Patterns, causes and consequences of genome size variation in Restionaceae of the Cape flora

Abstract

Little is known about genome size (GS) variation in the hyperdiverse Cape flora of southern Africa. Towards filling this gap, we measured GS of 158 species of Cape Restionaceae and demonstrated > 16-fold variation in 1C-values (0.47-7.66 pg). We also report chromosome counts of nine species and show that 2n = 32 predominates. Patterns of GS variation were used to infer ploidy, and the variation at the holoploid level was partitioned into monoploid and ploidy variation. We show that at least 30% of the species measured contain several ploidies. The monoploid GS variation was phylogenetically constrained and 1Cx-values were significantly lower in areas near the centre of the Cape Floristic Region and in species which resprout after fire. A higher proportion of inferred polyploids were found in species with wide distribution ranges, which are smaller plants, resprout after fires and are therefore longer lived. In addition, polyploids prevail in areas at the periphery of the Cape Floristic Region, which are more likely to have been exposed to fluctuating climates in the past, and at higher elevations. This shows that monoploid and polyploid GS variation could be responding to different selection pressures.