Dissertation Research: The Effect of Miniaturization on Skeletal Morphology in Frogs

[00:73061]小型化是动物谱系中异常小的身体尺寸的进化。它具有广泛的生态学和生理学的特征，以及形态学的含义。它已经在多种动物中进化，包括所有主要的脊椎动物群体。小型化为研究形态的演变提供了独特的机会。在小型化中，形态进化与发展模式和机制之间存在着联系。这是由于观察到小型化通常是通过发育的早熟截断来实现的，从而导致幼体发育，即在后代物种的成年物种中保留了祖先物种的幼年特征。由于青蛙的小型化进化了无数次，并且在这个群体中也达到了令人印象深刻的极端，某些种类的青蛙被包括在现存最小的脊椎动物中，青蛙是研究小型化对形态进化影响的理想群体。研究生Jennifer Yeh，在David Cannatella博士的指导下，正在对青蛙的许多谱系的小型化进行比较，在它们的系统发育亲缘关系的背景下。首先，将小型化物种的骨骼与密切相关的大型物种的骨骼进行比较，以便通过标准测量和计算机辅助薄板样条分析来记录形态变化的一般模式。初步数据表明，小型青蛙偶尔会在发育后期骨化而失去骨骼。此外，对头骨形状的分析表明，许多小型化物种与它们的大型亲戚相比，表现出特定的差异，例如相对较大的脑壳和感觉囊。这些模式表明，功能需求约束了形态对尺寸减小的响应。其次，将研究发育截断在多大程度上解释小型化青蛙的形态模式。与小型化相关的进化模式将与物种内发育和生长特征的形态变化进行比较。最后，在不同的青蛙谱系中，形态学对小体型进化的反应程度的变化将被评估。

0073061Cannatella and Yeh Miniaturization is the evolution of unusually small body size within a lineage of animals. It has broad implications for features of ecology and physiology, as well as morphology. It has evolved in a taxonomically diverse array of animals, including all the major groups of vertebrates. Miniaturization offers unique opportunities for investigating the evolution of morphology. In miniaturization, there is an area of contact between morphological evolution and the patterns and mechanisms of development. This results from the observation that miniaturization is often achieved via a precocious truncation of development, resulting in paedomorphosis, the retention of juvenile features of an ancestral species in the adult of the descendant species. Because miniaturization has evolved numerous times in frogs, and has also reached impressive extremes in the group, with certain frog species included among the tiniest extant vertebrates, frogs make an ideal group in which to study the effects of miniaturization on morphological evolution. Graduate student Jennifer Yeh, under the direction of Dr. David Cannatella, is making a comparison of miniaturization across numerous lineages of frogs, in the context of their phylogenetic affinities. First, the skeletons of miniaturized species will be compared to those of closely related larger species in order to document general patterns of morphological change, both from standard measurements and from computer-assisted thin-plate spline analyses. Preliminary data suggest that miniaturized frogs occasionally lose bones which ossify late in development. In addition, analyses of skull shape indicate that many miniaturized species show specific differences compared to their largerrelatives, such as relatively larger braincases and sensory capsules. These patterns suggest that functional requirements constrain the response of morphology to size reduction. Second, the extent to which developmentaltruncation explains morphological patterns in miniaturized frogs will be investigated. Evolutionary patterns associated with miniaturization will be compared to the within-species morphological changes that characterize development and growth. Finally, variation in the degree to which morphology has responded to the evolution of small body size in different frog lineages will be assessed.