Effect of whole-genome duplication on the evolutionary rescue of sterile hybrid monkeyflowers

Abstract

Hybridisation is a creative evolutionary force, increasing genomic diversity, and facilitating adaptation and even speciation. Hybrids often face significant challenges to become established, including reduced fertility arising from genomic incompatibilities between their parents. Whole genome duplication in hybrids (allopolyploidy) can restore fertility, cause immediate phenotypic changes, and generate reproductive isolation. Yet the survival of polyploid lineages is uncertain, and few studies have compared the performance of recently formed allopolyploids and their parents under field conditions. Here we use natural and synthetically-produced hybrid and polyploid monkeyflowers (Mimulus spp.) to study how polyploidy contributes to the fertility, reproductive isolation, phenotype and performance of hybrids in the field. We find that polyploidisation restores fertility and that allopolyploids are reproductively isolated from their parents. The phenotype of allopolyploids displays the classic gigas effect of whole genome duplication, producing plants with larger organs and slower flowering. Field experiments indicate that survival of synthetic hybrids before and after polyploidisation is intermediate between the parents, whereas natural hybrids have higher survival than all the other taxa. We conclude that hybridisation and polyploidy can act as sources of genomic novelty, but adaptive evolution is key in mediating the establishment of young allopolyploid lineages.