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Experimental evidence of receiver bias for symmetry
Stockholm University, Faculty of Science, Department of Zoology.
Department of Animal Science & Animal Health, Royal Veterinary and Agricultural University.
Stockholm University, Faculty of Science, Department of Zoology.
2002 (English)In: Animal Behaviour, ISSN 0003-3472, Vol. 63, no 3, 617-621 p.Article in journal (Refereed) Published
Abstract [en]

This experiment provides the first empirical evidence that symmetry preferences may arise as a by-product of animals' recognition mechanisms. We used a computer touch screen to train domestic fowl, Gallus gallus domesticus, to discriminate between rewarding and nonrewarding stimuli. The rewarding stimuli consisted of two slightly asymmetrical crosses that were mirror images of each other. After training, all subjects preferred a novel symmetrical cross to the asymmetrical training stimuli. Naïve hens tested on the same symbols but without any previous training did not show any symmetry preferences. These results show that symmetry preferences can emerge after experiences with different stimuli that are asymmetrical but that are symmetrical when combined. A preference for symmetrical signals may thus arise as a consequence of generalization and without any link to, for instance, quality of the signal sender

Place, publisher, year, edition, pages
Elsevier , 2002. Vol. 63, no 3, 617-621 p.
Research subject
URN: urn:nbn:se:su:diva-23209DOI: 10.1006/anbe.2001.1936OAI: diva2:190701
Part of urn:nbn:se:su:diva-189Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2010-01-04Bibliographically approved
In thesis
1. Evolution of signal form
Open this publication in new window or tab >>Evolution of signal form
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Visual signals, used for communication both within and between species, vary immensely in the forms that they take. How is it that all this splendour has evolved in nature? Since it is the receiver’s preferences that cause selective pressures on signals, elucidating the mechanism behind the response of the signal receiver is vital to gain a closer understanding of the evolutionary process. In my thesis I have therefore investigated how receivers, represented by chickens, Gallus gallus domesticus, respond to different stimuli displayed on a peck-sensitive computer screen. According to the receiver bias hypothesis, animals and humans often express biases when responding to certain stimuli. These biases develop as by-products of how the recognition mechanism categorises and discriminates between stimuli. Since biases are generated from general stimulus processing mechanisms, they occur irrespective of species and type of signal, and it is often possible to predict the direction and intensity of the biases. One of the results from the experiments in my thesis demonstrates that similar experience in different species may generate similar biases. By giving chickens at least some of the experience of human faces as humans presumably have, the chickens subsequently expressed preferences for the same faces as a group of human subjects. Another kind of experience generated a bias for symmetry. This bias developed in the context of training chickens to recognise two mirror images of an asymmetrical stimulus. Untrained chickens and chickens trained on only one of the mirror images expressed no symmetry preferences. The bias produced by the training regime was for a specific symmetrical stimulus which had a strong resemblance to the familiar asymmetrical exemplar, rather than a general preference for symmetry. A further kind of experience, training chickens to respond to some stimuli but not to others, generated a receiver bias for exaggerated stimuli, whereas chickens trained on reversed stimuli developed a bias for less exaggerated stimuli. To investigate the potential of this bias to drive the evolution of signals towards exaggerated forms, a simplified evolutionary process was mimicked. The stimuli variants rejected by the chickens were eliminated, whereas the selected forms were kept and evolved prior to the subsequent display. As a result, signals evolved into exaggerated forms in all tested stimulus dimensions: length, intensity and area, despite the inclusion of a cost to the sender for using increasingly exaggerated signals. The bias was especially strong and persistent for stimuli varying along the intensity dimension where it remained despite extensive training. All the results in my thesis may be predicted by the receiver bias hypothesis. This implies that biases, developed due to stimuli experience, may be significant mechanisms driving the evolution of signal form.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen, 2004. 23 p.
National Category
Biological Sciences
urn:nbn:se:su:diva-189 (URN)91-7265-883-5 (ISBN)
Public defence
2004-06-09, Sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 10:00
Available from: 2004-05-19 Created: 2004-05-19Bibliographically approved

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