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

Abstract

Hybridization and changes in ploidy have been associated with shifts from sexuality to apomixis, and may explain isolation among populations and species. Hybrids resulting from interploidy crosses may contribute to a broader understanding of how these populations and species have originated and evolved. Stomatal morphometrics and flow cytometry analyses were carried out for seedlings from different populations of Eriotheca estevesiae, E. gracilipes and E. pubescens, a group of closely related tree species in the Central Brazilian Cerrados. Controlled cross-pollinations between individuals of different cytotypes of E. gracilipes (2n = 2x = 92 and 2n = 6x = 276) and between sexual cytotypes of E. gracilipes (2n = 2x = 92) and E. pubescens (2n = 4x = 184) were performed. Only one viable seed was obtained from interploidy crosses of E. gracilipes. The hybridization between sexual cytotypes did not produce fruits. Genome size analyses indicated that there were apparently no natural hybrids or mixed ploidy populations among the seedlings analyzed. Seedlings stomatal size was consistent with previously reported cytotypes and ploidy levels; and when compared with the stomata of the viable interploidy hybrid of E. gracilipes, indicated a tetraploid, intermediate ploidy level. Although the data suggest the possibility of interploidy hybridization, cytotypes appeared relatively stable and natural interploidy hybridization seems to be uncommon among Eriotheca trees.

Phylogeography of Eriotheca species complex: insights into the origin and range expansion of apomictic and polyploid trees in Neotropical Savannas

“…These mixed populations may evidence gene flow between apomictic and sexual individuals and, in some cases, may promote the restoration of genetic variability in apomictic lineages (Karunarathne & Hojsgaard, 2021). But, as previously mentioned, hybridization does not seem to be common (Serra et al ., 2022).…”

“…10 out of 30 accepted species) seem to have originated <10 mya and are associated with the rise of seasonal C 4 grass savanna environments and frequent fires (Simon & Pennington, 2012). Despite sympatry and breeding similarities, common Cerrado Eriotheca are not sister groups, and hybridization does not seem to be common, although it cannot be ruled out (Serra et al ., 2022).…”