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Abstract
Predators have profound effects on prey behavior and some adult brood parasites use predator resemblance to exploit the antipredator defenses of their hosts. Clarifying host perception of such stimuli is important for understanding the adaptive significance of adult brood parasite characteristics, and the mechanisms by which they misdirect hosts. Here I review the literature to explore the adaptive basis of predator resemblance in avian brood parasites, and natural variation in host responses to these stimuli. I also provide a framework for the information ecology of predator resemblance, which is based on the principles of signal detection theory and draws from empirical evidence from the common cuckoo, Cuculus canorus, as the most widely studied system. In this species, visual and acoustic hawk-like stimuli are effective in manipulating host defenses. Overall, contrasts across host responses suggest that different modalities of information can have independent effects on hosts, and that predator resemblance takes advantage of multiple sensory and cognitive processes. Host perception of these stimuli and the degree to which they are processed in an integrated manner, and the physiological processes underlying regulation of the responses, present new avenues for brood parasitism research.
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Howell N, Sheard C, Koneru M, Brockelsby K, Ono K, Caro T. Aposematism in mammals. Evolution 2021; 75:2480-2493. [PMID: 34347894 DOI: 10.1111/evo.14320] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 06/26/2021] [Accepted: 06/29/2021] [Indexed: 12/25/2022]
Abstract
Aposematic coloration is traditionally considered to signal unpalatability or toxicity. In mammals, most research has focused on just one form of defense, namely, noxious anal secretions, and its black-and-white advertisement as exemplified by skunks. The original formulation of aposematism, however, encompassed a broader range of morphological, physiological, and behavioral defenses, and there are many mammal species with black-and-white contrasting patterns that do not have noxious adaptations. Here, using Bayesian phylogenetic models and data from 1726 terrestrial nonvolant mammals we find that two aspects of conspicuous coloration, black-and-white coloration patterns on the head and body, advertise defenses that are morphological (spines, large body size), behavioral (pugnacity), and physiological (anal secretions), as well as being involved with sexual signaling and environmental factors linked to crypsis. Within Carnivora, defensive anal secretions are associated with complex black-and-white head patterns and longitudinal black-and-white body striping; in primates, larger bodied species exhibit irregular patches of black-and-white pelage; and in rodents, pugnacity is linked to sharp countershading and irregular blocks of white and black pelage. We show that black-and-white coloration in mammals is multifunctional, that it serves to warn predators of several defenses other than noxious anal secretions, and that aposematism in mammals is not restricted to carnivores.
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Affiliation(s)
- Natasha Howell
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, United Kingdom
| | - Catherine Sheard
- School of Earth Sciences, University of Bristol, Bristol, BS8 1TQ, United Kingdom
| | - Manisha Koneru
- Department of Ecology and Evolution, University of California, Davis, Davis, California, 95616
| | - Kasey Brockelsby
- Department of Ecology and Evolution, University of California, Davis, Davis, California, 95616
| | - Konatsu Ono
- Department of Animal Biology, University of California, Davis, Davis, California, 95616
| | - Tim Caro
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, United Kingdom.,Center for Population Biology, University of California, Davis, Davis, California, 95616
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Nekaris KA, Campera M, Watkins AR, Weldon AV, Hedger K, Morcatty TQ. Aposematic signaling and seasonal variation in dorsal pelage in a venomous mammal. Ecol Evol 2021; 11:11387-11397. [PMID: 34429927 PMCID: PMC8366853 DOI: 10.1002/ece3.7928] [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: 12/17/2020] [Revised: 07/01/2021] [Accepted: 07/02/2021] [Indexed: 12/21/2022] Open
Abstract
In mammals, colouration patterns are often related to concealment, intraspecific communication, including aposematic signals, and physiological adaptations. Slow lorises (Nycticebus spp.) are arboreal primates native to Southeast Asia that display stark colour contrast, are highly territorial, regularly enter torpor, and are notably one of only seven mammal taxa that possess venom. All slow loris species display a contrasting stripe that runs cranial-caudally along the median sagittal plane of the dorsum. We examine whether these dorsal markings facilitate background matching, seasonal adaptations, and intraspecific signaling. We analyzed 195 images of the dorsal region of 60 Javan slow loris individuals (Nycticebus javanicus) from Java, Indonesia. We extracted greyscale RGB values from dorsal pelage using ImageJ software and calculated contrast ratios between dorsal stripe and adjacent pelage in eight regions. We assessed through generalized linear mixed models if the contrast ratio varied with sex, age, and seasonality. We also examined whether higher contrast was related to more aggressive behavior or increased terrestrial movement. We found that the dorsal stripe of N. javanicus changed seasonally, being longer and more contrasting in the wet season, during which time lorises significantly increased their ground use. Stripes were most contrasting in younger individuals of dispersal age that were also the most aggressive during capture. The dorsal stripe became less contrasting as a loris aged. A longer stripe when ground use is more frequent can be related to disruptive colouration. A darker anterior region by younger lorises with less fighting experience may allow them to appear larger and fiercer. We provide evidence that the dorsum of a cryptic species can have multimodal signals related to concealment, intraspecific communication, and physiological adaptations.
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Affiliation(s)
- K. Anne‐Isola Nekaris
- Nocturnal Primate Research GroupFaculty of Humanities and Social SciencesOxford Brookes UniversityOxfordUK
- Little Fireface ProjectCipagantiJavaIndonesia
| | - Marco Campera
- Nocturnal Primate Research GroupFaculty of Humanities and Social SciencesOxford Brookes UniversityOxfordUK
- Little Fireface ProjectCipagantiJavaIndonesia
| | - Anna R. Watkins
- Nocturnal Primate Research GroupFaculty of Humanities and Social SciencesOxford Brookes UniversityOxfordUK
| | - Ariana V. Weldon
- Nocturnal Primate Research GroupFaculty of Humanities and Social SciencesOxford Brookes UniversityOxfordUK
| | | | - Thais Q. Morcatty
- Nocturnal Primate Research GroupFaculty of Humanities and Social SciencesOxford Brookes UniversityOxfordUK
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Crofts SB, Stankowich T. Stabbing Spines: A review of the Biomechanics and Evolution of Defensive Spines. Integr Comp Biol 2021; 61:655-667. [PMID: 34038530 DOI: 10.1093/icb/icab099] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Spines are ubiquitous in both plants and animals, and while most spines were likely originally used for defense, over time many have been modified in a variety of ways. Here we take an integrative approach to review the form, function, and evolution of spines as a defensive strategy in order to make new connections between physical mechanisms and functional behavior. While this review focuses on spines in mammals, we reference and draw ideas from the literature on spines in other taxa, including plants. We begin by exploring the biomechanics of defensive spines, their varied functions, and nondefensive modifications. We pay particular attention to the mechanics involved in passive puncture and the ways organisms have overcome limitations associated with the low energy input. We then focus on the ecological, physiological, and behavioral factors that promote the evolution of spiny defenses, including predator- and habitat-mediated hypotheses. While there is considerable evidence to support both, studies have generally found that (1) defensive spines are usually effective against one class of attacker (e.g., larger predators) but ineffective against or even facilitate predation by others and (2) species that are more visible or exposed to predators are under much stronger selection to evolve defensive spines or some other robust defense. What type of defensive morphology that evolves, however, is less predictable and probably strongly dependent on both the dominant source of predation and the habitat structure of the organism (e.g., arboreal, terrestrial, and fossorial). We then explore traits that often are correlated with defensive spines and armor, potentially forming armor syndromes, suites of traits that evolve together with body armor in a correlated fashion. In mammals, these include aposematic warning coloration, locomotion style, diet, metabolic rate, and relative brain size. Finally, we encourage integration of mechanistic, behavioral, and evolutionary studies of defensive spines and suggest future avenues of research in the biomechanics, evolution, and behavior of spines and spiny organisms.
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Affiliation(s)
| | - Theodore Stankowich
- Department of Biological Sciences, California State University Long Beach, Long Beach, CA, USA
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Almeida DA, Mappes J, Gordon S. Predator-Induced Plasticity on Warning Signal and Larval Life-History Traits of the Aposematic Wood Tiger Moth, Arctia plantaginis. Front Ecol Evol 2021. [DOI: 10.3389/fevo.2021.658177] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Predator-induced plasticity in life-history and antipredator traits during the larval period has been extensively studied in organisms with complex life-histories. However, it is unclear whether different levels of predation could induce warning signals in aposematic organisms. Here, we investigated whether predator-simulated handling affects warning coloration and life-history traits in the aposematic wood tiger moth larva, Arctia plantaginis. As juveniles, a larger orange patch on an otherwise black body signifies a more efficient warning signal against predators but this comes at the costs of conspicuousness and thermoregulation. Given this, one would expect that an increase in predation risk would induce flexible expression of the orange patch. Prior research in this system points to plastic effects being important as a response to environmental changes for life history traits, but we had yet to assess whether this was the case for predation risk, a key driver of this species evolution. Using a full-sib rearing design, in which individuals were reared in the presence and absence of a non-lethal simulated bird attack, we evaluated flexible responses of warning signal size (number of orange segments), growth, molting events, and development time in wood tiger moths. All measured traits except development time showed a significant response to predation. Larvae from the predation treatment developed a more melanized warning signal (smaller orange patch), reached a smaller body size, and molted more often. Our results suggest plasticity is indeed important in aposematic organisms, but in this case may be complicated by the trade-off between costly pigmentation and other life-history traits.
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Echeverri SA, Miller AE, Chen J, McQueen EW, Plakke M, Spicer M, Hoke KL, Stoddard MC, Morehouse NI. How signaling geometry shapes the efficacy and evolution of animal communication systems. Integr Comp Biol 2021; 61:787-813. [PMID: 34021338 DOI: 10.1093/icb/icab090] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Animal communication is inherently spatial. Both signal transmission and signal reception have spatial biases-involving direction, distance and position-that interact to determine signaling efficacy. Signals, be they visual, acoustic, or chemical, are often highly directional. Likewise, receivers may only be able to detect signals if they arrive from certain directions. Alignment between these directional biases is therefore critical for effective communication, with even slight misalignments disrupting perception of signaled information. In addition, signals often degrade as they travel from signaler to receiver, and environmental conditions that impact transmission can vary over even small spatiotemporal scales. Thus, how animals position themselves during communication is likely to be under strong selection. Despite this, our knowledge regarding the spatial arrangements of signalers and receivers during communication remains surprisingly coarse for most systems. We know even less about how signaler and receiver behaviors contribute to effective signaling alignment over time, or how signals themselves may have evolved to influence and/or respond to these aspects of animal communication. Here, we first describe why researchers should adopt a more explicitly geometric view of animal signaling, including issues of location, direction, and distance. We then describe how environmental and social influences introduce further complexities to the geometry of signaling. We discuss how multimodality offers new challenges and opportunities for signalers and receivers. We conclude with recommendations and future directions made visible by attention to the geometry of signaling.
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Affiliation(s)
| | - Audrey E Miller
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ
| | - Jason Chen
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA.,Department of Biology, Emory University, Atlanta, GA
| | - Eden W McQueen
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA
| | - Melissa Plakke
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA.,Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS
| | - Michelle Spicer
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA.,Biology Department, University of Puget Sound, Tacoma, WA
| | - Kim L Hoke
- Department of Biology, Colorado State University, Fort Collins, CO
| | | | - Nathan I Morehouse
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA.,Department of Biological Sciences, University of Cincinnati, Cincinnati, OH
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Barnett JB, Varela BJ, Jennings BJ, Lesbarrères D, Pruitt JN, Green DM. Habitat disturbance alters color contrast and the detectability of cryptic and aposematic frogs. Behav Ecol 2021. [DOI: 10.1093/beheco/arab032] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Animals use color both to conceal and signal their presence, with patterns that match the background, disrupt shape recognition, or highlight features important for communication. The forms that these color patterns take are responses to the visual systems that observe them and the environments within which they are viewed. Increasingly, however, these environments are being affected by human activity. We studied how pattern characteristics and habitat change may affect the detectability of three frog color patterns from the Bocas del Toro archipelago in Panama: Beige-Striped Brown Allobates talamancae and two spotted morphs of Oophaga pumilio, Black-Spotted Green and Black-Spotted Red. To assess detectability, we used visual modeling of conspecifics and potential predators, along with a computer-based detection experiment with human participants. Although we found no evidence for disruptive camouflage, we did find clear evidence that A. talamancae stripes are inherently more cryptic than O. pumilio spots regardless of color. We found no evidence that color pattern polytypism in O. pumilio is related to differences in the forest floor between natural sites. We did, however, find strong evidence that human disturbance affects the visual environment and modifies absolute and rank order frog detectability. Human-induced environmental change reduces the effectiveness of camouflage in A. talamancae, reduces detectability of Black-Spotted Green O. pumilio, and increases chromatic contrast, but not detectability, in Black-Spotted Red O. pumilio. Insofar as predators may learn about prey defenses and make foraging decisions based on relative prey availability and suitability, such changes may have wider implications for predator–prey dynamics.
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Affiliation(s)
- James B Barnett
- Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, ON, Canada
- Redpath Museum, McGill University, Montreal, QC, Canada
| | | | - Ben J Jennings
- The College of Health, Medicine and Life Sciences, Brunel University London, Kingston Lane, Uxbridge, UK
| | | | - Jonathan N Pruitt
- Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, ON, Canada
| | - David M Green
- Redpath Museum, McGill University, Montreal, QC, Canada
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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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Abstract
AbstractEastern spotted skunks (Spilogale putorius) have suffered a dramatic range-wide decline leading to concern that the species is likely vulnerable to extinction, but were recently discovered to persist in a portion of the southern Appalachian Mountains (United States). For 2 years we investigated habitat selection by eastern spotted skunks to develop an understanding of their habitat and conservation needs in northwestern South Carolina. We used a discrete choice modeling framework to evaluate vegetative and topographic features that we predicted would influence rest site selection by male and female spotted skunks. Using VHF telemetry, we tracked 15 spotted skunks (10 males and 5 females) to 215 day-time rest sites between the months of April and August. Spotted skunks selected rest sites in close proximity to drainage channels, where the relative probability of selection decreased 18% and 50% with every 20-m increase in distance to a drainage channel for males and females, respectively. Relative probability of selection by female spotted skunks increased 30% for every one-unit increase in coarse woody debris (CWD), and relative probability of selection by male spotted skunks increased 25% for every 10% increase in understory cover. These results are consistent with previous studies that have identified cover as important for protection from predators; however, we additionally identified CWD and drainage channels as important to habitat selection by spotted skunks. These latter attributes are likely selected based on prey availability, but alternate ecological functions of these features warrant further investigation. Preservation of understory vegetation and CWD within drainage networks might benefit conservation of eastern spotted skunks in the southern Appalachians.
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Affiliation(s)
- Robin Y Y Eng
- Clemson University, Department of Forestry and Environmental Conservation, Clemson, SC, USA
| | - David S Jachowski
- Clemson University, Department of Forestry and Environmental Conservation, Clemson, SC, USA
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Fisher KA, Stankowich T. Antipredator strategies of striped skunks in response to cues of aerial and terrestrial predators. Anim Behav 2018. [DOI: 10.1016/j.anbehav.2018.06.023] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Briolat ES, Burdfield-Steel ER, Paul SC, Rönkä KH, Seymoure BM, Stankowich T, Stuckert AMM. Diversity in warning coloration: selective paradox or the norm? Biol Rev Camb Philos Soc 2018; 94:388-414. [PMID: 30152037 PMCID: PMC6446817 DOI: 10.1111/brv.12460] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 07/25/2018] [Accepted: 07/27/2018] [Indexed: 01/03/2023]
Abstract
Aposematic theory has historically predicted that predators should select for warning signals to converge on a single form, as a result of frequency‐dependent learning. However, widespread variation in warning signals is observed across closely related species, populations and, most problematically for evolutionary biologists, among individuals in the same population. Recent research has yielded an increased awareness of this diversity, challenging the paradigm of signal monomorphy in aposematic animals. Here we provide a comprehensive synthesis of these disparate lines of investigation, identifying within them three broad classes of explanation for variation in aposematic warning signals: genetic mechanisms, differences among predators and predator behaviour, and alternative selection pressures upon the signal. The mechanisms producing warning coloration are also important. Detailed studies of the genetic basis of warning signals in some species, most notably Heliconius butterflies, are beginning to shed light on the genetic architecture facilitating or limiting key processes such as the evolution and maintenance of polymorphisms, hybridisation, and speciation. Work on predator behaviour is changing our perception of the predator community as a single homogenous selective agent, emphasising the dynamic nature of predator–prey interactions. Predator variability in a range of factors (e.g. perceptual abilities, tolerance to chemical defences, and individual motivation), suggests that the role of predators is more complicated than previously appreciated. With complex selection regimes at work, polytypisms and polymorphisms may even occur in Müllerian mimicry systems. Meanwhile, phenotypes are often multifunctional, and thus subject to additional biotic and abiotic selection pressures. Some of these selective pressures, primarily sexual selection and thermoregulation, have received considerable attention, while others, such as disease risk and parental effects, offer promising avenues to explore. As well as reviewing the existing evidence from both empirical studies and theoretical modelling, we highlight hypotheses that could benefit from further investigation in aposematic species. Finally by collating known instances of variation in warning signals, we provide a valuable resource for understanding the taxonomic spread of diversity in aposematic signalling and with which to direct future research. A greater appreciation of the extent of variation in aposematic species, and of the selective pressures and constraints which contribute to this once‐paradoxical phenomenon, yields a new perspective for the field of aposematic signalling.
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Affiliation(s)
- Emmanuelle S Briolat
- Centre for Ecology & Conservation, College of Life & Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, U.K
| | - Emily R Burdfield-Steel
- Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, 40014, Finland
| | - Sarah C Paul
- Centre for Ecology & Conservation, College of Life & Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, U.K.,Department of Chemical Ecology, Bielefeld University, Universitätsstraße 25, 33615, Bielefeld, Germany
| | - Katja H Rönkä
- Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, 40014, Finland.,Organismal and Evolutionary Biology Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, 00014, Finland
| | - Brett M Seymoure
- Department of Biology, Colorado State University, Fort Collins, CO 80525, U.S.A.,Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 80525, U.S.A
| | - Theodore Stankowich
- Department of Biological Sciences, California State University, Long Beach, CA 90840, U.S.A
| | - Adam M M Stuckert
- Department of Biology, East Carolina University, 1000 E Fifth St, Greenville, NC 27858, U.S.A
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Distance-dependent defensive coloration in the poison frog Dendrobates tinctorius, Dendrobatidae. Proc Natl Acad Sci U S A 2018; 115:6416-6421. [PMID: 29866847 DOI: 10.1073/pnas.1800826115] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Poison dart frogs provide classic examples of warning signals: potent toxins signaled by distinctive, conspicuous coloration. We show that, counterintuitively, the bright yellow and blue-black color of Dendrobates tinctorius (Dendrobatidae) also provides camouflage. Through computational modeling of predator vision, and a screen-based detection experiment presenting frogs at different spatial resolutions, we demonstrate that at close range the frog is highly detectable, but from a distance the colors blend together, forming effective camouflage. This result was corroborated with an in situ experiment, which found survival to be background-dependent, a feature more associated with camouflage than aposematism. Our results suggest that in D. tinctorius the distribution of pattern elements, and the particular colors expressed, act as a highly salient close range aposematic signal, while simultaneously minimizing detectability to distant observers.
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Barnett JB, Cuthill IC, Scott-Samuel NE. Distance-dependent pattern blending can camouflage salient aposematic signals. Proc Biol Sci 2018; 284:rspb.2017.0128. [PMID: 28679722 DOI: 10.1098/rspb.2017.0128] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 06/01/2017] [Indexed: 11/12/2022] Open
Abstract
The effect of viewing distance on the perception of visual texture is well known: spatial frequencies higher than the resolution limit of an observer's visual system will be summed and perceived as a single combined colour. In animal defensive colour patterns, distance-dependent pattern blending may allow aposematic patterns, salient at close range, to match the background to distant observers. Indeed, recent research has indicated that reducing the distance from which a salient signal can be detected can increase survival over camouflage or conspicuous aposematism alone. We investigated whether the spatial frequency of conspicuous and cryptically coloured stripes affects the rate of avian predation. Our results are consistent with pattern blending acting to camouflage salient aposematic signals effectively at a distance. Experiments into the relative rate of avian predation on edible model caterpillars found that increasing spatial frequency (thinner stripes) increased survival. Similarly, visual modelling of avian predators showed that pattern blending increased the similarity between caterpillar and background. These results show how a colour pattern can be tuned to reveal or conceal different information at different distances, and produce tangible survival benefits.
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Affiliation(s)
- James B Barnett
- School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Innes C Cuthill
- School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Nicholas E Scott-Samuel
- School of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK
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Barnett JB, Redfern AS, Bhattacharyya-Dickson R, Clifton O, Courty T, Ho T, Hopes A, McPhee T, Merrison K, Owen R, Scott-Samuel NE, Cuthill IC. Stripes for warning and stripes for hiding: spatial frequency and detection distance. Behav Ecol 2016. [DOI: 10.1093/beheco/arw168] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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19
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Abstract
In this review I survey pelage and skin colouration patterns of the 29 orders of extant mammals and assess their functional significance. The vast majority of mammals are shades of grey or brown. Concealment is probably the principal evolutionary driver of pelage colouration in this Class likely through background matching and self-shadow concealment. A small minority of species are aposematic while many others have distinctive markings used in intraspecific and interspecific communication although the meaning of these markings is unclear. Colouration in mammals also has physiological consequences but these are barely understood as yet.
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Affiliation(s)
- Tim Caro
- Department of Wildlife, Fish and Conservation Biology, and Center for Population Biology, University of California, Davis, CA 95616, USA.
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