Genomic differentiation and polyploidy in Sowerbaea (Liliaceae)

Abstract

Sowerbaea is an endemic Australian genus of five allopatric, vicarious species. A basic genome of three long subacrocentric chromosomes and one shorter acrocentric chromosome is constant in the genus, but within this overall genomic uniformity there are distinct karyotypic differences between species. There are also quantitative differences in nuclear DNA with a twofold difference between the species with the greatest and least amounts of DNA per genome. The quantitative DNA measurements have been combined with measurements of relative chromosome length to obtain estimates of differences in absolute chromosome sizes. Polyploidy is widespread in the genus, and diploid (n = 4), tetraploid (n = 8) and octoploid (n = 16) biotypes occur. Structural differences in the genomes were established at the diploid level, and have arisen during an early stage in differentiation of biotypes in the genus. The polyploid forms are mostly located in eastern Australia, and the establishment of polyploid races was probably a later phase of biotype differentiation associated with late Tertiary and Quaternary climatic changes. The tetraploids are structural autoploids, and have probably arisen within established biotypes. The octoploid form of S. juncea is probably an autoallo-octoploid, derived from tetraploid stocks which were ancestral to S. juncea and S. subtilis respectively.