Motion perception and visual signal design in Anolis lizards

Scientific Reports, 2021

Habitat-specific characteristics can affect signal transmission such that different habitats dictate the optimal signal. One way to examine how the environment influences signals is by comparing changes in signal effectiveness in different habitats. Examinations of signal effectiveness between different habitats has helped to explain signal divergence/convergence between populations and species using acoustic and colour signals. Although previous research has provided evidence for local adaptations and signal divergence in many species of lizards, comparative studies in movement-based signals are rare due to technical difficulties in quantifying movements in nature and ethical restrictions in translocating animals between habitats. We demonstrate herein that these issues can be addressed using 3D animations, and compared the relative performance of the displays of four Australian lizard species in the habitats of each species under varying environmental conditions. Our simulations s...

Proceedings of the National Academy of Sciences, 2014

Significance Communication often is a major component of social interactions. Signaling individuals are faced with the challenge of capturing the attention of intended receivers while limiting eavesdropping by potential predators. We conducted an experiment in nature to evaluate the hypothesis that prey species can modulate the physical properties of movement-based displays in response to the presence of predators. We found that male brown anoles dramatically decreased the amplitude of their head-bob displays in the presence of a predatory lizard, resulting in less conspicuous signals. Although less conspicuous signals may be safer for the signaling individuals, they also reduce the distance from which potential mates or competitors can detect them, which might affect the territory size and reproductive success of signaling males.

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1999

The evolutionary relationship between visual system response and visual signal design was investigated in four species of anoline lizards which occupy distinctly dierent habitats. Anoles display with motion patterns of a colorful throat fan called the dewlap. We assessed signal visibility by recording evoked potentials from the optic tectum in response to a moving stimulus ag (a dewlap-like stimulus), and, in one species, by testing behavioral response. The motion pattern, intensity and spectral quality of the stimulus¯ag, and the background against which it was viewed, were independently manipulated. In all cases, high-velocity motion patterns with a high percentage of brightness contrast between stimulus and background produced the greatest response. Dierences in spectral quality between stimulus and background (color contrast) had no eect on tectal responses, but did in¯uence the behaviorally measured detection probability. Using habitat light data we estimated the visibility of the dewlap of each species in dierent natural habitats. Each species' dewlap was highly visible in its own habitat, but some were much less visible in the habitats of some other species. Habitat light conditions and visual system response properties appear to have constrained the evolution of dewlap design, in at least some of the species.

Ethology, 2006

Variation in habitat structure can profoundly affect the evolution of visual displays in animals. We compared the field display behavior of two populations of the green anole lizard (Anolis carolinensis) in Southern Louisiana. These two populations occupy habitats varying markedly in structure (clumped vs. continuous), ecological setting (urban vs. natural) and the degree of male competition and predation. We filmed 56 large adult male lizards during the active spring reproductive period and detected substantial divergence in display behavior between populations. We found that (1) relative dewlap areas did not differ significantly between populations, (2) Tulane anoles spent about twice as much time displaying compared with Good Hope field anoles, although the average display duration did not differ significantly between populations, and (3) the two populations differed significantly in the relative frequency of display types: lizards from the Tulane population used a higher proportion of A and B display types, whereas Good Hope Field anoles used C displays more often. Finally, we detected differences in other aspects of display behavior (use of display modifiers, volley length distributions). We suggest that these display differences may result from differences in green anole male density (three times higher at Tulane), combined with habitat differences (clumped vs. continuous).

Behavioral Ecology, 2013

Male Anolis lizards exhibit an impressive diversity of dewlap color patterns and motion displays. These traits are thought to mediate species recognition, but direct experimental support is limited. It is also unclear if and how color and display behavior each may contribute to the signaling of species identity. We used a programmable robotic lizard to manipulate these signal components independently in Anolis grahami. Four robot variants were used: a control treatment that displayed the conspecific (orange) dewlap color and headbobbing sequence, 2 treatments that differed from the control only in dewlap coloration (light or dark blue), and a fourth treatment that differed from the control only in headbob display pattern (reversed headbob display structure). Artificial dewlaps were calibrated in color and brightness to the A. grahami visual system using a computational model. We presented robots to 102 adult male subjects and quantified their responses for durations of dewlap pulsing and headbob displays. Subjects spent significantly more time pulsing their dewlaps in response to control (conspecific) robot displays than to treatments that deviated from the control either in dewlap color or in headbob display structure. Our findings implicate both morphology and behavior as functional components of social signaling in A. grahami, thus underscoring the complex, multicomponent nature of anoline displays.

Current Zoology, 2011

Signals used for species identity ought to be highly stereotyped so as to facilitate immediate recognition by conspecifics. It is surprising therefore to find variability in putative species signature displays. The brown anole Anolis sagrei has a high degree of variability in its signature bobbing display. In this study we collected descriptive data on variability in the temporal structure of wild brown anole bobbing patterns, finding that no two displays analyzed had the same temporal structure, and we also tested whether wild brown anoles prefer the signature display over an alternate display pattern by using mechanical robot playbacks in the field. As a response metric we assessed whether or not the lizards showed social responses (pushup, dewlap extension, or head-nod) in response to the robotic presentations. We found that the lizards responded slightly more to the signature than to the alternate pattern, providing support for the idea that despite the variability seen in displays, the signature pattern is meaningful to them. We tested two other independent variables: speed of the display and elevation of the robot during its display, neither of which was significant. Dewlap extensions were given predominantly by adult males and were more likely to be given in the breeding season than the nonbreeding season. Pushups and head-nods were given equally by males and a combined class of females and juveniles, and were not seasonal. Head-nods increased after the robot turned off, suggesting that they may be used in a conversational turn-taking style during communication [Current Zoology 57 (2): 140-152, 2011].

American Naturalist, 2004

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 under the spectral conditions of a mesic habitat. The converse is true for a dewlap from a mesic habitat. We propose that sensory drive has promoted divergence in dewlap design in distinct habitat light conditions, and we discuss the possibility that selection might promote early stages of reproductive isolation as a by-product of selection on dewlap design to distinct habitat light conditions. Animals communicate with an amazing variety of signals, and even closely related species often exhibit great signal diversity. A number of studies suggest that divergence in

2008

The Journal of experimental biology, 2001

Anoline lizards communicate with visual displays in which they open and close a colourful throat fan called the dewlap. We used a visual fixation reflex as an assay to test the effects of stimulus versus background chromatic and brightness contrast on the probability of detecting a moving coloured (i.e. dewlap-like) stimulus in Anolis cristatellus. The probability of stimulus detection depended on two additive visual-system channels, one responding to brightness contrast and one responding to chromatic contrast, independent of brightness. The brightness channel was influenced only by wavelengths longer than 450nm and probably received input only from middle- and/or long-wavelength photoreceptors. The chromatic contrast channel appeared to receive input from three, or possibly four, different classes of cone in the anoline retina, including one with peak sensitivity in the ultraviolet. We developed a multi-linear regression equation that described most of the results of this study to...

Herpetologica, 2019

Some of the most striking behaviors of animals are displays used in courtship, territorial behavior, and in defense against predators. Among reptiles, lizards exhibit enormous diversity in the stereotyped motion patterns of their bobbing displays. Although the bobbing displays of numerous lizard species have been described to date, those of the Galá pagos Lava Lizards (Microlophus spp., Tropiduridae) have received comparatively little attention. Here, we analyze bobbing displays from four of the nine lava lizard species: Microlophus albemarlensis, M. bivittatus, M. grayii, and M. indefatigabilis. Field-recorded displays first were standardized to a common amplitude scale, and attributes of display duration and head amplitude were measured. Next, a discrete Fourier transform (DFT) was computed for each display, and data were gathered on 13 frequency and amplitude variables. Then, we conducted a principal components analysis on the Fourier transform-based variables, and used discriminant function analyses (both standard and permuted) to test the strength of species specificity in display structure. Results showed that displays with simpler structure (M. albemarlensis and M. grayii) were more often correctly assigned to species than were displays with more complex structure (M. bivittatus and M. indefatigabilis). We offer predictions for further tests on the bobbing displays of additional species of Galá pagos lava lizards, and suggest that DFT represents a promising tool for the analysis of animal motion displays.