Hybrid vigor: The best of both parents, or a genomic clash?

Abstract

During evolution, mutations produce new lineages that gradually diverge in sequence and regulatory properties. Related strains or species can hybridize to produce viable offspring. Hybrids often outperform their parents, producing more biomass or growing more rapidly. This superior performance, termed heterosis, contrasts the more expected clash between the genomes, and has puzzled geneticists and evolutionary biologists for many years. In this review, we describe two classes of models explaining heterosis: the prevailing view attributes heterosis to rapid repair or enhancement of growth promoting pathways. An alternative view attributes heterosis to the impairment of growth-limiting pathways. The two classes are not mutually exclusive and can result from similar types of genetic interactions. We discuss the possible implications of heterosis on tradeoffs in species evolution.