Hammer Christine L, Atukorala A D S, Franz-Odendaal Tamara A
Department of Biology, Mount Saint Vincent University, 166, Bedford Highway, Halifax, Nova Scotia B3M 3J8, Canada.
Department of Biology, Mount Saint Vincent University, 166, Bedford Highway, Halifax, Nova Scotia B3M 3J8, Canada.
Mech Dev. 2016 Aug;141:100-108. doi: 10.1016/j.mod.2016.04.001. Epub 2016 May 26.
Teeth are integrated into the vertebrate oral jaws to provide a functional unit for feeding, however little is known about how this integration occurs during growth and development. The purpose of this study is to identify the ontogenetic changes in oral jaw shape that are associated with the transition of the oral dentition from unicuspid teeth to multicuspid teeth. Here, we compare the shape of the occluding upper (premaxilla) and lower (mandible) jaws of the toothed Mexican tetra (Astyanax mexicanus) and the toothless (oral teeth present, pharyngeal teeth absent) zebrafish (Danio rerio) over development. Gross morphology combined with morphometric analyses were used to analyse shape changes of the occluding oral jaws in each species. Histological analyses were also used to examine the development of the mandibular symphysis.
The occluding edge of the premaxilla is the first region to ossify in the Mexican tetra, but the last to ossify in zebrafish. Morphometric analyses revealed that the early shape of the premaxillae (in fish younger than 8mm SL) is the same in each species but that the premaxilla shape changes significantly at larger sizes. These changes are apparent in the tooth bearing region of the Mexican tetra. The rostral region of the mandible also houses teeth, however ossification and shape in this region were surprisingly similar between species despite differences in the presence of oral dentition. Furthermore, we found that the mandibular symphysis of the Mexican tetra is composed of interdigitating bone, while the symphyseal region of the zebrafish is composed of fibrous connective tissue.
These differences in the jaw skeleton have likely evolved due to different feeding strategies utilised by each species. Our results show that premaxillae shape correlates strongly with the development of complex dentitions unlike in the mandible. This study provides important insights into the relationship between jaw and tooth development in bony fishes and suggests that these mechanisms may be similar amongst vertebrates.
牙齿融入脊椎动物的口腔颌骨，形成一个用于进食的功能单元，但对于这种融合在生长发育过程中如何发生，我们知之甚少。本研究的目的是确定与口腔牙列从单尖牙向多尖牙转变相关的口腔颌骨形状的个体发育变化。在此，我们比较了有齿的墨西哥丽脂鲤（Astyanax mexicanus）和无齿（有口腔牙齿，无咽齿）的斑马鱼（Danio rerio）在发育过程中咬合的上颌（前颌骨）和下颌（下颌骨）的形状。采用大体形态学结合形态测量分析来分析每个物种咬合口腔颌骨的形状变化。还使用组织学分析来检查下颌联合的发育情况。
前颌骨的咬合边缘是墨西哥丽脂鲤中最早骨化的区域，但在斑马鱼中是最后骨化的区域。形态测量分析表明，每个物种中前颌骨的早期形状（体长小于8毫米的鱼）是相同的，但在较大尺寸时前颌骨形状会发生显著变化。这些变化在墨西哥丽脂鲤的牙齿承载区域很明显。下颌骨的吻部区域也有牙齿，然而，尽管口腔牙列存在差异，但该区域的骨化和形状在物种之间惊人地相似。此外，我们发现墨西哥丽脂鲤的下颌联合由相互交错的骨组成，而斑马鱼的联合区域由纤维结缔组织组成。
这些颌骨骨骼的差异可能是由于每个物种采用的不同进食策略而进化而来的。我们的结果表明，与下颌骨不同，前颌骨形状与复杂牙列的发育密切相关。这项研究为硬骨鱼类颌骨和牙齿发育之间的关系提供了重要见解，并表明这些机制在脊椎动物中可能是相似的。
