Molecular Systematics of Galeomorph Sharks

9707145内勒巨型鲨是现存鲨鱼中分类学上最多样化和最具优势的一类，其中包括许多大型的众所周知的物种，如大白鲨、虎鲨、锤头鲨和鲸鲨。从侏罗纪开始，鲨鱼就拥有丰富的化石记录，这表明鲨鱼是脊椎动物谱系中的一个早期分支。在这项研究中，爱荷华州立大学的加文·奈勒将利用从线粒体和核基因组中获得的DNA序列来研究100多种鲨鱼的系统发育关系，其中包括7个不同目的代表。奈勒将测试这四种体型鲨鱼是否每一种都来自同一个祖先，还将研究每一种体型鲨鱼中不同血统的物种之间的关系。系统发育假说将被用于(I)结合丰富的盖氏形态化石记录来评估鲨鱼特有的许多形态适应的时间或来源，以及(Ii)作为解释丰富的、现有的鲨鱼寄生虫多样性数据库的框架。奈勒还将调查DNA序列在多大程度上形成不同的基因，以及来自同一基因不同区域的DNA序列在同一谱系树上的融合程度。这一分析将提供有关DNA如何随时间变化以及如何从DNA序列数据中改进对谱系树的估计的信息。

9707145 Naylor Galeomorph sharks are the most taxonomically-diverse and dominant group of living sharks, and include many of the large and well known species such as the great white, tiger, hammerhead, and whale sharks. The galeomorphs have an extensive fossil record that extends to the Jurassic, demonstrating that sharks represent an early offshoot in the vertebrate genealogical tree. In this research, Gavin Naylor of Iowa State University will employ DNA sequences acquired from both the mitochondrial and nuclear genomes to study phylogenetic relationships among well over 100 species of sharks, including representatives of seven different orders. Naylor will test whether each of the four orders of galeomorph sharks were derived from a common ancestor, and also will examine relationships among species in several lineages within each galeomorph order. The phylogenetic hypothesis will be used (i) in conjunction with the rich galeomorph fossil record to assess the time or origin of many morphological adaptations unique to sharks, and (ii) as a framework for interpreting the rich, existing database on shark parasite diversity. Naylor also will investigate the extent to which DNA sequence form different genes and from different regions of the same gene converge on the same genealogical tree. This analysis will provide information as to how DNA changes over time and how estimation of genealogical trees from DNA sequence data can be improved.