Ants are crucial ecosystem engineers, and their ecological success is facilitated by a division of labour among sterile “workers”. In some ant lineages, workers have undergone further morphological differentiation, resulting in differences in body size, shape, or both. Distinguishing between changes in size and shape is not trivial. Traditional approaches based on allometry reduce complex 3D shapes into simple linear, areal, or volume metrics; modern approaches using geometric morphometrics typically rely on landmarks, introducing observer bias and a trade‐off between effort and accuracy. Here, we use a landmark‐free method based on large deformation diffeomorphic metric mapping (LDDMM) to assess the co‐variation of size and 3D shape in the mandibles and head capsules of Atta vollenweideri leaf‐cutter ants, a species exhibiting extreme worker size‐variation. Body mass varied by more than two orders of magnitude, but a shape atlas created via LDDMM on μ‐CT‐derived 3D mesh files revealed only two distinct head capsule and mandibles shapes—one for the minims (body mass < 1 mg) and one for all other workers. We discuss the functional significance of the identified 3D shape variation, and its implications for the evolution of extreme polymorphism in Atta.

中文翻译：

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3D形状变化的大变形微分异形映射揭示了Atta vollenweideri切叶工蚁的两种不同的下颌骨和头囊形态

蚂蚁是重要的生态系统工程师，它们的生态成功得益于不育“工人”之间的分工。在一些蚂蚁谱系中，工蚁经历了进一步的形态分化，导致身体大小、形状或两者都有差异。区分大小和形状的变化并非易事。基于异速生长的传统方法将复杂的 3D 形状简化为简单的线性、面积或体积度量；使用几何形态测量学的现代方法通常依赖于地标，引入观察者偏差以及努力和准确性之间的权衡。在这里，我们使用基于大变形微分同形度量映射 (LDDMM) 的无界标方法来评估下颌骨和头囊的尺寸和 3D 形状的协变。阿塔·沃伦韦德里切叶蚁，一种表现出极端工蚁体型变化的物种。体重变化超过两个数量级，但通过 LDDMM 在 μ-CT 衍生的 3D 网格文件上创建的形状图集仅显示两种不同的头囊和下颌骨形状 - 一种是迷你型动物（体重 < 1 毫克），另一种是迷你型动物（体重 < 1 毫克）对于所有其他工人。我们讨论了已识别的 3D 形状变异的功能意义及其对极端多态性进化的影响阿塔。