Cranial Develpment in Direct-Developing Anurans

在脊椎动物和无脊椎动物中，直接发育是一种进化衍生的生活史模式，在这种模式中，自由生活的水生幼虫阶段已经丧失。这个项目研究了直接发育的无尾两栖动物的颅骨发育模式和机制，以及这些与变态类群的不同之处。实验和描述性方法包括免疫组织化学(定位II型胶原在胚胎中的分布并显示最初的骨骼模式)、扫描电子显微镜(记录神经脊的形态和迁移)、异种移植迁徙前的颅神经脊和颅外胚层(研究作为颅骨组织发育和丧失基础的诱导性组织相互作用)；甲状腺激素和TH阻滞剂的体内给药；TH放射免疫分析(以测量来自母体和胚胎来源的TH的贡献)；以及传统组织学。分析将集中在Eleutherodactylus coqui(Leptodactylidae)，就颅骨发育的祖先变质模式而言，它的个体发育是任何直接发育的无尾两栖动物中最具衍生性的。有关祖先模式的参考数据将从几个系统发育不同的物种中获得，包括东方文昌鱼(Discoglossidae)、非洲爪哇(Xenopus Laevis)和淡水蛙(Rana Piiens)。这些结果将有助于我们理解两栖动物直接发育的基础，以及这一重要的生活史模式是如何演变的。它们还将被用来解决发育和系统生物学中的一系列问题，涉及发育和形态进化之间的关系。这些包括颅型形成机制的进化意义；个体发育模式重塑与异时性的重要性；诱导性组织相互作用的作用；以及胚胎发育的激素调节。最后，它们将允许将两栖动物的直接发育与其他具有复杂生命周期的群体的直接发育进行比较。

Direct development is an evolutionarily derived life history mode in vertebrates and invertebrates in which the free living, aquatic larval stage is lost. This project examines the pattern and mechanisms of cranial development in direct developing anurans, and how these differ from those in metamorphosing taxa. Experimental and descriptive methods include immunohistochemistry (to localize the embryonic distribution of type II collagen and visualize the initial skeletal pattern); scanning electron microscopy (to document neural crest morphology and migration); heterospecific transplantation of premigratory cranial neural crest and cranial ectoderm (to examine inductive tissue interactions that underlie the development, and loss, of cranial tissues); in vivo administration of thyroid hormone and TH- blocking agents; TH radioimmunoassay (to measure the contribution of TH from maternal and embryonic sources); and conventional histology. Analyses will focus on Eleutherodactylus coqui (Leptodactylidae), whose ontogeny is among the most derived of any direct developing anuran with respect to the ancestral metamorphic pattern of cranial development. Reference data concerning the ancestral pattern will be obtained from several phylogenetically diverse species,including Bombina orientalis (Discoglossidae), Xenopus laevis (Pipidae), and Rana pipiens (Ranidae). Results will contribute to our understanding of the basis of direct development in amphibians and how this important life history mode has evolved. They also will be used to address a series of issues in developmental and systematic biology, concerning the relation between development and morphological evolution. These include the evolutionary implication of mechanisms of cranial pattern formation; the importance of ontogenetic repatterning vs. heterochrony; the role of inductive tissue interactions; and the hormonal mediation of embryonic development. finally, they will allow comparison of direct development in amphibians with that in other groups with complex life cycles.