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Once the allometric factor has been discarded, results show that no significant differences regarding sex among any of the species studied were found. From these results we can say that the only differences between males and females of the studied
species are in size. In conclusion, if we don't look at the size of the species, there are no differences in locomotor behaviors -conditioned by the sex of the individual- that affect the wrist ligaments in the different species studied.
Aroa Casado, Juan Francisco Pastor, Felix Jesús de Paz, Miquel Llorente, David Riba, Josep Maria Potau
A. C. and J.M.P authors works in Unit of Human Anatomy and Embryology, University of Barcelona, Barcelona, Spain. J.F.P and
F.J.P works in Department of Anatomy and Radiology, University of Valladolid, Valladolid, Spain M.L and D.R works in Research
Unit and Ethology Laboratory, Fundació Mona, Riudellots de la Selva, Girona, Spain
Contact: aroa.casado@ub.edu
Gorilla F -- Gorilla M
Difference between means:
Procrustes distance: 0,01952833
Mahalanobis distance: 3,6022
T-square: 99,6224, P-value (parametric): 0,5153
P-values for permutation tests (1000 permutation runs):
Procrustes distance: 0,9510
T-square: 0,5000
Pan F -- Pan M
Difference between means:
Procrustes distance: 0,02728404
Mahalanobis distance: 4,5325
T-square: 128,1917, P-value (parametric): 0,9461
P-values for permutation tests (1000 permutation runs):
Procrustes distance: 0,9630
T-square: 0,9460
Pongo F -- Pongo M
Difference between means:
Procrustes distance: 0,06305566
Mahalanobis distance: 1,5990
T-square: 7,4576, P-value (parametric): 0,9956
P-values for permutation tests (1000 permutation runs):
Procrustes distance: 0,5510
T-square: 0,7720
Fig. 3 Scatter plot of PC1 versus PC2 derived from the PCA of the GM analysis. The ellipses include 95% confidence intervals of the group mean. The 3D models of the distal radial
epiphysis correspond to the individuals at the positive extreme of the PC1 (Gorilla), at the positive extreme of the PC2 (Pongo), and the negative extreme of the PC2 (Pan)
Sexual dimorphism has been studied extensively throughout history through several different approaches. In anatomy studies, much research has been done based on the sexual dimorphism existing in the general morphology of the species.
However, there is a research gap on the difference between males and females in specific anatomical structures associated with certain functions, such as the primates upper limbs. This study aims to explore whether chimpanzees, gorillas, and
orangutans uses of their wrists are different depending on their sex and if those sex-related variations would modify their locomotor behavior. Therefore, sexual dimorphism in the insertion sites of the palmar radiocarpal ligaments amidst several
species of wild hominoid primates was examined.
We have used three-dimensional geometric morphometrics (3D GM) to analyze the distal radius ligament insertion sites in 25 Pan troglodytes, 31 Gorilla gorilla, and 15 Pongo pygmaeus which have been raised in a wild context. We have also
dissected the radioscaphocapitate (RSC), long radiolunate (LRL) and short radiolunate (SRL) ligaments in some species to study their insertion sites. Each distal radial epiphysis, where the two insertion sites of the RSC + LRL and SRL ligaments
are located, was scanned with a 3D Next Engine Ultra HD laser surface scanner, at a resolution of 0.1 mm space-point separation with a density of 40 k (2×) points. We used a set of nine Type II and one Type III landmarks to represent the
morphology of the two insertion sites of the RSC + LRL and SRL ligaments in the distal epiphysis of the radius. The L1–L4 landmarks defined the insertion site of the SRL ligament, while the L5–L10 landmarks define the insertion site of the RSC +
LRL ligaments. The raw data obtained with the Landmark Editor software based on the landmark coordinates were exported into the MorphoJ statistical package. In order to determine the influence of size on variation in shape (allometric scaling),
a multivariate regression analysis (MRA) was performed, with the main principal component, indicative of shape, as the dependent variable and the centroid size (CS), indicative of size, as the independent variable. MorphoJ can carry out
multivariate regressions with a permutation test with 1,000 randomizations and pool the regression within defined subgroups as an external variable, which makes it an ideal procedure when a correction for size between groups. Subsequently, the
differences between the groups were statistically studied using MorphoJ.
Fig. 1 Disection of the palmar radiocarpal ligament in human wrist Fig. 2 Human distal radius