Observing the observers

The behaviour of laboratory animals often depends on the person carrying out the experiment. This could explain why many animal tests can’t be reproduced. By Ori Schipper

(From "Horizons" no. 106, September)
Image: © Keystone / Science Photo Library / Visuals Unlimited / Ken Lucas

For several years now, behavioural scientists have been investigating themselves. Before this, they rarely paid much attention to the influence of people on laboratory animals.

Indeed, since 2004, several independent investigations have suggested that female common marmosets are superior to the male of the species when it comes to solving problems, such as picking out a raisin from an empty film container. The females did not just find more varied ways of opening the container, but they also reached their goal quicker and more efficiently than the males. So are female marmosets simply cleverer?

As Judith Burkart and her team from the Anthropological Museum of the University of Zurich have shown in a recently published study, it’s probably not quite so simple. In this new test, the males were still the less efficient gender, but the researchers were able to show that the male marmosets were more often distracted from their task than the females.

Burkart’s team recorded the behaviour of 14 common marmosets that watched from their cages how four different people carried out tasks such as pouring sand from one glass into another, or placing a grasshopper – a delicacy to marmosets – under one of three black cups on the table in front of the animals’ cage.

Of the four researchers, two of them, both women, were known to the marmosets from previous experiments. But they had never before seen the other two researchers. As expected, the unknown visitors unsettled the male monkeys far more than the females. This was why the male marmosets were worse at guessing correctly which cup hid the grasshopper. Instead of watching what was happening, they were trying to get out of their test cage to return to the other group of primates.

Lack of motivation

But when the males did concentrate on their task, they were as competent as the females in finding the grasshopper. “The fact that the males perform their task less well is not because they’re less intelligent than the females. They’re just less motivated”, says Burkart.

Maria Emília Yamamoto of the University of the Rio Grande do Norte in Brazil is the behavioural scientist who was the first to demonstrate that female marmosets solve problems better than the males. But the idea that the males are less attentive is an explanation that she, too, finds compelling. Yamamoto finds the new study important because it shows “that animals behave differently when they’re under stress”. For Burkart, the well-being of the marmosets is also a primary concern. For this reason, she defined abort criteria that would enable the animals to be taken back to their group as soon as they no longer showed any interest in the experiment.

“The smaller the laboratory animal, the greater the probable influence exerted by the person carrying out the experiment; and the greater is its fear of people”, says Burkart. For example, a study by researchers in Montreal in Canada in 2014 proved that even the scent of male researchers is enough to put mice under stress – which means that they display less signs of feeling pain than when they are examined by female researchers. We have to become aware of this kind of influence, says Burkart, so that we can do our best to avoid research results being unreproducible, or even falsified.