Sexual selection for spatial-learning ability

Abstract

Sex differences in spatial learning have been thought to be universal among mammals, but their adaptive significance has been neglected. Spatial-learning skills are hypothesized to evolve in proportion to nagivational demands, and it is predicted that sex differences in spatial ability will evolve only in species where range expansion contributes differentially to the reproductive success of males and females. This prediction was tested via field studies of ranging behaviour and laboratory studies of spatial ability in two congeneric rodent species whose mating systems differ. Radiotelemetric studies showed that, in a polygynous species (meadow voles, Microtus pennsylvanicus), males expanded their ranges only during the breeding season and only when they attained full reproductive status. Females showed neither response. This suggests that range expansion was a male reproductive tactic. In contrast, a monogamous congener (prairie voles, M. ochrogaster) showed no sex differences in ranging, regardless of reproductive status. This probably reflects the relative inability of monogamous males and females to benefit from increased exposure to members of the opposite sex. When subsequently tested in a series of seven symmetrical mazes, subjects from the field studies exhibited the predicted sex-by-species patterns of spatial ability: only meadow voles showed consistent male superiority on these spatial tasks.