DISSERTATION RESEARCH: Systematics, Colony Form Evolution and Phenotypic Plasticity within the Family Hydrodictyaceae (Sphaeropleales, Chlorophyta)

绿藻（绿藻）包括五个主要类群，存在于海洋和淡水中，以及陆地上的土壤和雪中。它们形态多样，无处不在，但只有17000个物种被定义为这个群体。绿藻的分类是基于形态学的，很少有研究纳入额外的数据来定义物种和评估多样性。外观相似的藻类传统上被归类在一起，但是随着DNA（分子序列数据）的可用性和使用来重建进化关系（系统发育），人们发现形态学在定义物种边界时可能会产生误导，导致对关系的不正确解释和不同的物种名称。这反过来又导致对生物多样性、水质和古指标值的评估不准确，因此非常需要使用多种形式的数据来测试形态物种及其关系。本研究将结合分子和形态学的数据，分析淡水绿藻科（Hydrodictyaceae，吊藻门）的进化关系和物种边界，该科由Hydrodictyon、Pediastrum、Sorastrum和Euastropsis四属组成。为了更好地评估这一群体内的多样性，并测试南北半球物种之间是否存在地理差异，将从澳大利亚收集水螅科的多个物种。将分析从澳大利亚收集的物种的DNA序列，并与从北半球获得的物种进行比较。以计算机为基础的方法将用于分析这些序列并确定这些物种之间的进化关系，结果将构成关于扩散趋势和形态进化的假设的基础。由于已经发现一些淡水绿藻可以由于环境因素（表型可塑性）如营养、光照水平和温度而改变其外观，从而导致不正确的物种定义，因此本项目包括一个改变这些参数的生长实验，以检查用于定义Pediastrum物种的形态特征的稳定性。由于Pediastrum是在化石记录中发现的，并且特定的物种被用来重建过去的湖泊水体生物群落，因此增加地理采样和可塑性知识的结合，将有助于解释形态物种，也可能对依赖这组生物来解释过去湖泊条件的孢粉学家有用。对水藻科分类群形态种的检测和进化关系的解决将有助于更好地理解绿藻的形态进化和整体多样性，而新分离物的收集将大大增加其他研究人员可获得的分类群数量。研究结果还将有助于更好地评估古生态重建的指标值，提高淡水生态系统生物多样性估算的准确性。拟议的研究提供了与澳大利亚科学家合作的机会，其中一位是绿藻超微结构和显微镜方面的专家。此外，这项研究还包括对一名女研究生进行有机生物学几个领域的培训，包括显微镜、分子和培养技术。这些知识将通过对参与生理学研究的学生的教学来传播。

The green algae (Chlorophyta) comprise five major groups that occur in marine and fresh waters, as well as terrestrially in soil and snow. They are morphologically diverse and ubiquitous, yet only 17,000 species have been defined for this group. The classifications within Chlorophyta have been based on morphology, and few studies incorporate additional data to define species and assess diversity. Algae of similar appearance have traditionally been grouped together, but with the availability and use of DNA (molecular sequence data) to reconstruct evolutionary relationships (phylogenies), it has been found that morphology can be misleading when defining species boundaries, resulting in incorrect interpretations of relationships and disparate species designations. This in turn leads to inaccurate assessments of biodiversity, water quality and paleo-indicator value, therefore the need is great to test morphological species and their relationships using multiple forms of data. This study will combine molecular and morphological data to resolve evolutionary relationships and test species boundaries within the freshwater green algal family Hydrodictyaceae (Chlorophyta), which consists of four genera, Hydrodictyon, Pediastrum, Sorastrum and Euastropsis. Multiple species within the Hydrodictyaceae will be collected from Australia to better assess the diversity within this group, and to test whether there is geographic variation between species of the Northern and Southern Hemispheres. DNA sequences will be analyzed from species collected in Australia and compared to those that were obtained from the Northern Hemisphere. Computer-based methods will be used to analyze the sequences and determine the evolutionary relationships between these species and the results will form the basis for hypotheses regarding trends of dispersal and morphological evolution. Because it has been found that some freshwater green algae can change their appearance due to environmental cues (phenotypic plasticity) such as nutrients, light levels, and temperature, and therefore leading to incorrect species definitions, this project includes a growth experiment varying these parameters to examine the stability of the morphological characters used to define species of Pediastrum. Because Pediastrum is found in the fossil record and particular species are used to reconstruct past lake water biotopes, the combination of an increased geographic sampling, and knowledge of plasticity, will assist in the interpretation of morphological species and may also be of use to palynologists who rely on this set of organisms for interpretation of past lake conditions. Testing the morphospecies and resolving the evolutionary relationships of the Hydrodictyaceae taxa will contribute a better understanding of morphological evolution and overall diversity of the green algae (Chlorophyta), and collections of new isolates will greatly expand the number of taxa publicly available to other researchers. Results will also lead to better assessments of indicator value for paleoecological reconstructions and increased accuracy of biodiversity estimates in freshwater ecosystems. The proposed research provides opportunities to collaborate with scientists in Australia, one of which is a specialist in green algal ultrastructure and microscopy. Furthermore, this study involves training of a female graduate student in several fields of organismal biology, including microscopy, molecular and culturing techniques. This knowledge will be disseminated through instruction to students involved in phycological studies.