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Evolution of signal form
Stockholm University, Faculty of Science, Department of Zoology.
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
Identifiers
URN: urn:nbn:se:su:diva-189ISBN: 91-7265-883-5 (print)OAI: oai:DiVA.org:su-189DiVA: diva2:190706
Public defence
2004-06-09, Sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-05-19 Created: 2004-05-19Bibliographically approved
List of papers
1. Experimental evidence of receiver bias for symmetry
Open this publication in new window or tab >>Experimental evidence of receiver bias for symmetry
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
Research subject
Zoology
Identifiers
urn:nbn:se:su:diva-23209 (URN)10.1006/anbe.2001.1936 (DOI)
Note
Part of urn:nbn:se:su:diva-189Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2010-01-04Bibliographically approved
2. Receiver bias does not generate a general preference for symmetry
Open this publication in new window or tab >>Receiver bias does not generate a general preference for symmetry
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23210 (URN)
Note
Part of urn:nbn:se:su:diva-189Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2010-01-13Bibliographically approved
3. Receiver bias for colourful signals
Open this publication in new window or tab >>Receiver bias for colourful signals
2003 (English)In: Animal Behaviour, ISSN 0003-3472, Vol. 66, no 5, 965-971 p.Article in journal (Refereed) Published
Abstract [en]

Animals tend to respond more strongly to signals that are more colourful and such signals are also common in nature. This is the first study to explore experimentally the possibility that response biases arising in an animal's recognition mechanisms can explain these findings. We trained domestic fowls, Gallus gallus domesticus, to respond by pecking or not pecking to different colours displayed on a touch-sensitive computer screen. The colours changed in response to the birds' choices, which mimicked a simple evolutionary process. Discrimination training generated response biases for the colours more distinct from the nonrewarding colour. As a result the signals evolved towards distinct coloration. The biases developed in directions towards more intense and towards less intense colour, depending on the colour of the nonrewarding stimulus. The result may be applicable to all sorts of visual signals encountered during the same kind of experiences, that is, when one signal should be avoided and another should be approached

Place, publisher, year, edition, pages
Elsevier, 2003
National Category
Zoology
Research subject
Zoology
Identifiers
urn:nbn:se:su:diva-23211 (URN)10.1006/anbe.2003.2249 (DOI)
Note
Part of urn:nbn:se:su:diva-189Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2010-01-04Bibliographically approved
4. Testing the receiver bias hypothesis empirically with “virtual evolution”
Open this publication in new window or tab >>Testing the receiver bias hypothesis empirically with “virtual evolution”
2005 (English)In: Animal Behaviour, ISSN 1095-8282, Vol. 70, no 4, 865-875 p.Article in journal (Refereed) Published
Abstract [en]

Many signals found in nature seem exaggerated, for instance in size or colour. According to the receiver bias hypothesis such signal features evolve as a consequence of nonfunctional response biases in receivers. In this study we tested this hypothesis using chickens, Gallus gallus domesticus, in a virtual evolution experiment testing the potentiality of receiver bias to drive the evolution of exaggerated signals. The chickens played the role of receivers that can respond to the preferred stimuli displayed by the sender on a peck-sensitive computer screen. The preferred stimulus was kept and evolved, in the direction specified by the chicken, before being introduced to the next chicken of the successive generation. The chickens were tested on signals changing in three dimensions: length, intensity and area. In all three cases, the signals became considerably exaggerated and beyond what was required for accurate discrimination. Our results support the hypothesis that response biases emerging in discrimination tasks are sufficient to cause the evolution of signal exaggeration

Place, publisher, year, edition, pages
Elsevier, 2005
National Category
Zoology
Research subject
Zoology
Identifiers
urn:nbn:se:su:diva-23212 (URN)10.1016/j.anbehav.2005.02.008 (DOI)
Note
Part of urn:nbn:se:su:diva-189Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2010-01-22Bibliographically approved
5. Chickens prefer beautiful humans
Open this publication in new window or tab >>Chickens prefer beautiful humans
2002 (English)In: Human Nature, ISSN 1936-4776, Vol. 13, no 3, 383-389 p.Article in journal (Refereed) Published
Abstract [en]

We trained chickens to react to an average human female face but not to an average male face (or vice versa). In a subsequent test, the animals showed preferences for faces consistent with human sexual preferences (obtained from university students). This suggests that human preferences arise from general properties of nervous systems, rather than from face-specific adaptations. We discuss this result in the light of current debate on the meaning of sexual signals and suggest further tests of existing hypotheses about the origin of sexual preferences.

Place, publisher, year, edition, pages
Springer, 2002
Research subject
Zoology
Identifiers
urn:nbn:se:su:diva-23213 (URN)10.1007/s12110-002-1021-6 (DOI)
Note
Part of urn:nbn:se:su:diva-189Available from: 2004-05-19 Created: 2004-05-19 Last updated: 2010-01-04Bibliographically approved

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