MICE become more timid and stressed when they smell a man, but are unaffected by the presence of a woman, researchers have discovered.
Scientists found that pheromones excreted by men make rats and mice believe they are under threat. The research "could have major implications" for laboratory tests that involve rodents, the Daily Telegraph says.
Professor Jeffrey Mogil of McGill University in Montreal, who led the study, says that scientists have long suspected that rodents might be aware of their presence, and that this might affect the results of experiments, but "this has never been directly demonstrated until now".
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The report could endanger the findings of many previous studies where the presence of scientists in the study has not been adequately accounted for or controlled. "At the very least, published papers should state the gender of the experimenter who performed the behavioural testing," Mogil says.
The report, published in Nature Methods says that "male-related stimuli" induce "robust physiological stress" in lab rats. Scientists believe that chemical signals humans produce, known as pheromones, can affect animals' behaviour.
Men are known to produce more pheromones than women, although humans don't tend to consciously notice the difference in smell.
According to researchers, mice and rats do notice that difference though, and when they smell a male nearby, behave as though they are under threat. Rodents also become anxious in the presence of other male smells, including those from dogs, guinea pigs and cats.
The animals also react to remnant pheromones on garments that have been worn by a male, though they "lose their fear" within an hour.
This last finding may offer a solution to the problem, researchers suggest. The best way to circumvent the problem may be simply to have male experimenters spend time around the rodents before beginning an experiment.