Phylogeography: The History and Formation of Species

Abstract

Phylogeography: The History and Formation of Species. John C. Avise. Harvard University Press, Cambridge, Massachusetts, 2000, viii + 447 pp., $49.95, (ISBN 0-674-66638-0). Breakthroughs in DNA sequencing technology in the 1980's revolutionized evolutionary biology, and out of this revolution emerged what has become a highly influential discipline known as phylogeography. Formally introduced a little more than a decade ago by John Avise and his colleagues (Avise et al., 1987), phylogeography is a highly integrative approach used to investigate the relationship between earth history, ecology, and biotic diversification. Phylogeography combines information from population genetics, phylogenetics, geoclimatic history, paleontology, population biology, molecular evolution, and historical biogeography in order to characterize the geographic distributions of genealogical lineages across the geographic landscape (referred to as phylogeographic patterns), and to infer the evolutionary, demographic and biogeographic processes that have shaped these patterns. In this book, Avise provides an overview of the historical development of phylogeography, from its early stages when animal mitochondrial DNA (mtDNA) was used (almost exclusively) to examine phylogeographic patterns within single species, to today, when an increasingly wider range of additional molecular markers are being used to compare phylogeographic patterns among co-distributed taxa (comparative phylogeography). As the principle founder of the field, no one is better qualified to write a book recounting the history of phylogeography, and Avise excels at providing examples and figures to illustrate the key concepts which lie at the heart of the discipline. In particular, many of the previously unpublished figures in the first half of the book are exceptionally well done and informative. The book is divided into 3 sections, each containing 2 chapters (plus a preface and works cited), and is filled with over 100 figures. The first section of the book concentrates on the history and conceptual background of phylogeography, and includes a chapter on coalescence and the connection between population phylogeny and demography. This is perhaps the strongest section of the book, and serves as a great primer for beginning graduate students and non-specialists. This section also provides a wealth of information and examples for those interested in teaching principles of phylogeography. The second section reviews empirical studies that have examined phylogeographic patterns at the intraspecific level, and is divided into one chapter on humans and one on non-human animals. As such, this section reviews much of the early empirical work in phylogeography. Relative to humans, non-human animals tend to have deeper (older) phylogeographic subdivisions, and it is here that Avise compares and contrasts the phylogeographic patterns that have been observed in a variety of organisms. These cross-taxon comparisons are facilitated by Avise's division of types of phylogeographic structure into 4 basic categories (of which more than one can occur within a given species' overall gene tree). Special attention is given to different expected and observed patterns of phylogeographic subdivision as they relate to life history traits, such as those associated with dispersal ability. The final section deals with comparative studies and the issue of genealogical concordance (when co-distributed taxa exhibit the same general phylogeographic pattern) and includes a final chapter on the speciation process and the extension of phylogeographic analyses to higher taxa. Some of the comparative phylogeographic studies reviewed include those on Australian rainforest vertebrates, Hawaiian birds and arthropods, North American birds, plants of the Pacific Northwest, and cold-water marine faunas of the Northern Hemisphere. The final chapter includes a review of species concepts, an overview of the durations of species through geological time, and applications of phylogeography beyond the species level. The book concludes with a brief synopsis and commentary on the future of phylogeography. In some ways this book can be viewed as an update and expansion of chapters 6 and 8 of Avise's previous book, Molecular Markers, Natural History, and Evolution (1994). However, there have been so many developments in phylogeography over the past five years or so, especially in coalescent theory and comparative phylogeography, that much of the information presented is new. Therefore, despite some overlap, Avise's two books are largely complementary. Throughout Phylogeography: The History and Formation of Species there is a bias towards multicellular animals, as Avise acknowledges in the preface (this reflects a bias in existing empirical phylogeographic studies, rather than that of the author). However, since many phylogeographic principles should apply equally well to any taxon, researchers interested in other types of o