Adaptive Mechanisms and Evolution (MECADEV), Centre national de la recherche scientifique/Muséum national d'Histoire naturelle, Paris, France.
Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University Cracow, Cracow, Poland.
PeerJ. 2022 Mar 28;10:e13108. doi: 10.7717/peerj.13108. eCollection 2022.
During reach-to-grasp movements, the human hand is preshaped depending on the properties of the object. Preshaping may result from learning, morphology, or motor control variability and can confer a selective advantage on that individual or species. This preshaping ability is known in several mammals ( primates, carnivores and rodents). However, apart from the tongue preshaping of lizards and chameleons, little is known about preshaping of other grasping appendages. In particular, the elephant trunk, a muscular hydrostat, has impressive grasping skills and thus is commonly called a hand. Data on elephant trunk grasping strategies are scarce, and nothing is known about whether elephants preshape their trunk tip according to the properties of their food.
To determine the influence of food sizes and shapes on the form of the trunk tip, we investigated the morphology of the distal part of the trunk during grasping movements. The influence of food item form on trunk tip shape was quantified in six female African savannah elephants (). Three food item types were presented to the elephants (elongated, flat, and cubic), as well as three different sizes of cubic items. A total of 107 ± 10 grips per individual were video recorded, and the related trunk tip shapes were recorded with a 2D geometric morphometric approach.
Half of the individuals adjusted the shape of the distal part of their trunk according to the object type. Of the three elephants that did not preshape their trunk tip, one was blind and another was subadult.
We found that elephants preshaped their trunk tip, similar to the preshaping of other species' hands or paws during reach-to-grasp movements. This preshaping may be influenced by visual feedback and individual learning. To confirm these results, this study could be replicated with a larger sample of elephants.
在伸手抓握动作中，人手会根据物体的特性进行预塑形。预塑形可能源于学习、形态或运动控制的可变性，并为个体或物种带来选择性优势。这种预塑形能力在几种哺乳动物（灵长类动物、食肉动物和啮齿动物）中都有发现。然而，除了蜥蜴和变色龙的舌头预塑形之外，对于其他抓握附肢的预塑形知之甚少。特别是象鼻，作为一种肌肉液压器官，具有令人印象深刻的抓握能力，因此通常被称为手。关于象鼻抓握策略的数据很少，也不知道大象是否会根据食物的特性来预塑象鼻的末端。
为了确定食物大小和形状对象鼻末端形状的影响，我们研究了在抓握动作中象鼻远端部分的形态。通过向六头雌性非洲草原象（）展示三种食物类型（细长形、扁平形和立方体形）以及三种不同大小的立方体形食物，来量化食物形状对象鼻末端形状的影响。每个个体的视频记录了 107±10 次抓握动作，并使用二维几何形态测量方法记录了相关的象鼻末端形状。
一半的个体根据物体类型调整了它们的象鼻远端部分的形状。在没有预塑象鼻末端形状的三头大象中，有一头是盲象，另一头是亚成体。
我们发现大象会预塑它们的象鼻末端形状，类似于其他物种的手或爪子在伸手抓握动作中的预塑形。这种预塑可能受到视觉反馈和个体学习的影响。为了确认这些结果，可以用更大的象群样本重复进行这项研究。
