Allometry in the Bearded Dragon Pogona barbata (sauria: Agamidae): Sex and geographic differences

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Journal Article
Australian Zoologist, 2003, 32 (2), pp. 238 - 245
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Allometry in size and shape between sexes was investigated in preserved Bearded Dragon Pogona barbata museum specimens. Measurements for snout-vent, head, leg and tail lenghts were obtained from 236 individuals ranging from hatchlings to large adults. Juveniles and adults were sexed, and size at onset of maturity was determined. Geographic variation in P. barbata was also studied by comparing lizards from three regions in New South Wales (NSW), which differ in annual rainfall. Relative to snout-vent length, head and leg lengths were in negative allometry in all specimens, and tail length was in positive allometry in juveniles, but negative in adults. Sexual dimorphism was evident in body size and shape. Males grew larger and reached maturity at larger sizes than females. While juvenile shape did not differ between the sexes, mature males had proportionately longer heads, legs and tails than adult females. This generalisation in sexual shape dimorphism did not hold true for animals from different NSW regions. Western males had proportionately longer legs and heads than western females, but relative tail lengths were not significantly different. Sexual dimorphism in body shape was not seen in the central animal group. In the east, heads and tails were longer in males than in females. Both sexes showed lower relative head and leg lenghts in more arid regions. We suggest that a combination of genetic drift and phenotypic responses are likely causes of these variations.
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