Amphibolurus muricatus WHITE, 1790

Australische Felsenechse / Jacky Lashtail, Jacky Lizard

BARQUERO, M.D., PETERS, R. & M.J. WHITING (2015): Geographic variation in aggressive signalling behaviour of the Jacky Dragon. – Behav. Ecol. Sociobiol., 69 (9): 1501-1510.

Signal diversification is often the product of sexual and/or natural selection and may be accompanied by genetic differentiation or simply reflect a plastic response to social and environmental variables. We use an agamid lizard endemic to Australia, the Jacky dragon (Amphibolurus muricatus), to examine the relationships between population relatedness, morphology and signalling behaviour. We also tested whether males are able to discriminate among rivals from different populations and whether they respond more aggressively to more closely related populations. We studied three populations, two of which belong to the same genetic clade. Individuals from the two most closely related populations were also more similar in morphology than lizards from the third, more distant, population. However, all three populations differed in characteristics of their signalling behaviour including latency to display and the interval between displays. In addition, animals from all populations showed similar levels of aggression when matched with individuals from the same or different populations in staged trials and thus did not show evidence of population-level discrimination. We argue that display variation might be a consequence of behavioural plasticity and that, despite difference in genetic structure, morphology and behaviour, this species retains a cohesive communication system.

BARQUERO, M.D., PETERS, R. & M.J. WHITING (2019): Effect of temperature on the visual displays of the Jacky Dragon. - 20th European Congress of Herpetology, Milan, 2-6 September 2019. p. 55.

In ectotherms such as lizards, temperature is a key determinant of their behavior and their ability to signal to conspecifics. We asked whether changes in the thermal environment along the distribution of an agamid lizard, the Jacky dragon (Amphibolurus muricatus), modifies visual signal properties (frequency and duration). We first collected temperature data from 12 weather stations to understand variation in temperature across the species’ range. We then collected fiel body temperatures (Tb) for three populations before measuring preferred  body temperatures (Tpref) in the lab. Finally, we examined the role of temperature on the frequency and duration of display behavior at low (28 °C) and high (35 °C) temperatures consistent with what individuals experience in the wild. We found differences of 5.6-9.4 °C in mean air temperature across sites of the species’ range. Field body temperatures, but not preferred body temperatures (overall average = 32.4 °C), differed among populations, with individuals from one population attaining higher temperatures than the other two. We als found a positive relationship between air temperature and the number of displays used during intraspecific communication, as well as differences in the number of displays during high- and low-temperature treatments (more displays during the high-temperature treatment). We suggest that social signaling is plastic and able to respond to local conditions such that variation of body temperatures mirrors that of the thermal environment and in turn, influences the frequency and duration of Jacky dragon visual signals. Display behavior is therefore dependent on environmental temperature and future changes to the thermal environment could have an impact on communication through its effect on display duration and frequency

BRANDIS, B. (1912): Etwas über die Amphibolurus muricatus. – Blätter für Aquarien- und Terrarien-Kunde, 18: 339.

CARLILE, P.A., PETERS, R.A. & C.S. EVANS (2006): Detection of a looming stimulus by the Jacky Dragon: selective sensitivity to characteristics of an aerial predator. – Anim. Behav., 72 (3): 553-562.

Rapidly looming objects are highly salient to most animal visual systems. The sensory processing of such stimuli is now well understood in birds and insects. We conducted the first analogous study in lizards, concentrating on the ecologically realistic challenge posed by an approaching aerial predator. In an initial experiment, video footage of a trained raptor flying towards the camera produced flight responses in Jacky dragons, Amphibolurus muricatus, but control sequences showing a retreating or stationary stimulus were ineffectual. Two additional experiments then explored the processing of motion and of morphological attributes separately. We presented a series of expanding disks, systematically manipulating area/time characteristics to test looming sensitivity in the absence of other cues. Lizards oriented significantly more frequently to a sequence matching the area change of the approaching predator than to any other. Comparisons show that this response was specific to an exponential increase following a period of slow change, a pattern remarkably similar to those described in other taxa. In the final experiment, we presented a range of stimulus shapes, all with identical area and movement. Lizards were most responsive to a realistic raptor silhouette. Controls allowed us to exclude the possibility that this result was attributable to looming rate, size or the axis of asymmetric expansion. We conclude that response to an approaching aerial predator depends upon a hierarchical series of cues, including area/time profile, edge length, shape and orientation. The integration of this information will be an important problem for future work.

CHONG, G., HEATWOLE, H. & B.T. FIRTH (1973): Panting thresholds of lizards – 2. Diel variation in the panting threshold of Amphibolurus muricatus. – Comparative Biochem. Physiol. (A), 46 (4): 827-829.

DYK, D.A. van &. C.S EVANS (2007): Familiar-unfamiliar discrimination based on visual cues in the Jacky Dragon, Amphibolurus muricatus. – Anim. Behav., 74 (1): 33-44.

Territorial animals typically have the ability to discriminate between familiar and unfamiliar conspecifics. This enables residents to minimize the costs of resource defence by matching the intensity of their aggressive response to the level of threat posed by intruders. Although individual discrimination based upon chemical signals is well established in lizards, much less is known about the role of visual cues, despite the importance of this modality in social interactions. We conducted two series of video playback experiments, modelled on a habituationedishabituation design, to test for visually mediated individual discrimination in an Australian agamid lizard. Captive males were shown a different digital video sequence of the same life-sized conspecific every day for 4 days. They were then tested in probe trials with either a novel sequence of the same male, or a matched sequence of a different male. One such series was conducted with footage of inactive basking lizards to evaluate the role of static morphological cues, while the other presented displaying males so that signal structure was also available. Lizards responded to a change in the identity of both static and displaying video males with increased substrate licking, a chemosensory behaviour that has consistently been reported in previous work with live opponents. The unfamiliar basking conspecific also evoked increased locomotor activity. These results show that Jacky dragons are capable of discriminating between familiar and unfamiliar intruders based upon static morphological cues alone.

DYK, D.A. VAN, TAYLOR, A.J. & C.S. EVANS (2007): Assessment of repeated displays: a test of possible mechanisms. – J. Exp. Biol., 210 (17): 3027-3035.

Many animals signal their resource holding potential (RHP) to deter competitors from engaging them in potentially costly fights. Studies of this opponent assessment function have generated important insights into signal design and evolution. In the case of sounds, rate of production is often a salient feature. We used digital video playback to conduct analogous experiments exploring the importance of temporal variation in visual signals. Our study focused on the push-up display of male Jacky dragons Amphibolurus muricatus, an Australian agamid lizard. This stereotyped movement-based signal is commonly performed during male–male contests. A previous study has shown that Jacky dragons responses are influenced by the overall display rate of a video conspecific. We built upon this finding by investigating the effect of short-term variation in display rate. Each playback sequence varied systematically across a different combination of display parameters, while keeping the total number of push-ups constant. Other potential cues, such as morphology and the characteristics of individual motor patterns, were precisely controlled. The aggressive signalling and locomotor behaviour of subject males varied significantly between sequences. Most notably, performance of throat expansions, a typical agamid threat posture, was suppressed by video sequences with temporal clumping of displays. These results show that lizards are sensitive to differences in the temporal fine structure of display sequences and suggest that display concentration is an important assessment cue.

ESQUERRÉ, D., KEOGH, J.C. & L.E. SCHWANZ (2014): Direct effects of incubation temperature on morphology, thermoregulatory behaviour and locomotor performance in jacky dragons (Amphibolurus muricatus). – J. Therm. Biol., 43: 33-39.

FIRTH, B.T. & H. HEATWOLE (1976): Panting thresholds of lizards: The Role of Pineal Complex in Panting Responses in an Agamid Lizard, Amhibolurus muricatus. – Gen. Comp. Endocr., 29: 388-401.

HALL, J.M. & D.A. WARNER (2017): Winter microhabitat selection and growth of Jacky Dragons (Amphibolurus muricatus). – Copeia, 105 (4): 618–625.

Most temperate-climate lizards become inactive during the winter months of each year. As temperatures drop, they must find appropriate overwintering microhabitats to avoid lethal surface temperatures and/or thermoregulate. The environmental variables that characterize such microhabitats and the cues that lizards utilize to assess them are a critical but understudied component of their natural history. While many studies of overwintering site selection focus on temperature, other factors constituting microhabitats (e.g., surface structures, substrate) may play a role in site selection. We used the Jacky Dragon (Amphibolurus muricatus), an Australian agamid lizard, to test for preference of using various cover types (leaf litter, open sand, sticks, rocks) for overwintering as well as the consequences of cover type selection. Jacky Dragons preferred overwintering beneath leaves compared to other structures, and this choice was associated with growth during winter, but not with survival. Our study highlights the potential importance of cover structures in overwintering site selection, suggests that midwinter activity may be common in Jacky Dragons, and calls for further study of the winter ecology of temperate-climate lizard species.

HARLOW, P.S. & J.E. TAYLOR (2000): Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature-dependent sex determination. – Austral. Ecology 25: 640–652.

The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature-dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature-dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg-laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male-male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male-biased sex ratios, and that this provides an adaptive explanation for temperaturedependent sex determination in A. muricatus.

HEATWOLE, H. & B.T. FIRTH (1982): Voluntary maximum temperature of the jackie lizard Amphibolurus muricatus. – Copeia, 1982 (4): 824-829.

HEATWOLE, H., FIRTH, B.T. & H. STODDART (1975): Influence of season, photoperiod and thermal acclimation on the panting threshold of Amphibolurus muricatus. – Journal exp. Zool., 191 (2): 183-192.

HEATWOLE, H., FIRTH, B.T. & G.J.W. WEBB (1973): Panting thresholds of lizards – 1. Some methodological and internal influences on the panting threshold of an agamid, Amphibolurus muricatus. – Comparative Biochem. Physiol. (A), 46 (4): 799-826.

HOESE, F., PETERS, R.A. & C.S. EVANS (2008): The effect of variation in prey movement on the predatory response of Jacky Lizards (Amphibolurus muricatus). – Ethology. 114 (7): 718–727.

The sensory systems of animals have evolved to meet the demands of functionally critical events. Animals that rely on visual motion cues must ignore irrelevant movement and only attend to certain characteristics that warrant further consideration. For the Australian jacky lizard (Amphibolurus muricatus), movement is essential for detecting potential prey. Here we examine whether differences in the actual motion characteristics of a simulated prey item influence predatory behaviour. We begin with direct observations of responses to live prey items to define an ordinal scale for subsequent video playback experiments involving a synthetic prey item (an animated cricket). In expt 1, we show that the responses of lizards to the synthetic prey were matched to those given in response to video of an actual cricket. In expt 2 we manipulated the movement patterns of the synthetic cricket based on motion analysis of actual prey movement. Manipulating motion characteristics did not influence the level of predatory behaviour observed, however, lizards showed sustained predatory behaviour to stimuli with speed characteristics that were matched to those of real crickets. We discuss the possibility that recent experience of prey movement in captivity has influenced the foraging behaviour of these lizards.

KAMMERER, P. (1902): Australische Echsen in der Gefangenschaft. 2. Amphibolurus barbatus Cuv. und muricatus White. – Bl. Aquar. Terrar.-Kunde, 8: 146.

KUBIAK, P.J. (2011): Predation by a Jacky Lizard Amphibolurus muricatus (Agamidae) upon nesting Banded Bees Amegilla sp.(Apidae). - Victorian Naturalist, 128: 86-89.

McCOY, F. (1886): Grammatophora muricata (SHAW sp.). The Blood-sucker. – Prod. Zool. Vict., 12: 47-50.

ORD, T.J. & C.S. EVANS (2002): Interactive video playback and opponent assessment in lizards. – Behav. Proc., 59 (2): 55-65.

Video playback has been used to explore many issues in animal communication, but the scope of this work has been constrained by the lack of stimulus_/subject interaction. In many natural contexts, each participant’s signalling behaviour is dependent from moment-to-moment on that of the other. Analyses of acoustic communication demonstrate the value of reproducing such social contingencies. We assessed the utility of interactive playback for studies of visual signalling by comparing the responses of male Jacky dragons, Amphibolurus muricatus, to interactive and non-interactive digital video playbacks of a life-sized conspecific. Displays produced by lizards in the interactive condition had the effect of suppressing the aggressive display of their simulated opponent. Each stimulus sequence generated during an interactive playback was subsequently played to a size-matched control animal. Males that could interact with the video stimulus responded principally with aggressive displays, while those that could not produced a mixture of aggressive and appeasement signals. Adding a degree of receiver responsiveness is hence sufficient to alter the type of signal evoked, even when video stimuli are physically identical. Interactive playback permits the experimental study of a broader range of theoretical topics and can enhance the realism of video stimuli.

ORD, T.J. & C.S. EVANS (2003): Display rate and opponent assessment in the jacky dragon. – Behav., 140: 1495-1508.

ORD, T.J., PETERS, R.A., EVANS, C. & A.J. TAYLOR (2002): Digital video playback and visual communication in lizards. – Anim. Behav., 63 (5): 879-890.

Experimental analyses of dynamic visual signals have to overcome the technical obstacle of reproducing complex motor patterns such as those found in courtship and threat displays. Video playback offers a potential solution to this problem, but it has recently been criticized because of sensory differences between humans and nonhuman animals, which suggest that video stimuli might be perceived as deficient relative to live conspecifics. Quantitative comparisons are therefore necessary to determine whether video sequences reliably evoke natural responses. Male Jacky dragons, Amphibolurus muricatus, compete for territories using complex displays delivered in a rapid stereotyped sequence. We evaluated video playback as a technique for studying this visual signal. Digital video sequences depicting a life-sized displaying male were indistinguishable from live male conspecifics in the rate and structure of aggressive displays evoked. Other measures of social behaviour suggested that video stimuli were more effective in this context. Lizards produced significantly more appeasement displays and had higher rates of substrate licking and locomotor activity in response to video playback than to confined male opponents, which failed to produce aggressive displays. Lizards tracked temporal changes in the display rate of video stimuli and were also sensitive to individual differences in morphology and behaviour between video exemplars. These results show that video stimuli are appropriate for the experimental analysis of Jacky dragon aggressive displays. We compare the potential shortcomings of video playback with those of other techniques and conclude that no approach offers a panacea, but that several have complementary characteristics.

PEDERZANI, H.-A. (1967): Selten in Europa, aber haltbar: Die Australische Felsenechse. – Aquar. Terrar., Leipzig, 14 (2): 48-49.

PETERS, R.A. (2008): Environmental motion delays the detection of movement-based signals. – Biol. Lett., 4 (1): 2-5.

Animal signals are constrained by the environment in which they are transmitted and the sensory systems of receivers. Detection of movement-based signals is particularly challenging against the background of wind-blown plants. The Australian lizard Amphibolurus muricatus has recently been shown to compensate for greater plant motion by prolonging the introductory tail-flicking component of its movement-based display. Here I demonstrate that such modifications to signal structure are useful because environmental motion lengthens the time lizard receivers take to detect tail flicks. The spatio-temporal properties of animal signals and environmental motion are thus sufficiently similar to make signal detection more difficult. Environmental motion, therefore, must have had an influence on the evolution of movement- based signals and motion detection mechanisms.

PETERS, R.A. & S.J. ALLEN (2009): Movement signal choreography unaffected by receiver distance in the Australian Jacky lizard, Amphibolurus muricatus. – Behav. Ecol. Sociobiol., 63 (11): 1593-1602.

Theory explains the structure of animal signals in the context of the receiver sensory systems, the environment through which signals travel and their information content. The influence of signalling context on movementbased signalling strategies is becoming clearer. Building upon recent findings that demonstrated changing environmental plant motion conditions resulted in a change of signalling strategy by the Australian lizard Amphibolurus muricatus, we examined whether receiver distance also influences signalling strategies. We found that signalling lizards did not modify their introductory tail flicking in response to distant viewers in the absence of competing, irrelevant plant image motion despite significant reductions in signal structure at the eye of the viewer. The magnitude of resultant effect sizes strongly suggests that receiver distance does not contribute to signalling strategies as much as the presence of motion noise in the environment.

PETERS, R.A. & C.S. EVANS (2003): Design of the Jacky Dragon visual display: Signal and noise characteristics in a complex moving environment. – J. Comp. Physiol., 189A (6): 447-459.

Visual systems are typically selective in their response to movement. This attribute facilitates the identification of functionally important motion events. Here we show that the complex push-up display produced by male Jacky dragons (Amphibolurus muricatus) is likely to have been shaped by an interaction between typical signalling conditions and the sensory properties of receivers. We use novel techniques to define the structure of the signal and of a range of typical moving backgrounds in terms of direction, speed, acceleration and sweep area. Results allow us to estimate the relative conspicuousness of each motor pattern in the stereotyped sequence of which displays are composed. The introductory tail-flick sweeps a large region of the visual field, is sustained for much longer than other components, and has velocity characteristics that ensure it will not be filtered in the same way as wind-blown vegetation. These findings are consistent with the idea that the tail-flick has an alerting function. Quantitative analyses of movement-based signals can hence provide insights into sensory processes, which should facilitate identification of the selective forces responsible for structure. Results will complement the detailed models now available to account for the design of static visual signals.

PETERS, R.A. & C.S. EVANS (2003): Introductory tail-flick of the Jacky Dragon visual display: Signal efficacy depends upon duration. – J. Exp. Biol., 206 (23): 4293-4307.

Many animal signals have introductory components that alert receivers. Examples from the acoustic and visual domains show that this effect is often achieved with high intensity, a simple structure and a short duration. Quantitative analyses of the Jacky dragon Amphibolurus muricatus visual display reveal a different design: the introductory tail-flick has a lower velocity than subsequent components of the signal, but a longer duration. Here, using a series of video playback experiments with a digitally animated tail, we identify the properties responsible for signal efficacy. We began by validating the use of the computer-generated tail, comparing the responses to digital video footage of a lizard tail-flick with those to a precisely matched 3-D animation (Experiment 1). We then examined the effects of variation in stimulus speed, acceleration, duration and period by expanding and compressing the time scale of the sequence (Experiment 2). The results identified several variables that might mediate recognition. Two follow-up studies assessed the importance of tail-flick amplitude (Experiment 3), movement speed and signal duration (Experiment 4). Lizard responses to this array of stimuli reveal that duration is the most important characteristic of the tail-flick, and that intermittent signalling has the same effect as continuous movement. We suggest that signal design may reflect a trade-off between efficacy and cost.

PETERS, R.A. & C.S. EVANS (2007): Active space of a movement-based signal: response to the Jacky Dragon (Amphibolurus muricatus) display is sensitive to distance, but independent of orientation. – J. Exp. Biol., 210 (3): 395-402.

The efficacy of any animal signal is constrained by the range over which it remains above the sensory threshold of potential receivers. The spatial area in which reliable detection occurs defines active space; this is influenced by signal structure, the signalling environment and the sensory characteristics of receivers. Identification of the factors influencing active space has provided valuable insights into signal design, particularly in bioacoustics, in which signal distortion and degradation can be easily quantified. In the present study, we consider whether active space can similarly help to explain the design of a movement-based visual signal. The Jacky dragon (Amphibolurus muricatus) threat display is composed of five distinct motor patterns delivered in an obligatory sequence: tail-flicks, backward and forward foreleg waves, a push-up and a ‘body-rock’. In contrast to other communication systems, the introductory element is characterized by reduced intensity (average speed) but greater duration than subsequent motor patterns. Furthermore, the tail-flick sweeps a three-dimensional (3D) space around the lizard, whereas the motor patterns that follow are largely restricted to a single plane. Structural properties thus suggest that the active space of the tail-flick might be greater than that of the other motor patterns in the display, which would provide a parsimonious explanation for its use as an alerting component. We tested this prediction in a playback experiment incorporating 3D animations of lizard displays, comparing response probabilities to the factorial combination of three motor patterns, three viewing angles and three distances. Results suggest that the tail-flick does not have a greater active space than other display motor patterns, but that each degrades predictably with distance, thereby providing potential ranging cues. In addition, display components are remarkably robust to variation in receiver orientation, so that efficacy should be maximized in most potential signalling situations. These findings are consistent with the hypothesis that duration is the principal determinant of signal efficacy in this system.

PETERS, R.A. & T.J. ORD (2003): Display response of the Jacky Dragon, Amphibolurus muricatus (Lacertilia: Agamidae), to intruders: A semi-Markovian process. – Austral. Ecology, 28 (5): 499-506.

Abstract:
Movement-based visual signals are widely distributed among animal species. They are used in a variety of contexts including mate-choice, pursuit deterrence, alarm signalling and opponent assessment. Important contributions to general theories of animal communication have been made using lizards as model systems. However, much of this work has focused on the iguanids of North and South America. The agamid lizards of Australia have received little attention even though many species are characterized by complex visual displays. Here we present a detailed description of the push-up display of the Jacky Dragon (Amphibolurus muricatus), which comprises five distinct components, including tail-flicks, foreleg waves, and push-ups. Rival males exchange displays when competing for territory, but little is known about the rules that govern their expression. We set up simulated intrusions in a captive setting to overcome the inherent difficulty in observing these interactions in the field. An ‘intruder’ housed in a small tank was positioned in front of a larger enclosure containing a ‘resident’ male. The response of the resident was video-taped for subsequent analysis. We first examined characteristics of the initial display bout and explored sources of variation within and between residents. Measurements included bout duration, the number and hold duration of push-ups, the total number of components, and limb preferences during foreleg waves. Markov analysis was then used to measure serial dependencies among display components. This showed that the push-up display is a semi-Markovian process: the preceding component predicted the next one with high accuracy. The display is highly constrained irrespective of whether the bout was the first or subsequent response to an intruder, and irrespective of substrate, intruder identity and resident identity. These data are an important first step in understanding the design, perception and function of movement-based visual signals in agamid lizards.

PEPPER, M., BARQUERO, M.D., WHITING, M.J. & J.S. KEOGH (2014): A multi-locus molecular phylogeny for Australia’s iconic Jacky Dragon (Agamidae: Amphibolurus muricatus): Phylogeographic structure along the Great Dividing Range of south-eastern Australia. - Molecular Phylogenetics and Evolution 71: 149–156.

Jacky dragons (Amphibolurus muricatus) are ubiquitous in south-eastern Australia and were one of the first Australian reptiles to be formally described. Because they are so common, Jacky dragons are widely used as a model system for research in evolutionary biology and ecology. In addition, their distribution along the Great Dividing Range of eastern Australia provides an opportunity to examine the influence of past biogeographical processes, particularly the expansion and contraction of forest habitats, on the diversification of this iconic agamid lizard. We generated sequence data for two mitochondrial and three nuclear DNA loci (4251base pairs) for 62 Jacky dragons sampled from throughout their distribution. Phylogenetic analyses based on maximum likelihood and Bayesian species-tree methods revealed five geographically structured clades separated by up to 6% mitochondrial and 0.7% nuclear sequence divergence. We also quantified body proportion variation within and between these genetic clades for more than 500 specimens and found no evidence of any significant differentiation in body proportions across their range. Based on body proportion homogeneity and lack of resolution in the nuclear loci, we do not support taxonomic recognition of any of the mitochondrial clades. Instead, A. muricatus is best thought of as a single species with phylogeographic structure. The genetic patterns observed in the Jacky dragon are consistent with fragmented populations reduced to multiple refugia during cold, arid phases when forested habitats were greatly restricted. Consequently, the inferred biogeographic barriers for this taxon appear to be in line with lowland breaks in the mountain ranges. Our results are congruent with studies of other reptiles, frogs, mammals, birds and invertebrates, and together highlight the overarching effects of widespread climatic and habitat fluctuations along the Great Dividing Range since the Pliocene.

RADDER, R.S., WARNER, D.A. & R. SHINE (2007): Compensating for a bad start: catch-up growth in juvenile lizards (Amphibolurus muricatus, Agamidae). – J. Exp. Zool., 307A (9): 500-508.

Despite variations of environmental noise, signals are designed to be effective and conspicuous over an appreciable distance. In particular, visual signals must be perceptible against interference caused by natural elements, such as windblown vegetation. We examined the efficiency of aggressive and submissive displays to elicit behavioural responses from observers in the Jacky dragon (Amphibolurus muricatus) across relative environmental noise. Both displays have been reported to play an important role during social interactions in this species. We conducted two video playback experiments that utilised a high-resolution computer-generated lizard animation to produce social displays that were embedded within simulated windblown vegetation. First, we compared the efficiency a full aggressive display action pattern (comprised of a tail-flick, backward-forward arm wave, and push-up body rock) to a slow arm wave submissive display, against identical background of windblown vegetation. Second, we compared the tail-flick (alerting component) to the slow arm wave across three varying natural conditions, in which the vegetation behind the displays acted as simulated noise: calm, typical, and windy. We found that aggressive displays were more efficient to elicit an observer’s response than submissive signals. Furthermore, the tail-flick display is more efficient than submissive displays across a range of natural variation in windblown vegetation movement, but both signals remain efficient in the face of environmental motion noise. Our results suggest that

constraints from the environmental background scene play may have a critical role in the evolution of signal design used in Jacky dragon communication.

WOO, K.L. & G. RIEUCAU (2012): Aggressive signal design in the Jacky Dragon (Amphibolurus muricatus): display duration affects efficiency. – Ethology, 118 (2): 157-168.

Design characteristics of signals, such as their duration, may have evolved to maximize signal efficiency. It is commonly assumed that constraints on signal design have usually shaped the most optimal display characteristics to improve signal transmission and information transfer of the signaller, and detection by intended receivers. In this study, we tested whether the characteristics (duration, speed and frequency) of an aggressive display, the push-up body rock, exhibited by the Jacky dragon (Amphibolurus muricatus) have likely evolved for optimal signal efficiency, as it is able to draw attention to the signaller. We performed two video playback experiments using high-resolution 3D animations testing the effect of variation in push-up body rock structure. In experiment 1, we manipulated push-up body rock display structure. We gradually increased the number of push-ups exhibited by a digitally animated Jacky dragon increasing the overall display duration. In experiment 2, we developed four stimuli based on population-typical push-up body rock display for duration (short and long), and frequency of push-ups (1 or 5 consecutive push-ups) by manipulating push-ups’ speed. In both experiments, we measured the probability of an orienting response and response latency of focal lizards when being exposed to the different stimuli. Our results showed that display duration is critically important for signal efficiency in the aggressive push-up body rock display. If we are to understand the design characteristics of signals used in animal communication, then it appears important to consider the possible trade-off between signal efficiency and costs.

A recent study has shown that Jacky lizards adjust their movement based visual signaling in response to the varying environmental conditions; the results indicate that this species has highly sophisticated communication and sensory processing strategies.

Amphibolurus norrisi WITTEN & COVENTRY,1984

Mallee Heath Lashtail

SMITH, A.L., BULL, C.M. & D.A. DRISCOLL (2013): Skeletochronological analysis of age in three ‘fire-specialist’ lizard species. – S. Aust. Nat., 87 (1): 6-17.

Adverse fire regimes threaten the persistence of animals in many ecosystems. ‘Fire-specialist’ species, which specialise on a particular post-fire successional stage, are likely to be at greatest risk of decline under adverse fire regimes. Life history data on fire-specialists, including longevity, are needed to develop tools to assist fire management for conservation. We used skeletochronology to estimate the age of individuals of three South Australian fire-specialist lizard species: Amphibolurus norrisi (Agamidae), Ctenotus atlas (Scincidae) and Nephrurus stellatus (Gekkonidae). Bone samples were sourced from specimens captured in mallee vegetation predominantly on the Eyre Peninsula, South Australia. Transverse sections of femora were prepared using a standard histological procedure. We counted the minimum and maximum number of lines of arrested growth (LAG) in each sample to provide a conservative and non-conservative estimate of age for each individual. Our results showed that A. norrisi may live for at least five and up to seven years, C. atlas for at least three and up to four years and N. stellatus for at least four and up to seven years. The assumptions that one LAG was deposited per year and that endosteal resorption was minimal must be considered before using these estimates in further research. Our results provide a guide to the potential longevity of the three species which can be used in simulation modelling and genetic studies to improve fire management for animal conservation.

WITTEN, G.J. & A.J. COVENTRY (1984): A new lizard of the genus Amphibolurus (Agamidae) from southern Australia. – Royal Society of Victoria Proceedings, 96 (3): 155-159.

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