Dissertation Research: Historical Biogeography and Molecular Phylogenetics of Chamaeleonidae

地球上动植物物种的分布长期以来一直困扰着生物学家，因为经常出现的情况是，密切相关的物种出现在地理上分离的地区，而中间的地区却没有相同的群体成员。随着板块构造理论的出现，可以提出基于大陆漂移的物种分布的新想法，如果有可靠的支持该群体的系统学(进化谱系)，这些假说可以得到理想的检验。随着现代DNA测序工具现在可供系统学家使用，许多动物和植物群体的系统发育可以得到很好的支持，从而提供了测试板块构造事件导致的拟议分布模式的机会。研究生Ted Townsend在教师顾问Allan Larson的指导下，工作的主要目标是利用DNA序列数据构建蜥蜴科Chamaeleonidae的系统发育假说，然后利用这个系统发育图来测试关于该群体的各种生物地理假说。Chamaeleons包括大约130种容易辨认的蜥蜴，分布在非洲、马达加斯加和印度，还有几种分布在欧洲最南端。前三块大陆是南部超大陆冈瓦那的遗迹，根据板块构造理论，冈瓦那在大约1.4亿年前开始解体。一个可靠的查玛龙系统发育将允许对迁徙和谱系分裂的历史模式进行测试，这在传统分类特征的形态研究的基础上迄今是不可能的。来自线粒体基因序列和两个潜在核基因的新证据将有助于构建该小组的系统发育框架，该框架基于从非洲和马达加斯加收集的实地材料以及同事提供的样本和博物馆藏品。

0073323Larson and Townsend The distribution of animal and plant species over the earth has long puzzled biologists, as it often appears that closely related species are found in geographically separated areas while intervening regions are devoid of members of the same group. With the advent of plate tectonic theory, new ideas about species distributions based on continental drift could be formulated, and these hypotheses could ideally be tested if a reliably supported phylogeny (evolutionary genealogy) of the group in question were available. With the modern tools of DNA sequencing now available to systematists, well supported phylogenies can be obtained for numerous groups of animals and plants, providing opportunities to test proposed patterns of distribution resulting from plate tectonic events. The primary goal of work by graduate student Ted Townsend, with guidance from faculty adviser Allan Larson, is to construct a phylogenetic hypothesis for the lizard family Chamaeleonidae using DNA sequence data, and then to use this phylogeny to test various biogeographic hypotheses about the group. Chamaeleons include about 130 species of easily recognizable lizards, distributed in Africa, Madagascar, and India, with a few species ranging into southernmost Europe. The first three landmasses are remnants of the southern supercontinent of Gondwana which, according to plate tectonic theory, began its breakup about 140 million years ago. A reliable phylogeny of chamaeleons would allow tests of historical patterns of migration and of lineage splitting, which has so far not been possible on the basis of morphological studies of traditional taxonomic characters. New evidence from mitochondrial gene sequences and from two potential nuclear genes will help construct a phylogenetic framework for the group, based on field collected materials from Africa and Madagascar and from samples provided by colleagues and museum holdings.