How many generations does it take for phytophages to colonize invasive plants? Mathematical modeling predictions

Native phytophagous insects are often not adapted to novel chemistry of invasive plants, but over time they begin to adapt and feed on them. We simulated the spread of a mutant allele that enables phytophages to feed on invasive plant as effectively as on native plant. This simulation involved two insect populations associated with native and invasive plant species, with gene flow between them. Fitness was assigned using the Ricker function, which incorporated plant abundance, insect feeding efficiency, and competition between genotypes. For the mutation to become fixed in fewer than one hundred generations, invasive plant must be at least as abundant as native one. The effect of invasive plant relative abundance is larger than that of fitness differences in feeding efficiency of wild type phytophages between plants. The spread of this allele under natural selection is faster if it has come from standing genetic variation, rather than newly arisen mutation, or, in the latter case, if there is assortative mating.