3D Geometric Morphometrics of the cold-adapted thorax: eco-geographical variability of the human rib cage

GARCÍA MARTÍNEZ, D.; CUNHA, E.; NEVES, M. J.; FERREIRA, M. T.; NALLA, S.; GUICHÓN, R. A.; D'ANGELO DEL CAMPO, M. D.; CONSTANTINO, S.; GARCÍA RÍO, F.; TORRES, I. ; BASTIR, M.

Madrid

Simposio; II Iberian Symposium on Geometric Morphometrics; 2016

Universidad Autónoma de Madrid

Despite the major importance of the thorax for human biology, its 3D morphological variability associated to eco-geographical variation is poorly understood. Allen´s and Bergmann´s eco-geographic rules link body size and shape to climate conditions in homoeothermic mammals. The majority of the authors claim that these rules also apply for humans adapted to extreme climate conditions (cold/warm). Thus, circumpolar people would present broader trunks (and thus thoraces) than people inhabiting mid-latitudes. However, other authors defend that these rules do not apply for humans because of technological adaptations (e.g. clothing, and shelter). The present work aims to address whether there are differences in costal morphology between populations inhabiting different climatic conditions. We quantified 3D-morphology of individual ribs (rib number 2-10) from populations inhabiting different climatic conditions (moderate ? Europeans = 216; warm - Sub-Saharans = 126; cold - Greenland Inuits = 98 and Tierra del Fuego = 54) through 3D geometric morphometrics of landmarks and sliding semilandmarks (N=61). GPA and PCA was performed in order to reduce dimensionality of the 3D data and explore variability. PC1-PC2 projection shows morphological variability linked to position, from upper (short tubercle-angle distance; pronounced axial curvature; no torsion) to lower ribs (large tubercle-angle distance; less axial curvature; torsion). Upper ribs (rib number 2-4) from Tierra del Fuego present greater axial curvature than their counterparts of other populations, whereas rib number 10 from Inuit and Tierra del Fuego present less than their counterparts. PC3 is linked to differences in axial curvature not related to position, where Inuit ribs are different from rest of the sample by presenting less axial curvature and shorter rib shaft height. Our results show morphological differences along the costal sequence in Inuit and Tierra del Fuego which is probably due to morpho-functional adaptations of the thorax to cold climates. However, since they do not share a common morphological pattern, we hypothesize that this could be produced by different degrees of coldness.