Percent of speciation events in ferns that involve polyploidization

Value 7 %
Organism Plants
Reference Otto SP, Whitton J. Polyploid incidence and evolution. Annu Rev Genet. 2000 34: 401-437.PubMed ID11092833
Method According to odd and even chromosome base numbers, polyploidyzation index (PI). See equation 2 in p. 406.
Comments Ferns have a high polyploid index (41.7%), meaning that nearly half of recent changes in haploid chromosome number have occurred via polyploidization. To calibrate this measure per speciation event, we estimated the fraction of speciation events in ferns associated with a change in chromosome number, by totaling the minimum number of chromosome changes found within each genus, i.e. Sgenera(unique n values per genus minus one), and dividing this by the total number of speciation events represented, i.e. Sgenera(# species per genus minus one). They ignored genera with a chromosome count from only one species. This procedure indicated that ~16% of recent speciation events in ferns involved a change in chromosome number. Because chromosome numbers are known from only ~15% of fern species (L¨ove A, L¨ove D, Pichi Sermolli REG. 1977. Cytotaxonomical Atlas of the Pteridophyta. Vaduz, Germany: Cramer), this estimate is necessarily coarse. Furthermore, there will generally be more chromosome changes and speciation events in the history of these taxa than estimated above. Keeping in mind researchers' uncertainty, they estimate that ~7% (=41.7%×16%) of speciation events involve polyploidization in ferns.
Entered by Uri M
ID 105423