Intellagama Lesueurii Research Articles

A face in the crowd: a non-invasive and cost effective photo-identification methodology to understand the fine scale movement of eastern water dragons.

Ectothermic vertebrates face many challenges of thermoregulation. Many species rely on behavioral thermoregulation and move within their landscape to maintain homeostasis. Understanding the fine-scale nature of this regulation through tracking techniques can provide a better understanding of the relationships between such species and their dynamic environments. The use of animal tracking and telemetry technology has allowed the extensive collection of such data which has enabled us to better understand the ways animals move within their landscape. However, such technologies do not come without certain costs: they are generally invasive, relatively expensive, can be too heavy for small sized animals and unreliable in certain habitats. This study provides a cost-effective and non-invasive method through photo-identification, to determine fine scale movements of individuals. With our methodology, we have been able to find that male eastern water dragons (Intellagama leuseurii) have home ranges one and a half times larger than those of females. Furthermore, we found intraspecific differences in the size of home ranges depending on the time of the day. Lastly, we found that location mostly influenced females’ home ranges, but not males and discuss why this may be so. Overall, we provide valuable information regarding the ecology of the eastern water dragon, but most importantly demonstrate that non-invasive photo-identification can be successfully applied to the study of reptiles.

Showing Red: Male Coloration Signals Same-Sex Rivals in an Australian Water Dragon

Sexually dimorphic coloration that plays a role in social signaling during stereotypical displays is well known in lizards. Previous studies on a large Australian agamid lizard (Eastern Water Dragon, Intellagama lesueurii) documented male-biased sex differences in ventral coloration, but males were not observed to use postures that displayed their ventral surfaces. Male resource-holding potential (RHP) was determined by body size, with the largest individuals controlling territories in preferred riparian habitat. Both large males that defended territories and those that did not had fully developed ventral coloration. Together these observations suggested that male ventral coloration does not play a role in social communication in male Water Dragons. We tested this hypothesis by recording the behavior of free-ranging males during baseline social conditions and when the level of aggression was much higher because we temporarily removed and then reinstated territory owners. Male Water Dragons performed three behavior patterns that displayed their conspicuous ventral coloration when engaged in agonistic encounters with same-sex rivals, especially when social conditions among neighboring males were unstable. Rival males responded to these displays in all instances. A large, model Water Dragon male in which we manipulated ventral color elicited lower-intensity responses from rival males when the model ventral surface was red than when it was brown. This result is also consistent with the hypothesis that red coloration plays a role in signaling and perhaps in intimidation of rivals. Water Dragon displays that revealed ventral coloration were not given when males interacted with females, suggesting red coloration does not function in advertisement to potential female mates. Our results support the hypothesis that red ventral coloration in Eastern Water Dragons functions in advertisement to rival males similar to the function of red coloration in several other vertebrates.

Hatching and residual yolk internalization in lizards: evolution, function and fate of the amnion.

Most egg-laying vertebrates hatch without depleting the entire yolk reserve. The residual yolk is internalized before emergence from the egg is completed and the yolk is subsequently metabolized during early neonatal life. Here we provide the first description of the mechanism of yolk internalization in non-avian reptiles. We describe the hatching of two lizard species (Physignathus lesueurii and Varanus rosenbergii) and provide a step-by-step account of sequence of events leading to yolk internalization and emergence from the egg. We also conducted incubation experiments to determine the cause of failed yolk internalization. Contraction of the ruptured amnion is the mechanism by which the residual yolk is internalized, which provides an explanation for the functional significance of amniotic contractions. Failures of internalization occur when the amount of residual yolk exceeds that which can be enclosed by the ruptured amnion. We conclude that, because of the connections formed between the amnion and both the allantois and chorion, the pipping and retraction of the amnion pulls the chorioallantoic membrane (CAM) off the surface of the eggshell, which impairs the capacity for gas exchange and forces the embryo to breach the eggshell to commence breathing. We further speculate that the loss of amniotic contractions in mammals may indicate an incompatibility of amnion-assisted yolk internalization with viviparity, an evolutionary process that could be tested by examining viviparous squamates.

Aggressive transition between alternative male social tactics in a long-lived Australian dragon (Physignathus lesueurii) living at high density.

Theory predicts the evolution of alternative male social tactics when intense competition coupled with the superior competitive ability of some individuals limits access to reproductive opportunities by others. How selection has shaped alternative social tactics may be especially interesting in long-lived species where size among sexually mature males varies markedly. We conducted experimental studies on long-lived eastern Australian water dragons living where competition was intense to test the hypotheses that mature males adopt alternative social tactics that are plastic, and that large size and body condition determine resource-holding potential. Approximately one-half of mature males (N = 14) defended territories using high rates of patrol and advertisement display, whereas 16 smaller mature males having lower body condition indices utilized non-territorial social tactics. Although territorial males were larger in absolute size and head dimensions, their heads were not allometrically larger. Territorial males advertised very frequently using displays involving stereotypical movements of the head and dewlap. More aggressive displays were given infrequently during baseline social conditions, but increased during periods of social instability. Female home ranges overlapped those of several territorial and non-territorial males, but females interacted more frequently with territorial males. The extreme plasticity of social tactics in this species that are dependent on body size was confirmed by two instances when relatively large non-territorial males spontaneously evicted territory owners, and by marked shifts in tactics by non-territorial males in response to temporary experimental removals of territory owners, followed (usually) by their expulsion when original owners were reinstated. The high level of social plasticity in this population where same-sex competitors are densely concentrated in preferred habitat suggests that chronic high energetic costs of defense may select for males to cycle between territorial and non-territorial social tactics depending upon their changing energetic status and their current capacity for competition with rivals.

Intellagama lesueurii (Gray, 1831), the correct binomial combination for the Australian Eastern Water Dragon (Sauria, Agamidae)

The Eastern Water Dragon is a large, conspicuous agamid, well known to many inhabitants of eastern Australia. It was first described in the scientific literature as Lophura lesueurii by Gray (1831). Gray’s allocation of this taxon to his earlier genus Lophura Gray, 1827, created for the species Lacerta lophura Shaw, 1802, does not mention that Cuvier (1829) had erected Istiurus for amboinensis Schlosser, 1768, which Cuvier treated as a senior synonym of lophura. Cuvier considered the generic name Lophura to be too similar to Lophyrus Latreille, 1802, a genus of conifer sawflies belonging to the family Diprionidae, hence the need for a new genus. Both Gray and Cuvier were evidently unaware that Lophura was unavailable as this name had already been assigned to a genus of phasianid birds (Fleming 1822). The Eastern Water Dragon has subsequently appeared in the taxonomic literature under the following synonyms: Iguana paramatensis Fitzinger, 1843; Amphibolurus maculiferus Girard, 1857; Amphibolurus heterurus Peters, 1866 and Amphibolurus branchialis De Vis, 1884. The combination Physignathus lesueurii was first used in 1845 by Gray in his Catalogue of the Specimens of Lizards in the British Museum and has been in use ever since. The only other generic name proposed for this taxon is Intellagama Wells and Wellington, 1985, by which the authors implied its distinctiveness from the other member of Physignathus, the Chinese Water Dragon P. cocincinus Cuvier, 1829. However, as their description provided no evidence to demonstrate that Australian water dragons are generically distinct from their foreign congener, this name has not been adopted by subsequent authors, and has been informally treated as a synonym of Physignathus.

Isolation and characterisation of novel microsatellite and mitochondrial DNA markers for the Eastern Water Dragon (Physignathus lesueurii)

Habitat fragmentation as a result of urbanisation is a growing problem for native lizard species. The Eastern Water Dragon (Physignathus lesueurii) is a social arboreal agamid lizard, native to Australia. This species represents an ideal model species to investigate the effect of urbanisation because of their prominent abundance in the urban landscape. Here we describe the isolation and characterisation of a novel set of 74 di-, tri-, and tetramicrosatellites from which 18 were selected and optimised into two multiplexes. The 18 microsatellites generated a total 148 alleles across the two populations. The number of alleles per locus varied from 2 to 18 alleles and measures of Ho and He varied from 0.395 to 0.877 and from 0.441 to 0.880, respectively. We also present primers for four novel mitochondrial DNA (mtDNA) markers. The combined length of the four mtDNA marker pairs was 2,528 bp which included 15 nucleotides changes. In comparison to threatened species, which are generally characterised by small population sizes, the Eastern Water Dragon represents an ideal model species to investigate the effect of urbanisation on their behavioural ecology and connectivity patterns among populations.

Phylogeny of iguanian lizards inferred from 29 nuclear loci, and a comparison of concatenated and species-tree approaches for an ancient, rapid radiation

Iguanian lizards form a diverse clade whose members have been the focus of many comparative studies of ecology, behavior, and evolution. Despite the importance of phylogeny to such studies, interrelationships among many iguanian clades remain uncertain. Within the Old World clade Acrodonta, Agamidae is sometimes found to be paraphyletic with respect to Chamaeleonidae, and recent molecular studies have produced conflicting results for many major clades. Within the largely New World clade Pleurodonta, relationships among the 12 currently recognized major subclades (mostly ranked as families) have been largely unresolved or poorly supported in previous studies. To clarify iguanian evolutionary history, we first infer phylogenies using concatenated maximum-likelihood (ML) and Bayesian analyses of DNA sequence data from 29 nuclear protein-coding genes for 47 iguanian and 29 outgroup taxa. We then estimate a relaxed-clock Bayesian chronogram for iguanians using BEAST. All three methods produce identical topologies. Within Acrodonta, we find strong support for monophyly of Agamidae with respect to Chamaeleonidae, and for almost all relationships within agamids. Within Pleurodonta, we find strong Bayesian support for almost all relationships, and strong ML support for some interfamilial relationships and for monophyly of almost all families (excepting Polychrotidae). Our phylogenetic results suggest a non-traditional biogeographic scenario in which pleurodonts originated in the Northern Hemisphere and subsequently spread southward into South America. The pleurodont portion of the tree is characterized by several very short, deep branches, raising the possibility of deep coalescences that may confound concatenated analyses. We therefore also use 27 of these genes to implement a coalescent-based species-tree approach for pleurodonts. Although this analysis strongly supports monophyly of the pleurodont families, interfamilial relationships are generally different from those in the concatenated tree, and support is uniformly poor. However, a species-tree analysis using only the seven most variable loci yields higher support and more congruence with the concatenated tree. This suggests that low support in the 27-gene species-tree analysis may be an artifact of the many loci that are uninformative for very short branches. This may be a general problem for the application of species-tree methods to rapid radiations, even with phylogenomic data sets. Finally, we correct the non-monophyly of Polychrotidae by recognizing the pleurodont genus Anolis ( sensu lato) as a separate family (Dactyloidae), and we correct the non-monophyly of the agamid genus Physignathus by resurrection of the genus Istiurus for the former Physignathus lesueurii.

Superficial lizards in cold climates: Nest site choice along an elevational gradient

AbstractEmbryonic conditions may limit the distributions of egg‐laying ectotherms, and recent research suggests that nesting mothers of wide‐ranging species may use a number of factors to compensate for differing climates. However, while variation in temporal factors across environmental gradients are common or pervasive (i.e. seasonal timing of nesting), similar evidence for spatial factors is rare (e.g. aspect, openness and depth of nest sites). I tested the idea that a wide‐ranging lizard, the Australia water dragon (Physignathus lesueurii), uses nest depth to counter climate differences along a temperature cline at their cold‐end range margin. Two measures of nest depth were significantly, inversely related to elevation across six populations spanning 700 m. Elevation explained 83–86% of the variation in nest depth. These findings support a thermal compensatory mechanism for this pattern, although soil moisture compensation is plausible. My results directly support a recent, untested prediction that the evolution of viviparity in reptiles is preceded by a behavioural shift towards increasingly superficial nest sites in cold climates, followed by selection for increased egg retention to avoid temperature extremes. However, in the present study egg desiccation rates increased with increasing elevation in a dry year, suggesting that increased egg retention may evolve in response to lethal hydric conditions, rather than lethal temperatures. When considered alongside recent research, the present study indicates that water dragons possess several mechanisms for adjusting to climate change.

Telemetry tagging methods for some freshwater reptiles

Reptiles are often ignored or under-studied in freshwater systems. An understanding of their biology and thus their role in aquatic communities can be greatly advanced by studies using radio telemetry. In turn, the value of radio telemetry for research depends on the availability of suitable and reliable methods of attaching or implanting radio transmitters. The present study describes transmitter attachment and implantation techniques for selected freshwater reptiles, including the eastern and northern long-necked turtles (Chelodina longicollis and Chelodina rugosa, respectively), the pig-nosed turtle (Carettochelys insculpta), Mertens’ water monitor (Varanus mertensi) and the water dragon (Physignathus lesueurii). The effectiveness of the methods for each species is described and the potential pitfalls and challenges of each method are discussed. The literature abounds with techniques for attachment and implantation techniques, and the methods used in the present study are not wholly novel. The aim, however, is to provide detailed summaries, in one paper, of effective methods for attachment and implantation of radio-tags for freshwater reptiles with a diversity of sizes, shapes and attachment surfaces. Despite the focus on Australian freshwater reptiles, these methods are applicable to aquatic reptiles worldwide.

Molecular marker suggests rapid changes of sex-determining mechanisms in Australian dragon lizards

Distribution of sex-determining mechanisms across Australian agamids shows no clear phylogenetic segregation, suggesting multiple transitions between temperature-dependent (TSD) and genotypic sex determination (GSD). These taxa thus present an excellent opportunity for studying the evolution of sex chromosomes, and evolutionary transitions between TSD and GSD. Here we report the hybridization of a 3 kb genomic sequence (PvZW3) that marks the Z and W microchromosomes of the Australian central bearded dragon (Pogona vitticeps) to chromosomes of 12 species of Australian agamids from eight genera using fluorescence in-situ hybridization (FISH). The probe hybridized to a single microchromosome pair in 11 of these species, but to the tip of the long arm of chromosome pair 2 in the twelfth (Physignathus lesueurii), indicating a micro-macro chromosome rearrangement. Three TSD species shared the marked microchromosome, implying that it is a conserved autosome in related species that determine sex by temperature. C-banding identified the marked microchromosome as the heterochromatic W chromosome in two of the three GSD species. However, in Ctenophorus fordi, the probe hybridized to a different microchromosome from that shown by C-banding to be the heterochromatic W, suggesting an independent origin for the ZW chromosome pair in that species. Given the haphazard distribution of GSD and TSD in this group and the existence of at least two sets of sex microchromosomes in GSD species, we conclude that sex-determining mechanisms in this family have evolved independently, multiple times in a short evolutionary period.

Basking in the Australian water dragon Physignathus lesueurii; why do alpha males not respond to operative temperatures in the same way as adults and sub-adults?

AbstractObservations have been made on the behaviour of the Australian water dragon Physignathus lesueurii in southeast Australia. Physical models that explore the thermal environment at a similar spatial level as real lizards were related to ontogenetic changes in lizard behaviour. Current theory predicts that a heliotherm will bask in open locations to optimise heating rates in order to attain target body temperatures as quickly as possible. Movement to shaded or partially shaded areas then maintains thermal stability. Regression equations of basking intensity in relation to operative temperatures were employed to test this theory. The behaviour of adults, which were not alpha males, and sub adults was in agreement with the prediction, but the behaviour of alpha males was not: the regression coefficient did not differ significantly from 0. In general, sub adult lizards were more active and fed more often than larger lizards although this relationship changed with different times of the day. The results suggest differing costs for thermoregulation for different size classes, particularly in alpha males where territory defence has a key role.

Hues of a dragon's belly: morphological correlates of ventral coloration in water dragons

AbstractSexual dichromatism is common in lizards, and may play an important role in sex recognition and mating systems. Nonetheless, relatively few published papers provide quantitative analyses of colour, deal with Australian taxa or are based on large‐bodied species. Water dragons Physignathus lesueurii (Agamidae) from eastern Australia are very large (upto 1 m total length) and sexually dichromatic, with conspicuous red ventral coloration in adult males. We quantified coloration in three ventral regions (throat, chest and abdomen) of males and females using a spectroradiometer and looked for associations of colour with sex and with morphological traits predicted to correlate with fitness (body size, body condition, relative head size and asymmetry of femoral pores). Among adult males, larger individuals showed less red on the abdomen than did smaller animals, and males with relatively large heads had darker, less red abdomens than did males with smaller heads. Among adult females, larger animals had darker chests, and less red on the abdomen and chest, than did smaller females. The similarity in these trends between the sexes, and the location of the sexually dichromatic and size‐sensitive colours in an area (under the abdomen) where they presumably are not visible to other lizards cast doubt on their utility as sexual or dominance signals. Hence, although we documented significant sex and body‐size effects on ventral coloration, our results suggest that ventral colours in water dragons do not function in sex‐specific displays.

Nematodes from the water dragon, Physignathus lesueurii (Reptilia:Agamidae) in Australia, with a description of Spinicauda fluviatica, sp. nov. (Nematoda:Heterakoidea)

Abbreviata physignathi and Spinicauda fluviatica, sp. nov., were the predominant species of nematode recovered from the gastrointestinal tracts of 65 Physignathus lesueurii examined from eastern Australia. S. fluviatica, sp. nov., is distinguished from other known species by the large well sclerotised excretory sinuses in both sexes and by the relative lengths of the spicules and gubernaculum in males. This is the first species of Spinicauda to be described from an agamid lizard. Both these nematode species occur mainly or entirely in New South Wales within 100 km of the coast; P. lesueurii is the only known host of both species. The persistence of generalised apical dentition in A. physignathi and its high host-specificity suggests a long association with this lizard, which diverged early from the main agamid stock. The significant association of these two unrelated nematode species is attributed to the high density of P. lesueurii hosts along suitable rivers. Other nematode species identified in low numbers in one or two hosts only were Abbreviata antarctica, A. confusa, Maxvachonia brygooi and immature Dracunculus sp. in the gastrointestinal tract, encysted subserosal physalopterid larvae on two stomachs, and Oswaldofilaria samfordensis in the body cavity.

Microsatellite loci for Australian agamid lizards

AbstractWe characterize 15 microsatellite loci from two microsatellite libraries developed from the Australian agamid lizards Amphibolurus muricatus and Ctenophorus pictus. All loci were tested for amplification in four other agamids: Ctenophorus fordi, Ctenophorus decresii, Chlamydosaurus kingii, and Physignathus lesueurii. These loci were highly polymorphic within and across species, with nine to 12 loci amplifying for each species tested.

Nest site choice compensates for climate effects on sex ratios in a lizard with environmental sex determination

Theoretical models suggest that in changing environments natural selection on two traits, maternal nesting behaviour and pivotal temperatures (those that divide the sexes) is important for maintaining viable offspring sex ratios in species with environmental sex determination (ESD). Empirical evidence, however, is lacking. In this paper, we provide such evidence from a study of clinal variation in four sex-determining traits (maternal nesting behaviour, pivotal temperatures, nesting phenology, and nest depth) in Physignathus lesueurii, a wide-ranging ESD lizard inhabiting eastern Australia. Despite marked differences in air and soil temperatures across our five study sites spanning 19° latitude and 1200 m in elevation, nest temperatures did not differ significantly among sites. Lizards compensated for climatic differences chiefly by selecting more open nest sites with higher incident radiation at cooler sites. Clinal variation in the onset of nesting also compensated for climatic differences, but to a lesser extent. There was no evidence of compensation through pivotal temperatures or nest depth. More broadly, our results extend to the egg stage the life history prediction that behaviour is the chief compensatory mechanism for climatic differences experienced by species spanning environmental extremes. Furthermore, our study was unique in revealing that nest site choice influenced mainly the daily range in nest temperatures, rather than mean temperatures, in a shallow-nesting reptile. Finally, indirect evidence suggests that the cue used by nesting lizards was radiation or temperature (through basking or assessing substrate temperatures), not visual detection of canopy openness. We conclude that maternal nesting behaviour and nesting phenology are traits subject to sex ratio selection in P. lesueurii, and thus, must be considered among the repertoire of ESD species for responding to climate change.

Chemical Composition and Structure of the Eggshell of Three Oviparous Lizards

We investigated the structure of the eggshells of the oviparous scincid lizards, Lampropholis guichenoti and L. delicata, and the agamid Physignathus lesueurii. The eggshells of all three species consisted of an outer calcareous layer, a fibrous shell membrane, and an inner boundary layer. The eggshells of P. lesueurii had an additional amorphous layer between the calcareous and fibrous layers. The calcareous layer of all shells was relatively thin and contained calcium carbonate in the form of calcite, typical of oviparous squamates. The multilayered fibrous shell membrane constituted the majority of shell thickness. The calcareous layer contained the majority of inorganic ions, with calcium and magnesium being present in detectable quantities. Calcium carbonate crystals were also found on the inner boundary layer of the P. lesueurii shells. This phenomenon has only been described for one other species, the Tuatara.

Inclusions in the erythrocytes of eastern water dragons (Physignathus lesueurii)

Inclusions in the erythrocytes of eastern water dragons (Physignathus lesueurii)

Lectin‐binding patterns in the olfactory system of the lizard, Physignathus lesueurii

Lectin‐binding patterns in the olfactory system of the lizard, Physignathus lesueurii

Physiological correlates of vagal nerve innervation in lower vertebrates

In lower vertebrates, cardiac vagal innervation shows less anatomic complexity and specialization than in mammals. To assess the physiological development of vagal specialization in the vertebrates, we investigated cardiac chronotropic effects of electrical stimulation of left and right vagus nerves separately and the interactions between both nerves in anesthetized animals from three vertebrate groups, toad (Bufo marinus), shark (Heterodontus portusjacksoni), and lizard (Physignathus lesueurii). Atropine-sensitive slowing was effected equally by left or right vagi in all species, and chronotropic effects of simultaneous stimulation were the same as the sum of left and right responses. In sharks and lizards, no slowing after atropine was detected (10 Hz stimulation). In toads, after atropine, cardiac slowing was elicited equally by left or right vagal stimulation > 2 Hz. Simultaneous stimulation of both vagi after atropine caused significantly greater slowing than the sum of left and right responses. The results suggest even distribution of left and right vagal nerve endings to pacemaker cells, and limited competition for cardiac receptor sites in lower vertebrates.

Estimate of the population structure of the estern water dragon, Physignathus lesueurii (Reptilia : Agamidae), along riverside habitat

A population of eastern water dragons, Physignathus lesueurii, was investigated along 1.5km of the Gloucester River in central eastern New South Wales from November 1989 to December 1992. Dragons were caught in all months from September to April, but not in June. In all, 373 dragons were marked and 69 of these were recaptured on one or more occasions. Females are ovigarous in late October, November and December. Only about one third of females have palpable eggs during these months. Hatchlings enter the population in February and March at 4.5g, with a snout-vent length (SVL) of 53mm. In the next season they are 19.5g (SVL 80mm). The dragons grow rapidly for four years to reach adult size. Growth rates are fastest during the first year at 2.25mm SVL per month or 1.25 g per month. The Jolley-Seber population estimate for adult females was 103 +/-49 in the study site or 69 per km of river. Estimates for males and for the total population could not be calculated because individuals were not equally catchable (Leslie's test for equal catchability). However, theoretical considerations place the density of adult dragons at 138-215 per km of river. The largest male was 304mm SVL, 54mm longer than the next-largest water dragon reported. One male was heavier than 1000g. The largest female was 230mm SVL and the heaviest was 490g, or approximately half the mass of the heaviest male. Adult males and adult females have the same proportion of broken tails. Water dragons are fairly sedentary, with an average distance of 76m (range 0-785m) between captures.