Timetable for allopolyploidy in flowering plants (Viewpoint)

In contrast to our broad understanding of population and phylogenetic dynamics, we do not know when diploid taxa are sufficiently different to spawn allopolyploids with two very distinctive genomes (strict allopolyploids), i.e. when their diploid interspecific hybrids would be sterile or nearly so. Levin reviews and integrates published information and determines that despite limitations in methodology and sampling, the estimated times to hybrid sterility are somewhat congruent across disparate lineages. Whereas the waiting time for hybrid sterility is roughly 4–5 million years, that for cross-incompatibility is roughly 8–10 million years, sometimes considerably more. Strict allopolyploids may be formed in the intervening time window. The progenitors of several allopolyploids diverged between 4 and 6 million years before allopolyploid synthesis, as expected. This is the first study to propose a general temporal framework for strict allopolyploidy.