Evolutionary rescue through partly heritable phenotypic variability

Abstract

5Environmental variation is commonplace, but unpredictable. Populations that encounter a deleterious 6 environment can sometimes avoid extinction by rapid evolutionary adaptation. Phenotypic variability, 7 whereby a single genotype can express multiple different phenotypes, might play an important role in 8 rescuing such populations from extinction. This type of evolutionary bet-hedging need not confer a direct 9 benefit to a single individual, but it may increase the chance of long-term survival of a lineage. Here 10 we develop a population-genetic model to explore how partly heritable phenotypic variability influences 11 the probability of evolutionary rescue and the mean duration of population persistence in changing 12 environments. We find that the probability of population persistence depends non-monotonically on the 13 degree of phenotypic heritability between generations: some heritability can help avert extinction, but 14 too much heritability removes any benefit of phenotypic variability. We discuss the implications of these 15 results in the context of therapies designed to eradicate populations of pathogens or aberrant cellular 16 lineages. 17Keywords: 18 evolutionary rescue; time to extinction; bacterial persistence; stochastic switching; evolutionary bet-hedging; 19 fluctuating environments; adaptation to environmental change 20 from extinction depends on the rate of change (Dallinger, 1887). Evolutionary rescue is the process by 24 which a population is able to recover from abrupt environmental changes that would otherwise lead to 25 a demographic decline and eventual extinction (Gomulkiewicz and Holt, 1995; Bell and Gonzalez, 2009; 26 Alexander et al., 2014; Gonzalez et al., 2013; Lindsey et al., 2013; Carlson et al., 2014). Evolutionary 27 responses that allow populations to adapt to change on a sufficiently fast time scale to prevent extinction 28 have been the focus of considerable experimental and theoretical interest, across diverse biological systems. 29In the field of conservation biology, questions of rescue are framed around ensuring the survival of species in 30 deteriorating global habitats (Palumbi, 2001; Gonzalez et al., 2013; Davis et al., 2005). In contrast, in clinical 31 contexts, the goal is eradication of pathogens or harmful populations of cells (Gonzalez et al., 2013; Alexander 32 et al., 2014). These two bodies of work share a common thread (as Maynard Smith (1989) emphasized, 33 adaptation in threatened populations is not like ordinary adaptation, it is a race against extinction), yet 34 each presents unique difficulties. 35Here we focus on the questions of population eradication that arise in medically-relevant settings, where 36 populations are often surprisingly resilient or recalcitrant to treatment due to evolutionary adaptation. In 37 particular, we ask: how does heritable phenotypic variability alter the probability of evolutionary rescue? 38 We study the evolutionary advantage of heritable phenotypic variability in populations of non-constant si...

When does gene flow facilitate evolutionary rescue?

“…The theoretical foundations for evolutionary rescue in single panmictic populations are laid out [Orr and Unckless, 2014] and several demographic genetic and extrinsic features that affect the chance for rescue have been identified (see table 1 in Carlson et al [2014] for an overview), including the effects of recombination [Uecker and Hermisson, 2016], mating system [Uecker, 2017], intra-specific competition [Osmond and de Mazancourt, 2013, Bono et al, 2015], inter-specific competition [De Mazancourt et al, 2008], and phenotypic plasticity [Chevin et al, 2013, Carja and Plotkin, 2019]. A major goal of evolutionary rescue theory is to predict a populations chance of survival in the face of severe stress.…”