Evolutionary changes in telencephalon size affect both egocentric and allocentric spatial learning in guppies

Animals can employ various spatial learning strategies to navigate through their environment, and the proficiency in specific strategies varies greatly both intraspecifically and interspecifically. Currently, the neural basis of this variation is poorly understood. Here, we tested whether variation in performance in egocentric and allocentric spatial learning strategies is related to differential investment in distinct brain regions. To do so, we used guppies (Poecilia reticulata) from artificial selection lines expressing differences in relative telencephalon size, and tested their ability to learn a spatial task, based on either egocentric (left-right) or allocentric (environmental) cues. Surprisingly, fish with larger telencephalons showed enhanced performance in both tasks, regardless of cue type, suggesting a more complicated role of the fish telencephalon in spatial learning than previously thought. Our study provides the first direct evidence that evolutionary changes in relative telencephalon size lead to corresponding shifts in spatial cognition at the within-species level. Furthermore, our results offer critical and novel insights regarding the function of the telencephalon and its role in the evolution of spatial cognition.