Format: ORAL

Marcial Escudero1

1 Department of Plant Biology and Ecology, University of Seville, Seville, Spain

Chromosome evolution is a major driver of diversification in angiosperms. Whereas polyploidy has been investigated at a great deal in angiosperms, dysploidy (chromosome number changes by fission/agmatoploidy and fusion/symploidy without a significant change in DNA content) has been, in comparison, mostly ignored. The clade of family Cyperaceae, with holocentric chromosomes -kinetochoric activity is distributed along the whole chromosome-, and consequently a large range of chromosome number vatiation, is an ideal study system to investigate the consequences of chromosome fission and fusion. By fitting models of chromosome evolution in the phylogeny of the Cyperaceae, we have inferred that the rate of dysploidy, and also polyploidy, is not homogeneous across Cyperaceae, instead there are clades where rates of chromosome evolution accelerates or decelerates. Using comparative genomics of closely and distantly related species, we have also observed the pull of the present for chromosome evolution. The same way that the rates of molecular, morphological, fossil and speciation seem to accelerate towards the present in the tree of life, we have also found how the rates of fission and fusion seem to be much faster at microevolutionary scale than at macroevolutionary scale. Comparative genomics suggest that there is a strong genomic constraint that limits where fission and fusion may occur which results in parallel events of fission and fusion across different lineages and leads to underestimate the rates of dysploidy at the macroevolutionary scale. The inferred hotspots of dysploidy are very rich in repeat DNA, that is, the repeat landscape may determine the rates of fission and fusion and their location in the genome. Finally, at microevolutionary scale, we shed light into the crucial question of how new karyotypes become established. New chromosome variants may become fixed in the populations by both, stochastic processes like drift or selection of locally adapted karyotypes.