Size and shape sexual dimorphism in the skull of the South American fur seal, Arctocephalus australis (Zimmermann, 1783) (Carnivora: Otariidae)

L. R. Oliveira, E. Hingst-Zaher, J. S. Morgante

Abstract


We present a quantitative analysis of sexual dimorphism in the skull of Arctocephalus australis assessed by traditional and geometric morphometrics. Differences in size and shape of skulls of 386 adult males and females of A. australis from Uruguayan and Peruvian populations were analyzed using 15 linear measurements. These differences were also investigated applying geometric morphometrics techniques to two-dimensional images of 346 skulls in dorsal, ventral and lateral views. Results of traditional and geometric morphometrics revealed pronounced sexual dimorphism in size and shape of the skull for both populations of A. australis. Males are always larger than females, and differences in shape are concentrated mainly in the rostral region. Sexual dimorphism is more accentuated in the Uruguayan population. Differences in size and shape of the skulls between males and females of A. australis can be related to sexual selection, mating system and life history. In A. australis, as well as in other polygynous species, the selective pressures can favor the development of traits that enhance fighting ability in males, such as larger canines, increased rostral and mastoid widths and increased overall body size.

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DOI: http://dx.doi.org/10.5597/lajam00067

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