Stomatal size, ploidy and polyembryony in Eriotheca Stellate Trichome Species Complex (Bombacoideae – Malvaceae) in the Cerrados of Brazil

Abstract

• Geographic parthenogenesis, range expansion of apomictic plants after climate changes, has been described for Northern Hemisphere gametophytic apomicts. But similar trends have been observed for sporophytic apomicts of Cerrado, the savannas in Brazil. Eriotheca pubescens is a common Cerrado tree, an agamic complex of either hexaploid/polyembryonic apomicts or tetraploid/monoembryonic sexual individuals. Some populations have been described as a new species, Eriotheca estevesiae, all included in the Eriotheca Stellate Trichome Species Complex (ESTSC). Since breeding systems and ploidy are clearly associated with polyembryony and stomatal size, we used these ancillary features to map the reproductive and ploidy level traits of E. pubescens and E. estevesiae. • Leaves and seeds were collected from individuals of 19 populations. Seeds were evaluated for the presence of polyembryony and leaves for stomatal measurements. • Eight populations were monoembryonic while another eight were polyembryonic and for other three, the embryonic pattern was not readily verified. E. pubescens polyembryonic and hexaploid populations formed a homogeneous group, but monoembryonic plants were more variable. E. estevesiae populations were monoembryonic with smaller stomata. In contrast, some E. pubescens monoembryonic populations further south presented larger stomata. Despite these outliers, possibly mixed populations, stomatal size and embryonic pattern differed from northern to southern populations. • Embryonic pattern and stomatal size indicated that northernmost populations of Eriotheca STSC (E. estevesiae) are diploid and sexual. Southernmost populations, mostly polyembryonic and with large stomata, are hexaploid and apomictic. This is in agreement with geographic parthenogenesis and range expansion of apomictic lineages to southern habitats available after the last glacial maximum.

Interploidy hybridization in Eriotheca gracilipes and E. pubescens (Malvaceae): experimental evidence, genome and stomatal size

“…Only one seedling actually developed and although the number of hybridization pollinations prevents making generalizations and the early death of the putative hybrid seedling made impossible further ploidy assessment via flow cytometry, stomatal morphometrics suggested an intermediate ploidy level. Stomatal morphometry stomatal was consistent with ploidy level in Eriotheca (Marinho et al 2014a(Marinho et al , 2020. The Nested ANOVA analyzes showed that the species cytotypes (and pooled ploidy levels) were the most important factors explaining stomatal size variation, possibly because polyploidization affects cell size of Eriotheca, as it does in Citrus (Costa et al 2004), Musa (Vandenhout et al 1995) and other groups (Balao et al 2011).…”

“…Some cytotypes of E. gracilipes and E. pubescens occur sympatrically in the Triângulo Mineiro region and both sexual and apomictic individuals require pollination to set fruits and viable seeds (Mendes-Rodrigues et al 2019). As mentioned before, pollen and stomatal sizes are clearly correlated to ploidy levels in the three Eriotheca species (Marinho et al 2014a(Marinho et al , 2020Mendes-Rodrigues et al 2019).…”

“…The leaves were dried and preserved in silica gel. The morphometric analyses of seedling stomata followed methodology described for stomatal measurements of expanded leaves of adult individuals (Marinho et al 2014a(Marinho et al , 2020. We used cyanoacrylate instant glue (SuperBonder-Loctite®) to obtain leaf impressions (Chin et al 1995) of previously re-hydrated leaflets on glass microscope slides.…”

“…is phylogenetically related to E. pubescens (Carvalho-Sobrinho et al 2015). It is diploid, 2n = 2x = 92, and monoembryonic (Marinho et al 2020). Flow cytometry studies and stomatal measurements have been successfully used to corroborate Eriotheca ploidy levels (Marinho et al 2014a(Marinho et al , b, 2020Mendes-Rodrigues et al 2019).…”

“…Cerrado Eriotheca are pollinated by large solitary bees which are widely distributed and some of them were observed visiting both E. gracilipes and E. pubescens (Oliveira et al 1992). Although pollination biology studies for E. estevesiae are still lacking, flowers are similar to E. pubescens (Carvalho-Sobrinho et al 2015) and there are no clear hybridization barriers among populations and species (Marinho et al 2020). Some cytotypes of E. gracilipes and E. pubescens occur sympatrically in the Triângulo Mineiro region and both sexual and apomictic individuals require pollination to set fruits and viable seeds (Mendes-Rodrigues et al 2019).…”