Human Biology Program

Most organisms live in metapopulations, small groups or clusters of breeding individuals distributed across patchy environments. The populational processes of local extinction, recolonization, and interdemic migration have important affects on the evolutionary trajectory of any species with this kind of population genetic structure. Social behaviors and host-pathogen coevolution are two examples evolutionary processes affected by metapopulation structure. Altruistic social behaviors are a novel adaptation that can evolve only in kin-structured populations. For endosymbiotic and pathogenic microorganisms, each host individual can be viewed as a component of the symbionts metapopulation. The co-evolution of hosts and their pathogens and symbionts can only be understood from the perspective of evolution in genetically subdivided populations.

Although coordinated gene interactions (epistasis) are ubiquitous in development of all complex adaptations, epistasis has not yet been incorporated into evolutionary genetic theory. Epistatic gene interactions play a more important role in evolution in metapopulations than they do in evolution in very large, randomly mating populations. Metapopulations facilitate the origin of evolutionary novelties and complex adaptations in two ways: (1) they limit the ability of recombination to break apart gene complexes; and (2) they have unique processes, like interdemic selection, for promoting the spread of epistatic gene complexes. Maternal effect genes are a particularly good and interesting example. Genes with maternal effects play a central role in early development in most metazoans and in reproductive isolation in interspecific hybrids. The evolutionary genetics of maternal effects not only shares the kin-structure of behavioral evolution but also offers unique opportunities for the evolution of epistatic gene interactions between maternal and offspring genotypes.

Sexual selection is one of the strongest and fastest evolutionary processes even though it operates generally in only one sex and in only one life history stage. Owing to strong frequency-dependent selection during reproductive competition, male reproductive polymorphisms, called alternative mating strategies, are common in many organisms. Often they involve switching during male development from one morphology to another.

Both the mating structure of the population and the genetic structure of these male traits are of interest to me.

My students and I pursue this research using a combination of theoretical models, laboratory experimental populations, and natural populations of organisms. The range of projects studied by my doctoral students is very diverse. It includes:

• The genetic basis of female choice of mates in fruit flies;
• The evolution of pollen flow distance in Plantago lanceolata, the common plantain;
• Effects of dispersal on genetic population structure in the Fowler's toad;
• Genetic covariation between inter- and intraspecific competitive ability; and
• The evolution of annual, biannual, and perennial plant life histories.
• The research of most of my doctoral students combines mathematical modeling with field and laboratory experiments.