Allopolyploidy, diversification, and the Miocene grassland expansion

Area of Science:

• Plant evolutionary biology
• Genomics
• Speciation

Background:

• Polyploidy's role in plant diversification is debated, with some evidence suggesting it drives speciation while other studies indicate higher extinction rates for polyploid lineages.
• The grass tribe Andropogoneae, an economically important group of C4 plants, exhibits a high incidence of polyploidy.

Purpose of the Study:

• To investigate the frequency and impact of polyploidy on diversification within the Andropogoneae grass tribe.
• To determine if polyploidization events correlate with increased speciation or extinction rates in this clade.

Main Methods:

• Phylogenetic analysis of approximately 10% of Andropogoneae species using four concatenated low-copy nuclear loci.
• Identification of genetic allopolyploidy through characteristic double-labeled gene tree patterns.

Main Results:

• At least 32% of sampled Andropogoneae species originated via genetic allopolyploidy, stemming from a minimum of 28 tetraploidy and six hexaploidy events.
• Parental genomes of most Andropogoneae polyploids diverged in the Late Miocene, coinciding with the expansion of C4 grasslands.
• No evidence was found linking polyploidization to an increase in net diversification rate within the studied group.

Conclusions:

• Allopolyploidy is a significant mode of speciation in the Andropogoneae tribe.
• Despite its role in generating new species, polyploidization does not necessarily enhance overall diversification rates.