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: Specific, testable functional hypotheses are offered for the most common pigmentary and structural components of vertebrate colour patches and how multiple trait evolution theory can be applied to the components of single colour patches.
Abstract: Colour patches are complex traits, the components of which may evolve independently through a variety of mechanisms. Although usually treated as simple, two-dimensional characters and classified as either structural or pigmentary, in reality colour patches are complicated, three-dimensional structures that often contain multiple pigment types and structural features. The basic dermal chromatophore unit of fishes, reptiles and amphibians consists of three contiguous cell layers. Xanthophores and erythrophores in the outermost layer contain carotenoid and pteridine pigments that absorb short-wave light; iridophores in the middle layer contain crystalline platelets that reflect light back through the xanthophores; and melanophores in the basal layer contain melanins that absorb light across the spectrum. Changes in any one component of a chromatophore unit can drastically alter the reflectance spectrum produced, and for any given adaptive outcome (e.g. an increase in visibility), there may be multiple biochemical or cellular routes that evolution could take, allowing for divergent responses by different populations or species to similar selection regimes. All of the mechanisms of signal evolution that previously have been applied to single ornaments (including whole colour patches) could potentially be applied to the individual components of colour patches. To reach a complete understanding of colour patch evolution, however, it may be necessary to take an explicitly multi-trait approach. Here, we review multiple trait evolution theory and the basic mechanisms of colour production in fishes, reptiles and amphibians, and use a combination of computer simulations and empirical examples to show how multiple trait evolution theory can be applied to the components of single colour patches. This integrative perspective on animal colouration opens up a host of new questions and hypotheses. We offer specific, testable functional hypotheses for the most common pigmentary (carotenoid, pteridine and melanin) and structural components of vertebrate colour patches.
245 citations
TL;DR: It is found that populations from mesic and xeric conditions occupy two distinct habitats with respect to light intensity and spectral quality and that dewlap design has diverged between populations in a way that increases signal detectability in each habitat.
Abstract: We tested the prediction of the sensory drive hypothesis using four allopatric populations of the lizard Anolis cristatellus from two distinct environments (i.e., mesic and xeric conditions). For each population, we measured habitat light characteristics and quantified signal design by measuring the spectral and total reflectance and transmittance of the dewlap. We used these data to calculate dewlap detectability using an empirically based model of signal detection probability. We found that populations from mesic and xeric conditions occupy two distinct habitats with respect to light intensity and spectral quality and that dewlap design has diverged between populations in a way that increases signal detectability in each habitat. The major difference in dewlap design was in total reflectance and transmittance, making dewlaps from xeric habitats darker and dewlaps from mesic habitats brighter. Furthermore, dewlap detection decreased significantly when a dewlap from a xeric habitat is detected u...
230 citations
Cites background from "Habitat light, colour variation, an..."
...Second, there is evidence that differences in habitat light conditions have selected for different color patterns in different microhabitats (i.e., selection through the process of sensory drive; Fleishman et al. 1993; Fleishman 2000; Macedonia 2001; Leal and Fleishman 2002)....
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...vol. 163, no. 1 the american naturalist january 2004 Differences in Visual Signal Design and Detectability between Allopatric Populations of Anolis Lizards Manuel Leal* and Leo J. Fleishman† Department of Biology, Union College, Schenectady, New York 12308...
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TL;DR: It is found that the chromatic and brightness contrasts of golden patches used during courtship are greater against the cleared court than against adjacent litter, and that cleared courts provide a less variable background for these color patches, resulting in displays that consistently contrast the visual background.
Abstract: Effective visual communication requires signals that are easy to detect, transmit, receive, and discriminate. Animals can increase the probability that their visual signals would be detected by evolving signals that contrast with their visual background. Animals can further enhance this contrast by behaviorally modifying the existing visual background. Male golden-collared manakins (Manacus vitellinus) clear leaf litter from the ground to form courts, which are used as display arenas. Using reflectance measures of the signal (male plumage) and the visual background (cleared court and adjacent litter), the irradiance measures of ambient light during display, and published measures of photoreceptor sensitivity of a Passerine, we test the hypothesis that court-clearing augments the contrast between male plumage and the visual background. We find that the chromatic and brightness contrasts of golden patches used during courtship are greater against the cleared court than against adjacent litter. In addition, we find that cleared courts provide a less variable background for these color patches, resulting in displays that consistently contrast the visual background. These results suggest that behavioral modification of the visual background may act to increase the conspicuousness of colorful male plumage during display, providing an explanation for why golden-collared manakins, and possibly other species, build or clear display courts. Key words: chromatic contrasts, court-clearing, Manacus vitellinus, manakins, signaling, visual signals. [Behav Ecol 15:1003–1010 (2004)]
146 citations
TL;DR: D dwarf chameleons showed different behavioural responses, including colour change, towards multiple predators that detect and capture prey in different ways, and whether these antipredator responses varied geographically was consistent among populations.
Abstract: Potential prey are often exposed to multiple predators that vary in their foraging tactics and ability to detect prey. For animals that rely on crypsis to avoid predators, one solution is to alter their behaviour or appearance to maximize crypsis in ways that are specific to different types of predator. We tested whether dwarf chameleons (Bradypodion transvaalense) showed different behavioural responses, including colour change, towards multiple predators (bird and snake models) that detect and capture prey in different ways, and whether these antipredator responses varied geographically. Chameleons consistently used the same body postures (lateral compression and flipping to the opposite side of the branch) and displayed similar chromatic (colour) contrast against the natural background in response to both predator types. However, they became significantly more achromatically contrasting (brighter) in the presence of the snake compared to the bird. This relative difference in achromatic contrast towards the two types of predator was consistent among populations. There were also significant differences in both absolute achromatic and chromatic contrast among populations despite very similar light environment, background coloration and habitat structure. Our results highlight facultative crypsis as one type of flexible antipredator tactic and emphasize the importance of visual ecology in understanding prey–predator interactions. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88, 437–446.
143 citations
Cites methods from "Habitat light, colour variation, an..."
...The contrast measures we used are simple measures of contrast in radiance (Endler, 1990; Macedonia, 2001; Heindl & Winkler, 2003)....
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...The contrast measures we used are simple measures of contrast in radiance (Endler, 1990; Macedonia, 2001; Heindl & Winkler, 2003)....
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...and background, respectively, integrated over 320‐ 700 nm. To calculate chromatic contrast, all radiance spectra of the chameleons and backgrounds were standardized for brightness (area under the curve 320‐ 700 nm = 1). Chromatic contrast was then calculated as the Euclidean distance ( D s ) between the radiance spectrum of the chameleon vs. background (Endler, 1990; Macedonia, 2001; Heindl & Winkler, 2003), using:...
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...Chromatic contrast was then calculated as the Euclidean distance ( D s ) between the radiance spectrum of the chameleon vs. background (Endler, 1990; Macedonia, 2001; Heindl & Winkler, 2003), using: where Q t ( λ ) and Q b ( λ ) is the radiance at a given wavelength and summation is over each 5 nm…...
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TL;DR: The results confirmed that there are real differences in crypsis conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations.
Abstract: Many animal species display striking color differences with respect to geographic location, sex, and body region. Traditional adaptive explanations for such complex patterns invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Although there is now a substantial body of evidence supporting the role of sexual selection for signaling functions, quantitative studies of crypsis remain comparatively rare. Here, we combine objective measures of coloration with information on predator visual sensitivities to study the role of crypsis in the evolution of color variation in an Australian lizard species complex (Ctenophorus decresii). We apply a model that allows us to quantify crypsis in terms of the visual contrast of the lizards against their natural backgrounds, as perceived by potential avian predators. We then use these quantitative estimates of crypsis to answer the following questions. Are there significant differences in crypsis conspicuousness among populations? Are there significant differences in crypsis conspicuousness between the sexes? Are body regions "exposed" to visual predators more cryptic than "hidden" body regions? Is there evidence for local adaptation with respect to crypsis against different substrates? In general, our results confirmed that there are real differences in crypsis conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations. Body regions that varied most in contrast between the sexes and between populations were also most conspicuous and are emphasized by males during social and sexual signaling. However, results varied with respect to the aspect of coloration studied. Results based on chromatic contrast ("hue" of color) provided better support for the crypsis hypothesis than did results based on achromatic contrast ("brightness" of color). Taken together, these results support the view that crypsis plays a substantial role in the evolution of color variation and that color patterns represent a balance between the need for conspicuousness for signaling and the need for crypsis to avoid predation.
137 citations
References
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TL;DR: The results indicate that A. carolinensis can improve its water balance status in desiccating conditions by reducing water loss via evaporation, and that reduction of cutaneous evAPoration is an important component of this adjustment.
Abstract: Anolis carolinensis lizards maintained for 7+ days in dry air ( 95% rh). Evaporation rates from skin isolated from lizards living in dry air were also less than half those from skin of lizards kept in humid air. These results indicate that A. carolinensis can improve its water balance status in desiccating conditions by reducing water loss via evaporation, and that reduction of cutaneous evaporation is an important component of this adjustment. The plasticity of evaporation rates of individual lizards in response to prior conditioning is large, and raises the question of whether the well-known correlation between evaporation rate and habitat aridity in reptiles reflects primarily inherited or acquired characteristics.
48 citations
47 citations
TL;DR: Comparisons of the dewlaps of sympatric species do not support the hypothesis that differences in dewlap size aid in species recognition, and the data suggest the possibility that species in poorly lit habitats may have relatively larger dewlap than species in brighter habitats.
Abstract: The dewlaps of anoles vary greatly in size, including some species that have no dewlap at all. The dewlap serves many purposes-including courtship, territorial interactions, species recognition, and predator deterrence-and must be an effective communicatory signal in different light environments. We measured dewlap size in 52 species of Caribbean anoles to test a variety of hypotheses concerning the evolution of dewlap size. Species with conspicuous body coloration or patterning tend to have relatively smaller dewlaps than do other species. In addition, the data suggest the possibility that species in poorly lit habitats may have relatively larger dewlaps than species in brighter habitats. By contrast, no relationship exists between relative dewlap size and structural habitat, display rate, or sexual size dimorphism. Further, comparisons of the dewlaps of sympatric species do not support the hypothesis that differences in dewlap size aid in species recognition.
46 citations
TL;DR: It is hypothesized that the head movements which make up the introductory portion of the territorial “assertion” display of Anolis auratus function to draw the gaze of conspecifics.
Abstract: It is hypothesized that the head movements which make up the introductory portion of the territorial “assertion” display of Anolis auratus function to draw the gaze of conspecifics. Earlier experiments showed that two features of a motion pattern were critical in making it effective at gaining the attention of an anole: (1) it should consist of high acceleration and velocity, and (2) a Fourier transform of the motion pattern should reveal sinusoidal frequency components distinct from those present in motion patterns commonly present in the environment. The most common source of motion in the environment is windblown vegetation. Motion of vegetation typical of the A. auratus habitat was quantified and analyzed by Fourier transform. Assertion displays of a number of individual lizards were filmed and quantified. It was found that the first 3.6 s of the displays consisted of high acceleration/high velocity movements which contained, at certain sinusoidal frequencies, amplitude several times greater than what was present in the vegetation movement. Thus, motion detection properties of the visual system and movement properties of windblown vegetation combine to influence the physical form of this visual display.
40 citations
TL;DR: Microhabitat selection in the light gradient confirmed the hypotheses that light intensity at microsites selected by A. cristatellus and A. gundlachi would not use light intensity as a cue for selecting thermally appropriate microsites and tested these hypotheses in a laboratory experiment in which light intensity and operative temperature were uncoupled.
Abstract: Although basking behaviour has been widely cited as a thermoregulatory mechanism in reptiles, few previous researchers have studied how lizards select basking sites in nature. 2. We conducted field and laboratory studies to determine whether two species of Anolis lizards in Puerto Rico use light intensity as a proximal cue for recognizing the thermal properties of microhabitat patches. 3. Under natural conditions Anolis cristatellus, a behavioural thermoregulator that we sampled in an open woodland, frequently occupied microsites that were more brightly illuminated than randomly sampled microsites. In contrast, A. gundlachi, a behavioural thermoconformer that we sampled in a shaded forest, occupied perch sites randomly with respect to light intensity. Operative temperatures were significantly correlated with light intensity at all times of day in the A. cristatellus habitat; in the A. gundlachi habitat, however, operative temperatures and light mtensity were significantly correlated only at the higher and more variable light intensities prevalent at midday. 4. We therefore hypothesized that A. cristatellus, using light intensity as a proximal cue, would perch in brightly lighted microsites to raise its body temperature and more shaded microsites to lower its body temperature; we also hypothesized that A. gundlachi would not use light intensity as a cue for selecting thermally appropriate microsites. 5. We tested these hypotheses in a laboratory experiment in which light intensity and operative temperature were uncoupled. Lizards were offered a gradient of light intensities under three constant temperature conditions: 10$^\circ$C below acclimation temperature, the acclimation temperature (set equal to the mean field-active body temperature) and 4$^\circ$C above the acclimation temperature. 6. Microhabitat selection in the light gradient confirmed our hypotheses: light intensity at microsites selected by A. cristatellus varied inversely with experimental temperature but light intensity at microsites selected by A. gundlachi did not vary with experimental temperature.
40 citations
"Habitat light, colour variation, an..." refers methods in this paper
...Hertz et al. (1994) used a laboratory formation from the geological record, physiology, and apparatus in which light intensity and operative temthe characteristics of light habitats, a speculative yet perature were uncoupled to demonstrate that the belogical scenario emerges that provides a clear…...
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