Genome size evolution among closely related species in Gossypium

Genome size is an extremely labile characteristic of plant genomes, often experiencing rapid changes over short evolutionary time. The size differences among and lability of plant genomes can largely be attributed to the dynamics of the repetitive sequences that populate and influence these genomes. Thus far, research into genome size evolution in Gossypium has largely focused on intergenomic comparisons of repetitive populations among more distantly related genome groups; however, recent analyses have suggested that while genome size within groups of closely related species (e.g., within the diploid cotton A-genome group) can be nearly identical (1667 versus 1698 Mbp in G. herbaceum and G. arboreum, respectively), the repetitive profile for each genome can vary substantially. Here we extend intragenomic repetitive profile analysis to the smallest clade of cotton species (D-genome), whose 13 known species range in genome size from 841 Mbp in G. gossypioides and G. thurberi to 934 Mbp in G. laxum and G. lobatum. Using a cluster-based analysis, we profile the repetitive content for each species and evaluate the evolution these in a phylogenetic context, providing insight into the evolution of repeats over short evolutionary distances and in the presence of introgression.