Max-Planck Institute for Evolutionary Biology, Plön, Germany.
Laboratoire d'Écologie des Hydrosystèmes Naturels et Anthropisés (LEHNA), ENTPE, Université de Lyon, Université Claude Bernard Lyon 1, UMR 5023 CNRS, Villeurbanne, France.
J Anat. 2022 Jan;240(1):66-83. doi: 10.1111/joa.13529. Epub 2021 Aug 1.
Molar morphology is shaped by phylogenetic history and adaptive processes related to food processing. Topographic parameters of the occlusal surface, such as sharpness and relief, can be especially informative regarding diet preferences of a species. The occlusal surface can however be deeply modified by wear throughout an animal's life, potentially obliterating other signals. Age being difficult to assess in wild populations, especially small rodents, experimental studies of wear through age in laboratory populations may constitute a powerful way to assess its impact on molar geometry and topography, and to validate descriptors of molar morphology that could mitigate this issue. Molar morphology was therefore quantified using 3D geometric morphometrics and topographic estimates in four groups of house mice: wild-trapped mice, lab-bred offspring of these wild mice, typical laboratory mice, and their hybrids. Three descriptors of the molar morphology were considered: the surface of the whole molar row, the surface of the first upper molar, and a truncated template of the first upper molar mimicking advanced wear. Increasing wear with age was demonstrated in the different groups, with a more pronounced effect in the wild-trapped population. The geometry of the molar row is not only modified by wear, but also by the relative position of the late developing molars on the jaw due to loading during mastication. As a consequence, the alignment of the molars is modified in wild mice, showing a qualitative difference between wild animals and their lab-bred offspring. Results obtained from the lab should thus be transferred with caution to the interpretation of differences in wild populations. Topographic estimates computed for the first upper molar seems to provide more stable parameters than those based on the whole molar row, because issues related to non-planar occlusal surface along the molar row are discarded. The truncated template was proven efficient in discarding the wear effect to focus on genetic differences, allowing an efficient characterization of the hybridization signature between wild and lab mice. Dominance of the wild phenotype for the first molar shape supports that the lab strain evolved in a context of relaxation of the selective pressures related to nutrition.
磨牙形态受系统发育历史和与食物加工相关的适应过程的影响。咬合面的地形参数，如锐利度和凸起度，对于确定物种的饮食偏好特别有用。然而，在动物的一生中，咬合面可能会因磨损而被严重改变，从而可能消除其他信号。在野外种群中，尤其是小型啮齿动物，年龄很难评估，因此通过实验室种群的年龄进行磨损的实验研究可能是一种评估其对磨牙几何形状和地形影响的有力方法，并验证可以减轻此问题的磨牙形态描述符。因此，使用 3D 几何形态计量学和地形估计方法，对 4 组家鼠的磨牙形态进行了量化：野外捕获的老鼠、这些野生老鼠的实验室繁殖后代、典型的实验室老鼠及其杂种。考虑了 3 个磨牙形态描述符：整个磨牙列的表面、第一上磨牙的表面和模仿先进磨损的第一上磨牙的截断模板。在不同的组中都证明了随着年龄的增长而增加磨损，在野外捕获的种群中磨损的影响更为明显。磨牙列的几何形状不仅受磨损影响，还受咀嚼过程中磨牙在颌骨上的相对位置的影响。因此，野生老鼠的磨牙排列发生了变化，野生动物与其实验室繁殖后代之间存在定性差异。从实验室获得的结果因此应谨慎转移到对野生种群差异的解释。对于第一上磨牙计算的地形估计似乎比基于整个磨牙列的参数更稳定，因为沿磨牙列的非平面咬合面相关问题被排除在外。截断模板被证明在消除磨损效果方面非常有效，可以专注于遗传差异，从而有效地描述野生和实验室老鼠之间的杂交特征。第一磨牙形状的野生表型优势支持实验室品系在与营养相关的选择压力放松的环境中进化的观点。
