Habitat light, colour variation, and ultraviolet reflectance in the Grand Cayman anole, Anolis conspersus
01 Jul 2001-Biological Journal of The Linnean Society (No longer published by Elsevier)-Vol. 73, Iss: 3, pp 299-320
TL;DR: Evidence is presented to show how geological, ecological, and physiological factors could have interacted to select for a short wavelength-reflective dewlap from a long wavelength- reflective precursor following the colonization of Grand Cayman from Jamaica by A. grahami between 2 and 3 Mya.
Abstract: Data from a diversity of sources are consistent with the hypothesis that the Grand Cayman anole, Anolis conspersus, is descended directly from Anolis grahami of Jamaica. Although the two species have remained morphologically similar, coloration in A. conspersus has changed considerably from that of its ancestor. The most dramatic difference is seen in dewlap colour, where A. conspersus has evolved a blue and highly UV-reflective dewlap from the ancestral orange-and-yellow colour state. In addition, variation in normal (non-metachrosis) dorsum coloration in A. grahami populations is limited to shades of green (olive, emerald, teal), whereas in A. conspersus dorsum coloration varies from green to blue and to brown. This increased colour variation occurs despite Grand Cayman being a small, relatively featureless island only 35 km in length. Results of this study suggest that ambient light differences associated with precipitation-related vegetation structure may have played an important role in the evolution of A. conspersus body colour variation. Evidence is presented to show how geological, ecological, and physiological factors could have interacted to select for a short wavelength-reflective dewlap from a long wavelength-reflective precursor following the colonization of Grand Cayman from Jamaica by A. grahami between 2 and 3 Mya.
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TL;DR: This work investigated how sexual selection acts on various male traits in three populations in which males differed in coloration of the chuckwalla, Sauromalus obesus, and found that phenotypic selection was acting on territory quality in all three populations.
Abstract: Geographic variation in selection pressures may result in population divergence and speciation, especially if sexual selection varies among populations. Yet spatial variation in targets and intensity of sexual selection is well studied in only a few species. Even more rare are simultaneous studies of multiple populations combining observations from natural settings with controlled behavioral experiments. We investigated how sexual selection varies among populations of the chuckwalla, Sauromalus obesus. Chuckwallas are sexually dimorphic in color, and males vary in coloration among populations. Using field observations and multiple regression techniques, we investigated how sexual selection acts on various male traits in three populations in which males differed in coloration. The influence of sexual selection on male coloration was then investigated in more detail using controlled experiments. Results from field observations indicate that phenotypic selection was acting on territory quality in all three populations. In two populations, selection was also acting either directly or indirectly on male coloration. Male color likely functions as an indicator of food resources to females because male color is based partly on carotenoid pigments. In controlled experiments, significantly more females from these two populations chose males with brighter colors over dull males, a result consistent with studies on carotenoid pigments in other taxa. In a third population, no evidence of sexual selection on male coloration was found in either the field study or controlled experiment. Lack of female preferences for male color in this population, in which chuckwalla densities are low and home ranges are large, may result from searching costs to females.
115 citations
TL;DR: The results support the view that selection for signal efficacy plays an important role in the evolution of animal signals and suggest a color pattern that may maximize detectability across all habitat types, potentially explaining female conservatism.
Abstract: Whether general patterns of signal evolution can be explained by selection for signal efficacy (detectability) has yet to be established. To establish the importance of signal efficacy requires evidence that both signals and their detectability to receivers have evolved in response to habitat shifts in a predictable fashion. Here, we test whether habitat structure has predictable effects on the evolution of male and female display coloration in 21 lineages of African dwarf chameleon (Bradypodion), based on a phylogenetic comparative analysis. We used quantitative measures of display coloration and estimated signal detectability as the contrast of those colors among body regions or against the background vegetation as perceived by the chameleon visual system. Both male and female display colors varied predictably with different aspects of habitat structure. In several (but not all) instances, habitat-associated shifts in display coloration resulted in habitat-associated variation in detectability. While males exhibit a remarkable variety of colors and patterns, female display coloration is highly conserved, consisting in all populations of contrasting dark and light elements. This color pattern may maximize detectability across all habitat types, potentially explaining female conservatism. Overall, our results support the view that selection for signal efficacy plays an important role in the evolution of animal signals.
111 citations
Cites background from "Habitat light, colour variation, an..."
...…differences in the contrast of colors against the background for sympatric or allopatric populations differing in their habitat characteristics and signaling traits (Macedonia 2001; Leal and Fleishman 2002, 2004; Heindl and Winkler 2003a, 2003b; Doucet et al. 2007; Gomez and Théry 2007)....
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TL;DR: Results suggest that combined visual/seismic components of multimodal displays may serve as ‘backup signals’, ensuring reception under different environmental conditions.
100 citations
Cites background from "Habitat light, colour variation, an..."
...…species have evolved signals that function best in specific environments by matching signals and transmission characteristics of the environment (Fleishman 1992; Endler & Thery 1996; Macedonia 2001; Boughman 2002; Gray et al. 2008; Seehausen et al. 2008; Cocroft et al. 2010; Elias et al. 2010)....
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TL;DR: The results suggest that UV brightness serves as an important intraspecific sexual signal in C. eurytheme, and they provide the clearest evidence to date regarding the functional relevance of structural coloration to female mate choice in butterflies.
87 citations
Cites methods from "Habitat light, colour variation, an..."
...All three of these techniques have been used by other investigators (e.g. Macedonia 2001; Acorn 2002; Raguso & Willis 2005), and while all three techniques have been shown to be valid at measuring UV reflectance accurately, no single method has been widely accepted as best....
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TL;DR: Evidence is provided that the spectral properties of colorful plumage predict male mating success in a lekking species and provide important insight into why many leKking birds are dichromatic and elaborate in coloration.
Abstract: The evolution of colorful plumage has been dramatic in lekking species. Several studies show that the size of colorful traits influence female choice in leks; however, relatively little is known about the specific function of color, in particular its spectral properties, in lekking taxa. To determine the importance of color in a lekking species, we monitored the mating success of male golden-collared manakins, Manacus vitellinus, and related this to spectral measures of their colorful plumage, as well as other morphological and behavioral traits shown to be important in other lekking species. We found that lek centrality, male body size, and plumage brightness were associated with male mating success. Only plumage brightness, however, entered a multiple regression model, indicating that plumage is the overall best predictor of mating success. These results provide evidence that the spectral properties of colorful plumage predict male mating success in a lekking species and provide important insight into why many lekking birds are dichromatic and elaborate in coloration. Copyright 2006.
84 citations
Cites methods from "Habitat light, colour variation, an..."
...This is a standard method to handle spectral data (e.g., Bennett et al., 1997; Endler and Théry, 1996; Hunt et al., 1998; Macedonia, 2001; Sheldon et al., 1999), especially well suited for spectra with multiple peaks (Cuthill et al., 1999)....
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...This is a standard method to handle spectral data (e.g., Bennett et al., 1997; Endler and Théry, 1996; Hunt et al., 1998; Macedonia, 2001; Sheldon et al., 1999), especially well suited for spectra with multiple peaks (Cuthill et al....
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References
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TL;DR: Sensory systems, signals, signaling behavior, and habitat choice are evolutionarily coupled and should coevolve in predictable directions, determined by environmental biophysics, neurobiology, and the genetics of the suites of traits.
Abstract: There is a bewildering diversity of signals, sensory systems, and signaling behavior. A consideration of how these traits affect each other's evolution explains some of this diversity. Natural selection favors signals, receptors, and signaling behavior that maximize the received signals relative to background noise and minimize signal degradation. Properties of sensory systems bias the direction of evolution of the signals that they receive. For example, females may prefer males whose signals they can perceive more easily, and this will lead to the spread of more easily perceived male traits. Environmental conditions during signal transmission and detection also affect signal perception. Specific environmental conditions will bias the evolutionary direction of behavior, which affects the time and place of signaling as well as microhabitat preferences. Increased specialization of microhabitats and signaling behavior may lead to biased evolution of the sensory systems to work more efficiently. Thus, sensory...
1,717 citations
TL;DR: The first observation may be related to the first in the following way: nonsynchronous spatial overlap could dictate relatively great resource overlap for species coinhabiting patchy or edge areas, requiring great differences between the species in prey size in addition to those in climatic habitat.
Abstract: Sympatric native Anolis species with similar structural habitats but contrasting climatic habitats are closer in head and body size on species—rich than on depauperate islands. In two localities, sympatric Anolis species with differential occurrences in sun or shade sought lower, more shaded perches during midday, resulting in partly nonsynchronous utilization of the vegetation by the two species. The second observation may be related to the first in the following way: nonsynchronous spatial overlap could dictate relatively great resource overlap for species coinhabiting patchy or edge areas, requiring great differences between the species in prey size in addition to those in climatic habitat. The extent of such overlap on small depauperate islands could be greater if these contained a greater proportion of patchy or edge habitats (with respect to insolation), or if climatic preferences were broader and more overlapping than on large, species—rich islands. In each locality, the relatively more shade—inhab...
1,562 citations
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...Schoener TW. 1970....
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TL;DR: Until the authors know more about how and why natural selection occurs, attempts to measure it are quixotic, and discussions of its importance are theandric.
Abstract: All too often in evolutionary biology we are led to speculate or infer the mode of action of natural selection; we usually do not know why some individuals are more adaptive than others. Very often attempts to measure natural selection are unsuccessful, leading to heated arguments about' the relative importance of selection, genetic drift, and epistasis in evolution (Lewontin, 1974). Until we know more about how and why natural selection occurs, attempts to measure it are quixotic, and discussions of its importance are theandric. It is no coincidence that most of the successful studies of natural selection have dealt with animal color patterns; it should be obvious which color patterns are more adaptive in the presence of visually hunting predators. The adaptive significance of warning coloration and mimicry of distasteful species has been worked out (Cott, 1940; Wickler, 1968; Edmunds, 1974; Rothschild, 1975; Turner, 1977). But most species are neither distasteful nor mimetic; most have inconspicuous or cryptic color patterns in their natural habitats (Poulton, 1890; Thayer, 1909; Cott, 1940; Endler, 1978). Most field and experimental studies have shown that the overall color or tone of inconspicuous species matches or approximates the background (DiCesnola, 1904; Sumner, 1934, 1935; Isley, 1938; Popham, 1942; Dice, 1947; Kettlewell, 1956, 1973; Turner, 1961; Kaufman, 1974; Wicklund, 1975; Curio, 1976), but they treated species with solid colors or
1,290 citations
TL;DR: New methods make it practical to measure the colour spectrum of pattern elements (patches) of animals and their visual backgrounds for the conditions under which patch spectra reach the conspecific's, predator's or prey's eyes.
Abstract: In studies of animal colouration it is no longer necessary to rely on subjective assessments of colour and conspicuousness, nor on methods which rely upon human vision. This is important because animals vary greatly in colour vision and colour is context-dependent. New methods make it practical to measure the colour spectrum of pattern elements (patches) of animals and their visual backgrounds for the conditions under which patch spectra reach the conspecific's, predator's or prey's eyes. These methods can be used in both terrestrial and aquatic habitats. A patch's colour is dependent not only upon its reflectance spectrum, but also upon the ambient light spectrum, the transmission properties of air or water, and the veiling light spectrum. These factors change with time of day, weather, season and microhabitat, so colours must be measured under the conditions prevalent when colour patterns are normally used. Methods of measuring, classifying and comparing colours are presented, as well as techniques for assessing the conspicuousness of colour patterns as a whole. Some implications of the effect of environmental light and vision are also discussed.
1,140 citations
TL;DR: The structure of forests leads to four major light habitats when the sun is not blocked by clouds: forest shade, woodland shade, small gaps, and large gaps, respectively, characterized by yellow—green, blue—gray, reddish, and "white" ambient light spectra, respectively.
Abstract: Forests exhibit much variation in light environments, and this can affect communication among animals, communication between animals and plants, photosynthesis, and plant morphogenesis. Light environments are caused by, and can be predicted from, the geometry of the light paths, the weather conditions, and the time of day. The structure of forests leads to four major light habitats when the sun is not blocked by clouds: forest shade, woodland shade, small gaps, and large gaps. These are characterized by yellow—green, blue—gray, reddish, and "white" ambient light spectra, respectively. When the sun is blocked by clouds, the spectra of these four habitats converge on that of large gaps and open areas, so the single light environment during cloudy weather will be called open/cloudy. An additional light environment (early/late) is associated with low sun angles (near dawn or dusk); it is purplish. Each light environment is well defined and was found in forests of Trinidad, Panama, Costa Rica, Australia, California, and Florida. Scattered literature references suggest similar patterns elsewhere in North America, Europe, and Java. Perceived colors of animals, flowers, and fruits depend upon the interaction between ambient light color and the reflectance color of the animal or plant parts. As a result, an animal or plant may have a different appearance in each environment, i.e., a color pattern may be relatively cryptic in some light environments while relatively conspicuous in others. This has strong implications for the joint evolution of visual signals and vision, as well as microhabitat choice. Plant growth and form may also be affected by variation in the color of forest light.
1,108 citations
"Habitat light, colour variation, an..." refers background in this paper
...For visual signals, FOR ANIMAL COLOUR SIGNALS relevant ecological variables include the ambient light Endler (1992, 1993) has shown that, under sunnyspectrum in which a signal is viewed and features of skies, four types of structural light habitats occur inthe visual background from which the…...
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...…because their reflectance spectra will mented, anoles that inhabit dark forest environmentschange with changing light conditions, making them exhibit dewlaps that may be white or yellow, butharder to recognize and track (Endler, 1993). which are never orange or red (Fleishman, 1992)....
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...Legend as in Table 1. different forest light environments (e.g. Endler, 1992, 1993)....
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...…& Leal, 1993; Macedonia et al., 2000; Stoehr & McGraw, 2001).most reflective colour patch would be yellow-green because it most closely resembles the ambient spec- Traditionally, the function ascribed to dewlap colour has been one of species recognition and reproductivetrum (e.g. Endler, 1993)....
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