Phenotypic developmental modularity in living and extinct fishes

对生物和化石形式进化的研究得益于古生物学和进化发育生物学之间的联系。新生物学家和古生物学家现在都把成体生物看作是发育稳定性机制和发育不稳定性之间复杂相互作用的结果。在稳定性过程中，表型模块性由于其在复杂解剖系统进化中的重要性而受到广泛关注。在模块化的各种定义中，模块可以被定义为相互作用的元素的网络，表现为相对独立的开发单元。个体发育过程中大小和形状的高度整合变化已被确定为潜在模块化单位作用的结果（例如，人类头骨和四肢）。另一种类型的个体发生变化对应于软骨化（软骨形成）和骨化（骨形成）的序列，其可以根据（1）元素首次出现的时间，（2）形态单位内的相对时间和（3）形态单位内系列元素之间的形成方向来描述。骨化方向已被用来确定表型发育模块。在鱼类的骨骼中只发现了少数几个模块（例如，背鳍和臀鳍之间的相似性）。本研究将从外部（大小和形状）和内部（骨化和骨化序列）三个层面研究活鱼和化石鱼颅后元素（脊柱和鳍支撑）的表型模块性：（1）个体发育过程中的整合，（2）个体发育与环境之间的整合，（3）个体发育与发育之间的整合。换句话说，我们将解决三个关于发育模块的基本问题：（1）它们在鱼的早期生命阶段是如何形成的？(2)它们是否受到环境因素或压力的影响？（3）我们能追踪它们的进化吗？这项研究计划将有助于了解已经并仍然负责鱼类进化的发育机制，鱼类是最多样化的脊椎动物。

Research on the evolution of living and fossil forms has benefited from the linkage between paleontology and evolutionary developmental biology (evo-devo). Both, neontologists and paleontologists are now viewing adult organism as the result of complex interactions among developmental stability mechanisms and developmental instability. Among the stability processes, phenotypic modularity has been given much attention because of its importance in the evolution of complex anatomical systems. Among the various definitions of modularity, a module could be defined as a network of interacting elements behaving as relatively independent units of development. Highly integrated changes in size and shape during ontogeny have been identified as the result of the action of underlying modular units (e.g., human skull and limbs). Another type of ontogenetic change corresponds to sequences of chondrification (cartilage formation) and ossification (bone formation) that can be described in terms of (1) the time of first appearance of an element, (2) the relative timing within morphological units and (3) the direction of formation among serial elements within morphological units. Direction of ossification has been used to identify phenotypic developmental modules. Only a few modules have been identified in the skeleton of fishes (e.g., the similarity between the dorsal and anal fins). Phenotypic modularity of postcranial elements (vertebral column and fin supports) in living and fossil fishes will be investigated externally (size and shape) and internally (chondrification and ossification sequences) at three levels: (1) integration during ontogeny, (2) integration between ontogeny and environment, and (3) integration between ontogeny and phylogeny. In other words, we will be addressing three fundamental questions about developmental modules: (1) How do they form during the early life stages of a fish?; (2) Are they influenced by environmental factors or stresses?; and (3) Can we track down their evolution? This research program will help to understand developmental mechanisms that have been and are still responsible for the evolution of fishes, the most diversified group of living backboned animals.