| 1. |
- Aronsson, Marianne, 1978-, et al.
(författare)
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Colour and pattern similarity in mimicry : evidence for a hierarchical discriminative learning of different components
- 2012
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 84:4, s. 881-887
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Tidskriftsartikel (refereegranskat)abstract
- Many aposematic species combine their bright colours with a black pattern that produces internal contrasts. Studies have shown that birds often pay attention to some parts of a signalling pattern and disregard others, which could be of importance in Batesian mimicry, where a palatable species copies the visual appearance of a distasteful model in order to deceive predators. We used domestic chicks, Gallus gallus domesticus, and artificial prey signals to investigate whether predators use different warning colour components for discrimination depending on the degree of information about prey quality they convey. This study supports earlier findings of the importance of colour for discrimination among prey but also provides evidence that other less associable signal properties such as internal patterning, when holding valuable discriminatory information, can be used to assess prey quality in a hierarchical manner. The results also suggest that, in certain circumstances, the presence of a palatable mimic can have positive effects on learning, resulting in 'super-Mullerian' effects. We propose that the degree of selection for perfect mimicry may be dependent on the proportion of well-educated predators in the population.
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| 2. |
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| 3. |
- Aronsson, Marianne, 1978-
(författare)
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Colour patterns in warning displays
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Aronsson, Marianne, et al.
(författare)
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Domestic chicks primarily attend to colour, not pattern, when learning an aposematic coloration
- 2008
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 75, s. 417-423
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Aronsson, Marianne, et al.
(författare)
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Evidence of signaling benefits to contrasting internal color boundaries in warning coloration
- 2013
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Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 24:2, s. 349-354
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that the common existence of regular patterning in aposematic prey animals makes them stand out from the background, improving detection and recognition. Another suggestion is that internal patterns could have a similar positive effect on predator aversion learning as prey-to-background contrast. We used wild caught blue tits (Cyanistes caeruleus) and artificial prey signals to investigate if internal color boundaries, pattern regularity and pattern symmetry affect learning. Birds in different treatments were trained, on a complex background, to discriminate between artificial prey with different nonrewarding color stimuli with a black pattern and rewarding stimuli without a black pattern, followed by a generalization test. This study provides evidence of learning benefits to internally contrasting patterns as the striped prey stimuli were learned faster than the unstriped. Also, we found no beneficial effects of pattern regularity and symmetry. The birds generalized more between prey with different black patterns than to the profitable prey, suggesting that color is of foremost importance. The generalization test also showed a greater avoidance of striped than that of unstriped prey, suggesting some attention on patterns. Thus, internal patterning may affect signal salience and in some circumstances benefit prey due to both a faster avoidance learning and generalization behavior.
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| 6. |
- Aronsson, Marianne, et al.
(författare)
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Importance of internal pattern contrast and contrast against the background in aposematic signals.
- 2009
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Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 20:6, s. 1356-1362
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
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| 8. |
- Balogh, Alexandra C.V., et al.
(författare)
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Feature theory and the two-step hypothesis of Müllerian mimicry evolution
- 2010
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 64:3, s. 810-822
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Tidskriftsartikel (refereegranskat)abstract
- The two-step hypothesis of Müllerian mimicry evolution states that mimicry starts with a major mutational leap between adaptive peaks, followed by gradual fine-tuning. The hypothesis was suggested to solve the problem of apostatic selection producing a valley between adaptive peaks, and appears reasonable for a one-dimensional phenotype. Extending the hypothesis to the realistic scenario of multidimensional phenotypes controlled by multiple genetic loci can be problematic, because it is unlikely that major mutational leaps occur simultaneously in several traits. Here we consider the implications of predator psychology on the evolutionary process. According to feature theory, single prey traits may be used by predators as features to classify prey into discrete categories. A mutational leap in such a trait could initiate mimicry evolution. We conducted individual-based evolutionary simulations in which virtual predators both categorize prey according to features and generalize over total appearances. We found that an initial mutational leap towards feature similarity in one dimension facilitates mimicry evolution of multidimensional traits. We suggest that feature-based predator categorization together with predator generalization over total appearances solves the problem of applying the two-step hypothesis to complex phenotypes, and provides a basis for a theory of the evolution of mimicry rings.
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| 9. |
- Balogh, Alexandra C.V., et al.
(författare)
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Learning and the mimicry spectrum: from quasi-Bates to super-Müller
- 2008
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472. ; 76:5, s. 1591-1599
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Tidskriftsartikel (refereegranskat)abstract
- Müllerian mimicry is the mutualistic resemblance between two defended species, while Batesian mimicry is the parasitic resemblance between a palatable species (the mimic) and an unpalatable one (the model). These two kinds of mimicry are traditionally seen as extreme ends of a mimicry spectrum. For the range in between, it has been suggested that mimetic relations between unequally defended species could be parasitic, and this phenomenon has been referred to as quasi-Batesian mimicry. Where a mimetic relation is placed along the mimicry spectrum depends on the assumptions made about predator learning. In this work, we use a variant of the Rescorla-Wagner learning model for virtual predators to analyse the different possible components of the mimicry spectrum. Our model entails that the rate of associative learning is influenced by variation in the stimuli to be learned. Variable stimuli, i.e. unequal defences, can increase the predator learning rate and thus lead to an increased level of mutualism in a mimetic relation. In our analysis, we make use of the concepts of super-Müllerian mimicry, where the benefit of mimicry is even greater than in traditional Müllerian mimicry, and quasi-Müllerian mimicry, where mimicry by a palatable mimic is mutualistic. We suggest that these types of mimicry should be included in the mimicry spectrum along with Müllerian, Batesian and quasi-Batesian mimicry.
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| 10. |
- Bohlin, Titti, et al.
(författare)
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The detectability of the colour pattern in the aposematic firebug, Pyrrhocoris apterus : an image-based experiment with human 'predators'
- 2012
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 105:4, s. 806-816
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Tidskriftsartikel (refereegranskat)abstract
- Crypsis and aposematism are often regarded as two opposite protective strategies. However, there is large variation in prey appearance within both strategies. In this article, we investigated the conspicuousness of the aposematic red-and-black firebug, Pyrrhocoris apterus, by presenting images of natural and digitally manipulated phenotypes in their natural habitat on a computer screen to human predators, and comparing the detection times. We asked whether the natural colour pattern can be made more or less conspicuous by rearranging the spatial distribution of colour elements. Hence, we created a phenotype in which the black colour elements were moved to the body outline to test for a possible disruptive effect. In the black and red manipulations, we removed one of the two colours, creating two uniform colour variants. We found that some of our manipulations increased, but none reduced, the detection time significantly; this indicates that the naturally coloured firebug is highly conspicuous. The detection time varied among backgrounds and there was a significant relationship between detection time and chromatic similarity between the bug and the background for the natural and black phenotypes. Although background colour composition has an important effect on the signal, we argue that the coloration of P. apterus has evolved for high conspicuousness.
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