Hybridization can act as an evolutionary stimulus, but we know little about how ecological context influences the outcomes of hybridization. Mechanistically, interspecific hybridization can produce increased genetic and phenotypic variation for selection to act upon in a rapid and more efficient manner than random mutation. Here we used an experimental system to ask whether the evolutionary outcomes of hybridization are ecologically context-dependent using hybrids of two sunflower species, Helianthus annuus and H. debilis. We used a field experiment through eight generations comparing experimentally-generated BC1 hybrids and nonhybrid controls grown at three different sites in Texas across an environmental gradient spanning almost 300 km. We used two final common gardens to examine local patterns of evolution in terms of fitness and traits related to both abiotic and biotic pressures. Specifically, we asked 1) Do hybrids evolve more than controls across sites?, and 2) Do patterns of trait evolution differ across sites?
Results/Conclusions
Overall, we found that hybrid evolution was significant, greater than controls, and fairly correlated across environments. Hybrid fitness evolved significantly at each site towards higher values, while there was no significant change in control fitness at any site across generations. Likewise, across sites, total evolutionary change in 18 different traits was higher in hybrids than in controls. Evolution of individual traits were significantly correlated in hybrid lineages across sites but not in control lineages. Additionally, many traits exhibited phenotypic plasticity in both controls and hybrids. We preliminarily conclude that hybrids consistently evolved faster than controls, while site-level differences in trait values are mainly due to phenotypic plasticity rather than local adaptation.