Collaborative Research: Segment development in select trilobite species - glimpses into the evolution of body organization in an early arthropod clade

合作研究：三叶虫物种的节段发育”早期节肢动物分支的身体组织进化[j] .徐志强，加州大学河滨分校，ei: 0616574h。发育遗传学和细胞生物学的最新进展正在彻底改变人们对动物形态发育基础的认识。在包括所有现存节肢动物类群的真节肢动物中，身体节段（即节肢动物机体构成的模块）被指定和分化的机制正在逐渐为人所知。已灭绝的进化支三叶虫也属于真节肢动物，但就其身体模式的控制而言，并没有明显偏离祖先的真节肢动物状态。因此，早古生代岩石中保存完好的三叶虫个体发育和系统发育记录，作为早期真节肢动物身体模式实验的编年史，具有特殊的意义。志留系aulacopleurakonincki三叶虫已被证明是一个特殊的模型系统，用于探索三叶虫如何控制分配给躯干区域的节段数量，以及它们如何控制将躯干节段分配给胸腔或胸肌（由连体节段组成的终端盾）。在成熟的、节段不变的生长阶段，科宁基胸椎体的胸椎节数发生了不寻常的变化。PI Hughes之前的工作已经测试了关于成熟片段数量控制的假设，结果支持早期决定假设（EDH），其中最终片段数量在个体发育早期决定。这表明，在早期节肢动物中，即使是那些在身体结构方面明显具有可塑性的动物，也有高度调控的发育控制。然而，确定一个4.35亿年前的物种的发育控制是一项严峻的挑战。该项目将探索硬膜形状变化的个体发生轨迹，主要基于独立于躯干分割的头（头）区域的形状变化模式，为EDH提供额外的测试。并通过地球化学代理方法探讨了分割变化的古环境背景。该项目将涉及研究生培训和与捷克共和国、意大利和加拿大科学家的广泛合作，并将涉及开发新的统计软件，这些软件将免费提供给科学界。

Collaborative Research: Segment development in select trilobite species"glimpses into the evolution of body organization in an early arthropod cladeNigel C. Hughes, U. California Riverside, EAR-0616574H. David Sheets, Canisius College, EAR-0616726ABSTRACTRecent advances in development genetics and cell biology are revolutionizing understanding of the developmental basis of animal form. The mechanisms by which body segments, the modules from which arthropod bodies are constructed, are specified and differentiated are becoming known across members of the crown group Euarthropoda, which contains all living arthropod groups. The extinct clade Trilobita also belonged to the Euarthropoda but with respect to the control of its body patterning did not depart markedly from what was apparently the ancestral euarthropod condition. Hence the exceptionally well-preserved record of trilobite ontogeny and phylogeny recorded in early Paleozoic rocks assumes special significance as a chronicle of early euarthropod experiments in body patterning. The Silurian aulacopleurid trilobite Aulacopleura konincki has proved to be an exceptional model system for exploring how trilobites controlled the number of segments assigned to the trunk region and the controls on their allocation of trunk segments to the thorax or to the pygidium - the terminal shield consisting of conjoined segments. Aulacopleura konincki shows unusual variation in the number of thoracic segments during the mature, segment-invariant growth phase. Previous work by the PI Hughes has tested hypotheses concerning control of the mature segment number, with results favoring the Early Determination Hypothesis (EDH), in which the ultimate number of segments was determined early in ontogeny. This suggests highly regulated developmental control among early arthropods, even those apparently plastic in aspects of body construction. However, determining the controls of development in a species 435 million years old presents a severe challenge. This project will explore ontogenetic trajectories of sclerite shape change to provide additional tests of the EDH, based primarily on the pattern of shape change in the cephalic (head) region that is independent of trunk segmentation. The paleoenvironmental context of changes in segmentation will also be explored through a geochemical proxy approach. The project will involve graduate student training and extensive collaboration with scientists in the Czech Republic, Italy, and Canada, and will involve the development of new statistical software that will be made freely available to the scientific community.