Résumé
Heterosis describes the phenotypic superiority of hybrids over their
parents in traits related to agronomic performance and fitness.
Understanding and predicting nonadditive inheritance such as heterosis is
crucial for evolutionary biology as well as for plant and animal breeding.
However, the physiological bases of heterosis remain debated. Moreover,
empirical data in various species have shown that diverse genetic and
molecular mechanisms are likely to explain heterosis, making it difficult
to predict its emergence and amplitude from parental genotypes alone. In
this study, we examined a model of physiological dominance initially
proposed by Sewall Wright to explain the nonadditive inheritance of traits
like metabolic fluxes at the cellular level. We evaluated Wright’s model
for two fitness-related traits at the whole-plant level, growth rate and
fruit number, using 450 hybrids derived from crosses among natural
accessions of A. thaliana. We found that allometric relationships between
traits constrain phenotypic variation in a nonlinear and similar manner in
hybrids and accessions. These allometric relationships behave predictably,
explaining up to 75% of heterosis amplitude, while genetic distance among
parents at best explains 7%. Thus, our findings are consistent with
Wright’s model of physiological dominance and suggest that the emergence
of heterosis on plant performance is an intrinsic property of nonlinear
relationships between traits. Furthermore, our study highlights the
potential of a geometric approach of phenotypic relationships for
predicting heterosis of major components of crop productivity and yield.