Seedy world

By Matt Walker MALE flour beetles can impregnate females they have never even met by getting another male to do the dirty work for them, biologists have found. Mating by proxy is unheard of in other animals, and might be a cunning evolutionary strategy. Matt Gage of Liverpool University and his colleagues were studying the mating behaviour of the flour beetle Tribolium castaneum to try to find ways of keeping their numbers down. The beetles are a major pest in stored cereal grain, and are becoming resistant to the insecticide malathion. The grain-gobbling insects have complicated sex lives. They crowd together in bundles of over 100 individuals and are very promiscuous. Males can mate with three females in a few minutes. The researchers watched as flour beetles mated several times with either malathion-resistant beetles or with a strain susceptible to the insecticide. Whether or not the offspring had the single gene that confers resistance revealed the father’s identity. Males increase their chances of fertilisation by using their spiny genitalia to scrape out a previous suitor’s sperm, the team found. Two-thirds of the time, the second male to mate, rather than the first, wins the battle to fertilise the female. But the sperm ousted by the second male seem to have developed a cunning counter-measure. They stick to a male’s genitalia, and if he mates again within a short period, they can survive the journey to a second female. In this way, around one in eight females are fertilised by males they have never met. “It seems unique. Mating by proxy is not known in any other organism,” says Gage. He believes that sperm have evolved this trick to counter the males’ ability to scoop them out of the females’ reproductive tract. By sticking to the genitalia and remaining viable, the sperm get a second chance. “We assume that it’s adaptive. Every male is trying to get the upper hand,” says Gage. The findings will appear later this year in Proceedings of the Royal Society B. “The results are bizarre and striking,” says Scott Pitnick, an evolutionary biologist at Syracuse University in New York State. However, he points out that the evolutionary “strategy” may simply be chance. The beetles’ sperm may survive no longer than those of other species, and the effect may simply occur because the animals mate again so quickly. “The jury’s out in terms of what this means for evolutionary thinking,” Pitnick says. Gage says the beetles’ behaviour could explain, however, why the pests are so hard to control. “Translocation of sperm results in an extra degree of gene mixing, which could in turn help the spread of malathion resistance,
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