Domestication is a recent evolutionary process of divergent selection between wild forms, subject to natural selection in their original habitats, and domesticated forms, shaped by a combination of natural and human selection and adapted to anthropogenic environments. It provides a model for studying the adaptive mechanisms underlying the domestication syndrome. One aspect that remains poorly studied is reproductive isolation between wild and domesticated forms, promoted by the counter-selection of hybrids in each environment. We used a comparative framework involving fourteen diploid species to study the investigate principle of phenotypic evolution and the emergence of reproductive isolation during domestication.
Focusing first on phenotypic data we showed a reduction of multivariate phenotypic space during domestication. We developed a multivariate phenotypic divergence index (mPDI) to rank species according to the extent of divergence between forms and showed a strong disjunction of the forms, with a progressive decoupling of trait correlations over time.
We then produced inter-form crosses, with intra-forms hybrids as controls to study hybrid depression. While most inter-form hybrids were intermediate, we identified cases of transgression, whose proportions tended to increase with time since domestication.
Lastly RIDGE was used to estimate the proportion of the genome acting as a barrier to gene flow and to identify the underlying loci. We were able to detect barrier loci between the two forms in seven pairs, and showed a progressive increase of the proportion of barrier loci over time. Those loci also tended to cluster in low recombination region, hinting at the role of pericentromeric and inverted region in reproductive isolation.
Through these three approaches we demonstrated that domestication is a relevant model for studying the early stages of reproductive isolation induced by ecological divergence. Reproductive isolation between wild and domesticated forms increases over time and appears to be independent of the reproductive system.
