We can learn a lot from studying the social life of rats

Besides white mice, one of the most widely used experimental animals is a species of rat, the white Rattus norvegicus. The main reason for this is that the biological properties of rats show a strong affinity with human cells and organs, with nearly 90% of their genes being similar. Although much research has been done on rat behaviour, no long-term, digitally automated studies have been carried out to date that compare and contrast both group and individual traits.

This important, gap-filling research has been carried out by the staff of the Department of Biological Physics at ELTE, in collaboration with Enikő Kubinyi of the Department of Ethology, and published in the Nature portfolio journal Scientific Reports. The research was initiated under a European ERC Advanced Grant awarded by Tamás Vicsek, Professor Emeritus of the Institute of Physics, and the resulting huge data set took years to process. However, the resulting publication is a unique work in the field because of the huge amount of data, the design of the experiments and the wide range of evaluation methods.

A central aim of the research was to gain insight into the hierarchical power relations within rat groups. To do this, several complex criteria had to be met: the ability to identify individuals continuously (this was done by colour coding), to make the animals' living quarters as welcoming as possible, to vary the day and night periods, and in general to automatically control the entire experiment, which lasted about 10 months, including, for example, the feeding and watering of the animals.

The right panel of the figure above shows the frequency averaged over a long period of time of the location of two animals (a3 and β1), where the intensity of the red and green colours indicate the frequency of the animals' location. The yellow colour shows the locations where both animals turn around occasionally (e.g. at the feeder). This simple figure also shows how differently the animals behave, even in such a simply composed space.

By the end of the experiments, the high-resolution camera, which can 'see' in the dark at night, had provided many terabytes of information, which had to be analysed by developing a special algorithm to digitally track the movements of the colour-coded rats. An important element of the experiments was that the initial groups of 7 rats (there were 4 groups) were sometimes rearranged in several variations to track how the behaviour of a particular animal or group depended on the composition of the group and how it changed.

Throughout the complex and long-running experiments, the staff of the Department of Biophysics have done a tremendous amount of work, developing a number of innovative solutions that have yielded many results beyond the main research questions. Máté Nagy played a key role in the design and implementation, while Gábor Vásárhelyi developed innovative software solutions for image data processing.

A series of recordings from the experiment can be seen in the video below: here you can see a week of nights of the 4 small colonies in fast motion (during the day the rats are inactive, mostly sleeping, hiding, or huddling together).

The evaluation of the automated observations consisted mainly of analysing the rats' movements, which led to valuable new insights. In similar studies, the movements of animals can be used to infer dominance and subordination relationships between them, and by subjecting individuals to standard behavioural tests, we can get an idea of their different traits (risk-taking, indecisive, etc.).

At the start of the experiment, the researchers hypothesised the emergence of a behavioural structure that would, over time, correspond to well-defined hierarchical power relations that would emerge in a similar way in different groups. They also made use of the obvious hypothesis that the individual personality traits of rats fundamentally determine their behaviour within the group. However, analysis of the data revealed that the reality was much more complex than they had imagined.

In some groups, hierarchies were established, with many "clashes", while in other groups, rats coexisted more peacefully. When members of a hierarchical group were confronted with a non-hierarchical group, the result was either a hierarchical group or a peaceful group. Another unexpected result was that relatively little correlation could be found between the 'personality traits' identified in classical personality and social tests - used in drug or behavioural research - and real-life behaviour within groups.

This suggests that the social life of rats, their socialisation and its relationship with their personality traits, is much more complex than to be interpreted by any simple mechanism. Since the social behaviour of rat groups appears to be paradoxical when the effects of certain psychotics are studied in animal experiments, researchers caution that conclusions should be drawn with extreme caution.

Publication details: M. Nagy, J.D. Davidson, G. Vásárhelyi, D. Ábel, E. Kubinyi, A. El Hady & T. Vicsek (2024) Long-term tracking of social structure in groups of rats. *Scientific Reports*, (2024) 14:22857, https://www.nature.com/articles/s41598-024-72437-5

Photo credit: The Department of Biological Physics at ELTE