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Throughout my career, my research in population genetics has focused on problems of the genetics of populations of very small size. Theoretical studies included the investigation of the genetic effects of population bottlenecks, and of the genetic characteristics of populations which are in "non-equilibrium" situations. Non-equilibrium conditions occur in a population when it has undergone recent change(s) in size. These questions formed the focus of a series of five papers that I co-authored with a Japanese colleague, Takeo Maruyama, on the genetic results of changes in populations size, especially changes that can be referred to as "population bottlenecks". More studies were envisioned by both collaborators, but the series was unfortunately cut short by the untimely death of my friend and collaborator. Because of the unique skills which we brought to our collaboration, Dr. Maruyama being a truly accomplished mathematician and myself bringing a biological foundation to our statistical and theoretical studies, I have not found the opportunity to aggressively pursue our unfinished works. However, these analyses laid the basis for research on a different tack, the analysis of natural populations which have undergone some of the changes which we were investigating in our theoretical modeling.
Over the past ten years, the availability of new tools from molecular biology have resulted in the development of highly variable genetic marker systems which allowed an integration between theoretical studies in population genetics of small populations and "experimental" studies of the genetics of natural populations which have undergone the types of changes in size modeled by theory. Because of interests in the theory of small populations, the lab became involved in two seemingly unrelated areas of molecular investigation. Both used molecular techniques to charactize population structure in natural populations. The two divergent areas of laboratory investigation are the genetic study of populations of obligate intracellular microorganisms (members of the Rickettsiaceae), and the genetic study of population structure of endangered species of vertebrates. "Population structure" refers to the factors (population size and migration between populations) which ultimately affect the levels of genetic variability which we can measure using molecular techniques within and between populations. We use the measures of molecular variation to obtain information about population size (current and historical) and about the degree to which migration has connected different geographical parts of a species. This emphasis on population structure is a central approach in the study of conservation genetics.
The study of the genetics of Intracellular bacteria of the genus Rickettsia provided an opportunity to investigate whether the population structure seems to be one in which all bacterial cells within a host behave (at the population level) as if they represent a single "individual", with a bottleneck occurring at each transfer between hosts. To study natural populations of Rickettsia, in addition to developing a set of marker loci, we had to investigate the evolutionary relationships among different "species" of these obligate intracellular forms. This forced us to develop approaches to isolating and sequencing the rRNA genes (prior to development of PCR).
The development of molecular methods to study intracellular bacteria in the genus Rickettsia fortuitously permitted the rapid development of molecular approaches to the study of endangered species of fish. Interests in the genetic theory of small populations, together with success in applying DNA methods to the analysis of population structure in bacteria, led to our involvement in the study of the genetics of captive-bred populations of endangered East African fishes. This developed into a large committment by the laboratory to the study of conservation genetics of fish .
Methods in molecular phylogenetics initially developed for the analysis of species of intracellular bacteria proved to be exceedingly important in research. The methods, which emphasized analysis of the ribosomal RNA genes, resulted in collaborative studies with Gary Floyd and Thomas Byers. Each collaboration initially involved the application of molecular phylogenetic methods similar to those developed for Rickettsia to the study of the evolutionary relationships among forms of green algae (Chlorophyceae) and among protists in or related to the genus Acanthamoeba.