New insights into the variability of reproduction modes in European populations of Rubus subgen. Rubus: how sexual are polyploid brambles?

Abstract

Rubus subgen. Rubus includes common European species with highly complicated taxonomy, ongoing hybridisation and facultative apomixis. Out of approximately 750 species recognised in Europe, only 3 diploid sexual species are known, along with numerous apomictic brambles that are highly connected to polyploidy. One exception of a tetraploid taxon is R. ser. Glandulosi, which is known for prevalent sexuality. This taxon highly hybridises with tetraploid members of R. ser. Discolores and leads to the origin of many hybridogenous populations and individuals. In this study, we verify reproduction modes in different diploid, triploid and tetraploid species of subgen. Rubus, with focus on taxa putatively involved in such hybridisation by applying flow cytometric seed screen analysis. We found 100 % sexuality of diploid species, whereas triploid species had obligate unreduced embryo sac development. In contrast, tetraploid plants had varying degrees of sexuality. Additionally, we discovered that R. bifrons has the ability to undergo a reproduction mode switch as a reaction to environmental conditions. These results provide insight into reproductive modes of European brambles and shed light on their reticulate evolution and speciation.

Capricious, or tied to history's apron strings? Floristic regions in north‐west European brambles (RubussubgenusRubus, Rosaceae)

“…The hypothesized process might be reinforced by the relatively high percentage of retained sexuality in Rubus ser. Glandulosi which are typically ancient woodland inhabitants, resulting in high rates of speciation (Šarhanová et al ., ) and high numbers of young species with small distributional areas. Retained sexuality is regarded as a motor of diversity in apomictic genera through hybridization, as was reported for instance for the Ranunculus auricomus aggregate (Hörandl et al ., ), but also for Rubus ser.…”

“…Retained sexuality is regarded as a motor of diversity in apomictic genera through hybridization, as was reported for instance for the Ranunculus auricomus aggregate (Hörandl et al ., ), but also for Rubus ser. Glandulosi , especially in some montane areas (Šarhanová et al ., ; Haveman & de Ronde, ). A final examination of these hypotheses (through scaling of distributional patterns) is only possible if more species are tested on their provenance.…”

Is evolution of apomicts driven by the phylogeography of the sexual ancestor? Insights from European and Caucasian brambles (Rubus, Rosaceae)

“…For instance, gametophytic apomixis (seed development from an unreduced megagametophyte) is almost always associated with, but possibly not caused by, polyploidy and hybridity (Lovell et al., ). Apomictic developmental pathways may be regulated by multiple loci, epigenetic mechanisms (Hand & Koltunow, ) and environmental factors (Evans & Knox, ; Šarhanová, Vašut, Dančák, Bureš, & Trávníček, ), but can also be induced by the expression of a single deregulated allele (Corral et al., ). In addition, most apomictic taxa maintain a normal sexual pathway (Asker & Jerling, ).…”

Concealed diversity : taxonomical, phytogeographical and phytosociological notes on brambles (Rubus L. subgen. Rubus) in north-west Europe

“…Most members are tetraploid pseudogamous apomict lineages, but other ploidylevels (triploids, pentaploids and hexaploids) are not uncommon (Gustafsson 1943;Krahulcová et al 2013). The mode of reproduction is highly variable, ranging from obligate sexual reproduction to obligate apomixis, both at the species level as well as at the individual or even floral level (Pratt & Einset 1955;Šarhanová et al 2012). Apomictic reproduction combines both diplospory and apospory, and this mode of reproduction can be influenced by environmental factors (Šarhanová et al 2012).…”

“…Retained sexuality is regarded as a motor of diversity in apomictic genera through hybridization, as was reported for instance for the Ranunculus auricomus aggregate (Hörandl et al 2009), but also for Rubus ser. Glandulosi, especially in some montane areas (Šarhanová et al 2012;Haveman & De Ronde 2013). A final examination of these hypotheses (through scaling of distribution patterns) is only possible if more species are tested on their provenance.…”