Facial asymmetry tracks genetic diversity among Gorilla subspecies

Mountain gorillas are particularly inbred compared to other gorillas and even the most inbred human populations. As mountain gorilla skeletal material accumulated during the 1970s, researchers noted their pronounced facial asymmetry and hypothesized that it reflects a population-wide chewing side preference. However, asymmetry has also been linked to environmental and genetic stress in experimental models. Here, we examine facial asymmetry in 114 crania from three Gorilla subspecies using 3D geometric morphometrics. We measure fluctuating asymmetry (FA), defined as random deviations from perfect symmetry, and population-specific patterns of directional asymmetry (DA). Mountain gorillas, with a current population size of about 1000 individuals, have the highest degree of facial FA (explaining 17% of total facial shape variation), followed by Grauer gorillas (9%) and western lowland gorillas (6%), despite the latter experiencing the greatest ecological and dietary variability. DA, while significant in all three taxa, explains relatively less shape variation than FA does. Facial asymmetry correlates neither with tooth wear asymmetry nor increases with age in a mountain gorilla subsample, undermining the hypothesis that facial asymmetry is driven by chewing side preference. An examination of temporal trends shows that stress-induced developmental instability has increased over the last 100 years in these endangered apes

Quantifying variation in human dental development sequences: An EVO-DEVO perspective

International audienceThe present paper describes a novel analytical approach to provide a comprehensive description of the complex interactions that exist between the growing permanent mandibular teeth (excluding the third molars), and to quantify variability in sequences of key events during crown and root formation, independent of chronological age. Importantly, our method integrates the fundamental concept of modularity and rejects the old statistical fallacy of analyzing data on the assumption that it contains no information beyond that revealed on a tooth-bytooth analysis. Indeed, interactions between growing teeth may also contain some information, which enables developmental or evolutionary information to be uncovered. Our training sample is based upon cross-sectional standardized panoramic radiographs of the teeth of a total of 2089 children (1206 girls and 883 boys) of different geographic origins (mainly Western Europe, Southern Iran, and Ivory Coast). We observe that, in extant humans sampled so far, the relative development of the permanent incisors is more plastic and varies more than for other teeth. Therefore, we consider that the quantification of possible variations between onsets, durations and rates of development of different teeth in any given child, within a large sample, is a prerequisite to the analysis of fossil hominids. In particular, we seriously question the assumption that the anterior teeth can serve as a reliable substitute for the other permanent teeth, and in particular for interpretations on somatic maturity and brain size. Our hypothesis of modularity in dental development and our method derived from this concept can serve as a basis for identifying and studying patterns of dental growth and, importantly, for comparisons between extant populations, and/or fossil species. These studies do not need to be hedged with age assessments of unknown accuracy and reliability levels (particularly in fossils), or the assumption of independence between growing teeth

Chronologie et étiologie de la maturation macrostructurale des dents définitives

Les deux principaux objectifs de cette thèse sont: (1) utiliser, tester et évaluer la qualité d une méthode d estimation d âge dentaire (Braga et al., 2004) la plus à même de rendre compte des caractéristiques de la maturation macrostructurale des dents définitives, (2) tester à l aide d un questionnaire, spécialement développé dans le cadre de cette étude, les éventuelles incidences d un certain nombre de facteurs biologiques et socioéconomiques sur l estimation de l a ge dentaire. Un échantillon de 863 enfants, recrutés dans le sud de la France, âgés de 3,5 à 16 ans est constitué. L ensemble des sujets est caractérisé par une orthopantomographie et un questionnaire rempli par les parents. Une nouvelle méthode d estimation d âge dentaire basée sur la méthode de codage de Demirjian et al. (1973) et sur le théorème de Bayes (1763) est présentée. Cette méthode respecte l originalité des séquences de minéralisation dentaire et permet, grâce à l emploi de probabilités a priori uniformes, la comparaison de résultats obtenus pour un même échantillon test à partir de deux référentiels distincts. Cette étude confirme l influence du sexe sur l estimation de l âge dentaire. L influence de l origine géographique sur l estimation de l âge dentaire n est quant à elle pas avérée. Il semble néanmoins que l origine géographique soit responsable d une certaine variabilité au niveau des séquences de minéralisation dentaire. Le poids à la naissance, l âge de la mère à la naissance de l enfant, le type d allaitement, le fait, pour la mère, d avoir fumé ou non durant la grossesse, ou encore l âge des premiers pas, n ont pas d influence sur la qualité de l estimation de l âge dentaire. L influence du niveau socioéconomique sur l estimation de l âge dentaire demeure non significative. Néanmoins, les résultats obtenus, notamment pour les filles, semblent indiquer un retard d âge dentaire chez les enfants pauvres relativement aux enfants non pauvres .The aim of this PhD is twice: (1) using, testing and estimating the quality of a dental age assessment method (Braga et al., online first) the best one to describe the macrostructural maturation of permanent teeth, (2) Testing with a questionnaire, specially devised for this study, the potential impact of biological and socioeconomic factors on dental age assessment. Our sample consists of 863 healthy children living in the south of France and aged 3.5 to 16 years. For all these children, we collect their first orthopantomography and a questionnaire filed by their parents. A new dental age assessment method, based on coding devised by Demirjian et al. (1973) and on Bayes theorem (1763), is presented. This method respects the originality of dental mineralization sequences (Bayes Dependent approach) and allows, thanks to the use of uniform prior probabilities, the comparison between the results made with one test sample according to two different reference samples. This study confirms the impact of gender on dental age assessment; the girls are ahead from boys. When Bayes Dependent approach is used, geographic origin has no influence on dental age assessment. Nevertheless, it seems that geographic origin has an impact on dental mineralization sequences. Weight at birth, maternal child s age at birth, type of feeding, maternal smoke habits during pregnancy and age at first steps, have no influence on dental age assessment. The socioeconomic level impact is not significant. Nevertheless, the results for girls show a tendency: poor girls are delayed in dental age in comparison with non poor girls.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

A new 3D morphometric method based on a combinatorial encoding of 3D point confguration: application to skull anatomy for clinical research and physical antropology.

International audienceThree-dimensional (3D) shape analysis of anatomical structures is currently based either on the analysis of distances or angles between landmarks or on the computation of metric parameters which characterize the deformation of landmark configurations. However, significant differences which are not related to the normal inter-individual variation are not only metrical but also "structural". For example, in prognathism, it is a whole subset of landmarks which protrudes relative to another subset, in a correlated way. Such a deformation is not directly emphasized by the variation of the landmark coordinates and this suggests the need for additional 3D morphometric tools. We propose to model the 3D landmark configurations by using the oriented matroid theory, a combinatorial mathematical structure which was developed over the past forty years. Oriented matroids allow one to model the relative positions of points in 3D without taking into account the distances between them. It is then possible to characterize some geometrical properties as the convexity or the alignment of subsets of landmarks and to detect structural changes as the crossing of a landmark through the plane defined by three others. We applied this new method on sets of 133 3D cranial landmarks collected on 43 individuals presenting with varying types of coronal craniosynostosis. We computed the oriented matroid-based models and introduced a new discrete distance between two individuals. The matrix of all the distances allows differentiation among the craniosynostosis variant groups. We will also show how it could be used to compare extant and fossil skulls as STS5