Environmental variation and its effect on the success of crop-wild hybridization in the Raphanus species complex
thesisposted on 23.05.2021, 13:26 by Kruti Shukla
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.