Three-spined sticklebacks show dimension-specific preferences for shelter

Shelter is an important resource, serving as protection from rivals, predators and environmental stressors. The physical dimensions of a potential shelter are an important factor that can affect decisions about potential shelter options. Animals must select a shelter that they can fit into and use as a refuge, but beyond that, do they show fine-scale preferences based on shelter dimensions? This question has been actively studied for species whose shelter use is closely connected to their life cycles, such as obligate shell dwellers and nest-inhabiting species. However, preferences and decision making for temporary shelters has received less attention. We tested whether three-spined sticklebacks, Gasterosteus aculeatus, a common laboratory model, exhibit preferences in shelter use (actively entering and spending time within a shelter) between shelters with different dimensions. We used PVC tubes of different dimensions as shelters and conducted a simultaneous choice assay where individual fish were presented with each of three tubes available for use as shelter. The fish showed a clear preference, using larger diameter shelters more frequently than either of the other two options. There was no difference in the number of nonsheltering visits fish made or time to enter a shelter across tube sizes, which suggests an active selection by the fish rather than passive bias. There was no difference in duration of time spent within a shelter, suggesting that despite these preferences, actual benefit derived by the fish may be decoupled from the shelter dimensions. Our results offer opportunities for future research that addresses longer term questions in both behavioural ecology and welfare. What drives the preference for larger diameter tubes, and are there are long-term benefits to shelter with preferred dimensions? Certainly, our results suggest that housing sticklebacks with larger diameter shelters may be a simple and convenient means to improve welfare.