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Stimulus Salience as an Explanation for Imperfect Mimicry
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0002-5884-8894
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0002-3445-3759
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-6319-009X
Stockholm University, Faculty of Science, Department of Zoology.
2014 (English)In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 24, no 9, 965-969 p.Article in journal (Refereed) Published
Abstract [en]

The theory of mimicry explains how a mimic species gains advantage by resembling a model species [1-3]. Selection for increased mimic-model similarity should then result in accurate mimicry, yet there are many surprising examples of poor mimicry in the natural world [4-8]. The existence of imperfect mimics remains a major unsolved conundrum. We propose and experimentally test a novel explanation of the phenomenon. We argue that predators perceive prey as having several traits, but that the traits differ in their importance for learning. When predators learn to discriminate prey, high-salience traits overshadow other traits, leaving them under little or no selection for similarity, and allow imperfect mimicry to succeed. We tested this idea experimentally, using blue tits as predators and artificial prey with three prominent traits: color, pattern, and shape. We found that otherwise imperfect color mimics were avoided about as much as perfect mimics, whereas pattern and shape mimics did not gain from their similarity to the model. All traits could separately be perceived and learned by the predators, but the color trait was learned at a higher rate, implying that it had higher salience. We conclude that difference in salience between components of prey appearance is of major importance in explaining imperfect mimicry.

Place, publisher, year, edition, pages
2014. Vol. 24, no 9, 965-969 p.
National Category
Biological Sciences
Research subject
Ethology
Identifiers
URN: urn:nbn:se:su:diva-106441DOI: 10.1016/j.cub.2014.02.061ISI: 000335542300032OAI: oai:DiVA.org:su-106441DiVA: diva2:736206
Note

AuthorCount:4;

Available from: 2014-08-05 Created: 2014-08-04 Last updated: 2017-11-08Bibliographically approved
In thesis
1. Evolution of Mimicry and Aposematism Explained: Salient Traits and Predator Psychology
Open this publication in new window or tab >>Evolution of Mimicry and Aposematism Explained: Salient Traits and Predator Psychology
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aposematic species have evolved conspicuous warning signals, such as bright colors and striking patterns, to deter predators. Some edible and harmless species take advantage of this deterrent effect by mimicking their appearance. Mimicry is a great example of how natural selection produces remarkable adaptations. However, while some species evolve a very close similarity to their models to effectively avoid attacks, others are successful in doing so despite an incomplete similarity, i.e. imperfect mimicry. In some cases, it is surprising how such a crude disguise can fool predators. Why and how imperfect mimicry can persist has been much discussed and considered as a problem for the theory of natural selection. It is therefore of great interest to understand what makes it possible.

Predator psychology is an important factor in the evolution of aposematism and mimicry. In the past decades it has been suggested that certain components of prey appearance are more important to predators than others during prey assessment. We developed this idea by incorporating concepts from associative learning, and presented a new approach to explain imperfect mimicry. Our general hypothesis is that prey traits have different salience to predators. Certain traits are perceived as highly salient and are thus used primarily in the discrimination and generalization of prey, while traits with low salience are overshadowed and not used in the assessment. The salience of a trait can depend on how conspicuous or discriminable it is in the particular context, and can vary due to for example previous predator experience.

We tested our ideas with wild blue tits and domestic chickens as predators, and artificial and semi-natural prey stimuli. In paper I we found that the trait that was perceived as most salient (color) was the one used to discriminate and generalize between prey. Mimics of that specific trait were highly avoided, despite differences in the other traits. We also found that salience is relative and context dependent (paper II). In a context where two traits were perceived as similarly salient, mimicry of a single trait offered intermediate protection, while mimicry of both offered high protection. In another context, the traits were perceived differently salient, and mimicry of one trait was enough for high protection. In paper III we tested a proposed scenario for the initiation of mimicry evolution in the edible butterfly mimic Papilio polyxenes asterius to its noxious model Battus philenor. The results showed that a partial similarity with the model in the salient black wing color offered intermediate protection from attacks, despite a general dissimilarity.

This thesis investigates the major questions of imperfect mimicry: the initial step of mimicry evolution, the persistence of imperfect mimicry, and variation in mimic-model similarity. We conclude that mimicry evolution can begin in a non-mimetic species that acquires similarity to a model species in a high-salience trait. When multiple traits have similar salience, multi-trait mimicry is needed for higher protection. Mimicry can remain imperfect if the differences are in traits with low salience, and therefore under low or no selection pressure to change.

To complete the picture, we showed that predators can have a biased generalization toward a more pronounced version of a salient trait (paper IV). The evolution of aposematism could therefore be explained by gradual enhancement of salient traits.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2017. 57 p.
Keyword
imperfect mimicry, mimicry evolution, predator learning, discrimination, generalization, salience, overshadowing, aposematism, warning signal evolution, generalization bias, peak shift
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-148488 (URN)978-91-7797-037-8 (ISBN)978-91-7797-038-5 (ISBN)
Public defence
2017-12-01, Vivi Täckholmssalen, NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 4: Manuscript.

Available from: 2017-11-08 Created: 2017-10-26 Last updated: 2017-11-08Bibliographically approved

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