Ongoing Research

More info is available from student and post-doc web pages, and from Doug's Publications or CV

Genetics of Structured Populations
Evolution of Organelle Genomes
Mitochondrial Transmission and Recombination
Invasive Species

Genetics of Structured Populations (or metapopulations):

Our research into metapopulation genetics focuses on two fundamental questions regarding the process of evolution in spatially structured populations. First, what are the forces that generate and destroy population structure? Second, given that there is population structure, how does it affect the process of evolution?

The theory of interconnected populations (metapopulations) has shown that conclusions regarding ecological and evolutionary dynamics derived from single populations can be radically different when considered in a spatial context. Nevertheless there is a deficit of long-term field data on spatially distributed populations to guide and focus this theory. We have been studying the metapopulation biology of the plant Silene latifolia and its associated pathogen, Microbotyrum violaceum for more than 20 years, collecting data on population demographics, sex ratio and disease incidence data in more than 800 populations. This project combines these long-term data with population genetic data to investigate how within population processes (selection, drift) and among population processes (founder effects, gene flow, and inter-demic selection, extinction and recolonization) combine to influence the genetic composition of (and divergence among) demes. Of particular interest is how metapopulation structure may enhance or retard adaptive evolution at different levels of selection.

Evolution of Organelle Genomes

The primary defining characteristic of eukaryotes is the presence of membrane-bound organelles, including mitochondria and plastids, that have retained their own genomes.  Basic cellular processes depend on these genomes and their functional coordination with the nucleus, and understanding how and why organelle genomes are maintained represents a fundamental evolutionary question. 

The rate of mutation has been hypothesized to be a driving force in organelle genome evolution, particularly with respect to genome size and architecture, the functional transfer of genes to the nucleus, and the origins of cyto-nuclear incompatibilities. Within the genus Silene, we have identified a handful of species have experienced recent mitochondrial rate accelerations of >100-fold and remarkably divergent genome structure (genome size, gene content, organization of repeats, RNA editing).  We are using comparative genomics to explore the relationship between mitochondrial genome mutation rate and genome structure, and how these processes affect the relationship between the mitochondrial genome and the nucleus.

Mitochondrial Transmission and Recombination:

In eukaryotes, the genomes of the different cytoplasmic organelles experience very different modes of inheritance. The nuclear genome, for example, is generally inherited bi-parentally with regular recombination. By contrast, mitochondrial genomes are generally assumed to be effectively haploid and undergo little, if any, recombination among genetically distinct partners. These contrasting mechanisms of inheritance are expected to have profound effects on the evolutionary forces shaping the different genomes. 

In angiosperms mitochondrial genomes are typically maternally inherited. However, there are some cases of occasional paternal leakage and subsequent recombination. Just how asexual are mitochondrial genomes and what does this tell us about the different evolutionary forces shaping nuclear and organellar genomes?  This work first involved a collaboration with Maurine Neiman (University of Iowa) where we published several papers on how asexual transmission affects molecular evolution. Now we are collaborating with Dave McCauley (Vanderbilt University) to examine how paternal leakage of organelle genomes may lead to rare but potentially important opportunities for sex and recombination in organelle genomes.

Invasive Species:

A lot of work in our lab involves the plants Silene vulgaris and Silene latifolia. Since these are native to Europe, much of our population genetic work is relevant to the biology of invasions.  Our current research is less active in this area, though we are interested in developing new projects while working our completed experiments into press.

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