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Literatur und Schriften
BRADSHAW, S.D. (1970): Seasonal changes in the water and electrolyte metabolism of Amphibolurus lizards in the field. Comp. Biochem. Physiol., 36: 689-717.
BRADSHAW, S.D. (1971): Growth and mortality in a field population of Amphibolurus lizards exposed to seasonal cold and aridity. J. Zool., London, 165: 1-25.
BRADSHAW, D. (1981): Ecophysiology of Australian desert lizards: Studies on the genus Amphibolurus. In: Keast, A. (ed.): Ecological biogeography of Australia. The Hague, Boston, London (W. Junk). 1393-1434.
BRADSHAW, S.D. & A:R. MAIN (1967): Behavioural attitudes and regulation of temperature in Amphibolurus lizards. J. Zool., London, 154: 193-221.
CARPENTER, C.C., BADHAM, J.A. & B. KIMBLE (1970): Behaviour patterns of three species of Amphibolurus (Agamidae). Copeia, 1970: 497-505.
GLAUERT, L. (1959): Herpetological miscellanea. XI. Dragon lizards of the genus Amphibolurus. W. Austr. Nat., 7: 42-51.
LOVERIDGE, A. (1933): New agamid lizards of the genera Amphibolurus and Physignathus from Australia. Proc. New. Engl. Zool. Blub, 13: 69-72.
PETERS, W.C.H. (1866): Mittheilung über neue Amphibien (Amphibolurus, Lygosoma, Cyclodus, Masticophis, Crotaphopeltis) und Fische (Diagramma, Hapalogenys) des Kgl. Zoologischen Muesums. Monatsber. Königl. Preuss. Akad. Wissensch. Berlin, 1866: 86-96.
WELLS, R.W. & C.R. WELLINGTON, 1985): A classification of the Amphibia and Reptilia of Australia. Australian Journal of Herpetology, Supplementary Series, (1):1-61.
Gilbert’s Wasseragame / Centralian Lashtail
Australische Felsenechse / Jacky Lashtail, Jacky Lizard
The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature-dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature-dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg-laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male-male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male-biased sex ratios, and that this provides an adaptive explanation for temperaturedependent sex determination in A. muricatus.
Jacky dragons (Amphibolurus muricatus) are ubiquitous in south-eastern Australia and were one of the first Australian reptiles to be formally described. Because they are so common, Jacky dragons are widely used as a model system for research in evolutionary biology and ecology. In addition, their distribution along the Great Dividing Range of eastern Australia provides an opportunity to examine the influence of past biogeographical processes, particularly the expansion and contraction of forest habitats, on the diversification of this iconic agamid lizard. We generated sequence data for two mitochondrial and three nuclear DNA loci (4251base pairs) for 62 Jacky dragons sampled from throughout their distribution. Phylogenetic analyses based on maximum likelihood and Bayesian species-tree methods revealed five geographically structured clades separated by up to 6% mitochondrial and 0.7% nuclear sequence divergence. We also quantified body proportion variation within and between these genetic clades for more than 500 specimens and found no evidence of any significant differentiation in body proportions across their range. Based on body proportion homogeneity and lack of resolution in the nuclear loci, we do not support taxonomic recognition of any of the mitochondrial clades. Instead, A. muricatus is best thought of as a single species with phylogeographic structure. The genetic patterns observed in the Jacky dragon are consistent with fragmented populations reduced to multiple refugia during cold, arid phases when forested habitats were greatly restricted. Consequently, the inferred biogeographic barriers for this taxon appear to be in line with lowland breaks in the mountain ranges. Our results are congruent with studies of other reptiles, frogs, mammals, birds and invertebrates, and together highlight the overarching effects of widespread climatic and habitat fluctuations along the Great Dividing Range since the Pliocene.
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.
Mallee Heath Lashtail