In the light of evolution X: Comparative phylogeography.

Phylogeography is the study of the spatial arrangement of genealogical lineages, especially within and among conspecific populations and closely related species (10). Ever since its inception in the late 1970s (11, 12) and mid-1980s (13), the field has sought to extend phylogenetic reasoning to the intraspecific level, and thereby build empirical and conceptual bridges between the formerly separate disciplines of microevolutionary population genetics and macroevolutionary phylogenetics. In the early years, phylogeographers relied on data from restriction-site surveys of mitochondrial (mt) DNA to draw inferences about population structure and historical demography, but stunning improvements in molecular techniques (14, 15) and extensions of coalescent theory and other analytical methods (16) later broadened the field’s scope dramatically (17). Phylogeographic perspectives have transformed aspects of population biology, biogeography, systematics, ecology, genetics, and biodiversity conservation. One aim of this colloquium was to bring together leading scientists to address the current state of phylogeography as the discipline enters its fourth decade. The broader goal was to update a wide audience on recent developments in phylogeographic research and their relevance to past accomplishments and future research directions. Many of the advancements in phylogeography have entailed comparative appraisals of one sort or another (18). (See refs. 1–9 for papers from previous colloquia in the series and Box 1 for an overview of the series.) Papers in Section I of this colloquium emphasize the word “comparative” in a spatial sense, where the phylogeographic assessments entail various species (sometimes generally codistributed) that may be representative of particular kinds of environmental settings, such as oceanic versus continental realms. Section II deals with comparative phylogeography in a genomic sense. Nonrecombining cytoplasmic genomes have been the standard workhorses of genealogical analyses, but in principle the primary library of evolutionary histories is ensconced in nuclear genomes that are increasingly accessible to scrutiny. Section III focuses on comparative phylogeography in a taxonomic sense, emphasizing how phylogeographic findings have impacted ecological and evolutionary thought in a diversity of organismal groups. Section IV focuses on comparative phylogeography in a conceptual sense by addressing the place of phylogeography in relation to various allied disciplines in the biodiversity sciences. Several papers in these proceedings inevitably overlap in their sectional assignments because (for example) disparate taxa tend to inhabit different environments, and because the researchers assembled here had a diversity of phylogeographic objectives, data types, and analytical approaches.