No sex-specific effects of artificial selection for relative telencephalon size in detour learning and spatial discrimination in guppies (Poecilia reticulata)

Over recent decades, substantial research has focused on fish cognitive evolution to increase our understanding of the evolution of the enormous diversity of cognitive abilities that exists in fishes. One important but understudied aspect of cognitive evolution is sexual dimorphism in cognitive abilities. Sex-specific variation in brain region morphology has been proposed to be an important mechanism in this context. However, it is also common to find sex-specific variation in behaviour and cognition without associated differences in brain morphology among the sexes. The telencephalon is the major cognitive center in the vertebrate brain and variation in telencephalon size has been associated with variation in cognition. Here we utilize recently developed guppy artificial selection lines with ca 10% differences in relative telencephalon size to investigate if similar responses to selection of the size of this region may affect cognitive abilities differently in males and females. We compared two ecologically relevant aspects of cognition, detour learning and binary spatial discrimination. We tested the significance of the interaction between telencephalon size and sex, and found no sex-specific effects of evolutionary increases in telencephalon size in the cognitive abilities tested. This study indicates that no clear cognitive sex-specific responses occur in response to rapid selection on telencephalon size. We suggest that future research on sexual dimorphism in cognitive abilities in fish could examine various cognitive tests and telencephalic subregions to gain a more comprehensive understanding of their evolution.