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Colour patterns in warning displays
Stockholm University, Faculty of Science, Department of Zoology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In aposematism a prey species use bright colours, often combined with a black contrasting pattern, to signal unprofitability as prey to potential predators. Although there are several different hypotheses about the presence of these internally contrasting patterns, there is little experimental evidence of any beneficial effects. In this thesis I have used bird predators and artificial prey signals to investigate if the contrasting internal patterns in warning displays may have evolved to increase signal efficacy, especially regarding the speed of avoidance learning. In paper I the relative importance of colour and pattern in avoidance learning was studied. The conclusion was that birds primarily attend to colour, not pattern, when learning the discrimination, which was further supported by the results in paper II-IV, all suggesting a secondary role of patterns. In paper II I show that predators may to some degree use patterns for discrimination, if they convey important information about prey quality. The predators showed a hierarchical way of learning warning colour components, where colour is learned to a higher degree than pattern. In paper III I investigate if internal contrasting patterns promote avoidance learning by increasing conspicuousness as prey-to-background contrast does. The study did not support this idea, as the presence of internal black patterns did not improve avoidance learning on a colour matching background. In paper IV, however, I show that the presence of many internal colour boundaries resulted in faster avoidance learning on a multi-coloured background, and predator generalization favoured more internal boundaries, while there was no effect of pattern regularity. From these studies I conclude that internal pattern contrasts may function to increase the efficacy of the warning colour, its salience, and as a means for aposematic prey to be discriminated from harmful mimics. However, the major finding is the importance of colour over pattern.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2012. , 44 p.
Keyword [en]
aposematism, warning colouration, colour patterns, avoidance learning, generalization behaviour, signal design, signal evolution, conspicuousness, mimicry
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
URN: urn:nbn:se:su:diva-75576ISBN: 978-91-7447-490-9 (print)OAI: oai:DiVA.org:su-75576DiVA: diva2:517288
Public defence
2012-05-31, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At  the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 2: Manuscript; Paper 4: Manuscript Available from: 2012-05-09 Created: 2012-04-23 Last updated: 2012-05-03Bibliographically approved
List of papers
1. Domestic chicks primarily attend to colour, not pattern, when learning an aposematic coloration
Open this publication in new window or tab >>Domestic chicks primarily attend to colour, not pattern, when learning an aposematic coloration
2008 (English)In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 75, 417-423 p.Article in journal (Refereed) Published
Abstract [en]

Aposematic conspicuous coloration consists of one or a few bright colours, often in combination with a black defined internal pattern. The function of conspicuousness in aposematism has been ascribed to signal efficacy, based on experimental evidence involving prey items with uniform colour that contrast with the background. Although there are several hypotheses about the existence of internal contrasts within warning coloration, little experimental evidence has been presented. Here we used domestic chicks, Gallus gallus domesticus, to investigate the relative importance of colour and pattern in avoidance learning. Birds in two groups were first trained to discriminate between a grey positive stimulus and a cyan negative stimulus with either black dots or stripes. Pieces of mealworms, untreated and palatable or made unpalatable by soaking in quinine were used as reinforcers. Secondly, to determine what birds had attended to when learning the discrimination, colour and/or pattern, we compared how they generalized their avoidance of the ‘training stimulus’ to either a ‘colour only’ or ‘pattern only’ stimulus. The chicks learned to avoid the unpalatable prey items but showed no difference in behaviour depending on the type of pattern presented. The generalization test showed that birds avoided the novel ‘colour only’ stimulus at least as much as the ‘training stimulus’, and did not generalize their avoidance to the ‘pattern only’ stimulus. We conclude that birds do not necessarily attend to complex patterns when learning a warning signal, and domestic chicks primarily learn a bright colour rather than an equally novel conspicuous black pattern.

Keyword
colour patterns; domestic chick; Gallus gallus domesticus; generalization behaviour; internal pattern contrast; signal design; signal evolution
National Category
Ecology
Identifiers
urn:nbn:se:su:diva-13269 (URN)doi:10.1016/j.anbehav.2007.05.006 (DOI)000253632100011 ()
Available from: 2008-03-10 Created: 2008-03-10 Last updated: 2017-12-13Bibliographically approved
2. Colour and pattern similarity in mimicry - evidence for a hierarchical discriminative learning of warning colour pattern components.
Open this publication in new window or tab >>Colour and pattern similarity in mimicry - evidence for a hierarchical discriminative learning of warning colour pattern components.
(English)Manuscript (preprint) (Other academic)
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-75571 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2014-10-28Bibliographically approved
3. Importance of internal pattern contrast and contrast against the background in aposematic signals.
Open this publication in new window or tab >>Importance of internal pattern contrast and contrast against the background in aposematic signals.
2009 (English)In: Behavioral Ecology, ISSN 1045-2249, E-ISSN 1465-7279, Vol. 20, no 6, 1356-1362 p.Article in journal (Refereed) Published
Abstract [en]

Aposematic color patterns that signal prey unprofitability are suggested to work best when there is high contrast within the animal color pattern or between the animal and its background. Studies show that prey contrast against the background increases the signal efficiency. This has occasionally been extended to also explain the presence of internal patterns. We used domestic chicks, Gallus gallus domesticus, to investigate the relative importance for avoidance learning of within-prey pattern contrast and prey contrast against the background. In a series of trials, birds were first trained to avoid artificially made aposematic mealworms that were plain red or red with black stripes, and to discriminate them from palatable brown mealworms, on either a red or a brown background. Second, we investigated how the birds generalized between striped and nonstriped prey. The chicks showed faster avoidance learning when the basic color of the aposematic prey (red) contrasted with the background color (brown). However, there was no similar effect of internal pattern contrast. The generalization test showed a complete generalization between the nonstriped and the striped prey. We conclude that contrasting internal patterns do not necessarily affect predator avoidance learning the same way as shown for prey-to-background contrast in aposematic prey.

National Category
Zoology
Identifiers
urn:nbn:se:su:diva-30044 (URN)10.1093/beheco/arp141 (DOI)000271813600028 ()
Available from: 2009-09-30 Created: 2009-09-30 Last updated: 2017-12-13Bibliographically approved
4. Why do aposematic prey often have contrasting internal patterns: Evidence of benefits through predator avoidance learning and generalization.
Open this publication in new window or tab >>Why do aposematic prey often have contrasting internal patterns: Evidence of benefits through predator avoidance learning and generalization.
(English)Manuscript (preprint) (Other academic)
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-75575 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2014-10-28Bibliographically approved

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