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.
