Meeting Abstract

90.3  Wednesday, Jan. 7  Ontogenetic convergence in ventral skull shape between males and females of a sexually dimorphic antelope BRAKORA, Katherine*; KHUC, Kim; University of California, Berkeley kbrakora@berkeley.edu

Although antelope provide many classic examples of sexual dimorphism among mammals, their morphology has not been systematically quantified in terms of sexual differences in size, shape or ontogeny. Furthermore, it is unknown whether the obvious sexual differences in the frontal region of the skull caused by the presence or enlargement of horns in males correlate with shape differences in other regions of the skull. We performed two-dimensional geometric morphometric analyses on the ventral skull of 25 female and 14 male springbok antelope (Antidorcas marsupialis), ranging from 7 months to >5 years old, which were harvested and age-estimated from a wild population in northern Namibia from 1992-1994. 22 paired and 5 midline landmarks of the ventral basicranial, zygomatic, palatal and maxillary regions were digitized, standardized for shape using Procrustes superimposition, and analyzed using standard software. Principle component analyses revealed a primary ontogenetic component characterized by lengthening of the tooth row, loss of the second adult premolar, and extension of the face and posterior palate. In a secondary sexual component, males had a longer, more posterior palatine bone, shorter tooth row, wider anterior palate, and more anterior facial tuberosity. In juveniles (12-14 months), the sexes differed more in shape than they did in sub-adults (22-24 months) or in adults (>3 years), although they were not statistically different in each age group. In dorsal view adults males are easily distinguished from females by their horn size and related frontal bone modifications, whereas the sexes are difficult to distinguish in juveniles. This suggests that the sexes become more similar through ontogeny in the ventral skull, while diverging markedly in the dorsal skull.