[I am currently reworking this slightly outdated statement -- CD 7/16/96]
I am interested in high-level phylogeny, with special emphasis on two basic problems: the nature of the green algal lineage that gave rise to land plants, and the origin and evolution of chloroplasts and their genomes. Because protists, including algae, are an artificial group defined primarily by their structural simplicity, relatively few structural characters are available for phylogenetic analysis. For this reason, the recent development of molecular systematics has had an especially large impact on the study of protist evolution.
Land plants, or 'embryophytes' are thought to be derived from the green algal class Charophyceae, but the Charophyceae are a diverse and relatively little-studied group. As a consequence many of the properties of the algal ancestor of plants remain obscure. There are three large orders in the Charophyceae: the Coleochaetales, the Charales, and the Zynematales. Understanding each of these orders is important if a reliable picture of the origin of land plants is to be developed. I have worked most extensively on the order Coleochaetales, including the genera Coleochaete and Chaetosphaeridium. By studying cell division, cell wall composition, sexual reproduction, plastid structure, biochemistry and molecular biology of these taxa and comparing them to other charophytes and to land plants I hope to identify critical features of the algal ancestor of land plants.
There are also many unanswered questions concerning plastid evolution. Plastids are endosymbiotic organelles derived from previously free-living cyanobacteria (also known as 'blue-green algae'). During the course of evolution, most of the original cyanobacterial genome has been lost from the chloroplast. Some genes have been transferred to the nuclear genome or undergone functional substitution by cytosolic homologs, while others have been lost, probably because they are no longer needed in a symbiotic environment. One of my primary interests is in understanding how the chloroplast has become genetically and developmentally integrated into the host cell. Many surprising evolutionary processes have occurred during plastid evolution, including horizontal gene transfer, ancient gene duplication, and the extreme reduction of plastids to barely recognizable form in parasitic taxa including the malarial parasite Plasmodium.
In addition, many algae have plastids that were acquired via an endosymbiotic event that involved two eukaryotes, one of which had already acquired a plastid, giving rise to a secondary plastid. Some taxa, such as Cryptomonas and Chlorarachnion have two eukaryotic nuclei, with one of these highly reduced in size and gene content. Other taxa, such as brown algae and diatoms, seem to have secondary plastids but have completely lost the second eukaryotic nucleus. It is clear that there have been several secondary endosymbioses, but there may have been as few as one primary endosymbiotic event. The similarities and differences among these different kinds of plastids, including the products of both primary and secondary endosymbioses, can give insight into the processes that underlie evolution.
Updated 6/8/96 - CFD