Mate preference in female weakly electric fish, Apteronotus leptorhynchus

This study explores the morphology and electrical behavior of breeding weakly electric fish. Wave-type electric fish communicate by means of a continuous oscillatory electric signal produced by an electric organ. The electric organ discharges at frequencies which are sexually dimorphic in many species of electric fish. This dimorphism is thought to be attributed to female mate choice, although to date, there is no evidence for mate choice or intrasexual competition to have driven the evolution of this signaling dimorphism in wave-type electric fish. Here, I have tracked changes in body shape and electric organ discharge (EOD) frequency of A. leptorhynchus throughout a breeding conditioning period. I find that only females alter the shape of their bodies, presumably to account for increasing egg mass, during the breeding conditioning period. Throughout this period, both females and males do not alter their EOD frequencies significantly. Gravid females were used in an unforced preference test, where they were presented with two live, male A. leptorhynchus. Female preference was indicated by a passage of the female into one of the two male compartments. I find that females show a preference for higher EOD frequency males, while no preference is shown for longer, heavier or larger-amplitude males. Further investigations are needed to dissociate the role of EOD frequency from potentially correlated male traits, such as rate and type of modulations of EOD frequency. The finding of this study that female A. leptorhynchus prefer males of higher EOD frequency establishes wave-type weakly electric fish as a promising model system for the study of the evolution and the sensory mechanisms of female choice.