Abstract
<p>Hybridization has been suggested as mechanism that can contribute to adaptive evolution and the success of crop-wild hybrid populations; but this response appears to depend upon environmental context. I explore how environmental variation affects crop trait expression, the strength and direction of selection on crop traits in radish weed populations, and the influence environmental variation has on crop-trait introgression across agricultural landscapes. Using the Raphanus crop-wild complex as a model system to study the environmental sensitivity of crop gene flow into weed populations, I first planted advanced-generation wild and crop-wild hybrid radish plants (that had previously evolved for three generations under relatively dry, relatively wet, or ambient control soil moisture or water-evolved conditions) into sheltered common gardens that were watered with low, ambient, or high soil moisture. From this work, hybridization and watering history did not enhance the success of advanced-generation hybrid plants relative to wild progenitors in Ontario, Canada. Next, I explored how phenotypic plasticity in response to environmental variation may distort a commonly used metric to measure the rate of evolution, the haldane. To determine the extent that plasticity affected estimates of evolutionary rate, I compared haldane estimates of advanced-generation water-evolved plants grown in a common garden that did not involve manipulation of ambient watering conditions. Estimates of the magnitude and direction of contemporary evolution differed significantly due to annual environmental variation, particularly for wild populations. Thus, I propose changes to the use of these equations and changes to the equation itself to help avoid generating false estimates of evolutionary rates. Finally, a meta-analysis of radish phenology and fecundity data collected from the last twelve years across four locations revealed that geography can affect the strength and direction of selection on crop- derived traits in weedy radish populations. This large, integrated study offers environmental risk assessment a new perspective on the role of environmental change on the success of crop-wild hybridization and its ability to generate weedy species. In summary, I provide evidence that environmental variation should be considered before making predictions about a crop trait’s evolutionary trajectory and persistence in a weedy plant population.</p>
Highlights
Hybridization, inter-specific mating, of crops and their wild relatives can produce aggressive, environmentally-damaging weeds in a diversity of environments (Campbell et al 2006; Ridley and Ellstrand 2008; Arnold and Martin 2010; Hovick et al 2012; Ellstrand et al 2013; but see Whitney et al 2010)
Since biomass was strongly correlated with the number of fruits, flowers, and seeds produced by all plants, I used these allometric relationships with biomass as a proxy of reproductive success in subsequent analyses that used data from the combined allometric and 50% experimental data
Abiotic environmental variation has been suggested as a mechanism that can affect gene flow which can alter opportunities for hybridization and influence the likelihood of crop alleles escaping into, and persisting, in wild populations (Arnold and Martin 2010; Arnold et al 2013; Goulet et al 2017; but see Campbell et al 2016)
Summary
Hybridization, inter-specific mating, of crops and their wild relatives can produce aggressive, environmentally-damaging weeds in a diversity of environments (Campbell et al 2006; Ridley and Ellstrand 2008; Arnold and Martin 2010; Hovick et al 2012; Ellstrand et al 2013; but see Whitney et al 2010). When crops mate with wild relatives, they can transfer cropspecific alleles to wild populations; these crop alleles can persist and contribute beneficial adaptive phenotypes that can be selectively advantageous (Campbell et al 2006; Whitney et al 2006; Snow et al 2010). Researchers measuring crop-wild hybridization in radish plants across environmental clines have demonstrated geographic variation in the success of hybrids and strength of selection on these populations (Whitney et al 2009; Campbell et al 2014). Variation in climate exists between experiments, studies explicitly evaluating how abiotic variation influences the persistence and success of late-generation hybrids are rare and necessary to assess the predictability of relative hybrid success across moisture conditions
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