What we still don't know about polyploidy

Abstract

During the past decade there has been a tremendous resurgence of interest in polyploidy that has in large part been stimulated by the development of increasingly powerful genetic and genomic tools. The result has been numerous new insights into the genomic and genetic consequences of polyploidy. The plethora of new discoveries has dramatically reshaped traditional views and concomitantly revealed that polyploidy is a highly dynamic and ubiquitous process. These recent advances in our understanding of polyploidy have stimulated numerous reviews, most focused on the various genetic, epigenetic, and genomic consequences of polyploid evolution. Whereas genetic and genomic attributes of polyploidization have received considerable attention, other crucial areas of polyploid evolution have received much less (e.g., ecology, pollination biology, physiology). The focus of this paper is not to review again recent discoveries, but to emphasize what we do not yet know about polyploidy, which despite all that has been learned about genome doubling is still an enormous amount. Our list is not meant to be comprehensive, but includes a range of topics that we have placed in several general categories, including mode of formation, ecological and physiological consequences, and genomic rules. Questions include: What is (are) the most frequent mechanism(s) of polyploidization? What factors promote/facilitate polyploidization? What factors favor autopolyploid vs. allopolyploid formation? Do multiple origins result in lineages with differing evolutionary trajectories and/or cryptic species? Our major goals are to stimulate discussion and promote further research.

Evidence of Genomic Exchanges between Homeologous Chromosomes in a Cross of Peanut with Newly Synthetized Allotetraploid Hybrids

“…The BKKK genotypic composition was regarded as a consequence of homeologous recombination during the meiosis of the parents particularly in the synthetic allotetraploid. In some species, homeologous pairing during meiosis is suspected to occur in the first generations following polyploid formation (Ramsey and Schemske, 2002; Soltis et al, 2010; Szadkowski et al, 2010). …”

“…Meiotic instabilities are common in interspecific and resynthesized lines (Gaeta et al, 2007; Lyrene, 2016). In some allopolyploid plants, recombination between subgenomes during meiosis was suspected to occur in newly formed polyploids (Ramsey and Schemske, 2002; Soltis et al, 2010) but was rarely observed among stabilized allopolyploids (Salmon et al, 2010; Ainouche and Wendel, 2014). …”

Through thick and thin: Cryptic sympatric speciation in the submersed genus Najas (Hydrocharitaceae)

“…Because broad-scale gene flow is not restricted by geographic segregation of individuals, allopolyploidy clearly represents not only an example of sympatric speciation (Bird et al, 2012), but ''instantaneous'' or ''nearinstantaneous'' speciation (Harrison, 2012Abbott et al, 2013). Consequently, it is regarded as ''the only widely accepted mode of sympatric speciation'' (Hendry, 2009;Soltis et al, 2010). Individual allele sequences derived from N. canadensis (orange), N. muenscheri (pink), or N. canadensis  N. flexilis (green) associated with alleles derived from both N. flexilis (brown) and N. guadalupensis (blue), indicating these taxa to be of hybrid origin (see also Table 6).…”

Life at the extreme: lessons from the genome

“…The initially increased gene dosage following duplication is often assumed to be beneficial for survival in new habitats, at least in the short term [32]. But although there are certainly polyploid species known for their extreme adaptations to abiotic stresses, an equal fraction are adapted to less harsh conditions, and there are also diploid extremophiles (including Thellungiella spp.).…”