Genetic Structure in the Sea

irtually all species of marine organisms, whether pelagic, dispersal, gene flow (i.e., migration of gametes or individuals v planktonic, or benthic, are patchily distributed, consisting of local populations linked to a greater or lesser extent by dispersal. Ecologists are primarily concerned with characterizing tlus geographic structure in terms of the distributions and movements of individual organisms within and among local populations. Evolutionary biologists, on the other hand, often think in terms of the spatial distribution of genetic variation within and among local populations. Ecological and evolutionary approaches thus differ in their emphasis on the spatial distribution of individuals versus genes; where they converge is in their attempts to understand the processes that cause geographic variation in a species. In other words, ecology shapes the distribution of genetic variation in a species (Endler 1992), whereas genetic structure provides the evolutionary context in which to interpret a species' ecological interactions with its environment. Genetic structure in marine populations reflects the historical and contemporary interplay among a complex set of eco-The combined effects of these mechanisms, acting across a range of spatial and temporal scales, determine rates and pattems of dispersal of gametes, zygotes, larvae, and adults. It is these movements , along with the survival and successful reproduction of immigrants, that, in turn, control the scale and rate at which random (i.e., genetic drift) and deterministic (i.e., natural selection) processes build or erode structure within and among groups of individuals. A number of recent papers have explored the population-level ramifications of genetic structure in marine systems, highlighting the relationships among developmental mode, that leads to the incorporation of their genes into a recipient population), and speciation (e. In keeping with the theme of this book, we expand this population level perspective to the community, and explore four facets of the following basic question: What can information about the spatial distribution of genetic variation within a species, and the processes that generate these patterns, tell ecologists about the nature and outcomes of species' interactions with their biotic and physical environment? The first aspect of the question relates to the scale at which a species' predators, competitors, parasites, pathogens, and symbionts regulate its population dynamics (Roughgarden The spatial scales over which marine populations exhibit "open" versus "closed" dynamics are generally not obvious, and they vary according to the magnitude of migration among subpopula-tions. Genetic structure can be used to place bounds on the spatial …