An Integrative Framework for the Appraisal of Coloration in Nature

Abstract

The world in color presents a dazzling dimension of phenotypic variation. Biological interest in this variation has burgeoned, due to both increased means for quantifying spectral information and heightened appreciation for how animals view the world differently than humans. Effective study of color traits is challenged by how to best quantify visual perception in nonhuman species. This requires consideration of at least visual physiology but ultimately also the neural processes underlying perception. Our knowledge of color perception is founded largely on the principles gained from human psychophysics that have proven generalizable based on comparative studies in select animal models. Appreciation of these principles, their empirical foundation, and the reasonable limits to their applicability is crucial to reaching informed conclusions in color research. In this article, we seek a common intellectual basis for the study of color in nature. We first discuss the key perceptual principles, namely, retinal photoreception, sensory channels, opponent processing, color constancy, and receptor noise. We then draw on this basis to inform an analytical framework driven by the research question in relation to identifiable viewers and visual tasks of interest. Consideration of the limits to perceptual inference guides two primary decisions: first, whether a sensory-based approach is necessary and justified and, second, whether the visual task refers to perceptual distance or discriminability. We outline informed approaches in each situation and discuss key challenges for future progress, focusing particularly on how animals perceive color. Given that animal behavior serves as both the basic unit of psychophysics and the ultimate driver of color ecology/evolution, behavioral data are critical to reconciling knowledge across the schools of color research.

Functional visual sensitivity to ultraviolet wavelengths in the Pileated Woodpecker (Dryocopus pileatus), and its influence on foraging substrate selection

“…Since the study subjects did behaviorally discriminate between control and treatment substrates, these perceptual model results suggest that the SWS1 λ max of the Pileated Woodpecker is similar to that of the Great Spotted Woodpecker. This finding is consistent with the conservative nature of avian visual systems [10]. Similarly, if an LWS Weber fraction estimate for PIWO of 0.06 is accurate, it would fall within the published range of values for avian species [49].…”

“…These data then can be incorporated into models to estimate the saliency of wavelengths, or the discriminability of colors, in species of interest [4] and [9]. Kemp et al [10] recognized such modeling as a valuable first step to investigating visual systems, but stressed the importance of behavioral studies in vision research. Behavioral studies may not categorize a species' visual system as UVS or VS, but they can demonstrate the ability to detect and respond to UV cues, and thus provide potentially useful insights into visual systems and the functional significance of UV sensitivity (i.e.…”

Improved color constancy in honey bees enabled by parallel visual projections from dorsal ocelli

“…5). Although the MT makes no assumptions about the underlying sensory or neural processing of the color signals (47,49), the RN predicts thresholds of chromatic discriminability based on the signal to noise ratio imposed by photon noise and internal receptor noise under photopic conditions (50,51). The use of these two color spaces A B C Simulation results show that a mechanism enabled by ocellar inputs improves color constancy by diminishing the magnitude of the chromatic shift (DI ), measured as the Euclidean distance between the first and the last points of each locus in the respective color space, expected from changes in illumination compared with the classic von Kries chromatic adaptation model (DvK ) in the two color spaces considered (Fig.…”

Variation in Display Behavior, Ornament Morphology, Sexual Size Dimorphism, and Habitat Structure in the Fan-Throated Lizard (Sitana, Agamidae)

“…S5 for examples; K¨astle, 1998). In light of recent research on the complex physiologies underlying color production and change in lizards (Saenko et al, 2014;Teyssier et al, 2015), and comprehensive frameworks for the analysis of coloration in natural populations (Kemp et al, 2015), FanThroated Lizards offer a veritable cornucopia to biologists interested in the physiological basis of coloration.…”