Sexual Imprinting in Zebra Finch Males:A Differential Effect of Successive and Simultaneous Experience With Two Colour Morphs

Recent developments in theories of sexual imprinting have emphasized that sexual imprinting may lead to a preference for partners that are slightly different from the stimuli an animal has originally been exposed to. Two mechanisms have been proposed to account for this phenomenon. 1. Separate representation model: This model assumes that as a result of imprinting an internal representation is formed of each individual which a bird experiences during early life. The imprinting process is thought to reduce the responsiveness to novel individuals, whereas at the same time a habituation process would have the effect that individuals resembling these representations too closely are refuted. 2. Mixed representation model: Young birds combine information about different individuals into one internal representation. As a consequence the later preference deviates from the original imprinting stimuli.There is evidence that zebra finch males use a number of stimuli for sexual imprinting, but it is unclear whether and how the way of exposure affects the internal representation. This was examined in zebra finch males that had either successive or simultaneous experience with two different colour morphs of the zebra finch. Each type of experience results in different effects on later preference. Successive experience leads to a preference for both colour morphs. That is, in multiple-stimuli tests with the imprinting morphs and intermediate colour morphs, males with successive experience showed a preference for both inprinting morphs. Simultaneous experience with both morphs does not lead to a double preference but to a preference for the colour morph of the mother. Comparison with the control groups revealed that males raised by mixed pairs had learned to suppress sexual responses to individuals of their father's morph. This implies that zebra finch males learn to discriminate male versus female conspecifics on morphological features during the time course of sexual imprinting. The results of neither type of exposure gave evidence for the formation of mixed representations, as was indicated by the lack of sexual interest which double imprinted males showed for intermediates between both morphs. It is suggested that the way information is stored during imprinting can better be viewed within the context of distributed representation models.