1
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Barrone J, Vidal MC, Stevenson R. Sphingid caterpillars conspicuous patches do not function as distractive marks or warning against predators. Ecol Evol 2023; 13:e10334. [PMID: 37492454 PMCID: PMC10363802 DOI: 10.1002/ece3.10334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2023] [Revised: 07/01/2023] [Accepted: 07/05/2023] [Indexed: 07/27/2023] Open
Abstract
To avoid predation by visual predators, caterpillars can be cryptic to decrease detectability or aposematic to warn predators of potential unpalatability. However, for some species, it is not clear if conspicuous patches are selected to avoid predation. For example, Pandora sphinx (Eumorpha pandorus, Lepidoptera: Sphingidae) caterpillars are assumed to be palatable and have both cryptic (green, brown) and conspicuous (orange, red) color morphs. Five lateral, off-white to yellow patches on either side may serve as a warning for predators or to draw attention away from the caterpillar's form to function as distractive marks. We conducted a field study in three temperate fragmented forests in Massachusetts to investigate the potential utility of E. pandorus coloration and conspicuous patches. Using four plasticine caterpillar prey model treatments, green and red with and without lateral conspicuous patches, we tested the effects of color, patch patterning, and seasonality on attack rates by a variety of taxa. We found that 43% of the prey models (n = 964) had bite marks by an array of predators including arthropods (67.5%), birds (18.2%), rodents (11.5%), and large mammals (2.8%). Arthropods as dominant predators align with conclusions from previous studies of prey models placed near ground level. Attack rates peaked for arthropods in late August and early September but were more constant across trials for vertebrates. Arthropods, a heterogeneous group, as indicated by the variety of bite marks, showed significantly higher attack rates on green colored prey models and a tendency of higher attack on solid (non-patch patterned) prey models. Vertebrates, more visually oriented predators, had significantly higher attack rates on red colored prey models and patch patterned prey models. Thus, our results did not suggest that conspicuous patch patterning reduced predation and therefore, we did not find support for the distractive mark hypothesis or warning hypothesis. Further, our study shows clear contrasting interpretations by different predators regarding visual defensive strategies.
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Affiliation(s)
- Julia Barrone
- Department of BiologyUniversity of Massachusetts BostonBostonMassachusettsUSA
| | - Mayra C. Vidal
- Department of BiologyUniversity of Massachusetts BostonBostonMassachusettsUSA
| | - Robert Stevenson
- Department of BiologyUniversity of Massachusetts BostonBostonMassachusettsUSA
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2
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Hughes AE, Briolat ES, Arenas LM, Liggins E, Stevens M. Varying benefits of generalist and specialist camouflage in two versus four background environments. Behav Ecol 2023; 34:426-436. [PMID: 37192921 PMCID: PMC10183209 DOI: 10.1093/beheco/arac114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 11/08/2022] [Accepted: 11/24/2022] [Indexed: 05/18/2023] Open
Abstract
Background-matching camouflage is a well-established strategy to reduce detection, but implementing this on heterogeneous backgrounds is challenging. For prey with fixed color patterns, solutions include specializing on a particular visual microhabitat, or adopting a compromise or generalist appearance, matching multiple backgrounds less well. Existing studies suggest both approaches can succeed, but most consider relatively simple scenarios, where artificial prey appear against two backgrounds differing in a single visual characteristic. Here, we used computer-based search tasks with human participants to test the relative benefits of specializing and generalizing for complex targets, displayed on either two or four types of naturalistic backgrounds. Across two background types, specialization was beneficial on average. However, the success of this strategy varied with search duration, such that generalist targets could outperform specialists over short search durations due to the presence of poorly matched specialists. Over longer searches, the remaining well-matched specialists had greater success than generalists, leading to an overall benefit of specialization at longer search durations. Against four different backgrounds, the initial cost to specialization was greater, so specialists and generalists ultimately experienced similar survival. Generalists performed better when their patterning was a compromise between backgrounds that were more similar to each other than when backgrounds were more different, with similarity in luminance more relevant than pattern differences. Time dependence in the relative success of these strategies suggests that predator search behavior may affect optimal camouflage in real-world situations.
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Affiliation(s)
- Anna E Hughes
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
- Department of Psychology, University of Essex, Wivenhoe House, Colchester CO4 3SQ, UK
| | - Emmanuelle S Briolat
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
| | - Lina María Arenas
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
| | - Eric Liggins
- QinetiQ, Cody Technology Park, Ively Road, Farnborough, Hampshire GU14 0LX, UK
| | - Martin Stevens
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
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3
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de Alcantara Viana JV, Vieira C, Duarte RC, Romero GQ. Predator responses to prey camouflage strategies: a meta-analysis. Proc Biol Sci 2022; 289:20220980. [PMID: 36100020 PMCID: PMC9470275 DOI: 10.1098/rspb.2022.0980] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 08/15/2022] [Indexed: 11/12/2022] Open
Abstract
Although numerous studies about camouflage have been conducted in the last few decades, there is still a significant gap in our knowledge about the magnitude of protective value of different camouflage strategies in prey detection and survival. Furthermore, the functional significance of several camouflage strategies remains controversial. Here we carried out a comprehensive meta-analysis including comparisons of different camouflage strategies as well as predator and prey types, considering two response variables: mean predator search time (ST) (63 studies) and predator attack rate (AR) of camouflaged prey (28 studies). Overall, camouflage increased the predator ST by 62.56% and decreased the AR of prey by 27.34%. Masquerade was the camouflage strategy that most increased predator ST (295.43%). Background matching and disruptive coloration did not differ from each other. Motion camouflage did not increase ST but decreases AR on prey. We found no evidence that eyespot increases ST and decreases AR by predators. The different types of predators did not differ from each other, but caterpillars were the type of prey that most influenced the magnitude of camouflage's effect. We highlight the potential evolutionary mechanisms that led camouflage to be a highly effective anti-predatory adaptation, as well as potential discrepancies or redundancies among strategies, predator and prey types.
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Affiliation(s)
- João Vitor de Alcantara Viana
- Programa de Pós-graduação em Ecologia, Universidade Estadual de Campinas (UNICAMP), Instituto de Biologia, Laboratório de Interações Multitróficas e Biodiversidade, Campinas, São Paulo, Brazil
- Laboratório de Interações Multitróficas e Biodiversidade, Departamento de Biologia Animal, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), CP 6109, CEP 13083-970 Campinas, São Paulo, Brazil
| | - Camila Vieira
- Departamento de Ciências Básicas, Universidade de São Paulo (USP), campus de Pirassununga, CEP 13635-900 Pirassununga, São Paulo, Brazil
| | - Rafael Campos Duarte
- Universidade Federal do ABC, CEP 09606-045 São Bernardo do Campo, São Paulo, Brazil
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
| | - Gustavo Quevedo Romero
- Laboratório de Interações Multitróficas e Biodiversidade, Departamento de Biologia Animal, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), CP 6109, CEP 13083-970 Campinas, São Paulo, Brazil
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4
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Camacho C, Sáez-Gómez P, Hidalgo-Rodríguez P, Rabadán-González J, Molina C, Negro JJ. Leucistic plumage as a result of progressive greying in a cryptic nocturnal bird. Sci Rep 2022; 12:3411. [PMID: 35233024 PMCID: PMC8888543 DOI: 10.1038/s41598-022-07360-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2021] [Accepted: 02/14/2022] [Indexed: 11/09/2022] Open
Abstract
Leucism, broadly defined as the lack of melanin pigmentation, occurs in many animal species. Most studies on leucism and other colour aberrations are based on opportunistic observations or small cross-sectional samples, thus limiting our ability to produce reliable results and test theoretical predictions. This study combines cross-sectional and longitudinal data collected in 2016-2020 from a population of red-necked nightjars (Caprimulgus ruficollis). The goals of the study are (i) to investigate sex and age effects on partial leucism, (ii) to separate within-subject effects (progressive greying) from between-subject effects (selective disappearance), and (iii) to examine differences in body mass, structural size, and life span between leucistic and non-leucistic individuals. The probability of leucism in nightjars increased from juveniles to adults at similar rates in males and females. Our longitudinal analysis and life-span comparisons indicated a minor contribution of selective disappearance to age-related changes in leucism, but rather suggested that the loss of melanin from feathers can be attributed to progressive greying in ageing adults. Body mass and size were consistently smaller (5% and 1.5%, respectively) in leucistic than in non-leucistic nightjars, although the reason for this difference remains unclear. Our study sheds light on the sources and mechanisms of variation in leucism in natural populations and its relationship with important life-history traits, such as life span.
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Affiliation(s)
- Carlos Camacho
- Department of Biological Conservation and Ecosystem Restoration, Instituto Pirenaico de Ecología - CSIC, Av. Nuestra Señora de la Victoria 16, 22700, Jaca, Huesca, Spain. .,Department of Biology, Centre for Animal Movement Research (CAnMove), Lund University, Ecology Building, S lvegatan 37, 223 62, Lund, Sweden.
| | - Pedro Sáez-Gómez
- Instituto Multidisciplinar para el Estudio del Medio "Ramon Margalef", Universidad de Alicante, 03080, Alicante, Spain
| | - Paula Hidalgo-Rodríguez
- Department of Molecular Biology and Biochemical Engineering, University Pablo de Olavide, Carretera Utrera km.1, 41013, Seville, Spain
| | | | - Carlos Molina
- Sociedad Española de Ornitología, Centro Ornitológico Francisco Bernis, Paseo Marismeño s.n., 21750, Huelva, Spain
| | - Juan José Negro
- Department of Evolutionary Biology, Estación Biológica de Doñana - CSIC, Av. Américo Vespucio, 26, 41092, Seville, Spain.
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5
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Arias M, Leroy L, Madec C, Matos L, Tedore C, Elias M, Gomez D. Partial wing transparency works better when disrupting wing edges: Evidence from a field experiment. J Evol Biol 2021; 34:1840-1846. [PMID: 34601773 DOI: 10.1111/jeb.13943] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 09/04/2021] [Accepted: 09/19/2021] [Indexed: 11/28/2022]
Abstract
Lepidoptera-a group of insects in which wing transparency has arisen multiple times-exhibits much variation in the size and position of transparent wing zones. However, little is known as to how this variability affects detectability. Here, we test how the size and position of transparent elements affect the predation of artificial moths by wild birds in the field. Morphs with transparent elements touching wing borders showed a reduced predation risk, with the effect being the same regardless of the number of wing borders being touched. By contrast, transparent element size had little to no effect on predation risk. Overall, this experiment shows for the first time that transparency offers higher protection when it disrupts prey contour in terrestrial habitats.
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Affiliation(s)
- Mónica Arias
- CEFE, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France.,ISYEB, CNRS, MNHN, Sorbonne Univ, EPHE, Univ. Antilles, 45 rue Buffon CP50, Paris, France
| | - Lucie Leroy
- CEFE, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France
| | - Clément Madec
- CEFE, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France
| | - Louane Matos
- CEFE, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France
| | - Cynthia Tedore
- CEFE, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France.,Faculty of Mathematics, Informatics and Natural Sciences, Institute of Zoology, Univ. Hamburg, Hamburg, Germany
| | - Marianne Elias
- ISYEB, CNRS, MNHN, Sorbonne Univ, EPHE, Univ. Antilles, 45 rue Buffon CP50, Paris, France
| | - Doris Gomez
- CEFE, CNRS, Univ. Montpellier, EPHE, IRD, Montpellier, France.,INSP, CNRS, Sorbonne Univ., Paris, France
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6
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Briolat ES, Arenas LM, Hughes AE, Liggins E, Stevens M. Generalist camouflage can be more successful than microhabitat specialisation in natural environments. BMC Ecol Evol 2021; 21:151. [PMID: 34344323 PMCID: PMC8330473 DOI: 10.1186/s12862-021-01883-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 07/25/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Crypsis by background-matching is a critical form of anti-predator defence for animals exposed to visual predators, but achieving effective camouflage in patchy and variable natural environments is not straightforward. To cope with heterogeneous backgrounds, animals could either specialise on particular microhabitat patches, appearing cryptic in some areas but mismatching others, or adopt a compromise strategy, providing partial matching across different patch types. Existing studies have tested the effectiveness of compromise strategies in only a limited set of circumstances, primarily with small targets varying in pattern, and usually in screen-based tasks. Here, we measured the detection risk associated with different background-matching strategies for relatively large targets, with human observers searching for them in natural scenes, and focusing on colour. Model prey were designed to either 'specialise' on the colour of common microhabitat patches, or 'generalise' by matching the average colour of the whole visual scenes. RESULTS In both the field and an equivalent online computer-based search task, targets adopting the generalist strategy were more successful in evading detection than those matching microhabitat patches. This advantage occurred because, across all possible locations in these experiments, targets were typically viewed against a patchwork of different microhabitat areas; the putatively generalist targets were thus more similar on average to their various immediate surroundings than were the specialists. CONCLUSIONS Demonstrating close agreement between the results of field and online search experiments provides useful validation of online citizen science methods commonly used to test principles of camouflage, at least for human observers. In finding a survival benefit to matching the average colour of the visual scenes in our chosen environment, our results highlight the importance of relative scales in determining optimal camouflage strategies, and suggest how compromise coloration can succeed in nature.
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Affiliation(s)
| | - Lina María Arenas
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, TR10 9FE, Penryn, UK
| | - Anna E Hughes
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, TR10 9FE, Penryn, UK
- Department of Psychology, University of Essex, Wivenhoe House, CO4 3SQ, Colchester, UK
| | - Eric Liggins
- , QinetiQ, Cody Technology Park, Ively Road, Farnborough, GU14 0LX, Hampshire, UK
| | - Martin Stevens
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, TR10 9FE, Penryn, UK
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7
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Troscianko J, Nokelainen O, Skelhorn J, Stevens M. Variable crab camouflage patterns defeat search image formation. Commun Biol 2021; 4:287. [PMID: 33674781 PMCID: PMC7935895 DOI: 10.1038/s42003-021-01817-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Accepted: 02/04/2021] [Indexed: 11/09/2022] Open
Abstract
Understanding what maintains the broad spectrum of variation in animal phenotypes and how this influences survival is a key question in biology. Frequency dependent selection - where predators temporarily focus on one morph at the expense of others by forming a "search image" - can help explain this phenomenon. However, past work has never tested real prey colour patterns, and rarely considered the role of different types of camouflage. Using a novel citizen science computer experiment that presented crab "prey" to humans against natural backgrounds in specific sequences, we were able to test a range of key hypotheses concerning the interactions between predator learning, camouflage and morph. As predicted, switching between morphs did hinder detection, and this effect was most pronounced when crabs had "disruptive" markings that were more effective at destroying the body outline. To our knowledge, this is the first evidence for variability in natural colour patterns hindering search image formation in predators, and as such presents a mechanism that facilitates phenotypic diversity in nature.
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Affiliation(s)
- Jolyon Troscianko
- Centre for Ecology and Conservation, College of Life and Environmental Science, University of Exeter, TR10 9FE, Penryn, UK.
| | - Ossi Nokelainen
- Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
| | - John Skelhorn
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, NE2 4HH, Newcastle upon Tyne, UK
| | - Martin Stevens
- Centre for Ecology and Conservation, College of Life and Environmental Science, University of Exeter, TR10 9FE, Penryn, UK
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8
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Mayekar HV, Kodandaramaiah U. Partially coupled reaction norms of pupal colour and spot size in a butterfly. Evol Ecol 2021. [DOI: 10.1007/s10682-020-10090-w] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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9
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Caro T, Koneru M. Towards an ecology of protective coloration. Biol Rev Camb Philos Soc 2020; 96:611-641. [PMID: 33258554 DOI: 10.1111/brv.12670] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 11/05/2020] [Accepted: 11/09/2020] [Indexed: 12/15/2022]
Abstract
The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life-history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small-scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self-shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad-scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.
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Affiliation(s)
- Tim Caro
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, U.K.,Center for Population Biology, University of California, Davis, CA, 95616, U.S.A
| | - Manisha Koneru
- Department of Evolution and Ecology, University of California, Davis, CA, 95616, U.S.A
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10
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Stuart GW, Yip D, Hogendoorn H. The role of hue in visual search for texture differences: Implications for camouflage design. Vision Res 2020; 176:16-26. [PMID: 32768744 DOI: 10.1016/j.visres.2020.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 04/16/2020] [Accepted: 07/13/2020] [Indexed: 11/18/2022]
Abstract
The purpose of camouflage is to be inconspicuous against a given background. Colour is an important component of camouflage, and the task of designing a single camouflage pattern for use against multiple different backgrounds is particularly challenging. As it is impossible to match the colour gamut of each background exactly, the question arises which colours from the different backgrounds should be incorporated in a camouflage pattern to achieve optimal concealment. Here, we used a visual search paradigm to address this question. Observers searched multi-coloured continuous textures for target regions defined by either the presence or absence of additional hues. Targets could be either a combination of five hues against a four-hued background ("patches"), or a combination of four hues against a five-hued background ("holes"). In Experiment 1, a search asymmetry was observed for the different targets, as observers were less accurate and slower at detecting holes than patches. Additionally, we observed a linear separability effect: search for a target was more difficult when the hue that defined the target was within the gamut of distractor colours (e.g. orange amongst reds and yellows). In Experiment 2, we further investigated "hole" targets designed for two different backgrounds and found that optimal concealment against both backgrounds was achieved by including intermediate colours that represented a compromise between the common colours and the unique colours of each background. The findings provide insights into how search asymmetries can be extended to complex texture properties and help inform the design process of camouflage for multiple backgrounds.
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Affiliation(s)
- Geoffrey W Stuart
- Melbourne School of Psychological Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia.
| | - Dominic Yip
- Melbourne School of Psychological Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia
| | - Hinze Hogendoorn
- Melbourne School of Psychological Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia
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11
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Galloway JAM, Green SD, Stevens M, Kelley LA. Finding a signal hidden among noise: how can predators overcome camouflage strategies? Philos Trans R Soc Lond B Biol Sci 2020; 375:20190478. [PMID: 32420842 PMCID: PMC7331011 DOI: 10.1098/rstb.2019.0478] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Substantial progress has been made in the past 15 years regarding how prey use a variety of visual camouflage types to exploit both predator visual processing and cognition, including background matching, disruptive coloration, countershading and masquerade. By contrast, much less attention has been paid to how predators might overcome these defences. Such strategies include the evolution of more acute senses, the co-opting of other senses not targeted by camouflage, changes in cognition such as forming search images, and using behaviours that change the relationship between the cryptic individual and the environment or disturb prey and cause movement. Here, we evaluate the methods through which visual camouflage prevents detection and recognition, and discuss if and how predators might evolve, develop or learn counter-adaptations to overcome these. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests'.
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Affiliation(s)
- James A M Galloway
- Centre for Ecology and Conservation, University of Exeter (Penryn Campus), Cornwall TR10 9FE, UK
| | - Samuel D Green
- Centre for Ecology and Conservation, University of Exeter (Penryn Campus), Cornwall TR10 9FE, UK
| | - Martin Stevens
- Centre for Ecology and Conservation, University of Exeter (Penryn Campus), Cornwall TR10 9FE, UK
| | - Laura A Kelley
- Centre for Ecology and Conservation, University of Exeter (Penryn Campus), Cornwall TR10 9FE, UK
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12
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Merwin JT, Seeholzer GF, Smith BT. Macroevolutionary bursts and constraints generate a rainbow in a clade of tropical birds. BMC Evol Biol 2020; 20:32. [PMID: 32093609 PMCID: PMC7041239 DOI: 10.1186/s12862-020-1577-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 12/31/2019] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Bird plumage exhibits a diversity of colors that serve functional roles ranging from signaling to camouflage and thermoregulation. However, birds must maintain a balance between evolving colorful signals to attract mates, minimizing conspicuousness to predators, and optimizing adaptation to climate conditions. Examining plumage color macroevolution provides a framework for understanding this dynamic interplay over phylogenetic scales. Plumage evolution due to a single overarching process, such as selection, may generate the same macroevolutionary pattern of color variation across all body regions. In contrast, independent processes may partition plumage and produce region-specific patterns. To test these alternative scenarios, we collected color data from museum specimens of an ornate clade of birds, the Australasian lorikeets, using visible-light and UV-light photography, and comparative methods. We predicted that the diversification of homologous feather regions, i.e., patches, known to be involved in sexual signaling (e.g., face) would be less constrained than patches on the back and wings, where new color states may come at the cost of crypsis. Because environmental adaptation may drive evolution towards or away from color states, we tested whether climate more strongly covaried with plumage regions under greater or weaker macroevolutionary constraint. RESULTS We found that alternative macroevolutionary models and varying rates best describe color evolution, a pattern consistent with our prediction that different plumage regions evolved in response to independent processes. Modeling plumage regions independently, in functional groups, and all together showed that patches with similar macroevolutionary models clustered together into distinct regions (e.g., head, wing, belly), which suggests that plumage does not evolve as a single trait in this group. Wing patches, which were conserved on a macroevolutionary scale, covaried with climate more strongly than plumage regions (e.g., head), which diversified in a burst. CONCLUSIONS Overall, our results support the hypothesis that the extraordinary color diversity in the lorikeets was generated by a mosaic of evolutionary processes acting on plumage region subsets. Partitioning of plumage regions in different parts of the body provides a mechanism that allows birds to evolve bright colors for signaling and remain hidden from predators or adapt to local climatic conditions.
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Affiliation(s)
- Jon T Merwin
- Department of Ornithology, American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024, USA.
- Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, 10027, USA.
| | - Glenn F Seeholzer
- Department of Ornithology, American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024, USA
| | - Brian Tilston Smith
- Department of Ornithology, American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024, USA
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13
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Affiliation(s)
- I. C. Cuthill
- School of Biological Sciences University of Bristol Bristol UK
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14
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Hughes A, Liggins E, Stevens M. Imperfect camouflage: how to hide in a variable world? Proc Biol Sci 2019; 286:20190646. [PMID: 31088268 PMCID: PMC6532520 DOI: 10.1098/rspb.2019.0646] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 04/25/2019] [Indexed: 12/12/2022] Open
Abstract
Camouflage is an important anti-predator strategy for many animals and is traditionally thought of as being tightly linked to a specific visual background. While much work focuses on optimizing camouflage against one background, this may not be relevant for many species and contexts, as animals may encounter many different habitats throughout their lives due to temporal and spatial variation in their environment. How should camouflage be optimized when an animal or object is seen against multiple visual backgrounds? Various solutions may exist, including colour change to match new environments or use of behaviour to maintain crypsis by choosing appropriate substrates. Here, we focus on a selection of approaches under a third alternative strategy: animals may adopt (over evolution) camouflage appearances that represent an optimal solution against multiple visual scenes. One approach may include a generalist or compromise strategy, where coloration matches several backgrounds to some extent, but none closely. A range of other camouflage types, including disruptive camouflage, may also provide protection in multiple environments. Despite detailed theoretical work determining the plausibility of compromise camouflage and elucidating the conditions under which it might evolve, there is currently mixed experimental evidence supporting its value and little evidence of it in natural systems. In addition, there remain many questions including how camouflage strategies should be defined and optimized, and how they might interact with other types of crypsis and defensive markings. Overall, we provide a critical overview of our current knowledge about how camouflage can enable matching to multiple backgrounds, discuss important challenges of working on this question and make recommendations for future research.
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Affiliation(s)
- Anna Hughes
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
| | - Eric Liggins
- QinetiQ, Cody Technology Park, Ively Road, Farnborough, Hampshire GU14 0LX, UK
| | - Martin Stevens
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
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15
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Troscianko J, Skelhorn J, Stevens M. Camouflage strategies interfere differently with observer search images. Proc Biol Sci 2018; 285:20181386. [PMID: 30185636 PMCID: PMC6158535 DOI: 10.1098/rspb.2018.1386] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 08/13/2018] [Indexed: 11/24/2022] Open
Abstract
Numerous animals rely on camouflage for defence. Substantial past work has identified the presence of multiple strategies for concealment, and tested the mechanisms underpinning how they work. These include background matching, D-RUP coloration to destroy target edges, and distractive markings that may divert attention from key target features. Despite considerable progress, work has focused on how camouflage types prevent initial detection by naive observers. However, predators will often encounter multiple targets over time, providing the opportunity to learn or focus attention through search images. At present, we know almost nothing about how camouflage types facilitate or hinder predator performance over repeated encounters. Here, we use experiments with human subjects searching for targets on touch screens with different camouflage strategies, and control the experience that subjects have with target types. We show that different camouflage strategies affect how subjects improve in detecting targets with repeated encounters, and how performance in detection of one camouflage type depends on experience of other strategies. In particular, disruptive coloration is effective at preventing improvements in camouflage breaking during search image formation, and experience with one camouflage type (distraction) can decrease the ability of subjects to switch to and from search images for new camouflage types (disruption). Our study is, to our knowledge, the first to show how the success of camouflage strategies depends on how they prevent initial and successive detection, and on predator experience of other strategies. This has implications for the evolution of prey phenotypes, how we assess the efficacy of defences, and predator-prey dynamics.
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Affiliation(s)
- Jolyon Troscianko
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK
| | - John Skelhorn
- Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Henry Wellcome Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Martin Stevens
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK
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16
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Walton OC, Stevens M. Avian vision models and field experiments determine the survival value of peppered moth camouflage. Commun Biol 2018; 1:118. [PMID: 30271998 PMCID: PMC6123793 DOI: 10.1038/s42003-018-0126-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 07/25/2018] [Indexed: 11/14/2022] Open
Abstract
Animal defensive coloration has long provided many important examples of evolution and adaptation. Of these, industrial melanism in the peppered moth is the classic textbook example of evolution in action, whereby dark and pale morphs suffer differential predation in polluted and unpolluted woodland based on their camouflage. Despite extensive work, a striking gap remains in that no study has ever objectively quantified their camouflage or related this directly to predation risk. Here we use image analysis and avian vision models to show that pale individuals more closely match lichen backgrounds than dark morphs. Artificial predation experiments in unpolluted woodland show 21% higher survival rates of pale than melanic individuals. Overall, we provide the strongest direct evidence to date that peppered moth morph frequencies stem from differential camouflage and avian predation, providing key support for this iconic example of natural selection.
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Affiliation(s)
- Olivia C Walton
- Centre for Ecology & Conservation, College of Life & Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK
| | - Martin Stevens
- Centre for Ecology & Conservation, College of Life & Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK.
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17
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Penacchio O, Lovell PG, Harris JM. Is countershading camouflage robust to lighting change due to weather? ROYAL SOCIETY OPEN SCIENCE 2018; 5:170801. [PMID: 29515822 PMCID: PMC5830711 DOI: 10.1098/rsos.170801] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Accepted: 12/11/2017] [Indexed: 05/16/2023]
Abstract
Countershading is a pattern of coloration thought to have evolved in order to implement camouflage. By adopting a pattern of coloration that makes the surface facing towards the sun darker and the surface facing away from the sun lighter, the overall amount of light reflected off an animal can be made more uniformly bright. Countershading could hence contribute to visual camouflage by increasing background matching or reducing cues to shape. However, the usefulness of countershading is constrained by a particular pattern delivering 'optimal' camouflage only for very specific lighting conditions. In this study, we test the robustness of countershading camouflage to lighting change due to weather, using human participants as a 'generic' predator. In a simulated three-dimensional environment, we constructed an array of simple leaf-shaped items and a single ellipsoidal target 'prey'. We set these items in two light environments: strongly directional 'sunny' and more diffuse 'cloudy'. The target object was given the optimal pattern of countershading for one of these two environment types or displayed a uniform pattern. By measuring detection time and accuracy, we explored whether and how target detection depended on the match between the pattern of coloration on the target object and scene lighting. Detection times were longest when the countershading was appropriate to the illumination; incorrectly camouflaged targets were detected with a similar pattern of speed and accuracy to uniformly coloured targets. We conclude that structural changes in light environment, such as caused by differences in weather, do change the effectiveness of countershading camouflage.
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Affiliation(s)
- Olivier Penacchio
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, Fife KY16 9JP, UK
| | - P. George Lovell
- Division of Psychology, Social and Health Sciences, Abertay University, Dundee DD1 1HG, UK
| | - Julie M. Harris
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, Fife KY16 9JP, UK
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18
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Humphreys RK, Ruxton GD. What is known and what is not yet known about deflection of the point of a predator’s attack. Biol J Linn Soc Lond 2018. [DOI: 10.1093/biolinnean/blx164] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Rosalind K Humphreys
- School of Biology, University of St Andrews, Dyer’s Brae House, St Andrews, Fife, UK
| | - Graeme D Ruxton
- School of Biology, University of St Andrews, Dyer’s Brae House, St Andrews, Fife, UK
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19
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Baños-Villalba A, Quevedo DP, Edelaar P. Positioning behavior according to individual color variation improves camouflage in novel habitats. Behav Ecol 2017. [DOI: 10.1093/beheco/arx181] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Adrián Baños-Villalba
- Department of Molecular Biology and Biochemical Engineering, University Pablo de Olavide Ctra, Utrera, Sevilla, Spain
| | - David P Quevedo
- Department of Molecular Biology and Biochemical Engineering, University Pablo de Olavide Ctra, Utrera, Sevilla, Spain
| | - Pim Edelaar
- Department of Molecular Biology and Biochemical Engineering, University Pablo de Olavide Ctra, Utrera, Sevilla, Spain
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20
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Xiao F, Cuthill IC. Background complexity and the detectability of camouflaged targets by birds and humans. Proc Biol Sci 2017; 283:rspb.2016.1527. [PMID: 27629039 DOI: 10.1098/rspb.2016.1527] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 08/22/2016] [Indexed: 11/12/2022] Open
Abstract
Remaining undetected is often key to survival, and camouflage is a widespread solution. However, extrinsic to the animal itself, the complexity of the background may be important. This has been shown in laboratory experiments using artificially patterned prey and backgrounds, but the mechanism remains obscure (not least because 'complexity' is a multifaceted concept). In this study, we determined the best predictors of detection by wild birds and human participants searching for the same cryptic targets on trees in the field. We compared detection success to metrics of background complexity and 'visual clutter' adapted from the human visual salience literature. For both birds and humans, the factor that explained most of the variation in detectability was the textural complexity of the tree bark as measured by a metric of feature congestion (specifically, many nearby edges in the background). For birds, this swamped any effects of colour match to the local surroundings, although for humans, local luminance disparities between the target and tree became important. For both taxa, a more abstract measure of complexity, entropy, was a poorer predictor. Our results point to the common features of background complexity that affect visual search in birds and humans, and how to quantify them.
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Affiliation(s)
- Feng Xiao
- School of Biological Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Innes C Cuthill
- School of Biological Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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21
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Penacchio O, Harris JM, Lovell PG. Establishing the behavioural limits for countershaded camouflage. Sci Rep 2017; 7:13672. [PMID: 29057907 PMCID: PMC5651847 DOI: 10.1038/s41598-017-13914-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 09/20/2017] [Indexed: 11/09/2022] Open
Abstract
Countershading is a ubiquitous patterning of animals whereby the side that typically faces the highest illumination is darker. When tuned to specific lighting conditions and body orientation with respect to the light field, countershading minimizes the gradient of light the body reflects by counterbalancing shadowing due to illumination, and has therefore classically been thought of as an adaptation for visual camouflage. However, whether and how crypsis degrades when body orientation with respect to the light field is non-optimal has never been studied. We tested the behavioural limits on body orientation for countershading to deliver effective visual camouflage. We asked human participants to detect a countershaded target in a simulated three-dimensional environment. The target was optimally coloured for crypsis in a reference orientation and was displayed at different orientations. Search performance dramatically improved for deviations beyond 15 degrees. Detection time was significantly shorter and accuracy significantly higher than when the target orientation matched the countershading pattern. This work demonstrates the importance of maintaining body orientation appropriate for the displayed camouflage pattern, suggesting a possible selective pressure for animals to orient themselves appropriately to enhance crypsis.
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Affiliation(s)
- Olivier Penacchio
- School of Psychology and Neuroscience, University of St. Andrews, St. Andrews, Fife KY16 9JP, UK.
| | - Julie M Harris
- School of Psychology and Neuroscience, University of St. Andrews, St. Andrews, Fife KY16 9JP, UK
| | - P George Lovell
- Division of Psychology, Social and Health Sciences, Abertay University, Dundee, DD1 1HG, UK
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22
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Fritsch R, Ullmann JFP, Bitton PP, Collin SP, Michiels NK. Optic-nerve-transmitted eyeshine, a new type of light emission from fish eyes. Front Zool 2017; 14:14. [PMID: 28261313 PMCID: PMC5327540 DOI: 10.1186/s12983-017-0198-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Accepted: 02/15/2017] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Most animal eyes feature an opaque pigmented eyecup to assure that light can enter from one direction only. We challenge this dogma by describing a previously unknown form of eyeshine resulting from light that enters the eye through the top of the head and optic nerve, eventually emanating through the pupil as a narrow beam: the Optic-Nerve-Transmitted (ONT) eyeshine. We characterize ONT eyeshine in the triplefin blenny Tripterygion delaisi (Tripterygiidae) in comparison to three other teleost species, using behavioural and anatomical observations, spectrophotometry, histology, and magnetic resonance imaging. The study's aim is to identify the factors that determine ONT eyeshine occurrence and intensity, and whether these are specifically adapted for that purpose. RESULTS ONT eyeshine intensity benefits from locally reduced head pigmentation, a thin skull, the gap between eyes and forebrain, the potential light-guiding properties of the optic nerve, and, most importantly, a short distance between the head surface and the optic nerves. CONCLUSIONS The generality of these factors and the lack of specifically adapted features implies that ONT eyeshine is widespread among small fish species. Nevertheless, its intensity varies considerably, depending on the specific combination and varying expression of common anatomical features. We discuss whether ONT eyeshine might affect visual performance, and speculate about possible functions such as predator detection, camouflage, and intraspecific communication.
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Affiliation(s)
- Roland Fritsch
- Institute of Evolution and Ecology, University of Tübingen, 72076 Tübingen, Baden-Württemberg Germany
| | - Jeremy F P Ullmann
- Centre for Advanced Imaging, University of Queensland, Brisbane, 4072 Queensland Australia.,Department of Neurology, Boston Children's Hospital & Harvard Medical School, Boston, MA 02115 USA
| | - Pierre-Paul Bitton
- Institute of Evolution and Ecology, University of Tübingen, 72076 Tübingen, Baden-Württemberg Germany
| | - Shaun P Collin
- School of Biological Sciences and the Oceans Institute, University of Western Australia, Crawley, 6009 Western Australia Australia
| | - Nico K Michiels
- Institute of Evolution and Ecology, University of Tübingen, 72076 Tübingen, Baden-Württemberg Germany
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23
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24
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Troscianko J, Wilson-Aggarwal J, Griffiths D, Spottiswoode CN, Stevens M. Relative advantages of dichromatic and trichromatic color vision in camouflage breaking. Behav Ecol 2017; 28:556-564. [PMID: 29622920 PMCID: PMC5873837 DOI: 10.1093/beheco/arw185] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Revised: 11/24/2016] [Accepted: 12/07/2016] [Indexed: 11/13/2022] Open
Abstract
There is huge diversity in visual systems and color discrimination abilities, thought to stem from an animal’s ecology and life history. Many primate species maintain a polymorphism in color vision, whereby most individuals are dichromats but some females are trichromats, implying that selection sometimes favors dichromatic vision. Detecting camouflaged prey is thought to be a task where dichromatic individuals could have an advantage. However, previous work either has not been able to disentangle camouflage detection from other ecological or social explanations, or did not use biologically relevant cryptic stimuli to test this hypothesis under controlled conditions. Here, we used online “citizen science” games to test how quickly humans could detect cryptic birds (incubating nightjars) and eggs (of nightjars, plovers and coursers) under trichromatic and simulated dichromatic viewing conditions. Trichromats had an overall advantage, although there were significant differences in performance between viewing conditions. When searching for consistently shaped and patterned adult nightjars, simulated dichromats were more heavily influenced by the degree of pattern difference than were trichromats, and were poorer at detecting prey with inferior pattern and luminance camouflage. When searching for clutches of eggs—which were more variable in appearance and shape than the adult nightjars—the simulated dichromats learnt to detect the clutches faster, but were less sensitive to subtle luminance differences. These results suggest there are substantial differences in the cues available under viewing conditions that simulate different receptor types, and that these interact with the scene in complex ways to affect camouflage breaking.
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Affiliation(s)
- Jolyon Troscianko
- University of Exeter, School of Biosciences, Penryn Campus, Penryn TR10 9FE, UK
| | | | - David Griffiths
- University of Exeter, School of Biosciences, Penryn Campus, Penryn TR10 9FE, UK.,FoAM - Kernow, Workshop E, Jubilee Warehouse, Commercial Road, Penryn TR10 8FG, UK
| | - Claire N Spottiswoode
- University of Cambridge, Department of Zoology, Downing Street, Cambridge CB2 3EJ, UK, and.,DST-NRF Centre of Excellence at the FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa
| | - Martin Stevens
- University of Exeter, School of Biosciences, Penryn Campus, Penryn TR10 9FE, UK
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25
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Quantifying camouflage: how to predict detectability from appearance. BMC Evol Biol 2017; 17:7. [PMID: 28056761 PMCID: PMC5217226 DOI: 10.1186/s12862-016-0854-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Accepted: 12/17/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Quantifying the conspicuousness of objects against particular backgrounds is key to understanding the evolution and adaptive value of animal coloration, and in designing effective camouflage. Quantifying detectability can reveal how colour patterns affect survival, how animals' appearances influence habitat preferences, and how receiver visual systems work. Advances in calibrated digital imaging are enabling the capture of objective visual information, but it remains unclear which methods are best for measuring detectability. Numerous descriptions and models of appearance have been used to infer the detectability of animals, but these models are rarely empirically validated or directly compared to one another. We compared the performance of human 'predators' to a bank of contemporary methods for quantifying the appearance of camouflaged prey. Background matching was assessed using several established methods, including sophisticated feature-based pattern analysis, granularity approaches and a range of luminance and contrast difference measures. Disruptive coloration is a further camouflage strategy where high contrast patterns disrupt they prey's tell-tale outline, making it more difficult to detect. Disruptive camouflage has been studied intensely over the past decade, yet defining and measuring it have proven far more problematic. We assessed how well existing disruptive coloration measures predicted capture times. Additionally, we developed a new method for measuring edge disruption based on an understanding of sensory processing and the way in which false edges are thought to interfere with animal outlines. RESULTS Our novel measure of disruptive coloration was the best predictor of capture times overall, highlighting the importance of false edges in concealment over and above pattern or luminance matching. CONCLUSIONS The efficacy of our new method for measuring disruptive camouflage together with its biological plausibility and computational efficiency represents a substantial advance in our understanding of the measurement, mechanism and definition of disruptive camouflage. Our study also provides the first test of the efficacy of many established methods for quantifying how conspicuous animals are against particular backgrounds. The validation of these methods opens up new lines of investigation surrounding the form and function of different types of camouflage, and may apply more broadly to the evolution of any visual signal.
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26
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Abstract
Camouflage is one of the most widespread forms of anti-predator defence and prevents prey individuals from being detected or correctly recognized by would-be predators. Over the past decade, there has been a resurgence of interest in both the evolution of prey camouflage patterns, and in understanding animal cognition in a more ecological context. However, these fields rarely collide, and the role of cognition in the evolution of camouflage is poorly understood. Here, we review what we currently know about the role of both predator and prey cognition in the evolution of prey camouflage, outline why cognition may be an important selective pressure driving the evolution of camouflage and consider how studying the cognitive processes of animals may prove to be a useful tool to study the evolution of camouflage, and vice versa. In doing so, we highlight that we still have a lot to learn about the role of cognition in the evolution of camouflage and identify a number of avenues for future research.
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Affiliation(s)
- John Skelhorn
- Centre for Behaviour & Evolution, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Candy Rowe
- Centre for Behaviour & Evolution, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
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27
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Background matching and camouflage efficiency predict population density in four-eyed turtle (Sacalia quadriocellata). Behav Processes 2016; 131:40-6. [PMID: 27542920 DOI: 10.1016/j.beproc.2016.08.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 08/10/2016] [Accepted: 08/15/2016] [Indexed: 11/23/2022]
Abstract
Background matching is an important way to camouflage and is widespread among animals. In the field, however, few studies have addressed background matching, and there has been no reported camouflage efficiency in freshwater turtles. Background matching and camouflage efficiency of the four-eyed turtle, Sacalia quadriocellata, among three microhabitat sections of Hezonggou stream were investigated by measuring carapace components of CIE L*a*b* (International Commission on Illumination; lightness, red/green and yellow/blue) color space, and scoring camouflage efficiency through the use of humans as predators. The results showed that the color difference (ΔE), lightness difference (ΔL(*)), and chroma difference (Δa(*)b(*)) between carapace and the substrate background in midstream were significantly lower than that upstream and downstream, indicating that the four-eyed turtle carapace color most closely matched the substrate of midstream. In line with these findings, the camouflage efficiency was the best for the turtles that inhabit midstream. These results suggest that the four-eyed turtles may enhance camouflage efficiency by selecting microhabitat that best match their carapace color. This finding may explain the high population density of the four-eyed turtle in the midstream section of Hezonggou stream. To the best of our knowledge, this study is among the first to quantify camouflage of freshwater turtles in the wild, laying the groundwork to further study the function and mechanisms of turtle camouflage.
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28
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Seymoure BM, Aiello A. Keeping the band together: evidence for false boundary disruptive coloration in a butterfly. J Evol Biol 2015; 28:1618-24. [PMID: 26109438 DOI: 10.1111/jeb.12681] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 06/12/2015] [Accepted: 06/15/2015] [Indexed: 11/28/2022]
Abstract
There is a recent surge of evidence supporting disruptive coloration, in which patterns break up the animal's outline through false edges or boundaries, increasing survival in animals by reducing predator detection and/or preventing recognition. Although research has demonstrated that false edges are successful for reducing predation of prey, research into the role of internal false boundaries (i.e. stripes and bands) in reducing predation remains warranted. Many animals have stripes and bands that may function disruptively. Here, we test the possible disruptive function of wing band patterning in a butterfly, Anartia fatima, using artificial paper and plasticine models in Panama. We manipulated the band so that one model type had the band shifted to the wing margin (nondisruptive treatment) and another model had a discontinuous band located on the wing margin (discontinuous edge treatment). We kept the natural wing pattern to represent the false boundary treatment. Across all treatment groups, we standardized the area of colour and used avian visual models to confirm a match between manipulated and natural wing colours. False boundary models had higher survival than either the discontinuous edge model or the nondisruptive model. There was no survival difference between the discontinuous edge model and the nondisruptive model. Our results demonstrate the importance of wing bands in reducing predation on butterflies and show that markings set in from the wing margin can reduce predation more effectively than marginal bands and discontinuous marginal patterns. This study demonstrates an adaptive benefit of having stripes and bands.
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Affiliation(s)
- B M Seymoure
- School of Life Sciences, Arizona State University, Tempe, AZ, USA.,Smithsonian Tropical Research Institute, Ancón, Panamá, Republic of Panama
| | - A Aiello
- Smithsonian Tropical Research Institute, Ancón, Panamá, Republic of Panama
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29
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Hauber ME, Tong L, Bán M, Croston R, Grim T, Waterhouse GIN, Shawkey MD, Barron AB, Moskát C. The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism. Ethology 2015. [DOI: 10.1111/eth.12359] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Márk E. Hauber
- Department of Psychology; Hunter College and the Graduate Center of the City University of New York; New York NY USA
| | - Lainga Tong
- Department of Psychology; Hunter College and the Graduate Center of the City University of New York; New York NY USA
| | - Miklós Bán
- Department of Evolutionary Zoology; MTA-DE ‘Lendület’ Behavioural Ecology Research Group; University of Debrecen; Debrecen Hungary
| | - Rebecca Croston
- Department of Psychology; Hunter College and the Graduate Center of the City University of New York; New York NY USA
| | - Tomáš Grim
- Laboratory of Ornithology and Department of Zoology; Palacky University; Olomouc Czech Republic
| | | | - Matthew D. Shawkey
- Department of Biology and Integrated BioScience Program; University of Akron; Akron OH USA
| | - Andrew B. Barron
- Department of Biological Sciences; Macquarie University; Sydney NSW Australia
| | - Csaba Moskát
- MTA-ELTE-MTM Ecology Research Group; Hungarian Academy of Sciences; c/o Biological Institute; Eötvös Lóránd University and Hungarian Natural History Museum; Budapest Hungary
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30
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Hughes AE, Troscianko J, Stevens M. Motion dazzle and the effects of target patterning on capture success. BMC Evol Biol 2014; 14:201. [PMID: 25213150 PMCID: PMC4172783 DOI: 10.1186/s12862-014-0201-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 09/09/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Stripes and other high contrast patterns found on animals have been hypothesised to cause "motion dazzle", a type of defensive coloration that operates when in motion, causing predators to misjudge the speed and direction of object movement. Several recent studies have found some support for this idea, but little is currently understood about the mechanisms underlying this effect. Using humans as model 'predators' in a touch screen experiment we investigated further the effectiveness of striped targets in preventing capture, and considered how stripes compare to other types of patterning in order to understand what aspects of target patterning are important in making a target difficult to capture. RESULTS We find that striped targets are among the most difficult to capture, but that other patterning types are also highly effective at preventing capture in this task. Several target types, including background sampled targets and targets with a 'spot' on were significantly easier to capture than striped targets. We also show differences in capture attempt rates between different target types, but we find no differences in learning rates between target types. CONCLUSIONS We conclude that striped targets are effective in preventing capture, but are not uniquely difficult to catch, with luminance matched grey targets also showing a similar capture rate. We show that key factors in making capture easier are a lack of average background luminance matching and having trackable 'features' on the target body. We also find that striped patterns are attempted relatively quickly, despite being difficult to catch. We discuss these findings in relation to the motion dazzle hypothesis and how capture rates may be affected more generally by pattern type.
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Abstract
Camouflage is the primary defence of many animals and includes multiple strategies that interfere with figure-ground segmentation and object recognition. While matching background colours and textures is widespread and conceptually straightforward, less well explored are the optical ‘tricks’, collectively called disruptive colouration, that exploit perceptual grouping mechanisms. Adjacent high contrast colours create false edges, but this is not sufficient for an object’s shape to be broken up; some colours must blend with the background. We test the novel hypothesis that this will be particularly effective when the colour patches on the animal appear to belong to, not merely different background colours, but different background objects. We used computer-based experiments where human participants had to find cryptic targets on artificial backgrounds. Creating what appeared to be bi-coloured foreground objects on bi-coloured backgrounds, we generated colour boundaries that had identical local contrast but either lay within or between (illusory) objects. As predicted, error rates for targets matching what appeared to be different background objects were higher than for targets which had otherwise identical local contrast to the background but appeared to belong to single background objects. This provides evidence for disruptive colouration interfering with higher-level feature integration in addition to previously demonstrated low-level effects involving contour detection. In addition, detection was impeded in treatments where targets were on or in close proximity to multiple background colour or tone boundaries. This is consistent with other studies which show a deleterious influence of visual ‘clutter’ or background complexity on search.
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Affiliation(s)
- Irene Espinosa
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
- * E-mail:
| | - Innes C. Cuthill
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
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Troscianko J, Lown AE, Hughes AE, Stevens M. Defeating crypsis: detection and learning of camouflage strategies. PLoS One 2013; 8:e73733. [PMID: 24040046 PMCID: PMC3769369 DOI: 10.1371/journal.pone.0073733] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Accepted: 07/21/2013] [Indexed: 11/18/2022] Open
Abstract
Camouflage is perhaps the most widespread defence against predators in nature and an active area of interdisciplinary research. Recent work has aimed to understand what camouflage types exist (e.g. background matching, disruptive, and distractive patterns) and their effectiveness. However, work has almost exclusively focused on the efficacy of these strategies in preventing initial detection, despite the fact that predators often encounter the same prey phenotype repeatedly, affording them opportunities to learn to find those prey more effectively. The overall value of a camouflage strategy may, therefore, reflect both its ability to prevent detection by predators and resist predator learning. We conducted four experiments with humans searching for hidden targets of different camouflage types (disruptive, distractive, and background matching of various contrast levels) over a series of touch screen trials. As with previous work, disruptive coloration was the most successful method of concealment overall, especially with relatively high contrast patterns, whereas potentially distractive markings were either neutral or costly. However, high contrast patterns incurred faster decreases in detection times over trials compared to other stimuli. In addition, potentially distractive markings were sometimes learnt more slowly than background matching markings, despite being found more readily overall. Finally, learning effects were highly dependent upon the experimental paradigm, including the number of prey types seen and whether subjects encountered targets simultaneously or sequentially. Our results show that the survival advantage of camouflage strategies reflects both their ability to avoid initial detection (sensory mechanisms) and predator learning (perceptual mechanisms).
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Affiliation(s)
- Jolyon Troscianko
- Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn, United Kingdom
- * E-mail:
| | - Alice E. Lown
- Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn, United Kingdom
| | - Anna E. Hughes
- Department of Physiology, Development, and Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - Martin Stevens
- Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn, United Kingdom
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Stevens M, Troscianko J, Marshall KLA, Finlay S. What is camouflage through distractive markings? A reply to Merilaita et al. (2013). Behav Ecol 2013. [DOI: 10.1093/beheco/art053] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Merilaita S, Schaefer HM, Dimitrova M. What is camouflage through distractive markings? Behav Ecol 2013. [DOI: 10.1093/beheco/art051] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Stevens M, Rong CP, Todd PA. Colour change and camouflage in the horned ghost crabOcypode ceratophthalmus. Biol J Linn Soc Lond 2013. [DOI: 10.1111/bij.12039] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Martin Stevens
- Department of Zoology; University of Cambridge; Cambridge CB2 3EJ UK
| | - Cheo Pei Rong
- Experimental Marine Ecology Laboratory; Department of Biological Sciences; National University of Singapore; Singapore 117543
| | - Peter A. Todd
- Experimental Marine Ecology Laboratory; Department of Biological Sciences; National University of Singapore; Singapore 117543
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Flores EE, Stevens M, Moore AJ, Blount JD. Diet, development and the optimization of warning signals in post‐metamorphic green and black poison frogs. Funct Ecol 2013. [DOI: 10.1111/1365-2435.12084] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Eric E. Flores
- Centre for Ecology and Conservation College of Life & Environmental Sciences University of Exeter Cornwall Campus Penryn TR10 9EZ UK
| | - Martin Stevens
- Department of Zoology University of Cambridge Downing Street Cambridge CB2 3EJ UK
| | - Allen J. Moore
- Centre for Ecology and Conservation College of Life & Environmental Sciences University of Exeter Cornwall Campus Penryn TR10 9EZ UK
- Department of Genetics University of Georgia Athens GA 30602 USA
| | - Jonathan D. Blount
- Centre for Ecology and Conservation College of Life & Environmental Sciences University of Exeter Cornwall Campus Penryn TR10 9EZ UK
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