Hybridization

Current understanding

Hybridization between diverged lineages exposes the genetic architecture of trait differences through the breakdown of co-adapted gene complexes in hybrid offspring. A key question in speciation research is how much of the phenotypic divergence between lineages is explained by additive versus epistatic (gene-by-gene interaction) effects — because epistasis is central to Bateson-Dobzhansky-Muller incompatibilities (BDMIs) and thus to the evolution of intrinsic reproductive isolation.

A growing body of quantitative-genetic work now suggests that the relative importance of epistasis varies systematically across the tree of life. A large-scale meta-analytic comparison reported that animals show significantly greater epistatic contributions to trait divergence than plants, with a mean difference of −0.08 and an empirical p-value of 0.01 Wright was right: leveraging 2024, Finding 1. If this pattern is robust, it implies that BDMIs may accumulate faster or more predictably in animal lineages, with consequences for how quickly intrinsic reproductive isolation evolves following population divergence.

Supporting evidence

Contradictions / open disagreements

The plant–animal contrast in epistatic contribution should be interpreted cautiously. The plant dataset is disproportionately composed of domesticated crop crosses and selfing species. Domestication and selfing both reduce effective population size and standing genetic variation, which could lower detectable epistasis independently of any fundamental biological difference between clades. It remains unclear whether the observed difference reflects a genuine divergence in genetic architecture between animals and plants, or an artifact of how the plant sample was assembled. Broader taxonomic sampling — particularly of outcrossing wild plant species — is needed to resolve this tension. Wright was right: leveraging 2024, Finding 1

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