Geographical Variation

AbstractGeographical variation refers to differences among populations in genetically based traits across the natural geographic range of a species. Understanding the factors that give rise to and maintain geographical variation helps elucidate the causes and consequences of evolution. In the simplest case, we divide these factors into purely genetic versus environmental components to tease apart their relative contributions to observed phenotypic variation. Subsequent experiments allow us to partition further the genetic components of phenotypic variation towards a molecular understanding, hopefully to reveal the actualdeoxyribonucleic acid(DNA)‐scale changes giving rise to adaptations we see at the population level. Studies of a select number of organisms – all of which begin with geographic variation – demonstrate this highly productive strategy. Given its relevance to differentiation among populations, geographic variation also has direct bearing on the question of species origins.Key Concepts:Geographical variation refers to differences among populations of organisms in genetically based traits across the natural geographic range of that species.Understanding how initial population size, gene flow, mutation frequency, and environmental (abiotic) factors give rise to and maintain geographical variation can shed light on direction and rate of evolutionary change.Clinal variation – a form of geographic variation – suggests past or present action of natural selection.Reciprocal transplantation and ‘common garden’ experiments are two effective manipulations that can reveal genetically based phenotypic variation.A number of studies of geographic variation, including those about sickle‐cell anaemia, warfarin‐resistance, and lepidopteran colouration, have shifted to a more molecular focus.A number of other studies attempt to understand geographic variation in the broader context of community and ecosystem structure.Given the multi‐faceted approach to understanding it, geographic variation can help address the question of species’ origins.