GENETIC ISOLATION BY ENVIRONMENT OR DISTANCE: WHICH PATTERN OF GENE FLOW IS MOST COMMON?

• Published in: Evolution Vol. 68; no. 1; pp. 1 - 15
• Main Authors: Sexton, Jason P., Hangartner, Sandra B., Hoffmann, Ary A.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01-01-2014; Wiley Subscription Services, Inc; Oxford University Press
• Subjects: Adaptation; Animals; Climate Change; Environment; environmental management; Evolution, Molecular; Gene Flow; Genes; Genetics; isolation by distance; isolation by ecology; isolation by environment; Reproductive Isolation; SPECIAL SECTION: Adaptation to Environmental Stress and Change; swamping gene flow; Climate change; isolation by distance; isolation by environment; swamping gene flow; isolation by ecology; environmental management
• ISSN: 0014-3820; 1558-5646
• DOI: 10.1111/evo.12258

Gene flow among populations can enhance local adaptation if it introduces new genetic variants available for selection, but strong gene flow can also stall adaptation by swamping locally beneficial genes. These outcomes can depend on population size, genetic variation, and the environmental context. Gene flow patterns may align with geographic distance (IBD—isolation by distance), whereby immigration rates are inversely proportional to the distance between populations. Alternatively gene flow may follow patterns of isolation by environment (IBE), whereby gene flow rates are higher among similar environments. Finally, gene flow may be highest among dissimilar environments (counter-gradient gene flow), the classic "gene-swamping" scenario. Here we survey relevant studies to determine the prevalence of each pattern across environmental gradients. Of 70 studies, we found evidence of IBD in 20.0%, IBE in 37.1%, and both patterns in 37.1%. In addition, 10.0% of studies exhibited counter-gradient gene flow. In total, 74.3% showed significant IBE patterns. This predominant IBE pattern of gene flow may have arisen directly through natural selection or reflect other adaptive and nonadaptive processes leading to nonrandom gene flow. It also precludes gene swamping as a widespread phenomenon. Implications for evolutionary processes and management under rapidly changing environments (e.g., climate change) are discussed.