Limits to adaptation along environmental gradients Journal Article

Author(s): Polechová, Jitka; Barton, Nicholas H
Article Title: Limits to adaptation along environmental gradients
Affiliation IST Austria
Abstract: Why do species not adapt to ever-wider ranges of conditions, gradually expanding their ecological niche and geographic range? Gene flow across environments has two conflicting effects: although it increases genetic variation, which is a prerequisite for adaptation, gene flow may swamp adaptation to local conditions. In 1956, Haldane proposed that, when the environment varies across space, "swamping" by gene flow creates a positive feedback between low population size and maladaptation, leading to a sharp range margin. However, current deterministic theory shows that, when variance can evolve, there is no such limit. Using simple analytical tools and simulations, we show that genetic drift can generate a sharp margin to a species' range, by reducing genetic variance below the level needed for adaptation to spatially variable conditions. Aided by separation of ecological and evolutionary timescales, the identified effective dimensionless parameters reveal a simple threshold that predicts when adaptation at the range margin fails. Two observable parameters determine the threshold: (i) the effective environmental gradient, which can be measured by the loss of fitness due to dispersal to a different environment; and (ii) the efficacy of selection relative to genetic drift. The theory predicts sharp range margins even in the absence of abrupt changes in the environment. Furthermore, it implies that gradual worsening of conditions across a species' habitat may lead to a sudden range fragmentation, when adaptation to a wide span of conditions within a single species becomes impossible.
Keywords: Genetic Drift; Genetic Variation; heterogeneous environment; Range margin; Species' range
Journal Title: PNAS
Volume: 112
Issue 20
ISSN: 1091-6490
Publisher: National Academy of Sciences  
Date Published: 2015-05-19
Start Page: 6401
End Page: 6406
Sponsor: European Research Council Grant 250152
DOI: 10.1073/pnas.1421515112
Notes: We thank S. Baird, A. Betancourt, J. P. Bollback, J. R. Bridle, R. Bürger, D. Field, A. Hancock, J. Hermisson, F. Jesse, T. Paixão, T. Priklopil, R. A. Nichols, S. Novak, S. Sarikas, J. R. G. Turner, H. Uecker, C. Vogl, and M. G. J. de Vos for discussions and comments on the earlier drafts, as well as the editor and the referees for their valuable comments.
Open access: yes (repository)
IST Austria Authors
  1. Nick Barton
    252 Barton