The role of molecular genetics in speciation studies.

Systematists and population geneticists can both use molecular data sets to construct evolutionary trees (species and gene trees, respectively), and then use the resulting historical framework to test a variety of hypotheses. The greatest prospect for future advances in our understanding of speciation is to extend these historical approaches to the species/population interface, for only by straddling this interface can we actually study the processes involved in the origin of a new species. This chapter illustrates how the bottom-up historical approaches used in population genetics can be extended upwards to this critical interface in order to separate the effects of population structure from population history, to rigorously test the species status of a group, and to test hypotheses about the process of speciation by using gene trees to define a nested, statistical analysis of biogeographic and other types of data.