DISSERTATION RESEARCH: Innovation and constraint: the evolution of power-amplified feeding in syngnathiform fishes

Syngnathiformes（海马、管鱼、喇叭鱼及其亲戚）是一组具有不同寻常和新颖的运动、繁殖和觅食模式的鱼类。几乎所有的物种都有一个细长的鼻子，它们在捕食时旋转着鼻子朝向猎物。最近的研究表明，海马和管鱼利用功率放大来实现极快的旋转，这使得它们的撞击速度在所有鱼类中名列前茅（不到2.5毫秒）。本研究将重建这种机械极端摄食机制的顺序进化装配，并将研究这种摄食机制对头部形状多样性的影响。这项工作的发现将推进关于复杂结构-功能关系如何演变和影响后续结构演变的知识。该研究将产生一套系统发育树，揭示200多个合甲状物种之间的进化关系。这些将是宝贵的资源，并与其他研究人员分享，以推进对这种独特而不寻常的鱼类群体的进化史的了解。这项研究的其他数据和产品，包括慢动作视频，将通过纳入加州大学戴维斯分校的现有课程和YouTube，让广大观众了解鱼类喂养策略的多样性。除了形成一篇雄心勃勃的综合博士论文外，这项研究还将涉及对从事STEM相关领域感兴趣的本科生，通过实践培训和经验。本研究将从利用现代杂交富集（超保守元件，UCEs）和下一代测序技术推断系统发育（目标#1）开始，研究合甲状鱼类机械极端和复杂摄食机制的进化。先前的研究表明，海马和管鱼利用力量放大来旋转头部，使其朝向猎物的速度比直接肌肉激活更快。有人提出，这种机制依赖于头骨上一个独特的中枢关节。形态学和功能方法的结合，包括高速视频、生物力学建模和微型ct扫描，将用于表征和比较与海马和管鱼相关的谱系的进食功能形态学（目标#2）。目标#1的系统发育将用于重建合颌形鱼类力量放大进食所需的结构和功能变化的进化史，并测试关于拥有这种特殊机制如何影响合颌形鱼类头部形状进化的假设（目标#3）。将连续特征进化模型拟合颅面形态数据，并在软件程序OUwie中进行比较，以验证功率放大的占有对颅面形态具有较强的稳定选择的假设。虽然文献关注的是增加多样性的创新，但这项工作结合了一种模型测试方法，以确定这种新的摄食机制是否会在宏观进化时间尺度上限制形态多样化。

Syngnathiformes (seahorses, pipefishes, trumpetfish and relatives) are a group of fishes with unusual and novel modes of locomotion, reproduction, and feeding. Nearly all species are characterized by an elongated snout, which they rotate towards prey during feeding strikes. Recent research has shown that seahorses and pipefish are using power amplification to achieve extremely fast rotations, resulting in strikes that are among the fastest recorded for any fish (less than 2.5 milliseconds). This research will reconstruct the sequential evolutionary assembly of this mechanically extreme feeding mechanism and will investigate the consequences of this feeding mechanism on head shape diversity. The findings of this work will advance knowledge about how complex structure-function relationships evolve and influence subsequent structural evolution. The study will produce set of phylogenetic trees that reveal the evolutionary relationships among over 200 syngnathiform species. These will be a valuable resource and shared with other researchers to advance knowledge of the evolutionary history of this unique and unusual group of fishes. Other data and products from this research, including slow-motion videos, will engage a wide audience in the diversity of fish feeding strategies by incorporation into existing coursework at the University of California, Davis and through YouTube. In addition to forming an ambitious and integrative doctoral dissertation, this research will involve undergraduates interested in pursuing STEM related fields through hands-on training and experience. This research will investigate the evolution of a mechanically extreme and complex feeding mechanism in syngnathiform fishes, beginning with the inference of a phylogeny using modern hybrid-enrichment (ultraconserved elements, UCEs) and next-generation sequencing technologies (Objective #1). Previous research has shown that seahorses and pipefish use power amplification to rotate their head towards prey faster than would be possible by direct muscle activation, and it has been proposed that this mechanism relies on a unique pivot joint in the skull. A combination of morphological and functional approaches including high-speed video, biomechanical modeling, and micro-CT scanning will be used to characterize and compare the feeding functional morphology of lineages related to seahorses and pipefish (Objective #2). The phylogeny from Objective #1 will be used to reconstruct the evolutionary history of the structural and functional changes necessary for power-amplified feeding in syngnathiform fishes and to test hypotheses about how the possession of this specialized mechanism has influenced the evolution of head shape in syngnathiforms (Objective #3). Models of continuous character evolution will to be fit to craniofacial shape data and compared in the software program OUwie to test the hypothesis that the possession of power amplification exerts strong stabilizing selection on craniofacial morphology. While the literature focuses on innovations that increase diversity, this work incorporates a model-testing approach to determine whether this novel feeding mechanism may constrain morphological diversification at macroevolutionary timescales.