Ancient polyploidization predating divergence of the cereals
At least 32% of the species sampled are the result of genetic allopolyploidy and result from 28 distinct tetraploidy events plus an additional six hexaploidy events. We found a remarkable number of allopolyploidization events, none of which correlate with shifts in diversification rate or with the origin of unique morphological characters.This number is a minimum, and the actual frequency could be considerably higher. Repeated formation of polyploids correlates with expansion of the CChronogram of the phylogeny of Andropogoneae produced in BEAST (57). This phylogenetic pattern has led to the hypothesis that polyploidy causes or promotes diversification. Ancient polyploidy correlates with major land-plant radiations (3) and the origins of orders, large families, and major clades (4–7) although, in many cases, sharp changes in diversification rates are delayed for millions of years after the polyploidization event (1).The parental genomes of most Andropogoneae polyploids diverged in the Late Miocene coincident with the expansion of the major C4 grasslands that dominate the earth today. Branch colors indicate Bayesian posterior probability with red highest, green lowest.
Wiley Online Library requires cookies for authentication and use of other site features; therefore, cookies must be enabled to browse the site.Whole-genome duplications precede the origins of many major clades (e.g., angiosperms, Brassicaceae, Poaceae), suggesting that polyploidy drives diversification. One reason for the difficulty of resolving the phylogeny may be a failure to account for polyploidy.However, theoretical arguments and empirical studies suggest that polyploid lineages may actually have lower speciation rates and higher extinction rates than diploid lineages. Mixing of orthologues and paralogues in gene trees, combined with extensive reticulation in the history of the genera, could easily destroy any phylogenetic signal. The tribe is morphologically diverse and contains some of our most economically important crop plants [maize (). Here, we focus on the tribe Andropogoneae (subfamily Panicoideae), a group of about 1,200 species in 90 genera.