Cane genealogies and population variation in plants

Early in the development of plant evolutionary biology, genetic drift, fluc tuations in population size, and isolation were identified as critical proc esses that affect the course of evolution in plant species. Attempts to ass ess these processes in natural populations became possible only with the de velopment of neutral genetic markers in the 1960s. More recently, the appli cation of historically ordered neutral molecular variation (within the conc eptual framework of coalescent theory) has allowed a reevaluation of these microevolutionary processes. Gene genealogies trace the evolutionary relati onships among haplotypes (alleles) with populations. Processes such as sele ction, fluctuation in population size, and population substructuring affect the geographical and genealogical relationships among these alleles. There fore, examination of these genealogical data can provide insights into the evolutionary history of a species. For example, studies of Arabidopsis thal iana have suggested that this species underwent rapid expansion, with popul ations showing little genetic differentiation. The new discipline of phylog eography examines the distribution of allele genealogies in an explicit geo graphical context. Phylogeographic studies of plants have documented the re colonization of European tree species from refugia subsequent to Pleistocen e glaciation, and such studies have been instructive in understanding the o rigin and domestication of the crop cassava. Currently, several technical l imitations hinder the widespread application of a genealogical approach to plant evolutionary studies. However, as these technical issues are solved, a genealogical approach holds great promise for understanding these previou sly elusive processes in plant evolution.