Sperm dangers

Abstract

Males have been shown to have evolved a number of methods to increase their chances of mating success and amongst insects they show as many different techniques as in other groups of animals. Apart from mechanical manipulations such as mate guarding and mating plugs, biochemical compounds of male glands can influence female fitness, for example by being toxic for the female, acting as an anti-aphrodisiac or inducing oogenesis and increasing oviposition rates. For example, the mating plug contains linoleic acid which acts as an anti-aphrodisiac and reduces the female's willingness to remate. But a new study by Boris Baer at Copenhagen University and Paul Schmid-Hempel at ETH Zurich, reporting in the Proceedings of the Royal Society, series B, published online, suggests that sperm itself may influence female fitness. The hymenopterans, bees, wasps and ants, are of particular interest because of their often complex social systems. The bumble bee, Bombus terrestris, usually mates with a single male before hibernating and rearing a colony of offspring the following year. But researchers believe that multiple mating would be beneficial for the females because of a reduction in parasitism in genetically heterogeneous offspring. But the researchers looked at something potentially far more sinister for the bees: that sperm itself may influence the breeding outcome of females. The researchers looked at the direct effect of sperm by artificially inseminating females with sperm from one or more male donors. In spite of the theoretical advantage of multiple matings, the researchers found that insemination with sperm from several males led to a reduction in female hibernation success, survival and fitness. The authors are unsure of the cause of their observations, but their results are likely to add to the intrigue and skulduggery surrounding the mating systems of social insects. “Harmful male traits as detected here are not necessarily expected to evolve in social insects because males depend on females for a successful completion of a colony cycle and thus have strong convergent interest with their mates.”