1 Phylogeography

Phylogeography comparable studies in plants often focus on another cytoplasmic genome ± chloroplast DNA (cpDNA) ± J C Avise rather than mtDNA. A future challenge for the field Copyright ß 2001 Academic Press of phylogeography centers on developing comparable doi: 10.1006/rwgn.2001.1470 genealogical methods for autosomal genes, a task made more difficult by a slow evolutionary pace for Avise, J C many nuclear DNA sequences and by the likelihood Department of Genetics, University of Georgia, of historical intragenic recombination. Athens, GA 30602-7223, USA Comparative studies in molecular phylogeography have revealed the following: (1) Most species are composed of geographic populations whose mem- The science of phylogeography is concerned with bers occupy recognizable phylogenetic branches in the principles and processes governing the geographic a matrilineal tree; (2) exceptional cases (in which distributions of genealogical lineages, especially those phylogeographic population structure is minimal or at the intraspecific level. The word itself was coined nonexistent) usually involve highly vagile organisms, in 1987, but the discipline's intellectual development and/or species that have occupied historically continu- began early in the century with studies of the popu- ous ranges; (3) historical population separations can lation dynamics of surname turnover in human range from temporally shallow to deep; and (4) pro- societies. The statistical and mathematical sides of nounced phylogenetic gaps often observed between phylogeography have developed in recent years into regional populations usually appear to have resulted what is now termed coalescent theory, which addres- from long-term biogeographic barriers to gene flow. ses how, as functions of population demography, Molecular phylogeographic patterns also are highly lineages trace back in time through extended pedigrees relevant to conservation biology and to an under- to common ancestors. standing of speciation processes. On the empirical side, phylogeographic analyses In broad terms, the most important contributions have been motivated primarily by molecular genetic of phylogeography to evolutionary analysis have appraisals of animal mitochondrial DNA (mtDNA). been to: (1) emphasize the historical, nonequilibrium Because this molecule evolves rapidly and is mater- aspects of microevolutionary change, (2) clarify the nally inherited without recombination, it provides tight connections between population demography a chronicle of matrilineal relationships within and and genealogy, and (3) build empirical and conceptual among related species. Thus, phylogenetic analyses bridges between the nominally separate fields of of mtDNA variants can be used to estimate the exten- population genetics and phylogenetic biology. ded matrilineal component of an organismal pedigree in much the same way that family surnames in many Further Reading human societies traditionally record patrilineal his- Avise JC (1999) Phylogeography: The History and Formation of tories. Unlike surnames, however, the mitochondrial Species. Cambridge, MA: Harvard University Press. genetic archives extend much farther back in time and in principle can be recovered from nearly any See also: 1016, 0995 multicellular animal species. For technical reasons,