Morphological and functional implications of sexual dimorphism in the human skeletal thorax

Abstract

Number of tables: 2Abbreviated title: 3D morphometrics of human rib cage.Key words: rib cage; geometric morphometrics; sex differences. This is the peer reviewed version of the following article: American Journal of Physical Anthropology 161(3): 467-477 (2016), which has been published in final form at http://dx.doi.org/10.1002/ajpa.23051. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. *Corresponding author:2 Title: Morphological and functional implications of sexual dimorphism in the human skeletal thorax. ABSTRACT Objectives:The human respiratory apparatus is characterized by sexual dimorphism, the cranial airways of males being larger (both absolutely and relatively) than those of females. These differences have been linked to sex-specific differences in body composition, bioenergetics and respiratory function. However, whether morpho-functional variation in the thorax is also related to these features is less clear. We apply 3D geometric morphometrics to study these issues and their implications for respiratory function. Material and methods:402 landmarks and semilandmarks were measured in CT-reconstructions of rib cages from adult healthy subjects (N male =18; N female =24) in maximal inspiration (MI) and maximal expiration (ME). After Procrustes registration, size and shape data were analyzed by mean comparisons and regression analysis. Respiratory function was quantified through functional size, which is defined as the difference of rib cage size between MI and ME.Results: Males showed significantly larger thorax size (p<0.01) and functional size (p<0.05) than females. In addition, the 3D-shape differed significantly between sexes (p<0.01). Male rib cages were wider (particularly caudally) and shorter, with more horizontally oriented ribs when compared to females. While thorax widening and rib orientation were unrelated to allometry, thorax shortening showed a slight allometric signal. Conclusions:Our findings are in line with previous research on sexual dimorphism of the respiratory system. However, we add that thorax shortening observed previously in males is the only feature caused by allometry. The more horizontally oriented ribs and the wider thorax of males may indicate a greater diaphragmatic contribution to rib cage kinematics than in females, and differences in functional size fit with the need for greater oxygen intake in males.3

Three-dimensional morphometrics of thoracic vertebrae in Neandertals and the fossil evidence from El Sidrón (Asturias, Northern Spain)

“…4) supports an assignment of SD-1619 to a young (and not so large) adult and of SD-1641 to In a more general morphological framework, the current study addressed the hypothesis that the enlarged thorax of Neandertals is not only the result of larger ribs (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a, Bastir et al, 2015a, but also of a more dorsal orientation of the transverse processes of the thoracic vertebrae (Bastir et al, 2015b). A similar kind of influence of vertebral shape on rib cage morphology has been proposed in Australopithecus (Ward et al, 2012) and Homo ergaster/erectus (Jellema et al, 1993;Latimer and Ward, 1993), and more recently also identified as a geometric feature of modern human sexual dimorphism García-Martínez et al, 2016a). Shape data of both El Sidrón (SD-1641-T3, -T4; SD-1619-T6, -T7) vertebral reconstructions available for 3D analysis (Figs.…”

“…However, transverse process orientation could also be important for respiratory function. In Homo sapiens, the thoracic capacity of males is greater than in females, both absolutely and relative to stature (Silbernagl and Despopoulos, 1991;Bellemare et al, 2003Bellemare et al, , 2006García-Martínez et al, 2016a). It has been shown recently that the larger male thoracic capacity can be related to a greater dorsal orientation of the transverse processes of their thoracic vertebrae, particularly the lower ones (T6-T9; Bastir et al, 2014).…”

Sex-Specificity of Mineralocorticoid Target Gene Expression during Renal Development, and Long-Term Consequences

“…Indeed, in contrast to the kidney, pulmonary Gilz mRNA expression, for instance, is upregulated to a greater degree in females compared to males. Recent studies have underlined sex differences in respiratory function during lung development and in adulthood [3,53,54,55]. Moreover, female smokers have an increased risk of chronic obstructive pulmonary disease in comparison to male smokers with similar history of cigarette smoke exposure, both in human and mice; however, the underlying mechanisms are still under investigation [56,57].…”

“…They have also recently been shown in various biological processes such as white matter development and brain volume [1], stress response and depression [2] or respiratory function [3]. …”

The costal remains of the El Sidrón Neanderthal site (Asturias, northern Spain) and their importance for understanding Neanderthal thorax morphology

“…Expansion of the lungs during breathing and consequent oxygen intake is facilitated by the action of the intercostal muscles, the diaphragm and other accessory muscles (Spalteholz, 1970;De Troyer et al, 2005). Therefore, oxygen availability, basal metabolic rate (BMR) and physical activity are also dependent on various aspects of rib cage morphology (Franciscus and Churchill, 2002;Churchill, 2006;Froehle and Churchill, 2009;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014, 2016aBastir et al, 2017a). In addition, the rib cage contributes to the configuration of gross trunk shape in hominins due to its morphological integration caudally with the pelvis (Jellema et al, 1993;Bastir et al, 2014a) and cranially with the upper limb (Churchill, 1994;Bastir et al, 2013;Schmid et al, 2013).…”