Differences in body mass and oral morphology between the sexes in the Artiodactyla: evolutionary relationships with sexual segregation

It has been hypothesized that the evolution of sexual dimorphism could lead to sexual dimorphism in trophic structures, mainly the mouthparts, through inter-sexual niche partitioning. This hypothesis is based on the assumption that females select habitats on the basis of their requirements for diets with high nutrient concentrations (due to pregnancy and lactation), whereas males select for habitats with abundant resources (due to their larger body size and higher absolute nutrient requirement). We analysed a data set of the morphological traits of the mouth and teeth, which have been proposed as being functionally related to food selection ability (muzzle width, incisor protrusion), food comminution (molar occlusal surface area) and intake (incisor breadth), in males and females of species from the mammalian order Artiodactyla. Our analyses showed that all of the morphological traits studied covaried isometrically with body mass. The effect of sharing common ancestors did not have a significant effect on oral morphology, which indicates that oral morphology evolved in parallel in both sexes. We detected differences in body mass between the sexes and these differences remained when phylogeny was taken into account. Our results demonstrate that the dimensions of the oral traits result primarily from differences in body mass between the sexes rather than differences in niche adaptation between the sexes. The relationship between sexual dimorphism in body mass and differences in niche partitioning between the sexes in the Artiodactyla is discussed