The influence of skull shape modularity on internal skull structures: a 3D-Pilot study using bears
Pérez-Ramos, Alejandro,Martín-Serra, Alberto,Pérez-Claros, Juan Antonio,Schubert, Blaine W,Pastor, Juan F.,Figueirido-Castillo, Francisco Borja
- Published
- 2015-10-02
- Language
- en
Abstract
In order to capture the phenotypic variation of the internal skull structures, such as the sinuses or the brain, it is necessary to perform CT scans in a large number of specimens, which is difficult and expensive. Therefore, while the external morphology of the mammalian cranium has been the subject of many morphometric studies, the internal structures of the cranium have been comparatively less studied. Here, we explore how the variation of external shape reflects the morphology of internal structures. We use the family Ursidae (Carnivora, Mammalia) as a case study because bears have a wide variability of cranial morphologies in part associated with different trophic ecologies. To do this, we digitized a set of landmarks in 3D with a Microscribe G2X from the external surface of the cranium in a wide sample of bears. Additionally, the crania of seven bear species were CT-scanned and prepared digitally to visualize the 3D models of the external cranium morphology and of internal structures. Subsequently, we divided the landmarks into two modules, splanchnocranium and neurocranium, and we perform a two-block partial least squares analysis (2B PLS) to explore the intraspecific (static) morphological changes associated with the covariation between them. These morphological changes were visualized using the morphing technique with the 3D models, looking at both the external shape and the internal structures. In addition, we inferred the volume of the sinuses and of the brain in each hypothetical model. Our results show that the first two PLS axes are associated externally with changes in the basicranial angle, face length and cranium height and width. Concerning the internal structures, there are parallel changes in dorso-ventral and medio-lateral expansion of sinuses and brain, accompanied by their corresponding changes in volume. In contrast, the third PLS axis is related to opposite changes in the volume of sinuses and brain. These preliminary results suggest that the opposite relationship between sinuses and brain volumes in the bear cranium is not as evident as expected, at least at intraspecific level.
Full text
THE INFLUENCE OF SKULL SHAPE MODULARITY ON INTERNAL SKULL STRUCTURES: A 3D-PILOT STUDY USING BEARS! Alejandro Pérez-Ramos, Alberto Martín-Serra, Juan A. Pérez-Claros, Blaine W. Schubert, Juan F. Pastor & Borja Figueirido! 1!1!1!2!3!1! 1:Departamento de Ecología y Geología; Facultad de Ciencias; Universidad de Málaga; 29071-Málaga (Spain); 2:East-Tenesse University, Johnson City, TN, USA; 3:Department of Anatomy, Universidad de Valladolid, Valladolid, (Spain).! ! ! The internal skull structures, such as the sinuses or the brain are usually studied using CT scans.! ! Therefore, the morphology of these internal structures have been comparatively less studied than the external morphology of the skull.! ! We explore sinuses and brain shape variation related to external skull shape modularity and we assess if these internal structures of the skull could be studied analyzing solely the external shape! ! We use the family Ursidae (Carnivora, Mammalia) as study case! INTRODUCTION! MATERIAL & METHODS! RESULTS & DISCUSSION! We digitized a set of landmarks in 3D with a Microscribe G2X! ! The skulls of seven bear species were CT-scanned ! ! We divided the landmarks in two modules (splanchnocranium and neurocranium) following previously published articles! ! We perform a 2B-PLS to explore the intraspecific (static) morphological changes in the skull of bears with the software MorphoJ! ! The external changes plus the associated variation for the sinuses and the brain accounted for the first three PLS axes were visualized by creating 3D models at the extremes of each axis using the morphing technique in the software Landmark (IDAV)! ! Models for the external shape plus the sinuses and the brain for each axis were created with each of the seven CT scans to explore if the associated internal shape variation depends on the CT scan used! ! We also calculated the volumes of the sinuses and the brain for each hypothetical morphology! The MODULARITY TEST indicates that the neurocranium and the splanchnocranium are two real modules in each bear species ! 1 ! 2 ! SINUSES!BRAIN! Landmarks digitized! RV coefficient = 0.294 ; P = 0.0078! Lateral!Dorsal!Frontal! Lateral!Dorsal!Ventral! PLS I! Lateral!Dorsal!Frontal! Lateral!Dorsal!Ventral! PLS 2!PLS 3! THE 2B-PLS ANALYSIS reveals that the three first PLS axes are associated externally with changes in basicranial angle, face length and skull height and width. The associated changes in the sinuses and the brain with these external shape variation, using a CT of a brown bear, are shown below as an example! 3! CONCLUSIONS! THE ESTIMATED VOLUMES OF THE SINUSES AND THE BRAIN USING THE CT SCAN FOR EACH BEAR SPECIES FOLLOW THE SAME TREND IN EACH PLS AXIS! ! This indicates that changes in the internal structures associated with the external shape do not depend on the CT scan used to create the 3D models of the extreme shapes in each PLS axis! We can extend morphological interpretations of external skull shape modularity to internal structures! ! In this particular case we have obtained that the external shape variation accounted for the first two PLS axes is accompanied by parallel changes in volume expansion of sinuses and brain. However, the third PLS axis account for an opposite trend in the volume expansion of sinuses an brain! Lateral!Dorsal!Ventral! Lateral!Dorsal!Frontal! +! -! +! -! +! -!
