Differential sexual dimorphism: size and shape in the cranium and pelvis of grey foxes (Urocyon)

Abstract

Patterns of sexual size dimorphism (SSD) and cranial dimorphism are well documented. However, limited examinations exist of the contrasts in the patterns and nature of dimorphism across body regions (e.g. cranium, pelvis), particularly when these regions have different sex-specific functions (e.g. display in mating, locomotion, and reproduction). Using landmark-based morphometric techniques, we investigated size and shape dimorphism variation in the crania and pelves of two closely-related fox species within the genus Urocyon. Although we found no significant size and shape dimorphism in the crania of either species, we did find significant dimorphism in the pelvis: its size was dimorphic in Urocyon littoralis (but not in Urocyon cinereoargenteus) and its shape was dimorphic in both species (though more pronounced in U. littoralis). The observation of greater dimorphism in the pelvis than in the cranium suggests that factors such as offspring size and locomotor mode play a greater role in sexual dimorphism than simple 'whole body' allometric affects associated with dimorphism in body size.

Sexual dimorphism, asymmetry, and the effect of reproduction on pelvis bone in the bank vole, Myodes glareolus

“…Among studies on osteological traits, sexual dimorphism of the pelvis (os coxa) has attracted the attention of several authors studying various mammalian species (Iguchi et al 1995;Schutz et al 2009a), including rodents (Trejo and Guthmann 2003;Berdnikovs et al 2007;Balčiauskienė and Balčiauskas 2009a). Some of those studies have focused on pelvic development (Polaćek and Novotny 1969;Uesugi et al 1992) and others on morphology (St. Clair 2007;Schutz et al 2009a). Mammalian pelvis is a compound structure consisting of the two pubis bones (os pubis), two ilium bones (os ilium), and two ischium bones (os ischii).…”

“…In most mammalian species, it varies across the sexes (Berdnikovs et al 2007) and, generally, females have relatively larger pelvises than males (Tague 2005). Sexual dimorphism, with regard to size and shape of the pelvis, exists even where there is a small difference in size between males and females (Schutz et al 2009a). …”

“…The main function of female pelvis shape is to enable the passage of young through the aperture. Changes in the shape of the os coxae appear as a result of the first parturition event, and these transformations correlated with the relative size of individual offspring (Schutz et al 2009a). Consequently, both maternal and neonatal sizes seemed to be very significant factor responsible for alterations to the female pelvis throughout parturition (Leutenegger 1974;Berdnikovs 2005;Tague 2005).…”

Sexual dimorphism of labrador retriever dogs by morphometry

“…In this species the variation in the skull and skeleton is superior to all other species of the Canidae family (WAYNE, 1986). Shultz et al (2009) asserted that current studies of sexual dimorphism focus mainly on body size. Although some studies include other parts of the body (FAIRBAIRN, 2005), they use linear measurements and necessarily the size of the body is incorporated in these data.…”

Variation in fur farm and wild populations of the red fox, Vulpes vulpes (Carnivora: Canidae) — Part I: Morphometry

“…Over time, farm foxes have become markedly bigger and heavier, while at the same time, the weights of certain internal organs, e.g., the liver, spleen, and kidneys, have increased considerably (Kulawik et al 2013). Wild canids exhibit marked differences in the morphology of both sexes (particularly the skull and dentition) (Gittleman 1997;Schutz et al 2009). In farm foxes, sexual dimorphism has been greatly reduced (Trut 1999), which is an evident effect of domestication (Hartova-Nentvichova et al 2010).…”