Proceedings of the Royal Society B: Biological Sciences, 2010
Anolis lizards communicate with displays consisting of motion of the head and body. Early portion... more Anolis lizards communicate with displays consisting of motion of the head and body. Early portions of long-distance displays require movements that are effective at eliciting the attention of potential receivers. We studied signal-motion efficacy using a two-dimensional visual-motion detection (2DMD) model consisting of a grid of correlation-type elementary motion detectors. This 2DMD model has been shown to accurately predict Anolis lizard behavioural response. We tested different patterns of artificially generated motion and found that an abrupt 0.38 shift of position in less than 100 ms is optimal. We quantified motion in displays of 25 individuals from five species. Four species employ near-optimal movement patterns. We tested displays of these species using the 2DMD model on scenes with and without moderate wind. Display movements can easily be detected, even in the presence of windblown vegetation. The fifth species does not typically use the most effective display movements and display movements cannot be discerned by the 2DMD model in the presence of windblown vegetation. A number of Anolis species use abrupt up-and-down head movements approximately 10 mm in amplitude in displays, and these movements appear to be extremely effective for stimulating the receiver visual system.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1997
The visual ecology of six closely related species of Puerto Rican anoline lizards was investigate... more The visual ecology of six closely related species of Puerto Rican anoline lizards was investigated and they were found to occupy four distinct habitat types in terms of light conditions:``full shade'',``partial shade'',`n o shade'', and``forest canopy.''The habitats diered substantially in total radiance and irradiance as well as in the shape of the irradiance spectrum. The shape of the radiance spectrum was similar in all of the habitats. We used electroretinogram (ERG)¯icker photometry to measure spectral sensitivity and found the curves for all six species to be similar. The spectral sensitivity peaked in the range 550±560 nm, which matched the peak in spectral radiance for all of the habitats. The shape of the spectral-sensitivity curve was similar to those of a number of other terrestrial vertebrates. We suggest that the convergence of the shape of the photopic ERG-determined spectral-sensitivity curve in many terrestrial vertebrates may, in part, be due to the fact that the background radiance of many terrestrial habitats is dominated by the re¯ectance spectrum of green vegetation which peaks at 550 nm.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1999
The evolutionary relationship between visual system response and visual signal design was investi... more 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. Key words Anolis á Optic tectum á Dewlap á Color á Brightness Abbreviations ERG electroretinogram á OT optic tectum á TEP tectal-evoked potential
... of part I. Wiley & Richards (1982) suggested that the detectability of a long-distance co... more ... of part I. Wiley & Richards (1982) suggested that the detectability of a long-distance communication ... Hailman & Dzelzkalns (1974) suggested that the 'tail-wagging' display of mallard ducks, Anas platyrhynchos, which ... Mallard tail-wagging: punctuation for animal communication? ...
Video playback experiments are potentially powerful tools in behavioral research. A video screen ... more Video playback experiments are potentially powerful tools in behavioral research. A video screen mimics natural color, brightness, texture, and motion to humans (for which it was designed) because monitors stimulate human photoreceptors in approximately the same relative proportions as the stimuli that they mimic. Because most animals have vision that is very different from that of humans their cones may be stimulated very differently from ours, and an image that looks excellent to us may be unrecognizable to them, and vice versa. In this article we summarize how the simulation of a monitor works and the ways it can go wrong, using a bird and a fish model retina as examples. Finally we make some recommendations for minimizing some of these problems.
Proceedings of the Royal Society B: Biological Sciences, 2011
Progress in developing animal communication theory is frequently constrained by a poor understand... more Progress in developing animal communication theory is frequently constrained by a poor understanding of sensory systems. For example, while lizards have been the focus of numerous studies in visual signalling, we only have data on the spectral sensitivities of a few species clustered in two major clades (Iguania and Gekkota). Using electroretinography and microspectrophotometry, we studied the visual system of the cordylid lizard Platysaurus broadleyi because it represents an unstudied clade (Scinciformata) with respect to visual systems and because UV signals feature prominently in its social behaviour. The retina possessed four classes of single and one class of double cones. Sensitivity in the ultraviolet region (UV) was approximately three times higher than previously reported for other lizards. We found more colourless oil droplets (associated with UV-sensitive (UVS) and short wavelength-sensitive (SWS) photoreceptors), suggesting that the increased sensitivity was owing to the...
This paper is the consensus of a workshop that critically evaluated the utility and problems of v... more This paper is the consensus of a workshop that critically evaluated the utility and problems of video playbacks as stimuli in studies of visual behavior. We suggest that video playback is probably suitable for studying motion, shape, texture, size, and brightness. Studying color is problematic because video systems are specifically designed for humans. Any difference in color perception must lead to a different color sensation in most animals. Another potentially problematic limitation of video images is that they lack depth cues derived from stereopsis, accommodation, and motion parallax. Nonetheless, when used appropriately, video playback allows an unprecedented range of questions in visual communication to be addressed. It is important to note that most of the potential limitations of video playback are not unique to this technique but are relevant to all studies of visual signaling in animals.
Closely related species often have signals that differ dramatically in design. The evolution of s... more Closely related species often have signals that differ dramatically in design. The evolution of such differences may be important in the process of speciation. Selection for signal detectability under different habitat conditions has been proposed as a mechanism leading to the evolution of signal diversity. We examined dewlap color in four closely related species of Anolis lizards that occupy habitats with different light conditions. Initially, we tested the hypothesis that lizards choose specific light conditions within each habitat in which to signal. We rejected this hypothesis for all four species. We next calculated the detectability of the dewlap color of all four species at display locations in each habitat. If selection for detectability under the different light conditions explained the divergence in signal design, the occupant of a given habitat was predicted to have the highest signal detectability in that habitat. However, the rank order of detectability of the four dewlap colors was nearly the same in all four habitats. We concluded that divergent selection for signal detectability does not, by itself, explain the evolution of dewlap color diversity. We hypothesize that the evolution of dewlap color diversity results from simultaneous selection for multiple functions of dewlap color.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 2003
Studies of visual ecology have typically focused on differences among species while paying less a... more Studies of visual ecology have typically focused on differences among species while paying less attention to variation among populations and/or individuals. Here, we show that the relative abundance of UV, violet, yellow, and red cones varies between two populations of bluefin killifish, Lucania goodei. Animals from a spring population (high-transmission UV/blue light) have a higher frequency of UV and violet cones and a lower frequency of yellow and red cones than animals from a swamp population (low-transmission UV/blue light). Visual sensitivity does not vary significantly between the populations, but spring animals tend to be more sensitive in the UV/blue wavelengths (360-440 nm) and less sensitive in longer wavelengths (560-600 nm) than swamp animals. The results have two important implications. First, the tight conservation of functional regions of opsin genes across taxa does not imply that visual systems are constrained in their evolution; differential sensitivity can arise through differential expression of cone classes within the retina. Second, intraspecific visual signals in this species may evolve to maximize contrast between the signaler and the background (as opposed to brightness); males with blue anal fins are most abundant in swamp habitats where animals express fewer UV and violet cones.
Proceedings of the Royal Society B: Biological Sciences, 2010
Anolis lizards communicate with displays consisting of motion of the head and body. Early portion... more Anolis lizards communicate with displays consisting of motion of the head and body. Early portions of long-distance displays require movements that are effective at eliciting the attention of potential receivers. We studied signal-motion efficacy using a two-dimensional visual-motion detection (2DMD) model consisting of a grid of correlation-type elementary motion detectors. This 2DMD model has been shown to accurately predict Anolis lizard behavioural response. We tested different patterns of artificially generated motion and found that an abrupt 0.38 shift of position in less than 100 ms is optimal. We quantified motion in displays of 25 individuals from five species. Four species employ near-optimal movement patterns. We tested displays of these species using the 2DMD model on scenes with and without moderate wind. Display movements can easily be detected, even in the presence of windblown vegetation. The fifth species does not typically use the most effective display movements and display movements cannot be discerned by the 2DMD model in the presence of windblown vegetation. A number of Anolis species use abrupt up-and-down head movements approximately 10 mm in amplitude in displays, and these movements appear to be extremely effective for stimulating the receiver visual system.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1997
The visual ecology of six closely related species of Puerto Rican anoline lizards was investigate... more The visual ecology of six closely related species of Puerto Rican anoline lizards was investigated and they were found to occupy four distinct habitat types in terms of light conditions:``full shade'',``partial shade'',`n o shade'', and``forest canopy.''The habitats diered substantially in total radiance and irradiance as well as in the shape of the irradiance spectrum. The shape of the radiance spectrum was similar in all of the habitats. We used electroretinogram (ERG)¯icker photometry to measure spectral sensitivity and found the curves for all six species to be similar. The spectral sensitivity peaked in the range 550±560 nm, which matched the peak in spectral radiance for all of the habitats. The shape of the spectral-sensitivity curve was similar to those of a number of other terrestrial vertebrates. We suggest that the convergence of the shape of the photopic ERG-determined spectral-sensitivity curve in many terrestrial vertebrates may, in part, be due to the fact that the background radiance of many terrestrial habitats is dominated by the re¯ectance spectrum of green vegetation which peaks at 550 nm.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1999
The evolutionary relationship between visual system response and visual signal design was investi... more 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. Key words Anolis á Optic tectum á Dewlap á Color á Brightness Abbreviations ERG electroretinogram á OT optic tectum á TEP tectal-evoked potential
... of part I. Wiley & Richards (1982) suggested that the detectability of a long-distance co... more ... of part I. Wiley & Richards (1982) suggested that the detectability of a long-distance communication ... Hailman & Dzelzkalns (1974) suggested that the 'tail-wagging' display of mallard ducks, Anas platyrhynchos, which ... Mallard tail-wagging: punctuation for animal communication? ...
Video playback experiments are potentially powerful tools in behavioral research. A video screen ... more Video playback experiments are potentially powerful tools in behavioral research. A video screen mimics natural color, brightness, texture, and motion to humans (for which it was designed) because monitors stimulate human photoreceptors in approximately the same relative proportions as the stimuli that they mimic. Because most animals have vision that is very different from that of humans their cones may be stimulated very differently from ours, and an image that looks excellent to us may be unrecognizable to them, and vice versa. In this article we summarize how the simulation of a monitor works and the ways it can go wrong, using a bird and a fish model retina as examples. Finally we make some recommendations for minimizing some of these problems.
Proceedings of the Royal Society B: Biological Sciences, 2011
Progress in developing animal communication theory is frequently constrained by a poor understand... more Progress in developing animal communication theory is frequently constrained by a poor understanding of sensory systems. For example, while lizards have been the focus of numerous studies in visual signalling, we only have data on the spectral sensitivities of a few species clustered in two major clades (Iguania and Gekkota). Using electroretinography and microspectrophotometry, we studied the visual system of the cordylid lizard Platysaurus broadleyi because it represents an unstudied clade (Scinciformata) with respect to visual systems and because UV signals feature prominently in its social behaviour. The retina possessed four classes of single and one class of double cones. Sensitivity in the ultraviolet region (UV) was approximately three times higher than previously reported for other lizards. We found more colourless oil droplets (associated with UV-sensitive (UVS) and short wavelength-sensitive (SWS) photoreceptors), suggesting that the increased sensitivity was owing to the...
This paper is the consensus of a workshop that critically evaluated the utility and problems of v... more This paper is the consensus of a workshop that critically evaluated the utility and problems of video playbacks as stimuli in studies of visual behavior. We suggest that video playback is probably suitable for studying motion, shape, texture, size, and brightness. Studying color is problematic because video systems are specifically designed for humans. Any difference in color perception must lead to a different color sensation in most animals. Another potentially problematic limitation of video images is that they lack depth cues derived from stereopsis, accommodation, and motion parallax. Nonetheless, when used appropriately, video playback allows an unprecedented range of questions in visual communication to be addressed. It is important to note that most of the potential limitations of video playback are not unique to this technique but are relevant to all studies of visual signaling in animals.
Closely related species often have signals that differ dramatically in design. The evolution of s... more Closely related species often have signals that differ dramatically in design. The evolution of such differences may be important in the process of speciation. Selection for signal detectability under different habitat conditions has been proposed as a mechanism leading to the evolution of signal diversity. We examined dewlap color in four closely related species of Anolis lizards that occupy habitats with different light conditions. Initially, we tested the hypothesis that lizards choose specific light conditions within each habitat in which to signal. We rejected this hypothesis for all four species. We next calculated the detectability of the dewlap color of all four species at display locations in each habitat. If selection for detectability under the different light conditions explained the divergence in signal design, the occupant of a given habitat was predicted to have the highest signal detectability in that habitat. However, the rank order of detectability of the four dewlap colors was nearly the same in all four habitats. We concluded that divergent selection for signal detectability does not, by itself, explain the evolution of dewlap color diversity. We hypothesize that the evolution of dewlap color diversity results from simultaneous selection for multiple functions of dewlap color.
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 2003
Studies of visual ecology have typically focused on differences among species while paying less a... more Studies of visual ecology have typically focused on differences among species while paying less attention to variation among populations and/or individuals. Here, we show that the relative abundance of UV, violet, yellow, and red cones varies between two populations of bluefin killifish, Lucania goodei. Animals from a spring population (high-transmission UV/blue light) have a higher frequency of UV and violet cones and a lower frequency of yellow and red cones than animals from a swamp population (low-transmission UV/blue light). Visual sensitivity does not vary significantly between the populations, but spring animals tend to be more sensitive in the UV/blue wavelengths (360-440 nm) and less sensitive in longer wavelengths (560-600 nm) than swamp animals. The results have two important implications. First, the tight conservation of functional regions of opsin genes across taxa does not imply that visual systems are constrained in their evolution; differential sensitivity can arise through differential expression of cone classes within the retina. Second, intraspecific visual signals in this species may evolve to maximize contrast between the signaler and the background (as opposed to brightness); males with blue anal fins are most abundant in swamp habitats where animals express fewer UV and violet cones.
Uploads
Papers by L. Fleishman