Genetic Paths to Evolutionary Rescue and the Distribution of Fitness Effects Along Them

• Published in: Genetics (Austin) Vol. 214; no. 2; pp. 493 - 510
• Main Authors: Osmond, Matthew M, Otto, Sarah P, Martin, Guillaume
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01-02-2020; Genetics Society of America
• Subjects: Adaptation; Adaptation, Biological - genetics; Adaptation, Physiological - genetics; Biodiversity; Biological Evolution; Demographics; Demography; Drug resistance; Environment; Environmental changes; Evolution; Evolution, Molecular; Fitness; Genetic Fitness - genetics; Genetics; Genotype; Genotypes; Investigations; Life Sciences; Loci; Models, Genetic; Mutation; Mutation rates; Populations; Populations and Evolution; Reproductive fitness; Selection, Genetic - genetics; Switches; Antimicrobial drug resistance; Genetic basis of adaptation; Fisher’s geometric model; Mathematical theory; Evolutionary escape; Fisher's geometric model
• ISSN: 1943-2631; 0016-6731; 1943-2631
• DOI: 10.1534/genetics.119.302890

Abstract
Novel environments can cause strong selection and rapid adaptation. The genetic basis of such rapid adaptation tends to be composed of few loci of large effect. Current theory qualitatively agrees but largely neglects the demographic...
The past century has seen substantial theoretical and empirical progress on the genetic basis of adaptation. Over this same period, a pressing need to prevent the evolution of drug resistance has uncovered much about the potential genetic basis of persistence in declining populations. However, we have little theory to predict and generalize how persistence—by sufficiently rapid adaptation—might be realized in this explicitly demographic scenario. Here, we use Fisher’s geometric model with absolute fitness to begin a line of theoretical inquiry into the genetic basis of evolutionary rescue, focusing here on asexual populations that adapt through de novo mutations. We show how the dominant genetic path to rescue switches from a single mutation to multiple as mutation rates and the severity of the environmental change increase. In multi-step rescue, intermediate genotypes that themselves go extinct provide a “springboard” to rescue genotypes. Comparing to a scenario where persistence is assured, our approach allows us to quantify how a race between evolution and extinction leads to a genetic basis of adaptation that is composed of fewer loci of larger effect. We hope this work brings awareness to the impact of demography on the genetic basis of adaptation.