Reproductive diversity, polyploidy, and geographical parthenogenesis in two Eriotheca (Malvaceae) species from Brazilian Cerrado

Abstract

Breeding systems have been associated with polyploidization and genomic change, which have a central role in the diversification of Angiosperms. Polyploidy commonly leads to isolated populations and species, and sometimes to apomixis, as observed for some woody plants of Cerrado, the Neotropical savannas in Central Brazil. Eriotheca gracilipes and E. pubescens are common trees in this region, and present both sexual and sporophytic apomictic individuals. We studied here how morphological features and breeding systems are linked to ploidy and genome size differences, and how these features may help to understand cytotypes distribution. We confirmed breeding systems by hand pollination experiments and complemented histological analyses to describe the apomixis and sexual process for individuals with previously defined ploidy levels. We used flow cytometry and morphometry data to verify the relationships among cytotypes. Fruit and seed features were also measured for extensive samples of both species to observe environmental correlates such as altitude of occurrence and distribution of each embryony pattern and cytotypes. In both species, agamic complexes included individuals with nucellar polyembryony associated to putatively neopolyploid, hexaploid cytotypes, while lower ploidy individuals were sexual and self-sterile. Higher genome sizes were also associated with larger pollen grains and stomata, besides other more complex morphological trends. Embryonic patterns were consistent for each site, individuals, and along years, although the percentage of polyembryonic seeds and number of embryos per seed varied. Monoembryonic sexual individuals were associated with higher elevation, allegedly last glacial maximum Cerrado refuges, while polyembryonic sporophytic apomicts appeared in lower areas.