Skull allometry and sexual dimorphism in the ontogeny of the Southern elephant seal (Mirounga leonina)

TARNAWSKI, BÁRBARA ALEJANDRA; CASSINI, GUILLERMO HERNÁN; FLORES, DAVID ALFREDO

CANADIAN JOURNAL OF ZOOLOGY

NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS

Lugar: Otawa; Año: 2014 vol. 92 p. 19 - 31

0008-4301

The Southern elephant seal, Mirounga leonina (Linneaus 1758), is one of the most dimorphic mammals but sexual dimorphism in its skull ontogeny is poorly known. We study ontogeny of sexual dimorphism (SD) by the allometric relationships between 21 measurements and its geometric mean. Based on 66 specimens (36 females, 30 males), the bivariate and multivariate analyses indicated that both approaches were congruent in most variables. We detected that SD was reached mostly by sexual shape differences in the ontogenetic trajectories of males and females. 24% of variables were associated with intercepts differences (pup size proportions), while 57% of variables were associated with slope intersexual differences (relative growth rates). Contrarily, SD was also achieved by size differences in adult stages (19% of variables), as males exhibited an extension of their common ontogenetic trajectories. Secondary growth spurt in males was detected for few variables. Our comparison with analogous data collected on Otaria byronia (de Blainville 1820), the southern sea lion, indicate that in both species SD was mostly pointed to an enhanced ability to defend territories, which was linked to with the polygynic behavior. However, discrepancies between both ontogenetic patterns of dimorphism were associated with interspecific differences in their life cycles.