Abstract
Compared to those of their parents, are the traits of first-generation (F1) hybrids typically in-termediate, biased toward one parent, or mismatched for alternative parental phenotypes? Andhow does hybrid trait expression affect fitness? To address this empirical gap, we compiled datafrom 233 crosses in which traits were measured in a common environment for two parent taxaand their F1hybrids. We find that individual traits in F1s are, on average, halfway between theparental midpoint and one parental value (e.g., hybrid trait values are 0.75 if parents’ values are 0& 1). When considering pairs of traits together, a hybrid’s bivariate phenotype tends to resembleone parent (pairwise parent-bias) about 50 % more than the other while also exhibiting a similarmagnitude of mismatch due to different traits having dominance in conflicting directions. Wedetect no phylogenetic signal nor an effect of parental genetic distance on dominance or mis-match. Using data from an experimental field planting of recombinant hybrid sunflowers, weillustrate that pairwise parent-bias improves fitness whereas pairwise mismatch reduces fitness.In sum, our study has three major conclusions. First, hybrids between ecologically divergentnatural populations are not phenotypically intermediate but rather exhibit substantial mismatchwhile also resembling one parent more than the other. Second, dominance and mismatch donot seem to be governed by general rules but rather by the idiosyncratic evolutionary trajectoriesof individual traits in individual populations or species. Finally, selection against hybrids likelyresults from selection against both intermediate and mismatched phenotypes.