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Being aggressive and by extension, dominant, is an important mechanism for determining access to resources such as mates or territories. While predictors of contest outcome and dominance are increasingly studied, we have a poor understanding of how they vary across populations. Here, I use the widely distributed Australian agamid lizard, the Jacky dragon (Amphibolurus muricatus), to quantify variation in features predicting contest outcome among males of different populations. I measured physical attributes, maximal physiological performance capacity (sprint speed, endurance, bite force) and visual displays during staged encounters. I found that morphology, performance capacity and the type and frequency of visual displays used during agonistic interactions varied significantly across populations. Contest winners from the Cann River State Forest population favored tail‐flicks and push‐up/body‐rocks, while those from Royal National Park were more likely to chase and individuals from Yarratt State Forest performed more bite‐lunges than other populations. The losers of contests also differed in their displays. Individuals from the Cann River population were dominant over the others based on behavioral attributes (i.e., aggressive visual displays, chases and bite‐lunges). I suggest that population differences in signal form and function could have implications for range dynamics as populations come into contact in an era of rapid environmental change. [ABSTRACT FROM AUTHOR]

Sex determination and differentiation in reptiles is complex. Temperature-dependent sex determination (TSD), genetic sex determination (GSD) and the interaction of both environmental and genetic cues (sex reversal) can drive the development of sexual phenotypes. The jacky dragon (Amphibolurus muricatus) is an attractive model species for the study of gene–environment interactions because it displays a form of Type II TSD, where female-biased sex ratios are observed at extreme incubation temperatures and approximately 50 : 50 sex ratios occur at intermediate temperatures. This response to temperature has been proposed to occur due to underlying sex determining loci, the influence of which is overridden at extreme temperatures. Thus, sex reversal at extreme temperatures is predicted to produce the female-biased sex ratios observed in A. muricatus. The occurrence of ovotestes during development is a cellular marker of temperature sex reversal in a closely related species Pogona vitticeps. Here, we present the first developmental data for A. muricatus, and show that ovotestes occur at frequencies consistent with a mode of sex determination that is intermediate between GSD and TSD. This is the first evidence suggestive of underlying unidentified sex determining loci in a species that has long been used as a model for TSD. [ABSTRACT FROM AUTHOR]

Selection for conspicuousness has been an important force on visual signal design. Although signal efficacy has been extensively studied in acoustic systems, few studies have examined this attribute in dynamic visual signals. Here, I simulated signal competition between Jacky lizards (Amphibolurus muricatus) by presenting the motor patterns (tail-flick, push-up body rock, and slow arm wave) in isolation that are typically used in social communication. Phase 1 used four digital video playback systems to present simultaneous animated display combinations on opposing monitors to a subject that was situated in the middle, and measured orientation towards the monitors and latency to respond. Phase 2 maintained the same set-up and simultaneous display combinations, but tested signal conspicuousness across three levels of visual noise (calm, typical, and windy) simulated by the movement of windblown vegetation in the background. The results suggest that the most conspicuous visual display is the tail-flick, followed by the push-up body rock, and the slow arm wave is the least conspicuous. Moreover, this relationship is robust across the full range of environmental wind conditions. No significant side biases in orientation to displays were detected, which suggested no lateralization in perceptual processes. Jacky lizard display motor patterns which address distinct functional requirements: the tail flick is an ideal alerting component, with high efficacy over a range of signaling conditions. The push-up body rock, which is used only in aggressive displays, has a more restricted range, and the submissive slow arm wave is likely designed to appease nearby dominant males.

Sex determination and differentiation in reptiles is complex. Temperature-dependent sex determination (TSD), genetic sex determination (GSD) and the interaction of both environmental and genetic cues (sex reversal) can drive the development of sexual phenotypes. The jacky dragon (Amphibolurus muricatus) is an attractive model species for the study of gene–environment interactions because it displays a form of Type II TSD, where female-biased sex ratios are observed at extreme incubation temperatures and approximately 50 : 50 sex ratios occur at intermediate temperatures. This response to temperature has been proposed to occur due to underlying sex determining loci, the influence of which is overridden at extreme temperatures. Thus, sex reversal at extreme temperatures is predicted to produce the female-biased sex ratios observed in A. muricatus. The occurrence of ovotestes during development is a cellular marker of temperature sex reversal in a closely related species Pogona vitticeps. Here, we present the first developmental data for A. muricatus, and show that ovotestes occur at frequencies consistent with a mode of sex determination that is intermediate between GSD and TSD. This is the first evidence suggestive of underlying unidentified sex determining loci in a species that has long been used as a model for TSD. [ABSTRACT FROM AUTHOR]

Temperature is a crucial environmental component that imposes physiological constraints and ultimately produces variation in life-history traits. Temperatures experienced by mothers can influence offspring phenotypes, including growth and sex ratios, especially in ectothermic species.However,mechanisms by which thermal information can be passed onto offspring have been underexplored. Here, we investigated corticosterone as a potential mediator of thermal maternal effects.We held female jacky dragons (Amphibolurus muricatus) in two different thermal regimes (short [7 h] or long [11 h] basking treatments), then quantified plasma corticosterone levels and tested for correlations between the resulting corticosterone levels and reproductive outputs. Lizards in the long-bask treatment had significantly higher corticosterone levels than those in the short-bask treatment. Maternal corticosterone, in turn, had sex-dependent effects on offspring hatching size but was not associated with maternal reproductive effort or offspring sex or growth. In contrast, maternal body condition was strongly positively related to both reproductive output (including clutch size and total number of eggs) and offspring size at hatching but had no effect on offspring growth. Basking treatment also interacted with condition and corticosterone to affect egg mass and hatchling snout-vent length, respectively. When we tested for relationships between corticosterone levels and body condition, we found corticosterone to be negatively related to condition in long-bask lizards but only in the post-breeding season. These findings indicate that thermal opportunity alters physiology, with potential consequences for fitness.Moreover, the results suggest interactive influences of temperature, corticosterone, and condition as mediators of maternal effects. [ABSTRACT FROM AUTHOR]

Embryonic development in oviparous organisms is fueled by maternally allocated yolk, and many organisms hatch before that energy store is used completely; the resultant leftover (residual) yolk is internalized and may support early posthatching life. However, embryos that use most, or all, of their yolk supply before hatching should hatch at a larger size than those that do not exhaust those energy reserves, which could also have benefits for posthatching growth and survival. To examine the trade-off between residual yolk and offspring size, we experimentally reduced yolk quantity at oviposition in lizard eggs (Amphibolurus muricatus) and then quantified offspring size and the amount of internalized residual yolk. This design enabled us to determine whether embryos (1) exhaust yolk supply during development (thereby maximizing neonatal size) or (2) reduce neonatal size by retaining yolk reserves at hatching. Our data support the latter scenario. Eggs from the yolk-reduced treatment produced smaller offspring with a proportion of residual yolk similar to that of offspring from unmanipulated eggs, suggesting that the fitness benefits of posthatching energy stores outweigh those of larger neonatal size. [ABSTRACT FROM AUTHOR]

Abstract: Thermoregulatory behaviour provides one of the main mechanisms by which animals compensate for fluctuations in environmental temperatures to maintain body temperatures within physiological optima. Thus, strategies of thermoregulation are predicted to be related to variation in environmental temperatures. We tested with jacky dragons (Amphibolurus muricatus) the prediction that the accuracy and effectiveness of thermoregulation would decrease as the costs of thermoregulation increase using experimental arenas to manipulate environmental temperature fluctuation. The results supported theoretical predictions on the costs of thermoregulation – environments that were fluctuating led to decreased accuracy of thermoregulation (increased deviations in body temperatures from preferred temperatures) and reduced thermoregulatory effort (effectiveness). Moreover, environments with a mean temperature farther from the preferred temperature also led to greater deviations in body temperature, although this had no significant effect on effectiveness of thermoregulation. Together, the results highlight the need to understand what influences the costs of thermoregulation (i.e. thermal variation and mean), and how great of costs will be accepted for the benefits associated with thermoregulation. [ABSTRACT FROM AUTHOR]

Abstract: Developmental plasticity creates marked variation in individual phenotypes when the environment is patchy, such as when the thermal environment varies. Plasticity may occur in response to the environment experienced during an individual's lifetime or to the environment experienced by parents (transgenerational plasticity), and may be adaptive if it enhances fitness. In particular, plasticity in thermal traits, such as preferred temperatures and thermal limits, may improve performance and fitness based on temperatures in the local environment. This study examined the influence of parental and offspring thermal environments (duration of access to a basking lamp) on offspring thermal traits (preferred temperatures and panting threshold) in jacky dragons (Agamidae: Amphibolurus muricatus). Long‐bask parental environments led, indirectly, to higher preferred temperatures of offspring due to increased offspring body mass compared to offspring of short‐bask parents. The increase in median temperature preference was associated with a higher voluntary minimum body temperature and a narrower preference range, suggesting tradeoffs in thermal behavior and a matching of offspring preferences to the parental environment. Parental thermal treatment did not influence offspring panting threshold. Instead, the panting threshold tended to be higher in offspring that were reared in the long‐bask treatment compared to those in the short‐bask treatment, suggesting longer basking environments increased thermal tolerance. Parental and offspring thermal environment did not exhibit any interactive effect on thermal traits. The results indicate that thermal environments experienced by lizards can have both transgenerational and within‐generation impacts on thermal traits, thus influencing how populations respond to fluctuating or changing climates. [ABSTRACT FROM AUTHOR]

Environmental and developmental conditions can drive substantial variation in offspring behaviour and developmental trajectory. While incubation temperature is well known to influence development in oviparous animals, little is known of the role of parental temperature on offspring phenotype (i.e. thermal parental effects). Following exposure of male and gravid female jacky dragons, Amphibolurus muricatus , to one of two thermal treatments (short-bask versus long-bask) and incubation of their eggs at a constant temperature, we examined whether the preovipositional parental treatment influenced offspring performance-related behaviours. We detected main and interactive effects of parental treatment on offspring behaviours including feeding, exploration and antipredator. Sex-specific effects of parental treatment included long-bask sons being more likely to feed and being bolder following predatory attack than short-bask sons, while the differences between treatments for daughters were smaller. Behaviours were not consistent between 1 week and 1 month of age and showed little correlation across behavioural contexts. Some behaviours emerged as promising mechanisms of documented parental effects on offspring growth and survival in these individuals. In particular, boldness among long-bask sons in an antipredator context may be linked to their greater rates of growth posthatching. Overall, our findings suggest that thermal parental effects influence variation in animal behaviours relevant for subsequent fitness outcomes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Habitat characteristics influence the efficacy of animal communication, and population differences in signal structure due to habitat variation are well known for sound and colour signals. However, this variation in signal structure has not been reported for motion-based signals. Here we tested the motion-based signalling displays of two populations of an Australian agamid lizard, Amphibolurus muricatus , in the context of their respective habitats. We employed a novel approach that calculates the distribution of motion speeds of lizard signals and environmental noise independently, before computing the difference in these distributions to obtain a measure of signal–noise contrast. Our results revealed variation in signal structure between the two populations and support the hypothesis that this variation can be explained by differences in the signalling environment. Signals from both populations showed similar contrast values at their respective habitats, but differed significantly when considered in the habitats of the allopatric population. These results are consistent with the hypothesis that habitat structure affects signal efficacy and causes population differences in motion signalling behaviour as a consequence of adaptations to enhance efficacy. [ABSTRACT FROM AUTHOR]

Identifying perceptual thresholds is critical for understanding the mechanisms that underlie signal evolution. Using computer-animated stimuli, we examined visual speed sensitivity in the Jacky dragon Amphibolurus muricatus, a species that makes extensive use of rapid motor patterns in social communication. First, focal lizards were tested in discrimination trials using random-dot kinematograms displaying combinations of speed, coherence, and direction. Second, we measured subject lizards' ability to predict the appearance of a secondary reinforcer (1 of 3 different computer-generated animations of invertebrates: cricket, spider, and mite) based on the direction of movement of a field of drifting dots by following a set of behavioural responses (e.g., orienting response, latency to respond) to our virtual stimuli. We found an effect of both speed and coherence, as well as an interaction between these 2 factors on the perception of moving stimuli. Overall, our results showed that Jacky dragons have acute sensitivity to high speeds. We then employed an optic flow analysis to match the performance to ecologically relevant motion. Our results suggest that the Jacky dragon visual system may have been shaped to detect fast motion. This pre-existing sensitivity may have constrained the evolution of conspecific displays. In contrast, Jacky dragons may have difficulty in detecting the movement of ambush predators, such as snakes and of some invertebrate prey. Our study also demonstrates the potential of the computeranimated stimuli technique for conducting nonintrusive tests to explore motion range and sensitivity in a visually mediated species. [ABSTRACT FROM AUTHOR]

It is evident that the environment has the potential to affect animal communication strategies. Species from diverse taxonomic groups using signals from different modalities are known to generate signals that suit the structure of their habitat in order to maximize efficiency. Studies of acoustically communicating species dominate the literature, but visual signals are also tailored to local conditions. There is now increasing evidence that dynamic visual signals, in the form of movement-based displays, are also influenced by habitat characteristics. Australia's dragon lizards ( Family: Agamidae) employ such dynamic signals in a variety of contexts but are particularly common in territory defence. With a few notable exceptions, the signalling behaviour of this group has been relatively overlooked, and the knowledge that does exist is contained in scientific papers focused on other topics or unpublished accounts from herpetologists. In this review, we collated information on the signalling behaviour of these animals and determined that 34 of the 78 species use movement-based signalling. This number is likely to be an underestimate, as knowledge of the signalling behaviour of many species is lacking. The richly contrasting environments of Australia inhabited by these lizards provide considerable variation in ecological context, so our second objective was to place known signalling behaviour in the context of species ecology. After controlling for phylogeny, we found that broad habitat classifications do not strongly influence the likelihood of motion signalling, and specific motor patterns are not more likely to occur in particular microhabitats. We conclude by suggesting that fully understanding the motion signalling behaviour of Australia's agamids will require documenting the displays of species for which there are no data, while taking into account the high variability existing within motor patterns and considering in detail the environmental context under which signalling takes place. [ABSTRACT FROM AUTHOR]

It is well established that recognition of complex acoustic signals, such as bird song, is dependent upon the temporal ordering of signal units or syntax. Much less is known about functionally analogous visual displays. The jacky dragon ( Amphibolurus muricatus) is a native Australian agamid lizard with a highly stereotyped visual display made up of three discrete motor patterns. We conducted a playback experiment using high-resolution computer animations of conspecifics to test the importance of temporal order for signal efficacy. Lizards were shown three different life-sized simulated animations of conspecific differing in their skin texture and morphology signatures ranging from highly natural to abnormal. We evaluated signal recognition and assessed the relative importance of syntax and morphology. Our results showed that signal recognition is highly sensitive to syntax and this largely determines the observers' behavioural responses. Stimuli with abnormal texture and shape were highly effective, as long as the natural order of motor patterns was preserved. Display recognition in jacky lizards hence depends upon syntax in just the same way as temporally constrained signals in other modalities. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Visual signals that are designed for effective communication are complex. Over the years, researchers interested in the study of animal communication have employed various artificial stimuli during behavioral experiments to precisely control what the observers get to see or experience. These diverse techniques to stage animal interactions have offered an alternative to the traditional experimental methods relying on the use of live companions or demonstrators. Current technological advances allow researchers to develop realistic computer-animated stimuli of social partners with high degree of fidelity for both morphological and dynamic behavioral characteristics. Because the computergenerated animation technique offers researchers with the ability to produce standardized visual stimuli while reducing the variable behavior of demonstrators across experimental sessions, its used is becoming increasingly popular in behavioral experiments in various taxa. In the following chapter, we provide an appraisal of the computer-generated animations efficiency to stage social interactions in lizards in general and the Jacky dragon (Amphibolurus muricatus) in particular. We present relevant experimental studies in which this innovative technique has been employed to simulate social partners in the Jacky dragon to address diverse ecological important questions. In addition, we consider the future of video and animation playback in the study of lizard's communication. [ABSTRACT FROM AUTHOR]

Incubation temperature is one of the most studied factors driving phenotypic plasticity in oviparous reptiles. We examined how incubation temperature influenced hatchling morphology, thermal preference and temperature-dependent running speed in the small Australian agamid lizard Amphibolurus muricatus. Hatchlings incubated at 32°C grew more slowly than those incubated at 25 and 28°C during their first month after hatching, and tended to be smaller at one month. These differences were no longer significant by three months of age due to selective mortality of the smallest hatchlings. The cooler incubation treatments (25°C and 28°C) produced lizards that had deeper and wider heads. Hatchlings from 28°C had cooler and more stable temperature preferences, and also had lower body temperatures during a 2-h thermoregulatory behaviour trial. Locomotor performance was enhanced at higher body temperatures, but incubation temperature had no measurable effect either independently or in interaction with body temperature. Our study demonstrates that incubation temperature has direct effects on morphology and thermoregulatory behaviour that appears to be independent of any size-dependent effects. We postulate a mechanistic link between these two effects. [ABSTRACT FROM AUTHOR]

Highlights: [•] Genetic data from five loci show genetic structure within A. muricatus. [•] Data from over 500 specimens shows little differentiation in body proportions. [•] Phylogenetic patterns are consistent with other taxa in the Australian Great Dividing Range. [•] Biogeographic barriers appear to correlate to lowlands between mountain ranges. [Copyright &y& Elsevier]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Over time native vegetation remnants in urban areas are typically eroded in size and number due to pressures from urban expansion and consolidation. Such remnants, frequently neglected and invaded by weeds, may constitute the last remaining habitat for some species' populations in urban areas. In the restoration of remnants for biodiversity, weed removal is often a high priority but there is a dearth of information on the role that exotic vegetation plays as habitat for fauna such as small reptiles. We investigated the vegetation type preference of urban remnants at the edge of a Sydney golf course by Amphibolurus muricatus, the native jacky lizard. The three vegetation types present were Eastern Suburbs Banksia Scrub (an Endangered Ecological Community) with sparse groundcover, dense stands of the introduced Eragrostis curvula African love grass, and open fairways of lawn: three structurally different habitats. Captured jacky lizards were spooled and their movements traced by following the thread left as they moved through their home range. Jacky lizards preferred areas that afford them most cover. While they foraged throughout the stands of love grass, they tended to avoid the edge of native vegetation remnants. They also basked on the lawn close to the vegetation where they had recently foraged, or traversed it to enter natural vegetation or grass. We concluded that introduced love grass offered additional habitat because of the relatively dense vegetation cover, and that areas should not be managed with the assumption that invasive weeds are detrimental to native species without appropriate assessment. [ABSTRACT FROM AUTHOR]

This paper reports observations of a single Jacky Lizard Amphibolurus muricatus (Agamidae) preying upon Banded Bees Amegilla sp. (Apidae) as they flew near their nesting aggregation in bushland of northern Sydney, NSW, Australia. The foraging behaviour of this wild A. muricatus individual may have been somewhat more complex than that previously reported for captive individuals of this species. Bees may constitute only a minor proportion of the diet of A. muricatus in the wild and lizards may be less effective predators upon nesting bees than birds. [ABSTRACT FROM AUTHOR]

In many animals, temperatures experienced by developing embryos determine offspring sex (e.g. temperature-dependent sex determination, TSD), but most studies focus strictly on the effects of mean temperature, with little emphasis on the importance of thermal fluctuations. In the jacky dragon (Amphibolurus muricatus), an Australian lizard with TSD, data from nests in the field demonstrate that offspring sex ratios are predictable from thermal fluctuations but not from mean nest temperatures. To clarify this paradox, we incubated eggs in a factorial experiment with two levels of mean temperature and three levels of diel fluctuation. We show that offspring sex is determined by an interaction between these critical thermal parameters. Intriguingly, because these two thermal descriptors shift in opposing directions throughout the incubation season, this interactive effect inhibits seasonal shifts in sex ratio. Hence, our results suggest that TSD can yield offspring sex ratios that resemble those produced under genotypic sex-determining systems. These findings raise important considerations for understanding the diversity of TSD reaction norms, for designing experiments that evaluate the evolutionary significance of TSD, and for predicting sex ratios under past and future climate change scenarios. [ABSTRACT FROM AUTHOR]

The complex ritualized displays of males in many territorial species suggest that selection has shaped male behaviors in ways that affect fitness. In this study, we evaluated the link between display behavior during male–male interactions and reproductive success in the Australian jacky dragon ( Amphibolurus muricatus), a lizard species that uses a complex series of movement patterns for communication. We quantified variation in male display behaviors by using video playback experiments in the laboratory, and subsequently assessed variation in male reproductive success by paternity analyses of offspring. Because the lizards used in this study came from eggs incubated under three thermal environments, we also could evaluate the impact of developmental temperature on adult behavior and reproductive success. Incubation temperature had a strong effect on male reproductive success; males produced under intermediate temperatures sired more offspring than those produced under extreme developmental temperatures. However, incubation temperature did not affect male display behavior, nor was male behavior associated with reproductive success. Our findings do not support the common assumption that display behaviors used during male–male interactions affect reproductive success. [ABSTRACT FROM AUTHOR]

Signal design can reflect the sensory properties of receivers. The death adder, Acanthophis antarcticus, attracts prey by wriggling the distal portion of its tail (caudal luring). To understand the design of this deceptive signal, we explored perceptual processes in a representative prey species: the Jacky dragon, Amphibolurus muricatus. We used 3D animations of fast and slow death adder luring movements against different backgrounds, to test the hypothesis that caudal luring mimics salient aspects of invertebrate prey. Moving stimuli elicited predatory responses, especially against a conspicuous background. To identify putative models for caudal luring, we used an optic flow algorithm to extract velocity values from video sequences of 61 moving invertebrates caught in lizard territories, and compared these to the velocity values of death adder movements. Caudal lures had motion characteristics that matched common invertebrate prey speeds, each corresponding to a peak in a bimodal distribution. Subsequent video playback tests using animations of crickets showed that significantly more attacks were evoked by stimuli moving at common than at rare invertebrate speeds. Overall, these results suggest that biases in the nervous system of the receiver, originally selected for prey recognition, might have been exploited by the design of the caudal luring signal. We suggest that viewing caudal luring from this perspective, rather than thinking of it as aggressive mimicry per se, may help us understand the function and evolutionary origin of this behaviour. [Copyright &y& Elsevier]

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 movement-based 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. [ABSTRACT FROM AUTHOR]

A vast literature suggests that maternal factors and egg incubation conditions have substantial effects on offspring phenotypes in oviparous species. However, many studies that evaluate these effects have relied on experimental conditions that are rarely, if ever, encountered under natural conditions. To address this issue, we evaluated relationships among maternal factors, natural nest conditions, egg development in the field, and the resultant offspring phenotypes in a lizard with temperature-dependent sex determination, the jacky dragon ( Amphibolurus muricatus, Agamidae). Many, but not all, of the relationships shown in our field-based study corroborate results from laboratory-based experiments. Offspring body size was affected primarily by egg size at oviposition, as well as by water uptake by eggs, rather than by environmental variables measured within the nest. Date of oviposition was related to offspring growth rate and body size prior to the onset of winter; this relationship is likely mediated through an influence on the timing of hatching. Nest temperature generated substantial variation in egg survival; nests that experienced higher temperatures and higher thermal fluctuations suffered relatively high egg mortality. Contrary to results from laboratory incubation, however, nest temperature did not predict offspring sex ratios. Hence, although many results from this field study corroborate those from the laboratory, caution is needed when extrapolating laboratory-incubation results to field conditions. [ABSTRACT FROM AUTHOR]

The evolution of movement-based signals is constrained by the successful segmentation of relevant movements from motion noise by the visual system of receivers. We tested five Jacky dragons, Amphibolurus muricatus, a species characterized by stereotyped movement-based social signals, for their ability to discriminate the direction of drifting dots against simulated background motion noise of varying angular speeds. Results from trials with artificial (dot) backgrounds suggested that Jacky dragons are most sensitive to high-speed movement, while background movement of similar angular speeds to target stimuli reduced performance. We also found differences in accuracy between natural backgrounds comprising footage of plant motion at two independent sites. We argue that detecting salient movement depends on the particular characteristics of the surrounding motion noise, and discuss its implications for movement-based signal design. [Copyright &y& Elsevier]

1. Energy allocation strategies for reproduction are viewed typically as a continuum between reliance on ‘income’ (recently acquired energy) vs. ‘capital’ (stored reserves) for fuelling reproduction. Because ectothermy facilitates long-term energy storage and often involves low feeding rates, traditional views suggest that many ectotherms rely heavily on stored reserves for egg production. 2. We explored the temporal relationship between energy intake and expenditure in a multi-clutching lizard ( Amphibolurus muricatus) by evaluating the effect of maternal nutrition on reproductive output and by contrasting δ13C measurements of the maternal diet and endogenous energy stores with that of the eggs produced. 3. Our experiment revealed that females utilize both endogenous energy stores and recently acquired food to fuel reproduction; this pattern did not shift seasonally from first to second clutches produced. Importantly, however, egg lipid was derived primarily from capital, whereas egg protein was derived about equally from both income and capital. 4. Overall, these results suggest that the energy allocation strategy used for reproduction differs among egg components, and that the use of recently acquired energy for reproduction may be more widespread in ectotherms than thought previously. [ABSTRACT FROM AUTHOR]

Maternal and environmental factors are important sources of phenotypic variation because both factors influence offspring traits in ways that impact offspring and maternal fitness. The present study explored the effects of maternal factors (maternal body size, egg size, yolk-steroid allocation, and oviposition-site choice) and seasonally-variable environmental factors on offspring phenotypes and sex ratios in a multi-clutching lizard with environmental sex determination ( Amphibolurus muricatus). Maternal identity had strong effects on offspring morphology, but the nature of maternal effects differed among successive clutches produced by females throughout the reproductive season (i.e. maternal identity by environment interactions). The among-female and among-clutch variation in offspring traits (including sex ratios) was not mediated through maternal body size, egg size, or variation in yolk steroid hormones. This lack of nongenetic maternal effects suggests that phenotypic variation may be generated by gene by environment interactions. These results demonstrate a significant genetic component to variation in offspring phenotypes, including sex ratios, even in species with environmental sex determination. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 256–266. [ABSTRACT FROM AUTHOR]

During conflict, males often assess their opponent's fighting ability and motivation via dynamic signals. We conducted an interactive video playback study using male Jacky dragons, Amphibolurus muricatus, to determine which signalling strategy was the most effective at deterring aggression and eliciting submission. A 3D computer-animated lizard was used to present aggressive signals (push-up displays) and submissive ones (slow arm-waves). This approach reproduced natural display motor patterns precisely while controlling variation in morphology. Treatments all commenced with the stimulus lizard producing bouts of push-ups, but then diverged after the subject lizard's responses, according to predetermined rules. Lizards attacked the stimulus more frequently when it responded to submission with slow arm-waves, revealing that their behavior during a contest is sensitive to social contingencies. Individuals that signal submission without retreating are likely to incur a receiver retaliation cost. In addition, assessment processes are surprisingly sophisticated, involving the monitoring of both an index signal (push-ups) and a conventional one (slow arm-waves) during a single interaction. [ABSTRACT FROM PUBLISHER]

In oviparous species, mothers can optimize the incubation environments of their offspring by selecting nest sites with conditions conducive to embryonic development. Hence, maternal nest-site selection can enhance egg survival and offspring fitness. However, the challenge to a nesting female is complex because of trade-offs among relevant parameters (e.g. hotter nests may be drier) and seasonal shifts in ambient conditions. Moreover, the influence of nest conditions on offspring sex ratios adds another level of complexity for species with environmental sex determination. To elucidate these issues, we need field data on nesting behaviour that incorporate the multiple influences that operate under natural conditions. We radiotracked gravid jacky dragons, Amphibolurus muricatus, in open forest habitats of southeastern Australia to document the lizards'' criteria for nest-site choice. Females selected sites with lower than average canopy cover, resulting in relatively warm nests throughout the prolonged nesting season. Although soil moisture levels decreased over this period and were strongly correlated with mean temperatures, female lizards were able to locate nesting sites that provided consistently moist (and increasingly warm) incubation conditions as the season progressed. Such sites apparently became more difficult to find later in the season, resulting in a higher incidence of test holes prior to nest excavation. Seasonal shifts in diel maximum temperatures also pushed the daily time of digging activity into the evening. Because jacky dragons have temperature-dependent sex determination, the seasonal shift in mean incubation temperatures of natural nests would generate seasonal shifts in offspring sex ratios in a direction likely to enhance maternal fitness. [Copyright &y& Elsevier]

To understand how selection shapes life-history traits, we need information on the manner in which offspring phenotypes influence fitness. Life-history allocation models typically assume that “bigger offspring are better”, but field data paint a more complex picture: larger offspring size sometimes enhances fitness, and sometimes not. Additionally, higher survival and faster growth of larger offspring might be due to indirect maternal effects (e.g., mothers allocate hormones or nutrients differently to different-sized eggs), and not to offspring size per se. Alternative factors, such as seasonal timing of hatching, may be more important. We examined these issues using 419 eggs from captive jacky dragon lizards ( Amphibolurus muricatus). The mothers were maintained under standardized conditions to minimize variance in thermal and nutritional history, and the eggs were incubated under controlled conditions to minimize variance in offspring phenotypes due to incubation temperature and moisture. We reduced the size of half the eggs (and, thus, the size of the resultant hatchlings) from each clutch by yolk extraction. The hatchlings were marked and released at a field site over a 3-month period, with regular recapture surveys to measure growth and survival under natural conditions. Growth rates and survival were strongly enhanced by early-season hatching, but were not affected by hatchling body size. [ABSTRACT FROM AUTHOR]

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 Ainphibolurus inuricatus, 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. [ABSTRACT FROM AUTHOR]

Temperature-dependent sex determination (TSD) occurs in all major reptile lineages, but the selective forces and physiological mechanisms that link sex to incubation temperature may differ among and within those groups. Different models for TSD evolution make different predictions about when offspring sex will respond to environmental cues. Although TSD has evolved in several lizard lineages, there is less detailed information on these taxa than in turtles and crocodilians with TSD. We incubated eggs of an agamid lizard (AmphiboIurus muricatus) and a scincid lizard (Bassiana duperreyi), two species with TSD. Rather than manipulate incubation temperature to identify periods of sexual lability (as in most previous studies of this topic), we topically applied the aromatase inhibitor fadrozole to eggs at a variety of times through the incubation period. Fadrozole application sex-reversed the resultant hatchlings if applied from the time of oviposition until at least 60% of the way through incubation. In all of the TSD lizard species studied so far, offspring sex is determined either while the eggs are held inside the mother's body or soon after oviposition, providing substantial maternal control over incubation temperatures at this critical period. Hence, the hypothesis that TSD evolves because it enables offspring sex to be matched to conditions that are unpredictable at the time of laying is less likely to apply to squamates than to turtles, sphenodontians, and (especially) crocodiles, in which the period of sexual lability is delayed until long after oviposition. [ABSTRACT FROM AUTHOR]

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 habituation–dishabituation 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. [Copyright &y& Elsevier]

Why is the sex of many reptiles determined by the temperatures that these animals experience during embryogenesis, rather than by their genes? The Charnov-Bull model suggests that temperature-dependent sex determination (TSD) can enhance maternal fitness relative to genotypic sex determination (GSD) if offspring traits affect fitness differently for sons versus daughters and nest temperatures either determine or predict those offspring traits. Although potential pathways for such effects have attracted much speculation, empirical tests largely have been precluded by logistical constraints (i.e., long life spans and late maturation of most TSD reptiles). We experimentally tested four differential fitness models within the Charnov-Bull framework, using a short-lived, early-maturing Australian lizard (Amphibolurus muricatus) with TSD. Eggs from wild-caught females were incubated at a range of thermal regimes, and the resultant hatchlings raised in large outdoor enclosures. We applied an aromatase inhibitor to half the eggs to override thermal effects on sex determination, thus decoupling sex and incubation temperature. Based on relationships between incubation temperatures, hatching dates, morphology, growth, and survival of hatchlings in their first season, we were able to reject three of the four differential fitness models. First, matching offspring sex to egg size was not plausible because the relationship between egg (offspring) size and fitness was similar in the two sexes. Second, sex differences in optimal incubation temperatures were not evident, because (1) although incubation temperature influenced offspring phenotypes and growth, it did so in similar ways in sons versus daughters, and (2) the relationship between phenotypic traits and fitness was similar in the two sexes, at least during preadult life. We were unable to reject a fourth model, in which TSD enhances offspring fitness by generating seasonal shifts in offspring sex ratio: that is, TSD allows overproduction of daughters (the sex likely to benefit most from early hatching) early in the nesting season. In keeping with this model, hatching early in the season massively enhanced body size at the beginning of the first winter, albeit with a significant decline in probability of survival. Thus, the timing of hatching is likely to influence reproductive success in this short-lived, early maturing species; and this effect may well differ between the sexes. [ABSTRACT FROM AUTHOR]