Host adaptation to novel pathogen introduction: Predicting conditions that promote evolutionary rescue

Abstract

Novel pathogen introduction can have drastic consequences for naive host populations, and outcomes can be difficult to predict. Evolutionary rescue (ER) provides a foundation for understanding whether hosts are driven to extinction or survive via adaptation. Currently, patterns of host population dynamics alongside evidence of adaptation are used to infer ER. However, the gap between established ER theory and complexity inherent in natural systems makes interpreting empirical patterns difficult because they can be confounded with ecological drivers of survival under current theory. To bridge this gap, we expand ER theory to include biological selective agents, such as pathogens. We find birth processes to be more important than previously theorised in determining ER potential. We employ a novel framework evaluating ER potential within natural systems and gain ability to identify system characteristics that make ER possible. Identifying these characteristics allows a shift from retrospective observation to a predictive mindset, and our findings suggest that ER occurrence may be more limited than previously thought. We use the plague system of Yersinia pestis infecting Cynomys ludovicianus (black‐tailed prairie dogs) and Spermophilus beecheyi (California ground squirrels) as a case study.

Host density has limited effects on pathogen invasion, disease‐induced declines and within‐host infection dynamics across a landscape of disease

“…Host density is hypothesized to be a major driver of variability in response trajectories following disease invasion in wildlife populations (Begon et al, 2019; Golas et al, 2021; Lloyd‐Smith et al, 2005). While the effects of host density on transmission have been extensively studied in host–parasite systems (reviewed in Hopkins et al, 2020), these studies are dominated by theoretical analyses and small‐scale experiments.…”

“…The fourth determines whether a host population that has been reduced in size by infection persists or experiences stochastic extinction (Golas et al, 2021). Finally, the fifth determines whether the population starts to recover towards a pre-invasion population size with or without the pathogen (Golas et al, 2021).…”

“…A central question in disease ecology is why host populations experience different responses and outcomes following the arrival of a pathogen (Davis et al, 2007; Deredec & Courchamp, 2003; Frick et al, 2017; Golas et al, 2021; Lloyd‐Smith et al, 2005). Observed variability in population responses and outcomes following pathogen arrival (henceforth ‘response trajectories’) depends on at least five different branch points (Figure 1; Wilber et al, 2019).…”

“…The third determines whether a population that has experienced disease‐induced declines experiences disease‐induced extinction or continues to persist at low densities with or without the pathogen (De Castro & Bolker, 2005). The fourth determines whether a host population that has been reduced in size by infection persists or experiences stochastic extinction (Golas et al, 2021). Finally, the fifth determines whether the population starts to recover towards a pre‐invasion population size with or without the pathogen (Golas et al, 2021).…”

Susceptibility to a sexually transmitted disease in a wild koala population shows heritable genetic variance but no inbreeding depression

“…Narrow sense heritability (h 2 ), as calculated in this study, can be used to predict the response to selection across generations (Walsh & Lynch, 2018), and can therefore be used to predict outcomes for populations facing disease outbreaks (Golas et al, 2021). Heritability is a population-level parameter which depends on population-specific factors (e.g., allele frequencies or the effects of gene variants), traits, and variation due to Age (years) Probability of testing positive for chlamydia environmental factors (Harrisson et al, 2014).…”