Chromosomal evolution in the genus Brachyscome (Asteraceae, Astereae): Statistical tests regarding correlation between changes in karyotype and habitusing phylogenetic information

Karyotype analyses were carried out on 73 taxa of Brachyscome and 8 taxa of ifs allied genera, Australian Astereae. Statistical tests regarding correl ations between changes in chromosome number, total chromosome length, mean chromosome length, karyotypic asymmetry and chromosome length heterogeneity and changes in habit were performed based on the matK molecular phylogenet ic tree. The reductions in chromosome number and total chromosome length, a nd the increases in mean chromosome length, chromosome length heterogeneity and karyotypic asymmetry were found to be correlated with the change in ha bit from perennial to annual. A reduction in total chromosome length is fav ored to shorten the mitotic cell cycle and to produce smaller cells conduci ve to more rapid development of smaller annuals under the time-limited envi ronment Stepwise dysploidal reductions in chromosome number were achieved t hrough the translocation of large chromosome segments onto other chromosome s, followed by the loss of a centromere, resulting in one fewer linkage gro up and one fewer haploid chromosome. The correlations between the dysploida l reduction in chromosome number and the increases in mean chromosome lengt h, length heterogeneity and asymmetry in karyotype can be attributed to thi s mode of chromosomal change. These changes occurred independently in sever al different lineages in Brachyscome.