Psammophilus Dorsalis Research Articles

Pests and predators interference on the stingless bee population inhabited at different habitats amidst south-eastern Karnataka, India

Stingless bees (Hymenoptera: Apidae: Meliponini) are called ‘Dammar bees’ live under cryptic conditions at diversified ecosystems. Stingless bees are one of the most important species, playing pivotal role as ‘Keystone Pollinators’ for various flowering plant species. Besides, they are cultured in the name of ‘Meliponi culture’ at various man-made agro-ecosystems. Reports on biological constraints of stingless bees is limited at south-eastern Karnataka, hence in the present study commonly occurring constraints and their per cent interference on stingless bee population under natural conditions from 2017 to 2019 in Bangalore Rural, Chikkaballapura and Kolar districts, Karnataka was made. The Megachile bee, Megachile (Callomegachile) disjuncta, beetle, Bitoma siccana, spider, Menemerus bivittatus, Crossopriza lyoni and Pholcus phalangioides, greater wax moth, Galleria mellonella, wall lizard, Hemidactylus species, garden lizard, Calotis versicolar and Psammophilus dorsalis acted as important constraints of stingless bee population and impacted more for their decline. Further, burning, hunting, closing their colony entrance by cow dung and cement, road construction and destruction of buildings and other man-made activities have created huge impact on stingless bee population. Stingless bee’s conservation is required to restore for conservation of local vegetation, to produce medicinally important honey and hence their natural colonies need special attention cum protection at their preferred abode.

Inferring Social Interactions Over a Lifespan from Space-Use Patterns in a Tropical Agamid

Establishing the social system of a population is key to studying the evolution of behaviors. However, observations of social interactions needed to infer social systems are difficult to obtain for many species. An alternative way of understanding social systems is by studying the space-use pattern of individuals. Along with ecological factors, space use is largely governed by interactions among individuals: typically, competing individuals avoid each other, and individuals benefitting from each other share space. We investigated the social system, specifically the mating system, and the nature of intrasexual interactions between adults, by quantifying space-use patterns of individuals over their adult lifespan in the tropical Psammophilus dorsalis lizard. Males had substantially larger home ranges than females during the mating season, but not during the nonmating season. Female home ranges were small, and showed minimal overlap with other females throughout their lifespan, suggesting consistent intrasexual competition among females. In contrast, males showed minimal overlap with other males in the nonmating season but increased overlap in the mating season, suggesting that males resolve intrasexual competition through other means, like contests, during the mating season. Patterns of overlap between male and female home ranges in the mating season indicated a socially polygynous mating system. Our study provides an initial understanding of home-range patterns and associated inferences of within- and between-sex interactions across the lifespan of a tropical lizard, Psammophilus dorsalis. It highlights the insights into the social structure of a population gained from dispersion patterns of individuals.

An expanding cityscape and its multi-scale effects on lizard distribution.

Urbanization results in complex and variable changes to environmental conditions, which translate to shifts in selection pressures for organisms. Size of a city as well as the intensity and extent of urbanization can synergistically influence how organisms are impacted. However, less is known about how landscape heterogeneity, rate of land-use change, and scale of urbanization affect species persistence. We evaluate the ways in which urbanization changes the environment and examine how some of these environmental factors influence the presence of the lizard Psammophilus dorsalis (Peninsular rock agama), in Bengaluru, India. Variability in environmental factors across the study area was characterised by measures of habitat composition and diversity, habitat connectivity, rate of habitat change, predation pressure, land surface temperature (LST) and artificial light at night (ALAN), that were derived from remotely sensed and citizen science data. Most of these factors showed high variance across two measures of urbanization: distance from city center and proportion of built-up area. Habitat diversity and ALAN were the only two factors that changed predictably and in a non-linear way, with distance from the city center and proportion of built-up area. We then used a multi-scale approach to examine the relative importance of some these environmental factors at the landscape scale, as well as additional factors at the microhabitat-scale, in predicting the presence and relative abundance of P. dorsalis respectively. At the landscape scale, LST, which is positively correlated with proportion of cropland, predicted lizard presence; whereas at the microhabitat scale, P. dorsalis was more likely to be found in sites with higher proportions of rocks. Overall, we demonstrate that urbanization can result in environmental predictors that do not vary linearly across the urbanization gradient. For the iconic rock agama, many of these environmental factors do not seem to be strong selection pressures that influence their distribution in the expanding cityscape. Whether this urban utilizer can continue to persist with increasing anthropogenic development is uncertain. To better understand drivers of species persistence, we emphasize the importance of quantifying urbanization across multiple axes, considering environmental factors that are relevant to species at different spatial and temporal scales.

Colours of stress in male Indian rock agamas predict testosterone levels but not performance

Rapid physiological colour change offers dynamic signalling opportunities that can reveal distinct information to receivers in different contexts. Information content in dynamic colours, however, is largely unexplored. In males of the Indian rock agama (Psammophilus dorsalis), stressful events, including male-male agonistic interactions, induce a colour change, wherein the dorsal band turns yellow and the lateral bands turn orange. We aimed to determine whether these pigment-based dynamic colours convey information about individual quality. Using an agamid-specific visual model, we first quantified the chromatic and achromatic contrasts of each colour component displayed by males during handling stress, which induces the maximal response of aggression-typical colours. We then measured baseline testosterone levels, morphology (body mass and size), and performance measures (bite force and sprint speed) of these lizards. Chromatic contrasts of the dorsal yellow and lateral orange bands, individually and relative to each other (internal pair), were negatively correlated with testosterone levels, while the chromatic contrast of the internal pair was positively correlated with body condition. The lack of an association between colour contrasts and both bite force and sprint speed indicate that the conspicuousness of colours expressed during stressful events, such as agonistic interactions, do not reveal male performance ability. Despite our expectations of a positive relationship with testosterone, morphology (body condition), and performance (bite force, sprint speed), we find that for P. dorsalis, the conspicuousness of stress-induced colours provide only some information about individual quality. We speculate that the dynamicity of physiological colours may influence their function as content-containing signals in social interactions.

Urban lizards use sleep sites that mirror the structural, thermal, and light properties of natural sites

Global change processes such as urbanization are likely to affect sleep behavior, by altering abiotic (e.g., thermal and illumination) and biotic conditions (e.g., predation pressure) that influence sleep. However, little is known of how sleep behavior responds to urbanization and whether this response is flexible or conserved across populations. We quantified sleep site characteristics of the peninsular rock agama Psammophilus dorsalis in Bangalore city and surrounding rural areas. We find that P. dorsalis in urban areas display remarkable behavioral flexibility in response to the novel stressor of artificial light at night, being nine times more likely to use covered sleep sites that limit illumination, compared to lizards in rural areas. However, sleep sites in both populations were highly conserved in terms of substrate type (i.e., rocky with high surface rugosity) and their thermal properties. Our findings support behavioral amelioration of potentially adverse effects of night light in urban areas, even within the restricted availability of preferred substrates as sleep sites. Our study is one of the first to comprehensively compare sleep behavior in rural and urban areas and demonstrate substantial behavioral flexibility. The role of sleep behavior in the coping strategies of animals to urbanization needs further research attention. Sleep is essential to animal life, yet it imposes certain costs such as making sleeping individuals vulnerable to predators. “Where” an animal sleeps (or its sleep site) is therefore important to ensure safety from predators but also to provide conducive environmental conditions. Cities can transform the availability of ideal sleep sites and can alter their thermal properties, in addition to being intensely illuminated by night light that hampers sleep. In this study, we compared sleep site characteristics of rural and urban populations of the peninsular rock agama Psammophilus dorsalis. We find that urban lizards sleep in sheltered sleep sites that shield them from night light but are highly dependent on rough, rocky substrates in both the city and rural areas. The remarkable flexibility in sleep behavior displayed by urban lizards is likely to help them cope in a city.

Morphological divergence, tail loss, and predation risk in urban lizards

Urbanisation changes the structure of natural habitats and alters trophic interactions, pressuring urban species to adjust and adapt. Unlike behavioural shifts that tend to be more flexible, morphological characteristics in vertebrates are less plastic and changes may come at a greater cost. We explored the hypothesis that morphological characteristics in a tropical agamid lizard Psammophilus dorsalis are not only selected to suit altered habitat conditions in urbanised areas but reflect predation risk in urban habitats. In addition, we explored differences in tail loss in both sexes from urban and rural habitats. First, we find that predation risk did not differ between urban and rural habitats, but differed between sexes. Conspicuous courtship-coloured male lizards were more likely to be attacked compared to cryptically-coloured female lizards. Next, we find that P. dorsalis differed in key morphological characteristics, with greater urban-rural differences in males than females. Urban lizards had shorter proximal limb elements, longer 4th digits and greater body mass than rural lizards; and among males, urban lizards had significantly larger head sizes and longer distal limb elements than rural lizards. Finally, we find that the rates of tail loss differed between habitats and sexes, with urban male lizards having greater rates of tail loss than rural males and all females. Inter-sexual difference in tail loss was consistent with the difference in predation risk between sexes, but tail loss differences between urban and rural habitats could not be explained by predation risk. In sum, we find that adaptations to novel urban environments are not exclusively driven by a single promoter (e.g. predation risk) but are influenced by multiple selection pressures with associated fitness costs, such as tail loss.

Lizards from suburban areas learn faster to stay safe.

Enhanced cognitive ability is beneficial in unpredictable and harsh environments, as it enables animals to respond with flexibility. For animals living in urbanized areas, local environments not only are altered but can rapidly change during their lifetime. Urban residents are therefore challenged with identifying novel dangers and safe refuges in dynamic environments. We demonstrate that the tropical agamid lizard Psammophilus dorsalis experiences dramatically different habitats not only across the rural to urban spatial scale but also over the short temporal scale of a few years in suburban areas. Differences in environmental stability are expected to affect rates of learning and reversal learning in resident lizards. In testing arenas, lizards from these populations were required to choose a designated 'safe' refuge instead of an 'unsafe' one after simulated predator attacks. The contingency for safety was switched during the reversal learning task. In general, P. dorsalis showed high rates of learning and reversal learning, but lizards from suburban areas were quicker to learn and unlearn the location of the safe refuge than those from rural areas. This demonstrates for the first time to our knowledge that suburban lizards have faster learning and reversal learning skills for a key survival-related behaviour, finding safety in unpredictable environments.

Social coping styles of lizards are reactive and not proactive in urban areas

Animals engage in social interactions with changes in their behaviour and physiology. Environmental challenges, however, can influence social interactions by adding additional stressors. Here, we investigated the effects of urbanisation on the behaviour and hormonal responses of a tropical lizard species, Psammophilus dorsalis, during social interactions. We recorded behaviour of males from suburban and rural areas during controlled encounters with other males and females. We then measured corticosterone and testosterone levels of individuals at 10 min intervals, from immediately after the social encounter to 30 min later and then at 120 min after the interaction period. We found that differences in social behaviours and subsequent hormone levels were largely driven by habitat, and not social context. Overall, we found that fewer suburban males showed behavioural displays compared to rural males during social encounters. For those that displayed, intensity of aggression was similar across populations, but courtship intensity was lower for suburban males compared to rural males. Suburban males also had significantly elevated levels of corticosterone both under control conditions (no social encounter) and following intra- and intersexual interactions, while rural males retained low levels of corticosterone across contexts. Social interactions were associated with an increase in testosterone levels in all males, but only rural males maintained elevated levels for up to 120 min after interactions with females. Thus, lizards from these suburban and rural populations showed key differences in responsiveness to and recovery from social challenges, a pattern that suggests alternative coping styles (‘proactive’ vs. ‘reactive’). These differences in social coping styles could influence consequences of sexual selection in an urbanised world.

Measures of Health Provide Insights Into the Coping Strategies of Urban Lizards

Abstract The rapid rate of urbanization worldwide and its consequences for affected species and ecosystems urgently warrants research and action. Whether animals are effectively coping from urbanization is hotly debated, especially since interpretations are based on different measures of animal responses. Here, we take a physiology-centric view of animal coping strategies, and set up predictions for distinguishing urban adaptors and exploiters using multiple markers of health. Our study compares rural and urban populations of a tropical lizard species, the Indian rock agama (Psammophilus dorsalis), that lives in a rapidly changing and highly threatened semi-arid ecosystem in Southern India. Contrary to expectations, we did not find any significant differences in body condition, number of ectoparasites, and degree of cell-mediated immune response between lizards from urban and rural areas, despite previously documented differences in aspects of their behaviour. However, urban lizards had lower heterophil to lymphocyte ratios, as well as lower testosterone levels compared to rural lizards, which suggest active physiological coping responses. Notably, we find no correlation between the different physiological measures within individuals; strongly reflecting the flexible and independent axes of health responsiveness. Overall, the considerable overlap in responses by urban and rural lizards highlights the importance of using multiple measures of immunity to evaluate health status. These data collectively indicate that P. dorsalis is an urban adaptor, and that the tropical urban environment is not associated with harmful consequences for their health.

Why Do Males Use Multiple Signals? Insights From Measuring Wild Male Behavior Over Lifespans

Why animals commonly use multiple conspicuous and presumably costly signals is poorly understood. Tests of evolutionary hypotheses comprehensively covering the signalling repertoire in wild populations are crucial to establish biological relevance, yet are relatively rare. We tested a key hypothesis for the maintenance of multiple signals in a wild population of the lizard, Psammophilus dorsalis, specifically whether multiple signals are maintained as multiple messages directed at different receivers. In addition, we also examined patterns in covariation of signals as an initial test of an alternative hypothesis, that multiple signals may be maintained as redundant signals; such traits are proposed to convey and reinforce the same component of information and are expected to be strongly correlated. Breeding male P. dorsalis display from prominent rock perches within their territories, which overlap multiple female home ranges in rocky open habitats. We repeatedly measured the display behaviour, covering the entire signalling repertoire, of individually-tagged wild males on their territories over their lifespans. We quantified patterns of covariation in multiple traits and their relationship with multiple receiver contexts, specifically competitors, mates and predators. We also examined the association between male signalling and indices of lifetime fitness. Males commonly used multiple signals, including behavioural signals and a rare dynamic colour signal. These traits were strongly correlated and seemed largely directed towards females, suggesting that they were primarily maintained as redundant signals through female choice. However, other selection pressures also appeared to be important. One colour trait seemed to be directed at competitors, providing limited support to the multiple receiver hypothesis. Several traits were reduced in the presence of predators, suggesting that they carry the cost of increased predation risk. Thus, multiple selection pressures, primarily female choice and predation risk, appear to affect male signalling. Finally, signalling traits appeared to influence a measure of lifetime reproductive success, providing rare evidence for the biological relevance of signalling traits under natural contexts.

Lizards assess complex social signals by lateralizing colour but not motion detection.

Vertebrates lateralize many behaviours including social interactions. Social displays typically comprise multiple components, yet our understanding of how these are processed comes from studies that typically examine responses to the dominant component or the complex signal as a whole. Here, we examined laterality in lizard responses to determine whether receivers separate the processing of motion and colour signal components in different brain hemispheres. In Psammophilus dorsalis, males display colours that dynamically change during courtship and aggressive interactions. We tested the visual grasp reflex of both sexes using robotic stimuli that mimicked two signal components: (1) multiple speeds of head-bobbing behaviour and (2) multiple colours. We found no laterality in response to different motion stimuli, indicating that motion similarly attracts attention from the two visual fields across sexes. Notably, receivers showed left visual field dominance to colours, especially when males were exposed to 'aggression-specific' colours and females to 'courtship-specific' colours.

Breeding Phenology of <i>Psammophilus dorsalis</i>:Patterns in Time, Space and Morphology

Since reproduction is costly, animals are expected to invest in reproduction when abiotic and biotic conditions are optimal. Although tropical ecosystems are not as starkly seasonal as temperate ecosystems, some tropical ecosystems may experience high seasonality in conditions that affect reproduction. Systematic studies of breeding phenology from tropical ecosystems are scarce. We describe the breeding phenology of Psammophilus dorsalis, a sexually dimorphic, diurnal, rupicolous lizard found in the tropical scrub forests of peninsular India. Regular census was conducted covering multiple habitat patches for three years, recording age and breeding status of lizards. Lizards were systematically caught, tagged, measured and released. We report clear breeding seasonality, with most males showing breeding colouration from May to September and juveniles emerging from September until April. Timing of breeding coincides with the annual peak in daily maximum temperatures, while juvenile emergence might be affected by the timing of the annual precipitation peak. We report that this is a predominantly annual species with a female-biased sex ratio and strong male-biased dimorphism in multiple morphological traits. In the face of climate change, detailed studies of breeding phenology of tropical animals are important, particularly for ectotherms, since these taxa are easily affected by changes in temperature and precipitation patterns.

Intrinsic factors are relatively more important than habitat features in modulating risk perception in a tropical lizard

Anti-predator responses in animals are dynamic and depend on multiple factors. However, most of our understanding about animal escape responses comes from studies which examine only a small set of factors at a time and are done over a short period of animal life spans. This limits our understanding of the dynamic nature of animal escape behaviour and the relative importance of individual factors in determining their escape behaviour. We used a repeated-measures study design to assess the anti-predator response of a wild population of a sexually dimorphic tropical lizard, Psammophilus dorsalis. We followed marked individuals throughout their breeding lifespan, repeatedly assayed their escape response and measured representative intrinsic and extrinsic factors that could modulate their escape response. Our findings suggest that intrinsic factors, such as sex and body size, influenced escape response relatively more than extrinsic factors did, such as distance to refuge and perch height. Although individual variables influenced escape behaviour, in a direction mostly consistent with predictions from optimal escape theory, the interaction between factors led to novel insights into how animals dynamically evaluate multiple and changing costs throughout their lifetime to evade predation. Fleeing from a potential predator is crucial to animals and depends on different factors, as there are various costs to escaping. Although several studies in the past have evaluated the role of various factors in determining escape response, the relative importance of factors and how it changes across the lifetime of individuals are not clear. By assessing individuals repeatedly over a substantial part of their lifespan, we could gain insight into how escape response changes as associated factors, intrinsic or extrinsic, change for an individual over time. This approach provided us a more robust and accurate representation of the dynamic nature of escape decisions. We also demonstrate that when multiple factors are considered simultaneously, their relative importance in determining timing of escape can considerably differ from theoretical predictions.

Signalling with physiological colours: high contrast for courtship but speed for competition

Dynamic physiological colour change allows animals to alter colours and patterns for communication, camouflage and thermoregulation. Using reflectance spectrometry and digital photography, we found that males of the Indian rock agama, Psammophilus dorsalis, can rapidly express intense colours that are different from the neutral state and specific to the social context. The distinct bands on males shifted between yellow and red (dorsal) and between orange and black (lateral) within seconds, and the resulting colour pattern was diametrically different depending on whether males were in courtship or aggressive interactions. Although males showed higher chromatic contrast when courting females, the colour change was faster during competitive encounters with other males. The nature of this social colour communication also differed across populations in anthropogenically disturbed landscapes. Compared to males from rural areas, suburban males were slower to change colour and showed duller and paler colours during staged social encounters. Consistent with other disturbance-induced shifts in phenotypic traits seen in numerous taxa, we provide the first evidence that social signalling through dynamic colour change in terrestrial vertebrates is also affected by urbanization. (C) 2017 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

A multivariate approach to understanding shifts in escape strategies of urban lizards

Escape strategies of animals are economic decisions, expected to vary as a function of both intrinsic (e.g., performance ability) and extrinsic factors (e.g., level of threat and microhabitat). Anthropogenic disturbance, especially urbanization, changes a range of environmental factors including habitat characteristics and predation risk. As a consequence of differences in microhabitat structure and repeated exposure to anthropogenic disturbance, we hypothesize that animals in urban environments will be less risk averse than those in rural environments. Here, we examined the importance of extrinsic and intrinsic factors to understand the escape strategies of Psammophilus dorsalis across an urban-rural gradient. First, urban lizards used lower perches and chose refuges that were closer to their perches compared to rural lizards. Flight initiation distance (FID) of urban lizards in the field was shorter than that of rural lizards, but only for males. In response to a second attack, only rural males decreased their FIDs, whereas urban males showed low and invariable FIDs. Laboratory measures of sprint performance showed expected differences between the sexes, but no significant difference between urban and rural populations. Unlike the strong differences between males across habitats, escape strategies of females were similar in urban and rural areas, most likely because females generally rely on crypsis to minimize predation risk and are resistant to flee when approached. In sum, urban lizards have access to a more complex structural environment, with greater perch and refuge options, and have habituated to non-lethal anthropogenic disturbance. These extrinsic and intrinsic factors combine to result in lower risk aversion and may explain the ability to tolerate urban environments. Significance statement Rapid urbanization is at its peak globally, and many animals are forced to adjust to the associated environmental changes or face local extinction. Some species, however, seem to persist in urban areas, and we hypothesize that they behaviorally respond by being less risk averse. We used a multivariate approach to understand the escape strategies of the peninsula rock agama across an urban-rural gradient. Lizards in urban areas use a more complex structural environment, with greater perch and refuge options, compared to rural lizards. Urban lizards also allow closer approaches. Because of the differences in body coloration and size, escape strategies of females were less affected by urbanization as they use crypsis to minimize predation risk. All these extrinsic and intrinsic factors combine to result in lower risk aversion by urban lizards and may explain their tolerance of human altered environments.

Dining in the City: Dietary Shifts in Indian Rock Agamas across an Urban–Rural Landscape

Rapid urbanization is a growing threat to biodiversity, causing wide-scale extirpation of species from their natural habitats. Some species such as rock agamas, Psammophilus dorsalis, seem to be sufficiently tolerant and continue to persist in urban environments. Given that urbanization alters species composition at multiple trophic levels, we expect a shift in the diet composition and hunting modes of populations across rural and urban areas. Based on identified contents from stomach flushes, we found that P. dorsalis are generally myrmecophagous, and their diet is mainly composed of ants (Hymenoptera: Formicidae). Diet of males and females in each area overlapped highly (80–91%), even though males were significantly larger than females. Dietary overlap between urban and rural populations also was high (80.3%). Surprisingly, rural lizards had lower body mass indices than did urban lizards, despite the greater diversity of prey types and the larger volume of food consumed. This species uses a sit-and-wait hunting strategy, but we found that the rate of movement of males was higher in rural areas compared to urban areas, which likely results in higher energy expenditure. Individuals of P. dorsalis do not seem to be negatively affected by urbanization but instead manage to hunt in and around the small patches of vegetation that remain, enabling them to maintain a higher body condition than that of lizards in undisturbed rural habitats.

Influence of gaze and directness of approach on the escape responses of the Indian rock lizard, Psammophilus dorsalis (Gray, 1831)

Animals often evaluate the degree of risk posed by a predator and respond accordingly. Since many predators orient their eyes towards prey while attacking, predator gaze and directness of approach could serve as conspicuous indicators of risk to prey. The ability to perceive these cues and discriminate between high and low predation risk should benefit prey species through both higher survival and decreased energy expenditure. We experimentally examined whether Indian rock lizards (Psammophilus dorsalis) can perceive these two indicators of predation risk by measuring the variation in their fleeing behaviour in response to type of gaze and approach by a human predator. Overall, we found that the gaze and approach of the predator influenced flight initiation distance, which also varied with attributes of the prey (i.e. size/sex and tail-raise behaviour). Flight initiation distance (FID) was 43 percent longer during direct approaches with direct gaze compared with tangential approaches with averted gaze. In further, exploratory, analyses, we found that FID was 23 percent shorter for adult male lizards than for female or young male (FYM) lizards. In addition, FYM lizards that showed a tail-raise display during approach had a 71 percent longer FID than those that did not. Our results suggest that multiple factors influence the decision to flee in animals. Further studies are needed to test the generality of these factors and to investigate the proximate mechanisms underlying flight decisions.

Immunolocalization of Glucagon and Insulin Cells in Endocrine Pancreas and Cyclic Disparity of Plasma Glucose in the Lizard Psammophilus dorsalis

Reptiles are an interesting group to study the physiology of reproduction. As information on mobilisation of glucose and associated endocrine alterations in the pancreas are not known, a study on the lizard Psammophilus dorsalis was undertaken using immunohistochemistry. Glucagon-immunoreactive (IR) and insulin-IR cells never formed islets instead spread throughout the pancreas in P. dorsalis. Glucagon-IR cells appeared to release the secretory granules from all over the surface, insulin-IR cells are unidirectional in their secretion. Both cell types often have no direct contact with capillaries. The morphometric analysis showed that the glucagon-IR cells were the most abundant amounting approximately 63 % as against insulin-IR cells, amounting approximately to 37 % of the endocrine pancreatic mass in the present study. On an average P. dorsalis exhibited 288.3 ± 25.28 mg% of plasma glucose, the abdominal fat underwent clearance as there was energy demand during reproductive and recrudescent periods. Glycogen granules were evident in liver and this was inversely related with plasma glucose.

The language of lizards: interpreting the function of visual displays of the Indian rock lizard, Psammophilus dorsalis (Agamidae)

The first step in understanding any communication system is to document signal diversity relative to the context of signalling (e.g. sex of the signaller and audience). Observation of 30 free-ranging rock lizards (Psammophilus dorsalis) on rock outcrops in southern India over a period of 18 months revealed that these lizards produce a complex array of ritualized signals involving push-ups (head-bobbing), dorsal flattening, extension of the legs or gular region, and tail-raising. Push-ups were performed by both sexes, usually after moving from one location to another. Push-ups were rarely accompanied by other postural modifications, and seem to function as non-directed signals. Dorsal flattening was elicited by birds flying overhead, and seems to make the lizard less conspicuous to predators. There was, nonetheless, a strong sex difference in the frequency of this behaviour, because the habitats used by males (open rocks) exposed them to more birds. Males displayed to females by extending their gular folds and arching their backs; other animals (e.g. squirrels, monkeys) also elicited the latter posture from both sexes. Leg extension was observed for both males and females, but in different contexts—males in response to conspecifics, females in response to other animals. Females raised their tails in response to encountering a male. Thus, these lizards have a complex repertoire of postures for predator evasion, for interaction with other species and with conspecifics, and for communicating sex-specific social information about gender (tail-raise) or dominance status (gular extension, leg extension).

Big boys on top: effects of body size, sex and reproductive state on perching behaviour in the tropical rock dragon, Psammophilus dorsalis

Abstract Perching behaviour, in relation to sex, body size and reproductive phases, was studied in the field in a population of the tropical rock lizard, Psammophilus dorsalis. Adult lizards (n = 14 males and 16 females) were marked by toe clipping in November 2001. They were observed at intervals (n = 10 times) over the next 18 months encompassing post-breeding (December-early March), recrudescence (late March-April) and breeding (May-August) phases. In the post-breeding phase, males perched at lower heights. They began perching higher during the recrudescence phase with the highest perches in the breeding phase. In comparison to females, the males perched higher than females all year round and showed greater among-individual variations in perch height. The bigger males perched at greater heights compared to smaller ones during recrudescence and breeding phases. No such trend was evident during the post-breeding phase and perch height was not related to body size. Females moved within a narrow range of heights from the substrata and showed no size-specific relationship in perch selection throughout the reproductive cycle. Selection of higher perches by the males, despite high predation risk, possibly helps in territory defence, courtship displays and in advertising their presence to conspecifics. Further, size-specific perch selection prior to and during the breeding period, suggests that size vis-à-vis age and reproductive cycle also influences selection of perch height in males. In females perching close to the substrata, refuge sites and food sources, seems to be associated with escape from predators, foraging benefits and, in turn, reproductive fitness. Thus, in the seasonally breeding P. dorsalis, sex and reproductive status determine the complex pattern of perching behaviour and, possibly, circulating levels of androgens drive the bigger boys on top in accordance with their size or age.