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Thomas DHN, Kjernsmo K, Scott-Samuel NE, Whitney HM, Cuthill IC. Interactions between color and gloss in iridescent camouflage. Behav Ecol 2023; 34:751-758. [PMID: 37744171 PMCID: PMC10516679 DOI: 10.1093/beheco/arad050] [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: 06/01/2022] [Revised: 05/10/2023] [Accepted: 05/25/2023] [Indexed: 09/26/2023] Open
Abstract
Iridescence is a taxonomically widespread form of structural coloration that produces often intense hues that change with the angle of viewing. Its role as a signal has been investigated in multiple species, but recently, and counter-intuitively, it has been shown that it can function as camouflage. However, the property of iridescence that reduces detectability is, as yet, unclear. As viewing angle changes, iridescent objects change not only in hue but also in intensity, and many iridescent animals are also shiny or glossy; these "specular reflections," both from the target and background, have been implicated in crypsis. Here, we present a field experiment with natural avian predators that separate the relative contributions of color and gloss to the "survival" of iridescent and non-iridescent beetle-like targets. Consistent with previous research, we found that iridescent coloration, and high gloss of the leaves on which targets were placed, enhance survival. However, glossy targets survived less well than matt. We interpret the results in terms of signal-to-noise ratio: specular reflections from the background reduce detectability by increasing visual noise. While a specular reflection from the target attracts attention, a changeable color reduces the signal because, we suggest, normally, the color of an object is a stable feature for detection and identification.
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Affiliation(s)
- Dylan H N Thomas
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Karin Kjernsmo
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Nicholas E Scott-Samuel
- School of Psychological Science, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK
| | - Heather M Whitney
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Innes C Cuthill
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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2
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Hwang Y, Yoo S, Park C, Kang C. Comparative and experimental studies on the relationship between body size and countershading in caterpillars. J Evol Biol 2023; 36:1032-1039. [PMID: 36737844 DOI: 10.1111/jeb.14153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Revised: 10/04/2022] [Accepted: 12/14/2022] [Indexed: 02/05/2023]
Abstract
Countershading is a gradient of colouration in which the illuminated dorsal surfaces are darker than the unilluminated ventral surface. It is widespread in the animal kingdom and endows the body with a more uniform colour to decrease the chance of detection by predators. Although recent empirical studies support the theory of survival advantage conferred by countershading, this camouflage strategy has evolved only in some of the cryptic animals, and our understanding of the factors that affect the evolution of countershading is limited. This study examined the association between body size and countershading using lepidopteran larvae (caterpillars) as a model system. Specifically, we predicted that countershading may have selectively evolved in large-sized species among cryptic caterpillars if (1) large size constrains camouflage which facilitates the evolution of a trait reinforcing their crypsis and (2) the survival advantage of countershading is size-dependent. Phylogenetic analyses of four different lepidopteran families (Saturniidae, Sphingidae, Erebidae, and Geometridae) suggest equivocal results: countershading was more likely to be found in larger species in Saturniidae but not in the other families. The field predation experiment assuming avian predators did not support size-dependent predation in countershaded prey. Collectively, we found only weak evidence that body size is associated with countershading in caterpillars. Our results suggest that body size is not a universal factor that has shaped the interspecific variation in countershading observed in caterpillars.
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Affiliation(s)
- Yerin Hwang
- Department of Biosciences, Mokpo National University, Muan, South Korea
- Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea
| | - Sohee Yoo
- Department of Biosciences, Mokpo National University, Muan, South Korea
- Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea
| | - Chohee Park
- Department of Biosciences, Mokpo National University, Muan, South Korea
- Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea
| | - Changku Kang
- Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea
- Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, South Korea
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3
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Exnerová A, Kang C, Rowland HM, Kikuchi DW. Evolution of multiple prey defences: From predator cognition to community ecology. J Evol Biol 2023; 36:961-966. [PMID: 37449469 DOI: 10.1111/jeb.14196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Accepted: 06/07/2023] [Indexed: 07/18/2023]
Affiliation(s)
- Alice Exnerová
- Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Changku Kang
- Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea
- Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, South Korea
| | - Hannah M Rowland
- Max Planck Research Group Predators and Toxic Prey, Max Planck Institute for Chemical Ecology, Jena, Germany
| | - David W Kikuchi
- Department of Integrative Biology, Oregon State University, Corvallis, Oregon, USA
- Evolutionary Biology, Universität Bielefeld, Bielefeld, Germany
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4
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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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5
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Mavrovouna V, Penacchio O, Allen WL. Orienting to the sun improves camouflage for bilaterally symmetrical prey. Biol J Linn Soc Lond 2021. [DOI: 10.1093/biolinnean/blab130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
Here, we investigate the camouflage consequences of animal orientation behaviour. Shadows can be a conspicuous cue to the presence of prey. For bilaterally symmetrical animals, light field modelling indicates that camouflage will be improved when an animal orients its longitudinal axis directly towards or away from the sun, because the appearance of shadows is minimized. We test this prediction with a field predation experiment, in which wild birds hunt for artificial camouflaged prey oriented with the longitudinal axis either parallel or perpendicular to the sun. We find that prey oriented parallel to the sun are 3.93 times more likely to survive than prey oriented perpendicular to the sun. This result demonstrates the strong orientation dependence of camouflage. Given the dramatic difference in survival of prey with different orientations, we suggest that camouflage should be investigated as an important determinant of the positional behaviour of animals.
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Affiliation(s)
- Veronica Mavrovouna
- Department of Biosciences, Swansea University, Singleton Campus, Swansea SA2 8PP, UK
| | - Olivier Penacchio
- School of Psychology and Neuroscience, University of St Andrews, South Street, St Andrews, Fife KY16 9JP, UK
| | - William L Allen
- Department of Biosciences, Swansea University, Singleton Campus, Swansea SA2 8PP, UK
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7
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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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8
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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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9
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Donohue CG, Hemmi JM, Kelley JL. Countershading enhances camouflage by reducing prey contrast. Proc Biol Sci 2020; 287:20200477. [PMID: 32396802 DOI: 10.1098/rspb.2020.0477] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A three-dimensional body shape is problematic for camouflage because overhead lighting produces a luminance gradient across the body's surface. Countershading, a form of patterning where animals are darkest on their uppermost surface, is thought to counteract this luminance gradient and enhance concealment, but the mechanisms of protection remain unclear. Surprisingly, no study has examined how countershading alters prey contrast, or investigated how the presence of a dorsoventral luminance gradient affects detection under controlled viewing conditions. It has also been suggested that the direction of the dorsoventral luminance gradient (darkest or lightest on top) may interfere with predators' abilities to resolve prey's three-dimensional shape, yet this intriguing idea has never been tested. We used live fish predators (western rainbowfish, Melanotaenia australis) and computer-generated prey images to compare the detectability of uniformly pigmented (i.e. non-countershaded) prey with that of optimally countershaded prey of varying contrasts against the background. Optimally countershaded prey were difficult for predators to detect, and the probability and speed of detection depended on prey luminance contrast with the background. In comparison, non-countershaded prey were always highly detectable, even though their average luminance closely matched the luminance of the background. Our findings suggest that uniformly pigmented three-dimensional prey are highly conspicuous to predators because overhead lighting increases luminance contrast between different body parts or between the body and the background. We found no evidence for the notion that countershading interferes with predator perception of three-dimensional form.
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Affiliation(s)
- Callum G Donohue
- School of Biological Sciences, The University of Western Australia, Crawley, Western Australia 6009, Australia
| | - Jan M Hemmi
- School of Biological Sciences, The University of Western Australia, Crawley, Western Australia 6009, Australia.,The UWA Oceans Institute, The University of Western Australia, Crawley, Western Australia 6009, Australia
| | - Jennifer L Kelley
- School of Biological Sciences, The University of Western Australia, Crawley, Western Australia 6009, Australia.,The UWA Oceans Institute, The University of Western Australia, Crawley, Western Australia 6009, Australia
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10
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Affiliation(s)
- I. C. Cuthill
- School of Biological Sciences University of Bristol Bristol UK
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11
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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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12
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Seasonal pelage color change of two sympatric arboreal squirrel species in the subarctic region. THE EUROPEAN ZOOLOGICAL JOURNAL 2019. [DOI: 10.1080/24750263.2019.1682694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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13
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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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