Abstract
Resistance to xenobiotics remains a pressing issue in parasite treatment and global agriculture. Multiple factors may affect the evolution of resistance, including interactions between life‐history traits and the strength of selection imposed by different drug doses. We experimentally created replicate selection lines of free‐living Caenorhabditis remanei exposed to Ivermectin at high and low doses to assess whether survivorship of lines selected in drug‐treated environments increased, and if this varied with dose. Additionally, we maintained lines where mortality was imposed randomly to control for differences in density between drug treatments and to distinguish between the evolutionary consequences of drug‐treatment versus ecological processes due to changes in density‐dependent feedback. After 10 generations, we exposed all of the selected lines to high‐dose, low‐dose and drug‐free environments to evaluate evolutionary changes in survivorship as well as any costs to adaptation. Both adult and juvenile survival were measured to explore relationships between life‐history stage, selection regime and survival. Intriguingly, both drug‐selected and random‐mortality lines showed an increase in survivorship when challenged with Ivermectin; the magnitude of this increase varied with the intensity of selection and life‐history stage. Our results suggest that interactions between density‐dependent processes and life history may mediate evolved changes in susceptibility to control measures.
Highlights
Pesticide and drug treatments are designed to suppress populations of parasites, pests and disease vectors
We asked: (i) What is the relationship between C. remanei survival and Ivermectin dose over a range of concentrations within a single generation? (ii) Is there an increase in survivorship across generations of populations selected in drug-treated environments, and does this vary with dosage? (iii) Does density-dependent selection affect the apparent evolution of resistance in selected lines? (iv) Is there a cost of adaptation to drug-treated environments in terms of survival in drug-free environments? We explored the relationship between life-history and drug selection, asking: (v) Does survival of different life-history stages respond to drugselection in the same way?
Two Ivermectin doses were chosen as drug treatments for experimental evolution (Figure S1B): (i) a high dose that corresponded to 80% mortality at 75 h in naive populations; and (ii) a low dose that corresponded to 40% mortality
Summary
Pesticide and drug treatments are designed to suppress populations of parasites, pests and disease vectors. Lifehistory characteristics and reproductive strategies of parasites and pests could influence the rate at which resistance develops (Galvani and Gupta 1998; Lynch et al 2008; Kliot and Ghanim 2012).
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