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

Abstract

Sexual dimorphism in anatomical traits has been widely studied in animals. Although pelvis dimorphism was mostly studied in humans, it occurs also in many other mammalian species. Here, we investigated sexual dimorphism in the pelvis of the bank vole Myodes glareolus using individuals with known sex and reproductive status of females (parous vs nulliparous). The analyses revealed that the size and shape of pelvis differed significantly between sexes, as well as between nulliparous and parous females. In comparison with males, females had a significantly longer pelvis and pubis bones and a longer obturator foramen length, but a smaller pubis width. Interestingly, the difference between parous and nulliparous females resembles that between females and males: parous females had bigger pelvis, which probably resulted from changes during pregnancy and after birth. Left bones were on average larger than right ones, but the magnitude of directional asymmetry was not different between sex and reproduction group. Moreover, we noticed that fluctuating asymmetry of pelvis and pubis length was higher in females than in males and higher in parous than in nulliparous females, what is presumably associated with locomotor performance. A discriminant function analysis performed for the four bone size traits showed that the traits can be effectively used for a nearly perfect recognition of sexes and also a quite reliable recognition of the reproductive status of females.

Pelvic and sacral size dimorphism and allometry in two predatory carnivores with different life histories and locomotory adaptations

“…The differences between species were also confirmed by two-way ANOVA. Our analyses indicated small male-biased SSD with overlapping values between sexes for both species and were in accordance with results from previous studies (Nwoha, 2000;Tague, 2003;Carrier et al, 2005;Berdnikovs et al, 2007;Balčiauskas, 2009, 2016;Schutz et al, 2009aSchutz et al, , 2009bJurgelėnas, 2015;Matysiak et al, 2017;Nganvongpanit et al, 2017). Only the inner breadth of the obturator foramen (BFo) was slightly bigger in wolf females, which indicates a wider pelvic cavity.…”

“…Therefore, the SSD in the pelvic bones may be a result of global differences between the sexes in skeletal growth that are likely highlighted by hormonal differences typical for the sexes (Iguchi et al, 1995;Malashichev et al, 2005Malashichev et al, , 2008Berdnikovs, 2007;Pomikal and Streicher, 2010). The SSD was also different between parous and nulliparous females where parity events significantly affect the size and shape of the female pelvis and produce differences in the magnitude of the pelvic shape dimorphism (Johanson and Berger, 2003;Schutz et al, 2009a;Matysiak et al, 2017). In addition, the shape and size of innominate bones depend on several factors, such as the weight of the fetus, the specifics of parturition, the peculiarities of carriage, and the attachment of muscles (Carrier et al, 2005).…”

“…The hip bones are joined in the ventral region by the cartilaginous pubic symphysis (symphysis pelvina), whereas the sacrum (os sacrum) is joined in the dorsal portion of the pelvic bones de Lahunta, 2009, 2013). The pelvis forms a complex structure, which differs in both shape and size between the sexes, even in species that exhibit little or no sexual dimorphism in size or shape (Kryštufek, 1998;Schulte-Hostedde et al, 2001;Carrier et al, 2005;Clair, 2007;Berdnikovs et al, 2007;Balčiauskas, 2009, 2016;Schutz et al, 2009aSchutz et al, , 2009bCarlon and Hubbard, 2012;Parés-Casanova and Martinéz, 2014;Nganvongpanit et al, 2017;Matysiak et al, 2017). The pelvis serves two main functions, which largely determine its shape.…”

“…Second, the pelvis supports the posterior viscera and reproductive tract. Sexual size dimorphism (SSD) of the pelvis is a consequence of its differential role in male and female reproduction, as females are affected by bearing additional weight during pregnancy, and full-term fetuses pass through the female birth canal (Carrier et al, 2005;Schutz et al, 2009aSchutz et al, , 2009bNganvongpanit et al, 2017;Matysiak et al, 2017).…”