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Behavioral biologists have long been fascinated with the diversity of animal signals produced in the contexts of courtship and same-sex competition. In these contexts many lizards engage in conspicuous bobbing displays, and numerous studies have been devoted to describing these displays. Traditionally, bobbing displays are partitioned into units whose durations (and sometimes head amplitudes) are measured. Recently, Macedonia et al. (2019) introduced use of the Discrete Fourier Transform (DFT) as an alternative to unit-based variables for characterizing species-specific traits in display structure of Galapagos Lava Lizards (Microlophus spp.). The relative success of the two methods was not compared directly, however, because the homology of display units among species was uncertain. Here we overcome this problem using the “grahami series” of Anolis lizards—a monophyletic radiation of seven species on Jamaica and Grand Cayman. Our study had three primary goals. Our first goal was to discover whether DFT-based measures, unit-based measures, or their combination provided the best means to capture taxon-specific distinctiveness in display structure. To this end, we quantified bobbing displays and used nested analyses of variance (ANOVAs) to determine if particular variables were reliably superior at differentiating populations within a species. We then used principal components analysis to reduce the number of measurement variables, and entered the components into discriminant function analyses to determine which approach best discriminated among taxa. Results showed that no one type of measurement, or measurement combination, emerged as being consistently better at discriminating taxa across comparisons. Our second goal was to test a hypothesis that arose from our findings in Galapagos Lava Lizards—that the DFT may decrease in effectiveness as bobbing display structure increases in complexity. For this test we used four simple and compound display types from the species Anolis reconditus. Results of discriminant function analyses provided mixed support for the hypothesis, and we suggest that a definitive test of DFT performance and display complexity should utilize synthetic displays in which attributes of display structure are varied systematically. Last, we show how bobbing display structure maps onto alternative DNA-based phylogenies of the grahami series anoles. Whereas some species produced derived display types unanticipated from displays of more basal species in this adaptive radiation, others exhibited features that linked them to a particular population of a species in their clade.

In many species, outcomes of male duels determine access to females and, ultimately, male reproductive success. Ritualization of behavior in male contests can reduce the probability of injury, which benefits both contestants. Components of ritualized combat often include postures and displays that showcase a male’s quality in a sequential assessment of fighting ability. Among the most common contest acts in iguanine lizards are bobbing displays. Investigations of bobbing display dynamics often include experimental “playbacks,” in which video or robotic representations of conspecifics are presented to subjects. In most “playback” research, pre-programmed stimuli exhibit behavior that is independent of subjects’ responses, despite the fact that actual animal contests are highly interactive. In the present study, we utilized a robotic Galapagos lava lizard (Microlophus bivittatus) to investigate the importance of interaction in simulated contests under field conditions. Using a matched pairs design where each subject experienced two behavioral variants of the robotic stimulus, we tested the effect of a robot that displayed immediately following a subject’s display versus when the same robot display was postponed 30 s. Results showed that immediate response from the robot stimulated subjects to display significantly more often than when the stimulus was delayed. We speculate that subjects perceived a rapid response from their robotic contestant as being more aggressive than a delayed response. We discuss our results in light of relevant previous work, and we suggest possibilities for future research using interactive lizard robots. Some of the most impressive examples of ritualized animal behavior can be observed in male contests for access to reproductive females. The use of stereotyped displays in such duels allows males to assess one another’s quality while avoiding dangerous fighting that can lead to injury. For example, males in many lizard species perform bobbing displays where contestants respond to each other in reciprocal fashion. In this study, we used a realistic lizard robot as a stand-in for a contestant in simulated contests. We found that an immediate display response by the robot to a subject’s bobbing display stimulated subjects to display significantly more often than when the robot’s response was delayed by 30 s. To our knowledge, this is the first interactive robot “playback” experiment with lizards. Future research will further explore the “rules” underlying display behavior in lizard contests.

Differentiation in the structure of animal signals and displays among closely related species has intrigued biologists for centuries. Such divergence is often attributed to behavioural premating isolation, where sexual selection has favoured species recognition in environments containing sympatric congeners. However, in some cases closely related taxa have undergone speciation and display differentiation in isolation, in the apparent absence of benefits afforded by species recognition. Such is the case for the lava lizards (Microlophus spp.) endemic to the Galapagos Islands, where no two species overlap in distribution and all are thought to have evolved in allopatry from congeners. To test alternative evolutionary models, we used several phylogenetic comparative methods to assess how Microlophus displays have evolved. Results showed some potential for the influence of genetic drift, but little evidence of sexual selection (via male–male competition) or colonization history on the way displays have diverged among taxa. We then used lizard robots to test whether two representative Galapagos lava lizard species, Microlophus grayii and Microlophus indefatigabilis, would respond preferentially to a robot performing conspecific displays over those of the congener. We predicted that, in the absence of reinforcing selection, neither species would show a preference for conspecific displays. Results were mixed: whereas M. grayii showed no discrimination of conspecific over heterospecific displays, male M. indefatigabilis showed significantly stronger responses to their own displays than to those of the heterospecific. We then conducted the same experiment with a mainland congener, Microlophus occipitalis, to provide a broader view of potential responses across the group. Results revealed significant discrimination against heterospecific displays. We discuss our findings in light of hypotheses of signal differentiation, and suggest alternative interpretations for recognition of conspecific displays in species that are thought to have evolved in isolation.

Green Anoles (Anolis carolinensis) are comprised of red-dewlapped (RD) forms that are found throughout the southeastern USA and a gray-dewlapped (GD) form that is restricted to southwest Florida. Prior research has shown that RD A. carolinensis produce headbob displays of three distinct types that differ primarily in their temporal patterns. Based on known morphological, physiological, and genetic differences between GD and RD populations, we hypothesized that these populations also would differ in headbob display structure. To test this hypothesis we quantified 440 displays from 39 males (24 GD and 15 RD) and assigned displays to type using numerical decision criteria. Although comparison of the same display types between GD and RD males revealed differences in the durations of several homologous display units (i.e., bobs or interbob pauses), only one unit differed following statistical correction for multiple comparisons. By taking into account all display variation in both populations simult...

Several observational and experimental studies have shown that perch diameter has an impact on the development of hind-limb length (HL) in Anolis species. This “phenotypic plasticity” in relative hind-limb growth (RHG) has implications for short-term and long-term adaptation to different structural habitats. Our study is the first to replicate research in which hatchling/juvenile Anolis sagrei were reared on narrow-diameter or broad-diameter dowels in a laboratory setting. Although subjects reared on different dowel diameters did not differ significantly in RHG at 5 weeks into the experiment, results at 15 weeks revealed a significant effect of treatment but not of sex: subjects in the broad (N = 69) treatment group exhibited significantly greater RHG than did subjects in the narrow (N = 61) treatment group. We extended this research with a novel follow-up study: we placed our lab-reared subjects into outdoor enclosures where they had a choice of narrow- or broad-diameter dowels on which to perch...

Animal color signals evolve in response to selection by visual systems that perceive them, ambient light spectra that illuminate them, and features of the background against which they are juxtaposed. In Anolis lizards, males use a colorful dewlap, together with head-bobbing displays, to deter conspecific rivals and to attract females. As most anoles are both arboreal and sympatric with one or more congeners, selection should favor dewlap colors that contrast sufficiently with the visual background of foliage to be detectable, and that differ reliably from dewlaps of sympatric congeners to be discriminable. We used spectroradiometry and computational visual modeling for five species of closely related Jamaican anoles to calculate the detection probability of each species' dewlap in each of the species' light habitats. Despite substantial interspecific differences in dewlap colors, as well as moderate differences in habitat light spectra, results of our analyses did not support the prediction th...

Nature’s most striking, complex and innovative colour signals are generated via selective reflectance from optical nanostructures (rather than selective absorbance by pigments), a phenomenon known as structural coloration. These colours reach their height of visual brilliance as sexual signals, a context in which they also express both great functional innovation and high evolutionary lability. However, owing to a historical preoccupation with pigments, we know relatively little about the evolutionary causes and consequences of innovation in structurally coloured sexual signals, especially in exemplar arthropod taxa. In this study we addressed the possibility that species differences in intraspecific mating preferences may contribute to visual and functional variation in structural coloration. We contrasted mate preferences and signal properties between two closely related butterfly species (Hypolimnas alimena and Hypolimnas bolina) that possess male-elaborated structural coloration. Hypolimnas bolina offers a valuable comparative basis because females are known to prefer highly bright and limited-view ultraviolet markings, which males generate via complex nanoscale surface multilayer arrays. Male H. alimena ,b y contrast, display less bright and weakly iridescent dorsal blue, arising from a simpler surface microarchitecture. In two separate experiments, we found that female H. alimena did not distinguish between males spanning a graded range of 0.25e1.4� natural peak brightness. Only once the dorsal blue was completely obscured did male mating success suffer. Furthermore, a sample of wild phenotypes indicated greater variance for signal brightness in male H. bolina than H. alimena, but no difference in peak hue (i.e. signal colour). These results supported a priori predictions, and are consistent with a scenario whereby directional female preference has driven male signal exaggeration in H. bolina, but not its less ornamented close congener.

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...

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.

The visual displays of male anoles (Anolis sp.) are usually viewed as characters that facilitate species recognition. This presumption stems largely from the extensive variation in the head bobbing movements and dewlap colouration in males of this genus. However, few experimental data exist that illuminate the importance of these visual signals for species recognition. We presented adult male Anolis grahami with colour-videotaped sequences of displays from conspecifics and from three heterospecific species of anoles. The congenerics (A. carolinensis, A. conspersus, and A. sagrei) were chosen on the basis of their phylogenetic and geographical relationships with A. grahami. Stimulus males were filmed at a constant distance and orientation from the video camera, and edited sequences of their displays were presented at a standard distance from subjects. Video playbacks allowed us to equalize the quantity of display performed by each stimulus species, and to eliminate stimulus/subject interactions as well as inter-trial variation in stimulus behaviour. Results revealed that the subjects responded more strongly to conspecific than to heterospecific displays on all behavioural variables examined, but there was no indication of discrimination among the displays of the three congeneric species.

Two hypotheses of signal specificity in antipredator calls (“referential signalling” and “response urgency”) are discussed in light of prior research on ground squirrels and vervet monkeys. These hypotheses then are examined with data on responses of semi-captive ringtailed and ruffed lemurs to antipredator call playbacks. Although the responses of ringtailed lemurs support a referential-signalling interpretation of their antipredator calls, those of ruffed lemurs do not conform well to either hypothesis. Rather, ruffed lemur antipredator calls seem best viewed as “affective” signals that may only reflect underlying emotional/motivational states.

Summary 1. Iridescent colour signals are directional but, like diffusely reflected colours, vary within and among species in ways that may be adaptations to specific types of receivers in specific light environments. 2. The hindwings of pipevine swallowtail butterflies exhibit brilliant blue and iridescent colour patches on the ventral surface in both sexes and on the dorsal wing surface in males. Evidence suggests that the ventral iridescent blue is a component of the warning coloration of this distasteful species, while the dorsal blue iridescent wing area is a sexual signal. Given differences in the function and ecological context of signal production, we analysed reflectance spectra from the iridescent blue areas of both field-caught and laboratory-reared animals to test several predictions about the iridescent colour patches on these wing surfaces. 3. The ventral blue patches in the warning coloration of males and females should be most visible early and late in the day, due to wing orientation relative to sun angle. We therefore predicted that these iridescent colour patches would be brighter and of longer wavelengths than the male dorsal blue patch displayed during midday courtships. The prediction about reflectance intensity was supported but the prediction about hue was not. 4. We predicted that the sexually selected dorsal hindwing iridescence of males would be more variable among individuals and condition dependent than the naturally selected ventral iridescent colour patches. To assess variation and condition dependence, laboratory-reared and field-captured individuals were compared. The prediction about variation was not supported, but only the dorsal wing surfaces showed evidence of being condition dependent. 5. We investigated whether development of dorsal and ventral blue iridescence was coupled by determining correlations in colour properties between the wing surfaces. Our finding of positive correlations indicated a potential developmental constraint in the evolution of colour differences between the two wing surfaces. 6. Results of this study suggest that some properties of iridescent coloration on the hindwing of the pipevine swallowtail (especially intensity) may have been fine-tuned by evolution in response to prevailing ambient light conditions and viewing perspectives that differ among types of signal receivers.

Selection should favour coloration in organisms that is more conspicuous to their own visual system than to those of their predators or prey. We tested this prediction in Dickerson’s collared lizard (Crotaphytus dickersonae), a sexually dichromatic desert reptile that preys on insects and smaller lizard species, and which in turn is prey for birds and snakes. We modelled the spectral sensitivities of the lizards and their avian and snake predators, and compared the conspicuousness of the lizards’ entire colour patterns with each class of viewers. Almost all comparisons involving females strongly supported our prediction for greater chromatic and brightness conspicuousness against local terrestrial visual backgrounds to their own modelled visual system than to those of avian and snake predators. Males, in contrast, exhibited far fewer cases of greater conspicuousness to their own visual system than to those of their predators. Our own perception of spectral similarity between blue C. dickersonae males and a local nonterrestrial visual background (i.e. the Sea of Cortez) prompted a further investigation.We compared sea (and sky) radiance with dorsum radiance of C. dickersonae males and with males from two distantly-related Crotaphytus collaris populations in which males possess blue bodies. In all three visual models, C. dickersonae males exhibited significantly lower chromatic contrast with the sea (and sky) than did their noncoastal, blue-bodied congeners. Among potential explanations, the blue body coloration that is unique to male C. dickersonae may offset, if only slightly, the cost of visibility to predators (and to prey) through reduced contrast against the extensive, local, nonterrestrial blue backgrounds of the sea and sky

Female mate choice has been shown to provide direct mating benefits in several animal groups. In butterflies, for which there are increasing reports of fine-scale color-based mate choice, the evolutionary benefits that accrue from such mating biases, if any, are largely unknown. We addressed this issue in the butterfly Colias eurytheme, a species in which females choose mates on the basis of iridescent ultraviolet (UV) wing ornamentation and in which males donate reproductively beneficial nuptial gifts. In the first experiment, we assessed the mass of gifts donated to 77 virgin females by males sampled directly from a field encounter site. Despite large variance in the male adult phenotype and ejaculate, no single aspect of dorsal wing coloration, including UV brightness, chroma, or hue, was related to ejaculate mass. There was, however, an interesting interaction between the effects of male body size and copula duration upon ejaculate mass, with size scaling positively with ejaculate mass among males involved in shorter copulations (those lasting

In some species of sulphur butterflies (Pieridae: Coliadinae) females as well as males display bright structural reflectance on their dorsal wing surfaces, although comparatively little attention has been paid to this coloration in females. We examined the spectral properties of female dorsal coloration and scale structure in three species of sulphurs for which published images show bright UV reflectance in females: the Neotropical Anteos clorinde and two species of Indo-Australian Eurema, E. hecabe and E. candida. In A. clorinde and E. hecabe, female UV reflectance is iridescent and produced by thin film interference in a system of ridges and lamellae, as it is in conspecific males. Female A. clorinde exhibit the same spatial distribution and chromaticity of UV reflectance as seen in males, but the UV reflectance in female E. hecabe is much smaller in area compared to that of conspecific males and is both less bright and less chromatic than observed in males. In contrast, UV reflectance in E. candida females is diffuse, and arises from a lack of pterin pigments in the wings, which permits a broad-band scattered reflection to be seen. This is the mechanism that is known to produce bright UV reflectance in females of the confamilial whites. Our results highlight the diversity of UV reflectances and underlying mechanisms in sulphurs and suggest multiple evolutionary pathways leading to this diversity in female sulphur butterflies.

Many of nature’s most striking animal colours are iridescent, exhibiting a high degree of spectral purity and strong angular dependence of intensity and hue. Although a growing number of studies have detailed the intricate mechanisms responsible for producing iridescent colours, few attempts have been made to describe their dynamic appearance in ecologically and behaviourally realistic contexts. We suggest that the optical properties unique to iridescent structural colours are important for understanding how they function as signals during behavioural interactions. Using males of the orange sulphur butterfly, Colias eurytheme, which exhibit an iridescent ultraviolet (UV) reflectance on their dorsal wing surfaces, we develop a holistic framework for inferring the appearance of this signal to conspecifics under field conditions that incorporate data on their spectral sensitivity. We show that, during flight, the UV signal is brightest within a wing beat cycle when viewed from directly above the male. Spectral properties of the signal under natural lighting indicate that male wing colour should be readily perceived and distinguished from that of females and from the dark green visual background of UV-absorbing vegetation. Finally, our analyses permit predictions regarding how signal senders and receivers should orientate themselves for maximal transmission and reception of this ultraviolet iridescent signal. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 349–364.

Abstract Males of Dickerson's collared lizard (Crotaphytus dickersonae) are conspicuously bright blue in colour and can be detected at great distances. In contrast, females are brown and much less conspicuous. Given the visibility of males to predators, the question arises how they avoid predation and whether the sexes differ in anti-predator behaviour. Using a slowly approaching human as a simulated predator, approach and flight distances were recorded, as were the presence of other anti-predation responses such as pursuit deterrence signalling, distraction behaviour and aggressive threat. The lizards were captured and physical data such as cloacal temperatures, weight and snout-vent length were obtained. To assess further the effect of coloration on predation pressure, test subjects were painted to make them inconspicuous (brown) or conspicuous (blue) and recaptured after a week. After shedding their painted skin, subjects were approached one final time. Few direct relationships were found between anti-predation displays and body weight, size or temperature. Exhibition of pursuit deterrence signalling or distraction behaviour was rare, and no subject displayed aggressive behaviour (except when caught). Interestingly, males fled sooner, and tended to use more refuge than females, which probably indicates stronger predation pressure on males. However, an overall low use of refuge, the observer's ability to approach most subjects closely before they fled, and few sightings of potential predators, suggest that weak local predation pressure helps to explain why sexually selected conspicuous male coloration has been able to evolve in C. dickersonae.

Male mating biases may be a widespread feature of animal mating systems but the phenotypic consequences of these biases are often unclear, especially in species for which the operational sex ratio is strongly male-biased. In Colias butterflies, male choice is thought to be one of the factors responsible for maintaining a female-limited genetic color polymorphism, in which female wings appear either yellowish-orange or white (the “alba” variant). Previous studies have indicated that alba females of two montane Colias species mate fewer times during their lifetime, possibly as a partial consequence of this bias. Here we report the results of a field study of male mating behavior and female mating biology in Colias eurytheme, conducted under conditions of high (summer) and low (spring) population densities. Our data show that despite a substantial male bias in approaching alba vs yellowish-orange phenotypes [ratios of 0.08:1 (spring) and 0.28:1 (summer)], alba females did not contain, on average, fewer or smaller spermatophores. Not one of the 308 sampled females was virgin, but females of both phenotypes accumulated spermatophores with age, and tended to carry fewer, larger spermatophores in spring. These data suggest that significantly fewer (or lighter) spermatophores need not be an obligatory or simple consequence of a strong male bias in butterflies. We discuss these findings in light of the known, thermally and density-dependent complexities of alba reproductive biology and of the Colias mating system.

Animal color patterns are a compromise between sexual selection pressures that increase advantages accrued from conspicuousness, and natural selection pressures that decrease those advantages through reduced survivorship. Predation pressure, as a mode of natural selection, often is invoked as a counter-selective force to sexual selection, yet few studies have demonstrated empirically that more conspicuous individuals experience higher rates of predation. We quantified predator attacks on models of collared lizards, Crotaphytus collaris, in three well-studied populations (Oklahoma, USA). These populations differ in coloration and in visual backgrounds against which the lizards are viewed by conspecifics and predators. Attack frequencies varied considerably among study sites but at all sites the models exhibiting the strongest color contrast with local rocks were detected and attacked most often. By comparison, inconspicuous models of females were never attacked at any of the sites. These results suggest a survival cost of conspicuous coloration in collared lizards, and reiterate the importance of considering the visual environment as well as differences among populations when examining the influence of predation on the evolution of animal color patterns.

The coloration of animal integuments evolves in response to numerous and often competing selective pressures. Although male-male competition and female mate choice characteristically select for increased color conspicuousness, visibility to predators and to prey often select for decreased conspicuous- ness. We examined three populations of Common Collared Lizards, Crotaphytus collaris, in Oklahoma (Arcadia Lake, Glass Mountains, Wichita Mountains) that have been argued to differ in the intensity of natural and sexual selection acting on their color patterns. Our study had two main objectives. First, reflectance spectra were obtained from the lizards to replicate and extend previous work on differences in sexual dichromatism among these populations. Second, spectra were gathered on components of visual backgrounds at our study sites to explore the possibility that each population may be relatively cryptic within its own habitat. Results showed that most body regions differed significantly in sexual dichromatism among populations, but in contrast to prior work, no one population was more sexually dichromatic than another for all body regions examined. Males exhibited less overlap in coloration with their visual backgrounds than did females (i.e., males were more conspicuous), and females overlapped more in coloration with rocks than with other visual backgrounds. The population estimated previously to experience the strongest predation pressure (Arcadia Lake) was shown in the present study to be the least conspicuous. Some support also was found for the proposition that even the most ''colorful'' population (Wichita Mountains) may not always be conspicuous when viewed against its typical visual background.

A hallmark trait of the lizard genus Anolis is the presence of remarkable interspecific variation in dewlap color patterns. Yet, considerable intraspecific variation also occurs in many Anolis species. In Florida different populations of the Green Anole (Anolis carolinensis) exhibit red, pink, magenta, and even greenish-gray dewlaps. To date, comparisons of color variation in this species have used subjective techniques based on human color perception. Instead, we used an objective method—reflectance spectrometry—to quantify A. carolinensis dewlap and body color variation along a transect from northeastern to southwestern Florida. Reflectance readings of local vegetation allowed us to calculate contrast of the lizards with their visual backgrounds. By incorporating local ambient light and A. carolinensis spectral sensitivity into additional calculations, we were able to estimate lizard-background contrast from the perspective of the lizards. Results revealed dewlap and dorsum spectra to differ si...

Many members of the Iguania group of lizards engage in stereotyped and species-specific ''pushup'' or ''headbob'' displays. Temporal attributes of displays have been quantified for a number of species in the genus Anolis, but few of these studies have examined effects on display structure of signaler sex, display context, and population. With this goal in mind we conducted a comparative study of three Anolis species permanently established (''naturalized'') on the island of Bermuda: Anolis grahami from Ja- maica, Anolis extremus from Barbados, and Anolis leachi from Antigua and Barbuda. These anoles are dis- tantly related to each other and to Anolis carolinensis—the only Anolis species for which all of the above influences on display structure have been examined in detail. Adults were field-captured and transported to the laboratory where paired interactions were videotaped and headbob displays analyzed. Results re- vealed one or more variables to exhibit sexual dimorphism in each species, and display context had little influence on signal structure. We then compared results from our founder populations on Bermuda with those published for two of our study species' source populations. No significant differences in headbob display units were found between A. grahami on Bermuda and on Jamaica. In contrast, male A. extremus on Bermuda produced fewer units per display than did males from Barbados, although the nature of the published data prevented statistical comparison.

The common collared lizard (Crotaphytus collaris) exhibits considerable geographical colour variation, particularly among males. Populations of this diurnal saxicolous iguanian inhabit patches of rocky habitat throughout the species' broad distribution in North America and are anticipated to experience local differences in selective pressures that influence colouration. Specifically, while social interactions might favour conspicuous colouration, crypsis may be advantageous in interactions with visually orienting predator and prey species. To address the local relationship between lizard and substrate colouration we compared the reflectance spectra of two geographically distant and phenotypically divergent populations of collared lizards with the rocky substrates they inhabit. Our northern study population (C. c. auriceps in eastern Utah) occurs on red rocks, where males exhibit boldly coloured turquoise bodies and bright yellow heads. In contrast, our southern study population (C. c. fuscus in southern New Mexico) lives on grey and tan rocks, and males in this location exhibit subdued brown and tan dorsal colours. Spectral comparisons revealed that males in the northern population contrasted strongly with their local rocks, whereas males in the southern population matched their rock colours with reasonably good fidelity. This relationship held under a variety of lighting conditions. Females in both populations were less conspicuously coloured than males, although northern females contrasted more with their rocks than did southern females. In addition, sexual dichromatism was pronounced in the northern population but minimal in the southern population. Finally, sexual size and weight dimorphism was strong in the southern population while being virtually absent in the northern population. A comparison of the local predator and prey assemblages suggests that the conspicuous and sexually dichromatic colouration of the northern population may have evolved in response to reduced pressure from visually orienting predators as well as reduced dependence on saurian prey.

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.

Individual primates typically produce acoustically distinct calls. To investigate the factors that facilitate the evolution of individual vocal signatures, we examined two components of the call repertoire of chimpanzees: the pant hoot and pant grunt. Pant hoots are long-distance signals whose recipients can be several hundred meters away, while pant grunts are short-range calls given to conspecifics within close visual range. Given their markedly different contexts of emission, we predicted that natural selection would favor the elaboration of individually distinctive acoustic features in pant hoots compared with pant grunts. Analyses of nine acoustic features revealed that pant hoots are more stereotyped within-individuals and variable between-individuals than pant grunts. These data are consistent with the hypothesis that selection may act to encode varying degrees of individuality in different components of the vocal repertoire of a single species.

Phylogenetic relationships among the extant lemurid prosimians were assessed cladistically using stereotyped vocal, olfactory, and visual communication characters. Among our results are 3 findings of particular importance. First, our data are consistent with those from several recent studies of highly repeated DNA fragments in supporting a close phyletic affinity between Lemur catta and the genus Hapalemur. Moreover, our results indicate that L. catta is nested within the Hapalemur clade as the sister taxon to Hapalemur griseusi’Hapalemur aureus. We interpret character states shared between Hapalemur simus and L. catta as primitive retentions by L. catta. Second, our findings agree with the DNA data in proposing a sister group relationship for Eulemur coronatus and Eulemur rubriventer. Third, our results question the validity of assigning Varecia variegata to the Lemuridae. For the characters we examined, Varecia more resembled indrids than lemurids, and the position of Varecia could be swapped with any of our outgroups (Indri, Propithecus, Daubentonia) without affecting tree topology. Previous workers sometimes have linked Varecia with various lemurids on grounds of ambiguously defined characters or on incorrect data gleaned from the literature. In those studies, the placement of Varecia in the Lemuridae usually has depended more on the minimization of character state conflicts (i.e. parsimony), than on demonstrable synapomorphies. In addition, data from DNA research have failed to demonstrate any pattern that links Varecia with Lemur, Hapalemur, oτ Eulemur. Results of the present study suggest that shared Varecia-indrid character states may be symplesiomorphic retentions in the Indridae, and that Varecia could be phyletically more primitive than either the indrids or lemurids.

Abstract. Male chickens, Gallus gallus , produce aerial alarm calls in response to a broad range of stimuli moving overhead, including both predators and innocuous objects. Computer-generated animations of raptor-shaped images were presented on an overhead video monitor to explore the stimulus characteristics necessary for eliciting both aerial alarm calls and non-vocal anti-predator behaviour (e.g. crouching and visual fixation). In experiment 1, apparent size (angle subtended at the bird's eye) was varied from 1° to 8°. Stimuli subtending more than 4° elicited qualitatively more alarm calls than smaller stimuli. The magnitude of non-vocal responses also increased significantly with stimulus size. In experiment 2, apparent speed was varied over a range extending from values characteristic of soaring raptors at one end (1·875 lengths/s), to values near the highest recorded (30 lengths/s) at the other. Stimuli moving faster than 7·5 lengths/s evoked significantly more alarm calling than slower-moving stimuli. Increases in apparent speed also caused a small but significant increase in the magnitude of non-vocal responses. Hence, the non-vocal anti-predator behaviour elicited by overhead stimuli is strongly influenced by apparent size. In natural encounters, this cue varies with object altitude and is likely to be a good predictor of the probability of detection and attack by a raptor. The data on vocal responses suggest that, at least when shape is constant, the probability of alarm calling is dependent on whether stimuli exceed threshold values for apparent size and speed. This perceptual strategy has the advantage of requiring minimal processing and may be adaptive for species, like the jungle fowl, that have evolved in habitats where visibility is limited and reaction times must therefore be brief.

Antiraptor responses from forest-living ringtailed lemurs to advertisement calls of naturally-occurring red-tailed hawks suggested that the lemurs discriminated these calls from other environmental sounds. A series of playback experiments, using real animal sounds and synthetic sound probes, was conducted to investigate the acoustic basis of this putative discrimination. Two semi-captive groups of ringtails served as study subjects: one group had many years of experience living in the forest, whereas the other group had relatively little such experience. Responses to playbacks suggested that both groups used the same acoustic criteria to discriminate “calls of large hawks” from other sounds, but the range of auditory stimuli that evoked antiraptor responses was broader for the experienced group than for the inexperienced group. Although several interpretations of the experimental results are possible, one that seems particularly compatible with the data is the “prototype” concept of stimulus categorization.

Many animal species use stereotyped displays to attract the opposite sex and to intimidate same-sexed rivals. Research aimed at understanding display recognition, function, and usage can be aided through the use of animal robots that allow one side of signaler–receiver interactions to be controlled. Manipulation of displays in ways that do not occur in nature has the potential to determine the boundaries of display recognition, as well as to provide insights into the manner in which animal display contests are structured. We describe two experiments that extend previous work on display recognition in the lizard Anolis grahami. In the first experiment, we used robots to determine the relative importance of body coloration and headbob display structure for species recognition. The results showed that subjects responded more strongly to robots having both conspecific appearance and display structure than to robots that deviated in those characteristics from the conspecific stimulus. In the second ...

Physical prowess, a key determinant of fight outcomes, is contingent on whole-organism performance traits. The advertisement of performance, via display, is poorly understood because it is unclear how information about performance is encoded into display characteristics. Previous studies have shown that weapon performance (i.e., bite force) predicts dominance and reproductive success in male lizards. We tested the hypothesis that gaping displays by adult male collared lizards (Crotaphytus) can provide an index of weapon performance by exposing the major jaw-adductor muscle complex and that white patches at the mouth corners amplify this index. For territorial adult males, the breadth of the muscle complex, which is not correlated with body size, was a strong predictor of bite force. For nonterritorial yearling males and females, however, measures of body and head size predicted bite force. The patches are highly conspicuous, exhibit UV-reflecting properties within the visual range of lizards, and provide size-independent information about bite force only in adult males. We conclude that exposure of the muscle complex during gaping displays can provide rival males with a reliable, body-size independent, biomechanically based index of weapon performance, an index that the mouth-corner patches amplify. Indexes that transmit information through mechanistic links to performance are expected to be widespread among animals.

Video and computer technology have emerged as a powerful tool for controlling visual stimuli and investigating questions about perception in a variety of animal taxa, including spiders (Clark and Uetz, 1990, 1992, 1994), birds (Evans and Marler, 1991; Evans et al., 1993a, 1993b), lizards (Macedonia et al., 1994; Macedonia and Stamps, 1994), anuran amphibians (Roster et al. 1995), and teleost fishes (Rosenthal et al., 1996; Rowland et al., 1995a, 1995b). Video playback and computer animation of test stimuli afford several benefits over

Structurally generated colours are at least as commonplace and varied components of animal signals as pigment colours, yet we know far less about the former, both in terms of the patterns and phenotypic variation and of their underlying correlates and causes. Many butterflies exhibit bright and iridescent colour signals that arise from a characteristic ‘ridge-lamellar’ scale surface nanoarchitecture. Although there are multiple axes of functional variation in these traits, few have been investigated. Here we present evidence that sexual dimorphism in the expression of a sexually homologous ridge-lamellar trait (iridescent ultraviolet) is mediated by sex differences in the density of lamellar-bearing scale ridges. This trait – ridge density – has also been causally related to iridescent signal variation in other coliadines (e.g. C. eurytheme), which suggests that it may offer a common basis to both intra- and intersexual differences in ultraviolet wing reflectance among these butterflies.

The vocal repertoire of the ringtailed lemur (Lemur cαttα) is described quantitatively and spectrographically. Structure, usage and inferred function of the vocalizations of adults and immatures are examined and discussed. The size, acoustic variability and development of the ringtailed lemur’s vocal repertoire are compared to prior assessments for this species as well as for other primates. With up to 22 different adult call types, the ringtailed lemur has a moderately large vocal repertoire for a primate.

The antipredator responses of forest-living ringtailed (Lemur cafta) and ruffed (Varecia variegata) lemurs were documented over a three-year period at the Duke University Primate Center (DUPC, Durham, NC, USA). Vocal and nonvocal responses to naturally-occurring and simulated predators are described, and their functions are considered with respect to species-specific differences in body size, ecology, and reproductive biology. Nonvocal responses of the two lemur species differed most conspicuously in propensity of predator-directed aggression: whereas ringtailed lemurs generally evaded predators, ruffed lemurs were likely to confront or attack them. Interspecific variation in vocal responses to predators included differences in call diversity, stimulus specificity, and function. Ringtailed lemur antipredator behavior (including large group size) is viewed as an adaptation to nontrivial levels of predator pressure that stem from being a relatively small-bodied, semi-terrestrial primate living in an open habitat. In contrast, the highly aggressive antipredator behavior of the ruffed lemur is seen in part as an effect of a somewhat larger body size, but also as a constraint of producing sessile offspring that do not cling to the mother. Thus, in contrast to ringtailed lemurs, ruffed lemurs with infants cannot flee predators without risking their reproductive success.

Many butterflies exhibit structurally coloured wing patches that are stunningly bright and iridescent in their appearance, yet functionally obscure. These colours are often exaggerated in males, which suggests a sexually selected origin. We studied the visual properties, morphological basis, and interindividual variation of structural wing colouration in the common eggfly, Hypolimnas bolina L. (Nymphalidae). Males of this territorial species possess highly directional UV/violet colouration that fully overlaps smaller white patches on their dorsal wing surfaces. We sampled 56 males, including territorial residents and non-resident ‘floaters’ and assessed the properties of their structural colour using reflectance spectrometry and scanning electron microscopy. The patches reflect strongly in the UV range (300–400 nm), with a peak of ~360 nm, and the wing scales in these regions exhibit a ridge-lamellar surface architecture that has known function in other species as a multiple thin-film interference mirror. Peak UV brightness was variable, and both brightness and peak hue varied systematically across age classes. UV brightness was also related to hue independently of the age-related variation. Territorial residents possessed duller UV markings than their non-resident contemporaries, which is not consistent with exaggeration due to male–male competition. The high phenotypic variance is, however, consistent with a putative role for this male-limited trait as a sexual ornament.

Headbob displays from 22 adult male Anolis conspersus of three "color morphs" (green, brown, and blue) were videotaped in the laboratory. Frame-by-frame coordinates of the vertical head mo- tions were used to generate display-action-pattern (DAP) graphs. Field observations had revealed that only one type of headbob display ("Type A") was performed when males displayed to nonspecific audiences while moving around their territories ("male-alone context"). During staged male encounters in the lab ("male-male context"), Type A displays and a second type of display ("Type B") were produced. The two types of displays were partitioned into units that were compared among the color morphs. We then trans- formed the display units with principle components analysis and used one-way ANOVAs to test statistically for differences among the color morphs at the "unit" level. Finally, we used discriminant function analysis to test for color morph differences at the "display" level. Graphical visualization and statistical analyses showed that, like body coloration, the green and the brown morph are more distinctive from each other than either is from the blue morph, although the differences in display units among the color forms are subtle. Given that A. conspersus is a member of the seven-species Anolis radiation on Jamaica, we compare the structure of one of its displays (Type A) with that of its closest relative, Anolis grahami. Last, we speculate on the possible origin of the unusual display structure observed in the A. conspersus Type B display.

Visual assessment of avian stimuli as threatening or non-threatening was investigated experimentally in semi-captive, forest-living ringtailed lemurs (Lemur catta). Subjects were presented silhouettes of different sizes and shapes on overhead runs. Antiraptor calls elicited by the silhouettes were recorded and quantified. Realistic and stylized hawk shapes elicited more total calling per trial than did a square shape. Large hawk shapes elicited longer individual calls than a large goose shape, and all bird shapes elicited longer calls than did a square but not a diamond shape. We suggest the observed response patterns reflect a differential in perceived avian threat and that they support an ecologically-oriented view of the "short neck" interpretation for raptor shape recognition.

Activity budgets of captive sifakas (Propithecus verreauxi coquereli and Propithecus verreauxi verreauxi) were assessed from 500 hours of observational data obtained at the Duke University Primate Center (Durham, NC). Data were examined for behavioral differences according to gender, availability of intergroup contact, subspecies, indoor/outdoor housing, and enclosure size. Results showed few differences between the activity budgets of males and females. Several differences found in conjunction with availability of intergroup contact appeared to relate more to subspecific, than to contact, differences. Sifakas housed outdoors were more active, spending less time resting and more time in locomotion, feeding, and playing than sifakas housed indoors. The findings of this study implicate outdoor housing as a primary factor in stimulating activity in these rare prosimian primates.

A stable social group of 7 semifree-ranging black-and-white ruffed lemurs (Varecia variegata variegata) was studied for 4 months to catalog the behavioral repertoire of this species. Observations focussed on particular aspects of behavior were conducted before and after this 4-month period to supplement information gathered. Behavior in 11 major categories is detailed: postures, terrestrial locomotion, arboreal locomotion, feeding behavior, vocalizations, scent-marking, affinitive social behavior, agonistic social behavior, play behavior, sexual behavior, and parental behavior. Ruffed lemurs frequently used body positions and locomotor patterns unusual among lemurids, including bipedal hanging and long-descent leaps. These behaviors reinforce dental evidence that Varecia are among the most frugivorous of the Malagasy lemurs. Low intragroup cohesion, infrequent social interaction, and antiphonal use of several long-distance vocalizations suggest that ruffed lemurs naturally exhibit fission-fusion sociality. Social structure based on interindividual familiarity probably extends across foraging parties for several of the diurnally active lemurs; however, thus far only Varecia seems likely to exhibit fission-fusion sociality analogous to that seen in spider monkeys and chimpanzees.

A vocalization of the ringtailed lemur (Lemur catta) was examined for individual differences according to several temporal- and frequency-dependent variables. Vocalizations were tape recorded at the Duke University Primate Center (Durham, NC) and spectrographically analyzed. Significant differences were found in pair-wise comparisons of call structure among the study subjects, thus providing the physical basis for individual discrimination. A separate analysis comparing degree of kinship and vocal similarity revealed a positive but nonsignificant correlation between these two variables. This study represents an initial examination of vocal individuality in prosimian primates.