Dissertation Research: The Speciation Process in Orconectes, subgenus Procericambarus (Decapoda:Cambaridae)

当一个创始成员进入一个新的栖息地时，允许或至少与一个谱系的快速物种形成有关的因素很少被理解。然而，适应性辐射的现象被认为是重要的，多年来已经提出了许多案例。首先需要确定一个基本问题，即辐射组合的物种之间的系统发育关系。关于这一问题的一个测试案例正在对北美小龙虾属进行调查。在北美中部高海拔和低海拔的溪流、池塘和河流边缘，大约有24种Procericambarus亚属，为研究适应新生态栖息地的物种形成模式提供了机会。教授资助人艾伦·坦普尔顿和研究生基思·克兰德尔正在强调从线粒体和核DNA中获得的分子数据，以建立这群动物的系统发育。目前正在特别注意评估这些基于分子的系统发育重建的统计意义的问题，这种统计测试可能对其他研究人员的研究具有普遍适用性。有了可靠的系统发育估计，研究人员就可以探索这样的问题：物种之间的栖息地差异和地理隔离是通过进化时间独立联系在一起的，还是它们与物种形成事件相互作用？过渡到一个非常不同的栖息地类型是否会导致许多随后的物种形成（已故古生物学家g·g·辛普森著名的适应带假说）？只有当物种形成与栖息地分化有关时，物种形成才会发生在孤立的排水系统中吗？此外，研究人员还将研究这些小龙虾在分子系统发育背景下的形态学变化，包括总体大小的减少。

The factors that permit or, at the least, are correlated with rapid speciation of a lineage when a founding member moves into a new habitat are little understood. Yet the phenomenon of adaptive radiation is considered significant, and numerous cases have been proposed over the years. One basic issue at the start needs to be established solidly, that is the phylogenetic relationships among the species of the radiating assemblage. A test case of precisely this matter is under investigation with North American crayfish of the genus Orconectes. Approximately 24 species of the subgenus Procericambarus inhabit a variety of streams, pools, and river margins at high and low elevations in middle North America, and provide opportunities to study the pattern of adaptive speciation into new ecological habitats. Faculty sponsor Alan Templeton and graduate student Keith Crandall are emphasizing molecular data from mitochondrial and nuclear DNA to establish a phylogeny of this group of animals. Special attention is being given to issues of assessing the statistical significance of these molecule-based phylogenetic reconstructions, and such statistical tests are likely to have general applicability to studies by other researchers. With a robust phylogenetic estimate in hand, the investigators can then explore such questions as: are habitat divergence and geographic isolation among species independently associated through evolutionary time or do they interact with speciation events? Does a transition into a very different habitat type lead to much subsequent speciation (the well-known adaptive zone hypothesis of the late paleontologist G. G. Simpson)? Can speciation occur within an isolated drainage only if it is associated with habitat divergence? As well, the investigators will study aspects of morphological change including overall size reduction in these crayfish against the background of their molecularly based phylogeny.