BACKGROUND AND AIMS: For 84 years, botanists have relied on calculating the highest common factor for series of haploid chromosome numbers to arrive at a so-called basic number, x. This was done without consistent (reproducible) reference to species relationships and frequencies of different numbers in a clade. Likelihood models that treat polyploidy, chromosome fusion and fission as events with particular probabilities now allow reconstruction of ancestral chromosome numbers in an explicit framework. We have used a modelling approach to reconstruct chromosome number change in the large monocot family Araceae and to test earlier hypotheses about basic numbers in the family. METHODS: Using a maximum likelihood approach and chromosome counts for 26 % of the 3300 species of Araceae and representative numbers for each of the other 13 families of Alismatales, polyploidization events and single chromosome changes were inferred on a genus-level phylogenetic tree for 113 of the 117 genera of Araceae. KEY RESULTS: The previously inferred basic numbers x = 14 and x = 7 are rejected. Instead, maximum likelihood optimization revealed an ancestral haploid chromosome number of n = 16, Bayesian inference of n = 18. Chromosome fusion (loss) is the predominant inferred event, whereas polyploidization events occurred less frequently and mainly towards the tips of the tree. CONCLUSIONS: The bias towards low basic numbers (x) introduced by the algebraic approach to inferring chromosome number changes, prevalent among botanists, may have contributed to an unrealistic picture of ancestral chromosome numbers in many plant clades. The availability of robust quantitative methods for reconstructing ancestral chromosome numbers on molecular phylogenetic trees (with or without branch length information), with confidence statistics, makes the calculation of x an obsolete approach, at least when applied to large clades.
BACKGROUND AND AIMS: For 84 years, botanists have relied on calculating the highest common factor for series of haploid chromosome numbers to arrive at a so-called basic number, x. This was done without consistent (reproducible) reference to species relationships and frequencies of different numbers in a clade. Likelihood models that treat polyploidy, chromosome fusion and fission as events with particular probabilities now allow reconstruction of ancestral chromosome numbers in an explicit framework. We have used a modelling approach to reconstruct chromosome number change in the large monocot family Araceae and to test earlier hypotheses about basic numbers in the family. METHODS: Using a maximum likelihood approach and chromosome counts for 26 % of the 3300 species of Araceae and representative numbers for each of the other 13 families of Alismatales, polyploidization events and single chromosome changes were inferred on a genus-level phylogenetic tree for 113 of the 117 genera of Araceae. KEY RESULTS: The previously inferred basic numbers x = 14 and x = 7 are rejected. Instead, maximum likelihood optimization revealed an ancestral haploid chromosome number of n = 16, Bayesian inference of n = 18. Chromosome fusion (loss) is the predominant inferred event, whereas polyploidization events occurred less frequently and mainly towards the tips of the tree. CONCLUSIONS: The bias towards low basic numbers (x) introduced by the algebraic approach to inferring chromosome number changes, prevalent among botanists, may have contributed to an unrealistic picture of ancestral chromosome numbers in many plant clades. The availability of robust quantitative methods for reconstructing ancestral chromosome numbers on molecular phylogenetic trees (with or without branch length information), with confidence statistics, makes the calculation of x an obsolete approach, at least when applied to large clades.
Authors: Yuannian Jiao; Norman J Wickett; Saravanaraj Ayyampalayam; André S Chanderbali; Lena Landherr; Paula E Ralph; Lynn P Tomsho; Yi Hu; Haiying Liang; Pamela S Soltis; Douglas E Soltis; Sandra W Clifton; Scott E Schlarbaum; Stephan C Schuster; Hong Ma; Jim Leebens-Mack; Claude W dePamphilis Journal: Nature Date: 2011-04-10 Impact factor: 49.962
Authors: Douglas E Soltis; Victor A Albert; Jim Leebens-Mack; Charles D Bell; Andrew H Paterson; Chunfang Zheng; David Sankoff; Claude W Depamphilis; P Kerr Wall; Pamela S Soltis Journal: Am J Bot Date: 2009-01 Impact factor: 3.844
Authors: Liying Cui; P Kerr Wall; James H Leebens-Mack; Bruce G Lindsay; Douglas E Soltis; Jeff J Doyle; Pamela S Soltis; John E Carlson; Kathiravetpilla Arumuganathan; Abdelali Barakat; Victor A Albert; Hong Ma; Claude W dePamphilis Journal: Genome Res Date: 2006-05-15 Impact factor: 9.043
Authors: K Yoong Lim; Douglas E Soltis; Pamela S Soltis; Jennifer Tate; Roman Matyasek; Hana Srubarova; Ales Kovarik; J Chris Pires; Zhiyong Xiong; Andrew R Leitch Journal: PLoS One Date: 2008-10-09 Impact factor: 3.240
Authors: Andreas Fleischmann; Todd P Michael; Fernando Rivadavia; Aretuza Sousa; Wenqin Wang; Eva M Temsch; Johann Greilhuber; Kai F Müller; Günther Heubl Journal: Ann Bot Date: 2014-10-01 Impact factor: 4.357
Authors: Terezie Mandáková; Ales Kovarík; Judita Zozomová-Lihová; Rie Shimizu-Inatsugi; Kentaro K Shimizu; Klaus Mummenhoff; Karol Marhold; Martin A Lysak Journal: Plant Cell Date: 2013-09-30 Impact factor: 11.277
Authors: Prabhu Shankar Lakshmanan; Katrijn Van Laere; Tom Eeckhaut; Johan Van Huylenbroeck; Erik Van Bockstaele; Ludmila Khrustaleva Journal: Comp Cytogenet Date: 2015-05-11 Impact factor: 1.800