Institute of Zoology and Evolutionary Research, Friedrich-Schiller-University of Jena, Erbertstrasse 1, 07743 Jena, Germany
Institute of Zoology and Evolutionary Research, Friedrich-Schiller-University of Jena, Erbertstrasse 1, 07743 Jena, Germany.
J Exp Biol. 2019 Mar 21;222(Pt 6):jeb189886. doi: 10.1242/jeb.189886.
Food processing refers to any form of mechanical breakdown of food prior to swallowing. Variations of this behaviour are found within all major gnathostome groups. Chewing is by far the most commonly used intraoral processing mechanism and involves rhythmic mandibular jaw and hyobranchial (tongue) movements. Chewing occurs in chondrichthyans (sharks and rays), actinopterygians (ray-finned fishes), dipnoi (lungfishes) as well as amniotes and involves similarities in the patterns of muscle activity and movement of the feeding apparatus. It has been suggested that amniote chewing, which involves the interaction of movements of the mandibular jaw and the muscular tongue, has evolved as part of the tetrapod land invasion. However, little is known about food-processing mechanisms in lissamphibians, which might have retained many ancestral tetrapod features. Here, we identified a processing mechanism in the salamandrid newt, , which after prey capture displays cyclic head bobbing in concert with rhythmic jaw and tongue movements. We used high-speed fluoroscopy, anatomical reconstructions and analyses of stomach contents to show that newts, although not using their mandibular jaws, deploy a derived processing mechanism where prey items are rasped rhythmically against the dentition on the mouth roof, driven by a loop motion of the tongue. We then compared patterns and coordination of jaw and tongue movements across gnathostomes to conclude that food processing in this newt species shares traits with processing mechanisms in fish as well as amniotes. This discovery casts salamanders as promising models for reconstructing the evolution of intraoral processing mechanisms at the fish-tetrapod split.
食品加工是指在吞咽之前对食物进行的任何形式的机械破坏。这种行为的变化在所有主要的颌口动物群体中都有发现。咀嚼是迄今为止最常用的口腔内加工机制，涉及节律性下颌颌骨和咽（舌）运动。咀嚼发生在软骨鱼类（鲨鱼和鳐鱼）、硬骨鱼类（硬骨鱼类）、肺鱼（肺鱼）以及羊膜动物中，涉及到摄食器官肌肉活动和运动模式的相似性。有人认为，羊膜动物的咀嚼，涉及到下颌颌骨和肌肉舌的相互作用，是作为四足动物陆地入侵的一部分进化而来的。然而，对于有尾两栖动物的食物加工机制知之甚少，它们可能保留了许多祖先四足动物的特征。在这里，我们在蝾螈新物种中发现了一种加工机制，在捕获猎物后，它会与节律性的颌骨和舌运动一起进行周期性的头部点头。我们使用高速荧光透视术、解剖重建和胃内容物分析表明，蝾螈虽然不使用下颌颌骨，但会部署一种衍生的加工机制，即在口腔顶部的牙齿上有节奏地刮擦猎物，由舌的环运动驱动。然后，我们比较了颌骨和舌运动的模式和协调性在颌口动物中，得出结论，这种新物种的食物加工与鱼类以及羊膜动物的加工机制具有共同特征。这一发现使蝾螈成为重建鱼类与四足动物分裂时口腔内加工机制进化的有前途的模型。
