virgins, and store the sperm of their mates for the rest of their long lives in a single specialised organ, the spermatheca," Dr Baer said. "In the Panamanian leaf cutting ants studied here, queens can initially store close to half a billion sperm and use them prudently over 20 or more years to sire tens of millions of offspring."
Picture: Thumbs Down by Jean-Léon Gérôme (Wikipedia)