Sex- and age-related morphofunctional differences in skulls ofTayassu pecariandPecari tajacu(Artiodactyla: Tayassuidae)

Abstract

Tayassuids exhibit little sexual dimorphism. Sex-related craniomandibular variation was tested in 2 tayassuid species with regard to morphology and function. We analyzed skull features from 61 adult and 37 subadult white-lipped peccaries (Tayassu pecari) and 49 adult collared peccaries (Pecari tajacu) of both sexes. Seventeen skull measurements were used for the morphological characterization, and from these, indexes were obtained for the functional analysis of bite performance (temporal and masseter muscular systems) and head elevation (semispinalis capitis/complexus muscular system). Skull sexual dimorphism of the 2 species and 2 age groups were evaluated independently through discriminant function analysis (DFA), principal component analysis (PCA), and univariate methods. The DFA characterized a slight secondary sexual dimorphism in adult T. pecari and P. tajacu skulls and provided sex classification functions. However, no sexual variation was detected in skull function of adults in either species. Nevertheless, subadult males and females of T. pecari displayed marked morphological and functional skull variation. Subadult females displayed greater skull robustness, and their force indexes indicate an enhancement on bite strength and in head elevation. This could suggest ecomorphological dissimilarities between subadult male and female T. pecari. The sexual precocity of the females reported in the literature could be the main determinant of the marked morphofunctional variation among the T. pecari subadults. These sexual differences in skull morphology seem to become reduced as males mature.