Date Published: March 17, 2017
Publisher: Public Library of Science
Author(s): Anders Ågmo, Eelke M. S. Snoeren, Juan M. Dominguez.
Intrasexual competition is an important element of natural selection in which the most attractive conspecific has a considerable reproductive advantage over the others. The conspecifics that are approached first often become the preferred mate partners, and could thus from a biological perspective have a reproductive advantage. This underlines the importance of the initial approach and raises the question of what induces this approach, or what makes a conspecific attractive. Identification of the sensory modalities crucial for the activation of approach is necessary for elucidating the central nervous processes involved in the activation of sexual motivation and eventually copulatory behavior. The initial approach to a potential mate depends on distant stimuli in the modalities of audition, olfaction, vision, and other undefined characteristics. This study investigated the role of the different modalities and the combination of these modalities in the sexual incentive value of a female rat. This study provides evidence that the presence of a single-sensory stimulus with one modality (olfaction, vision, or ‘others’, but not audition) is sufficient to attenuate the preference for a social contact with a male rat. However, a multisensory stimulus of multiple modalities is necessary to induce preference for the stimulus over social contact to a level of an intact receptive female. The initial approach behavior, therefore, seems to be induced by the combination of at least two modalities among which olfaction is crucial. This suggests that there is a cooperative function for the different modalities in the induction of approach behavior of a potential mate.
Natural selection is one of the key components of evolution theory. Charles Darwin described it as the differential survival and reproduction of individuals due to differences in phenotype. In order to have reproductive success, individuals must be more attractive within a population or preferring more attractive partners to produce offspring. While intrasexual competition for access to a mate is believed to be common among mammals, competition is unusual in wild rats [1, 2]. Though, even if intrasexual competition were unusual, rats still have to make a choice of partner with whom to initiate copulatory activity whenever there is more than one potential partner available.
This study provides evidence that the presentation of one modality can add incentive value to another modality when presented as a multisensory stimulus. A single-sensory stimulus is enough to attenuate the preference for a social contact (except for an auditory stimulus), while the addition of a second modality renders the receptive female more attractive than the social stimulus to a level similar to an intact receptive female. The condition is, however, that the multisensory stimulus contains olfaction in combination with vision or ‘others’ (and not audition in terms of USVs). Adding a third modality, on the other hand, does not change the incentive value of a multisensory stimulus of two modalities.