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Yeager J, Robison A, Wade CD, Barnett JB. Imperfections in transparency and mimicry do not increase predation risk for clearwing butterflies with educated predators. Ecol Evol 2024; 14:e70307. [PMID: 39310733 PMCID: PMC11413500 DOI: 10.1002/ece3.70307] [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: 04/25/2024] [Revised: 08/19/2024] [Accepted: 08/20/2024] [Indexed: 09/25/2024] Open
Abstract
Transparency is an intuitive form of concealment and, in certain butterflies, transparent patches on the wings can contribute to several distinct forms of camouflage. However, perhaps paradoxically, the largely transparent wings of many clearwing butterflies (Ithomiini, Nymphalidae) also feature opaque, and often colorful, elements which may reduce crypsis. In many instances, these elements may facilitate aposematic signaling, but little is known of how transparency and aposematism may interact. Here, we used field predation trials to ask two main questions regarding camouflage and signaling in Ithomiini clearwings. In Experiment 1, we focused on camouflage to ask where being transparent may have an advantage over being opaque. We predicted that, as a single opaque pattern can only match a limited range of backgrounds, transparent wings would offer more effective concealment, and experience lower predation risk, over a wider range of backgrounds colors (i.e., green vs. brown substrates) and behaviors (i.e., perched vs. flying) than opaque wings. In Experiment 2, we focused on the effect conspicuous opaque colors may have on clearwing survival. We predicted that although salient signals may increase detectability, those commonly associated with toxic Ithomiini clearwings would not increase predation risk. Both experiments were conducted among educated predators within the natural range of Ithomiini clearwings and we found predation rates to be very low. In Experiment 1, we found some marginal evidence to suggest that opaque, but not transparent, butterflies may suffer increased predation during flight, whereas in Experiment 2, we found equal survival across all model prey types regardless of coloration. Taken together we suggest that any loss of camouflage due to conspicuous coloration may be compensated by aversive signaling, and that educated predators may broadly generalize across a wide range of known and novel clearwing phenotypes.
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Affiliation(s)
- Justin Yeager
- Grupo de Investigación en Biodiversidad, Medio Ambiente y Salud (BIOMAS), Facultad de Ingenierías y Ciencas AplicadasUniversidad de Las AméricasQuitoEcuador
| | - Abigail Robison
- Dirección General de Investigación y VinculaciónUniversidad de Las AméricasQuitoEcuador
| | - Cordon D. Wade
- Dirección General de Investigación y VinculaciónUniversidad de Las AméricasQuitoEcuador
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2
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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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3
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King J, Hemmi JM, Kelley JL. Camouflage using three-dimensional surface disruption. Biol Lett 2023; 19:20220596. [PMID: 37528728 PMCID: PMC10394419 DOI: 10.1098/rsbl.2022.0596] [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: 12/15/2022] [Accepted: 07/17/2023] [Indexed: 08/03/2023] Open
Abstract
Disruptive markings are common in animal patterns and can provide camouflage benefits by concealing the body's true edges and/or by breaking the surface of the body into multiple depth planes. Disruptive patterns that are accentuated by high contrast borders are most likely to provide false depth cues to enhance camouflage, but studies to date have used visual detection models or humans as predators. We presented three-dimensional-printed moth-like targets to wild bird predators to determine whether: (1) three-dimensional prey with disrupted body surfaces have higher survival than three-dimensional prey with continuous surfaces, (2) two-dimensional prey with disruptive patterns or enhanced edge markings have higher survival than non-patterned two-dimensional prey. We found a survival benefit for three-dimensional prey with disrupted surfaces, and a significant effect of mean wing luminance. There was no evidence that false depth cues provided the same protective benefits as physical surface disruption in three-dimensional prey, perhaps because our treatments did not mimic the complexity of patterns found in natural animal markings. Our findings indicate that disruption of surface continuity is an important strategy for concealing a three-dimensional body shape.
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Affiliation(s)
- Jemma King
- School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Perth, Australia
| | - Jan M. Hemmi
- School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Perth, Australia
- UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Perth, Australia
| | - Jennifer L. Kelley
- School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Perth, Australia
- UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Perth, Australia
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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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Gomez D, Pinna C, Pairraire J, Arias M, Barbut J, Pomerantz A, Daney de Marcillac W, Berthier S, Patel N, Andraud C, Elias M. Wing transparency in butterflies and moths: structural diversity, optical properties, and ecological relevance. ECOL MONOGR 2021. [DOI: 10.1002/ecm.1475] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Doris Gomez
- CEFE University of Montpellier CNRS, EPHE, IRD Montpellier France
| | - Charline Pinna
- ISYEB UMR 7205 CNRS, MNHN EPHE Sorbonne University Paris France
| | | | - Mónica Arias
- CEFE University of Montpellier CNRS, EPHE, IRD Montpellier France
- ISYEB UMR 7205 CNRS, MNHN EPHE Sorbonne University Paris France
| | - Jérôme Barbut
- ISYEB UMR 7205 CNRS, MNHN EPHE Sorbonne University Paris France
| | - Aaron Pomerantz
- Marine Biological Laboratory Woods Hole Massachusetts 02543 USA
- Department Integrative Biology University of California Berkeley Berkeley California 94720 USA
| | | | | | - Nipam Patel
- Marine Biological Laboratory Woods Hole Massachusetts 02543 USA
- University of Chicago Chicago Illinois 60607 USA
| | | | - Marianne Elias
- ISYEB UMR 7205 CNRS, MNHN EPHE Sorbonne University Paris France
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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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Rohr VA, Volkmer T, Metzler D, Küpper C. Neoptile feathers contribute to outline concealment of precocial chicks. Sci Rep 2021; 11:5483. [PMID: 33750790 PMCID: PMC7943783 DOI: 10.1038/s41598-021-84227-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Accepted: 02/12/2021] [Indexed: 11/22/2022] Open
Abstract
Camouflage is a widespread strategy to increase survival. The cryptic plumage colouration of precocial chicks improves camouflage often through disruptive colouration. Here, we examine whether and how fringed neoptile feathers conceal the outline of chicks. We first conducted a digital experiment to test two potential mechanisms for outline concealment through appendages: (1) reduction of edge intensity and (2) luminance transition. Local Edge Intensity Analysis showed that appendages decreased edge intensity whereas a mean luminance comparison revealed that the appendages created an intermediate transition zone to conceal the object's outline. For edge intensity, the outline diffusion was strongest for a vision system with low spatial acuity, which is characteristic of many mammalian chick predators. We then analysed photographs of young snowy plover (Charadrius nivosus) chicks to examine whether feathers increase outline concealment in a natural setting. Consistent with better camouflage, the outline of digitally cropped chicks with protruding feathers showed lower edge intensities than the outline of chicks without those feathers. However, the observed mean luminance changes did not indicate better concealment. Taken together, our results suggest that thin skin appendages such as neoptile feathers improve camouflage. As skin appendages are widespread, this mechanism may apply to many organisms.
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Affiliation(s)
- Veronika A Rohr
- Research Group for Behavioural Genetics and Evolutionary Ecology, Max Planck Institute for Ornithology, Seewiesen, Germany.
- Division of Evolutionary Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.
| | - Tamara Volkmer
- Department of Migration, Max Planck Institute of Animal Behavior, Radolfzell, Germany
| | - Dirk Metzler
- Division of Evolutionary Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Clemens Küpper
- Research Group for Behavioural Genetics and Evolutionary Ecology, Max Planck Institute for Ornithology, Seewiesen, Germany.
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8
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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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Barnett JB, Michalis C, Anderson HM, McEwen BL, Yeager J, Pruitt JN, Scott-Samuel NE, Cuthill IC. Imperfect transparency and camouflage in glass frogs. Proc Natl Acad Sci U S A 2020; 117:12885-12890. [PMID: 32457164 PMCID: PMC7293656 DOI: 10.1073/pnas.1919417117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Camouflage patterns prevent detection and/or recognition by matching the background, disrupting edges, or mimicking particular background features. In variable habitats, however, a single pattern cannot match all available sites all of the time, and efficacy may therefore be reduced. Active color change provides an alternative where coloration can be altered to match local conditions, but again efficacy may be limited by the speed of change and range of patterns available. Transparency, on the other hand, creates high-fidelity camouflage that changes instantaneously to match any substrate but is potentially compromised in terrestrial environments where image distortion may be more obvious than in water. Glass frogs are one example of terrestrial transparency and are well known for their transparent ventral skin through which their bones, intestines, and beating hearts can be seen. However, sparse dorsal pigmentation means that these frogs are better described as translucent. To investigate whether this imperfect transparency acts as camouflage, we used in situ behavioral trials, visual modeling, and laboratory psychophysics. We found that the perceived luminance of the frogs changed depending on the immediate background, lowering detectability and increasing survival when compared to opaque frogs. Moreover, this change was greatest for the legs, which surround the body at rest and create a diffuse transition from background to frog luminance rather than a sharp, highly salient edge. This passive change in luminance, without significant modification of hue, suggests a camouflage strategy, "edge diffusion," distinct from both transparency and active color change.
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Affiliation(s)
- James B Barnett
- Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, ON L8S 4K1, Canada;
- School of Biological Sciences, University of Bristol, BS8 1TQ Bristol, United Kingdom
| | - Constantine Michalis
- School of Biological Sciences, University of Bristol, BS8 1TQ Bristol, United Kingdom
| | - Hannah M Anderson
- Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Brendan L McEwen
- Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Justin Yeager
- Biodiversidad Medio Ambiente y Salud, Universidad de Las Américas, 170125 Quito, Ecuador
| | - Jonathan N Pruitt
- Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, ON L8S 4K1, Canada
| | | | - Innes C Cuthill
- School of Biological Sciences, University of Bristol, BS8 1TQ Bristol, United Kingdom
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