磨牙形态是由系统发育历史和与食品加工相关的适应过程决定的。咬合面的地形参数,例如锐度和起伏,尤其可以提供有关物种饮食偏好的信息。然而,咬合面可能会因动物一生中的磨损而发生严重改变,从而可能消除其他信号。野生种群(尤其是小型啮齿动物)的年龄很难评估,因此对实验室种群中随年龄变化的磨损进行实验研究可能会成为评估其对臼齿几何形状和地形影响的有效方法,并验证可以缓解这一问题的臼齿形态描述符。因此,使用 3D 几何形态测量和地形估计对四组家鼠的臼齿形态进行量化:野生捕获的小鼠、这些野生小鼠的实验室繁殖后代、典型的实验室小鼠及其杂交小鼠。考虑了磨牙形态的三个描述符:整个磨牙行的表面、第一上磨牙的表面以及模仿高级磨损的第一上磨牙的截断模板。不同群体的磨损随着年龄的增长而增加,在野外捕获的群体中影响更为明显。磨牙列的几何形状不仅会因磨损而改变,还会因咀嚼过程中的负荷而受到迟发磨牙在颌上的相对位置的影响。因此,野生小鼠的臼齿排列发生了改变,显示出野生动物与其实验室培育的后代之间存在质的差异。因此,从实验室获得的结果应谨慎用于解释野生种群的差异。 针对第一上磨牙计算的地形估计似乎提供了比基于整个磨牙行的参数更稳定的参数,因为与沿磨牙行的非平面咬合面相关的问题被丢弃。事实证明,截短的模板可以有效地消除磨损效应,从而专注于遗传差异,从而可以有效地表征野生小鼠和实验室小鼠之间的杂交特征。第一磨牙形状的野生表型的优势支持实验室菌株是在与营养相关的选择压力松弛的背景下进化的。
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Wild versus lab house mice: Effects of age, diet, and genetics on molar geometry and topography
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.