Sexual dimorphism in body shape without sexual dimorphism in body size in water skinks (Eulamprus quoyii)

Schwarzkopf, Lin

Abstract

Sexual dimorphism in body size is often accompanied by shapedimorphism. Shape dimorphism may be selected directly, or may bean indirect result of selection for size dimorphism. To determinewhether shape differences are likely to have been directlyinfluenced by selection, the indirect effects of size dimorphismon shape can be removed statistically, the approach of mostprevious studies, or, alternatively, we can examine the patternsof shape dimorphism in species that are not size dimorphic. Here Idescribe sexual shape dimorphism in adults and neonates of alizard that is not dimorphic in body length, the eastern waterskink (Eulamprus quoyii). In this species, snout-vent length isnot significantly different between adult or neonate males andfemales, but there are significant shape differences between sexesin both adults and neonates. For a given body length, adult maleshave wider heads, longer limbs, shorter trunk length (the distancebetween the forelimb and the hindlimb), and greater mass thanfemales. In addition, head width, forelimb length and massincrease significantly more rapidly with body length in adultmales than in females, whereas the rate of change of hindlimblength and trunk length with length is not significantly differentin males and females. The shape of the body is more similar inneonates than adults, but female neonates have significantlylonger trunks than males. The intersexual shape difference inneonate E. quoyii suggests that, although growth rate differencesamong body parts are the main source of differences in shapebetween adults, the difference between male and female interlimblengths is present initially. Shape differences present at birththat are preserved until adulthood are less common than growthdifferences as a source of adult shape differences. Theintersexual shape differences among adult E. quoyii are similar tothose reported for species that are sexually size dimorphic,suggesting that selective forces have influenced body shape insimilar ways in both size dimorphic and nondimorphic species, andthat allometric relationships alone may not be responsible forshape differences between males and females in size dimorphic species.

Journal

Herpetologica

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1938-5099

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Herpetologists' League

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DOI

10.1655/04-66