The results of these two studies are in direct contrast to the results of this paper. These contradictions cannot be explained by different growing condition, because Vogel and Mitchell (2008) observed the strongest heterotic responses under simulated sward conditions, meant to mimic the seeded sward plots used in this study Genetic composition of the hybrids was another fundamental difference between these experiments: bulked population hybrids for Martinez-Reyna and Vogel (2008) and Vogel and Mitchell (2008) vs. individual two-parent hybrids for the current study. Despite this defference in conduct of these experiments, it is difficult to imagine this as a factor driving differential heterotic responses, largely because there was no opportunity for intergenotypic compertition in the studies of Martinez-Reyna and Vogel (2008) and Vogel and Mitchell (2008); all plants and plot were established by transplanting vigorous seedlings that had not undergone selection. Thus, there was no opportunity for selection to occur between plants from different crosses, and no reason to expect bulks of several crosses to differ from the average of individual crosses. Rather, if selection occurred during field evaluations, it could only have occurred in the present study, which was conducted under conditions (Casler and Smart, 2013). Nevertheless, because progenies from divergent upland or lowland parents were never placed in competition with each other, it is unlikely that selection played a strong role in causing the observed reciprocal effects.