Female lab mice behave very differently when placed outdoors

The research was published in the journal BMC Biology, took lab rats and housed them in large outdoor enclosures. The researchers found that male behavior was essentially the same as that of genetically wild mice, but females displayed radically different behavior.

“Given how much biological research is done on one strain of laboratory mice, it’s important that we treat them as living organisms,” said senior author Michael Sheehan, associate professor of neurobiology and behavior.

“These findings have broad implications for all biomedical studies using lab rats but especially those that use rats as models of social behavior,” Sheehan said. At the same time, the study’s insights don’t necessarily invalidate previous research, he said.

In the study, the researchers compared the most studied lab mouse strain — the genetically identical C57BL/6J — to house mice whose ancestors were captured in upstate New York and bred so Each individual is genetically distinct.

In each simulation trial, 10 male and 10 female C57 mice were housed in a 5,000-square-foot enclosure for a 10-day trial and compared to control trials with genetically wild-type mice.

After collecting 9 million data points, the researchers found that male C57 mice and wild-type mice behaved similarly when placed outdoors. In the laboratory, mice are kept in shoebox-sized cages with other mice. When space is limited, they form a hierarchy where a dominant male rules the territory. But when placed outside, males will establish their territories.

“That’s what people have reported from wild rat populations,” Sheehan said: “When you give them space, a fundamental feature of their social structure is that they will form territories — a behavior that We can’t study in a lab,” Sheehan said. .

Like males, when wild females have enough space, they avoid each other as they compete for food or nesting resources. They differ from males in that multiple females sometimes share space together, and when they do it is with sisters. On the other hand, the lab ladies in the spacious walls, often go everywhere, every night.

“Lab females also show no preferential interactions with their sisters, they basically randomly interact with every other female,” Sheehan said.

Because all lab mice are genetically identical, it is difficult to know whether there are behavioral differences between wild and lab mice because it is difficult for individual lab mice to tell each other apart or because of their social There is a more fundamental difference in structure, Sheehan said.

The research also revealed that when given plenty of space to themselves, mice choose to spend more than half of their time alone. In the lab, mice spend their entire lives in small cages with four other mice. Sheehan said the findings are consistent with studies that have examined social isolation as a predictor of health.

The researchers also found that these results were highly repeatable between trials. Despite all the complexities of social interactions in large groups, the two genotypes reliably evolved different social structures given the same initial starting conditions.

“This opens the door to experimentally manipulating the demographic or genetic makeup of free-living populations to ask questions about how realistic natural social environments shape individuals’ health, fitness, and life outcomes,” Sheehan said. affects.”

The study was funded by the US Department of Agriculture and the National Institutes of Health.