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Caves EM, Davis AL, Nowicki S, Johnsen S. Backgrounds and the evolution of visual signals. Trends Ecol Evol 2024; 39:188-198. [PMID: 37802667 DOI: 10.1016/j.tree.2023.09.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 09/04/2023] [Accepted: 09/08/2023] [Indexed: 10/08/2023]
Abstract
Color signals which mediate behavioral interactions across taxa and contexts are often thought of as color 'patches' - parts of an animal that appear colorful compared to other parts of that animal. Color patches, however, cannot be considered in isolation because how a color is perceived depends on its visual background. This is of special relevance to the function and evolution of signals because backgrounds give rise to a fundamental tradeoff between color signal detectability and discriminability: as its contrast with the background increases, a color patch becomes more detectable, but discriminating variation in that color becomes more difficult. Thus, the signal function of color patches can only be fully understood by considering patch and background together as an integrated whole.
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Affiliation(s)
- Eleanor M Caves
- Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
| | | | - Stephen Nowicki
- Department of Biology, Duke University, Durham, NC, 27708, USA
| | - Sönke Johnsen
- Department of Biology, Duke University, Durham, NC, 27708, USA
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Boycott TJ, Sherrard MG, Gall MD, Ronald KL. Deer management influences perception of avian plumage in temperate deciduous forests. Vision Res 2023; 213:108312. [PMID: 37703599 DOI: 10.1016/j.visres.2023.108312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2023] [Revised: 08/07/2023] [Accepted: 08/17/2023] [Indexed: 09/15/2023]
Abstract
Many animals use visual signals to communicate; birds use colorful plumage to attract mates and repel intruders. Visual signal conspicuousness is influenced by the lighting environment, which can be altered by human-induced changes. For example, deer-management efforts can affect vegetation structure and light availability. Whether these changes alter animal communication is still unknown. We investigated the effect of deer management on forest light and the contrast of understory birds against the forest background. We modeled visual perception using: (1) an ultraviolet-sensitive (UVS) avian model and plumage parameters representative of red, yellow, and blue birds (2) species-specific turkey visual and plumage parameters, and (3) individual-specific brown-headed cowbird visual and plumage parameters. Deer management led to greater light irradiance and lowered forest background reflectance. Management increased chromatic contrasts in the UVS model, primarily in deciduous forests and low understory, and across all habitat types in turkey and cowbird models. Deer management did not affect achromatic contrasts in the UVS model, but was associated with lower contrast in mixed forests for turkeys and across habitats for cowbirds. Together, this suggests that management of deer browsing is likely to impact visual signaling for a wide range of avian species. However, we also suspect that species- and individual-specific parameters increased the resolution of models, warranting consideration in future studies. Further work should determine if differences in visual perception translate to biologically relevant consequences. Our results suggest that, at least for some species, deer browsing and anthropogenic change may impose an evolutionary driver on visual communication.
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Affiliation(s)
- Timothy J Boycott
- Department of Biology, Vassar College, 124 Raymond Ave., Poughkeepsie, NY 12604, USA; New York Cooperative Fish and Wildlife Research Unit, Department of Natural Resources and the Environment, Cornell University, 226 Mann Drive, Ithaca, NY 14853, USA
| | - Morgan G Sherrard
- Department of Biology, Hope College, 35 East 12th Street, Holland, MI 49423, USA; University of Detroit Mercy School of Dentistry, 2700 Martin Luther King Jr. Blvd. Detroit, MI 48208-2576, USA
| | - Megan D Gall
- Department of Biology, Vassar College, 124 Raymond Ave., Poughkeepsie, NY 12604, USA; Neuroscience and Behavior Program, Vassar College, 124 Raymond Ave., Poughkeepsie, NY 12604, USA
| | - Kelly L Ronald
- Department of Biology, Hope College, 35 East 12th Street, Holland, MI 49423, USA.
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McCoy DE, Shultz AJ, Dall JE, Dionne JA, Johnsen S. The carotenoid redshift: Physical basis and implications for visual signaling. Ecol Evol 2023; 13:e10408. [PMID: 37693937 PMCID: PMC10485323 DOI: 10.1002/ece3.10408] [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: 07/17/2023] [Accepted: 07/21/2023] [Indexed: 09/12/2023] Open
Abstract
Carotenoid pigments are the basis for much red, orange, and yellow coloration in nature and central to visual signaling. However, as pigment concentration increases, carotenoid signals not only darken and become more saturated but they also redshift; for example, orange pigments can look red at higher concentration. This occurs because light experiences exponential attenuation, and carotenoid-based signals have spectrally asymmetric reflectance in the visible range. Adding pigment disproportionately affects the high-absorbance regions of the reflectance spectra, which redshifts the perceived hue. This carotenoid redshift is substantial and perceivable by animal observers. In addition, beyond pigment concentration, anything that increases the path length of light through pigment causes this redshift (including optical nano- and microstructures). For example, male Ramphocelus tanagers appear redder than females, despite the same population and concentration of carotenoids, due to microstructures that enhance light-pigment interaction. This mechanism of carotenoid redshift has sensory and evolutionary consequences for honest signaling in that structures that redshift carotenoid ornaments may decrease signal honesty. More generally, nearly all colorful signals vary in hue, saturation, and brightness as light-pigment interactions change, due to spectrally asymmetrical reflectance within the visible range of the relevant species. Therefore, the three attributes of color need to be considered together in studies of honest visual signaling.
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Affiliation(s)
- Dakota E. McCoy
- Department of Materials Science and EngineeringStanford UniversityStanfordCaliforniaUSA
- Hopkins Marine StationStanford UniversityPacific GroveCaliforniaUSA
- Department of BiologyDuke UniversityDurhamNorth CarolinaUSA
| | - Allison J. Shultz
- Ornithology DepartmentNatural History Museum of Los Angeles CountyLos AngelesCaliforniaUSA
| | - Jacqueline E. Dall
- Ornithology DepartmentNatural History Museum of Los Angeles CountyLos AngelesCaliforniaUSA
| | - Jennifer A. Dionne
- Department of Materials Science and EngineeringStanford UniversityStanfordCaliforniaUSA
- Department of RadiologyStanford UniversityStanfordCaliforniaUSA
| | - Sönke Johnsen
- Department of BiologyDuke UniversityDurhamNorth CarolinaUSA
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Davis A, Zipple MN, Diaz D, Peters S, Nowicki S, Johnsen S. Influence of visual background on discrimination of signal-relevant colours in zebra finches ( Taeniopygia guttata). Proc Biol Sci 2022; 289:20220756. [PMID: 35673868 PMCID: PMC9174715 DOI: 10.1098/rspb.2022.0756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Colour signals of many animals are surrounded by a high-contrast achromatic background, but little is known about the possible function of this arrangement. For both humans and non-human animals, the background colour surrounding a colour stimulus affects the perception of that stimulus, an effect that can influence detection and discrimination of colour signals. Specifically, high colour contrast between the background and two given colour stimuli makes discrimination more difficult. However, it remains unclear how achromatic background contrast affects signal discrimination in non-human animals. Here, we test whether achromatic contrast between signal-relevant colours and an achromatic background affects the ability of zebra finches to discriminate between those colours. Using an odd-one-out paradigm and generalized linear mixed models, we found that higher achromatic contrast with the background, whether positive or negative, decreases the ability of zebra finches to discriminate between target and non-target stimuli. This effect is particularly strong when colour distances are small (less than 4 ΔS) and Michelson achromatic contrast with the background is high (greater than 0.5). We suggest that researchers should consider focal colour patches and their backgrounds as collectively comprising a signal, rather than focusing on solely the focal colour patch itself.
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Affiliation(s)
- Alexander Davis
- Department of Biology, Duke University, Durham, NC 27708, USA
| | - Matthew N. Zipple
- Department of Biology, Duke University, Durham, NC 27708, USA,Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA
| | - Danae Diaz
- Department of Biology, Duke University, Durham, NC 27708, USA
| | - Susan Peters
- Department of Biology, Duke University, Durham, NC 27708, USA
| | - Stephen Nowicki
- Department of Biology, Duke University, Durham, NC 27708, USA
| | - Sönke Johnsen
- Department of Biology, Duke University, Durham, NC 27708, USA
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Kemp DJ, Edwards W, White TE. Captivating color: evidence for optimal stimulus design in a polymorphic prey lure. Behav Ecol 2022. [DOI: 10.1093/beheco/arac034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Abstract
Many species – humans included – employ color as an instrument of deception. One intriguing example of this resides in the conspicuous abstract color patterns displayed on the bodies of female orb weaving spiders. These displays increase prey interception rates and thereby function at least as visual lures. Their chromatic properties however vary extensively, both across and within species, with discrete forms often co-existing in the manner of a stable polymorphism. Variation is principally expressed in terms of signal hue (color per se), but it is unclear how attractiveness scales with this property and if extant morphs are maximally attractive relative to a graded range of potential alternatives. We examined these questions by assessing catch rates among color-manipulated females of the dimorphic jeweled spider Gasteracantha fornicata in their natural webs. The manipulation altered dorsal appearance in a manner akin to adding six new variants of their existing white/yellow phenotypes. This magnified the natural variation in stimulus hue independently of chroma (saturation) across a range spanning most of the color spectrum. Catch rate varied across treatments in simple accordance with how greatly stimulus hue deviated from either of the two extant spider phenotypes. Predictions based on fly-perceived chromatic and achromatic background contrast were clearly unsupported despite dipterans constituting ~60 % of identifiable prey. This study supports the importance of signal coloration per se in G. fornicata and suggests that extant lure phenotypes reside in a broadly optimal spectral range for stimulating their aggregate prey community.
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Affiliation(s)
- Darrell J Kemp
- Department of Biological Sciences, Macquarie University, North Ryde, New South Wales, Australia
| | - Will Edwards
- College of Science and Engineering, James Cook University, Cairns, Queensland, Australia
| | - Thomas E White
- School of Life and Environmental Sciences, University of Sydney, Sydney, New South Wales, Australia
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Chatragadda R, Dufossé L. Ecological and Biotechnological Aspects of Pigmented Microbes: A Way Forward in Development of Food and Pharmaceutical Grade Pigments. Microorganisms 2021; 9:637. [PMID: 33803896 PMCID: PMC8003166 DOI: 10.3390/microorganisms9030637] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 03/04/2021] [Accepted: 03/15/2021] [Indexed: 12/17/2022] Open
Abstract
Microbial pigments play multiple roles in the ecosystem construction, survival, and fitness of all kinds of organisms. Considerably, microbial (bacteria, fungi, yeast, and microalgae) pigments offer a wide array of food, drug, colorants, dyes, and imaging applications. In contrast to the natural pigments from microbes, synthetic colorants are widely used due to high production, high intensity, and low cost. Nevertheless, natural pigments are gaining more demand over synthetic pigments as synthetic pigments have demonstrated side effects on human health. Therefore, research on microbial pigments needs to be extended, explored, and exploited to find potential industrial applications. In this review, the evolutionary aspects, the spatial significance of important pigments, biomedical applications, research gaps, and future perspectives are detailed briefly. The pathogenic nature of some pigmented bacteria is also detailed for awareness and safe handling. In addition, pigments from macro-organisms are also discussed in some sections for comparison with microbes.
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Affiliation(s)
- Ramesh Chatragadda
- Biological Oceanography Division (BOD), Council of Scientific and Industrial Research-National Institute of Oceanography (CSIR-NIO), Dona Paula 403004, Goa, India
| | - Laurent Dufossé
- Chemistry and Biotechnology of Natural Products (CHEMBIOPRO Lab), Ecole Supérieure d’Ingénieurs Réunion Océan Indien (ESIROI), Département Agroalimentaire, Université de La Réunion, F-97744 Saint-Denis, France
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