Polyploidy in arctic plants

Abstract

The Arctic is an excellent model system for the study of polyploidy. It is one the Earth's most polyploid-rich areas, in particular of high-level and recently evolved polyploids. Here we re-address previous hypotheses on arctic polyploidy based on a new analysis of the circumarctic flora, and review recent molecular, cytological and reproductive studies. The frequency and level of polyploidy strongly increase northwards within the Arctic. We found no clear-cut association between polyploidy and the degree of glaciation for the arctic flora as a whole, which contains many widespread species. However, for 'arctic specialist' taxa with restricted distributions, the frequency of diploids is much higher in the Beringian area, which remained largely unglaciated during the last ice age, than in the heavily glaciated Atlantic area. This result supports the hypothesis that polyploids are more successful than diploids in colonizing after deglaciation. There is abundant molecular evidence for recurrent formation of arctic polyploids at different scales in time and space. Examples are given of low-level polyploids formed after the last glaciation and of repeated and successively more high-level polyploidizations throughout the Quaternary. Recurrent polyploid origins, followed by interbreeding within and across ploidal levels, provide a major explanation for the taxonomic complexity of the arctic flora. In the well-studied, recently deglaciated archipelago of Svalbard, most species are mainly selffertilizing or clonal. All Svalbard polyploids examined so far are genetic allopolyploids with fixed heterozygosity at isozyme loci. The level of heterozygosity in 65 taxa increases dramatically from diploids to high-level polyploids. In the circumarctic area, there is evidence for numerous recently evolved sibling species within diploid taxonomic species. Rapid evolution of crossing barriers at the diploid level promotes further diversification after expansion from different refugia, and may provide new raw materials for allopolyploid formation. We conclude that the evolutionary success of polyploids in the Arctic may be based on their fixed-heterozygous genomes, which buffer against inbreeding and genetic drift through periods of dramatic climate change.

Polyploidy and genome evolution in plants

“…Increased unreduced gamete production during times of environmental stress and/or fluctuation could thus be an important factor in explaining the apparent clustering of paleopolyploidizations at the K/Pg boundary. It could also explain why many present-day polyploids often are more abundant in stressful environments, such as the Arctic (Brochmann et al, 2004) or disturbed habitats (Mraz et al, 2012).…”

“…Despite these apparent barriers, polyploids are common elements of all floras worldwide and are particularly abundant at high latitudes and high elevations (e.g., Ehrendorfer 1980; Brochmann et al 2004). The 'success' of polyploids is often attributed to the increased genetic diversity held within single polyploid individuals relative to that of their diploid progenitors (e.g., Roose and Gottlieb 1976;Rieseberg and Soltis 1986;Soltis and Soltis 1989, 1993, 2000, 2009Brochmann et al 2004). Moreover, this genetic diversity may be manifested in novelty at the biochemical, physiological, morphological, and ecological levels, giving polyploids an advantage, at least in the short term, over their diploid parents (e.g., Levin 1983;Soltis et al 2014).…”

High mountain origin, phylogenetics, evolution, and niche conservatism of arctic lineages in the hemiparasitic genus Pedicularis (Orobanchaceae)

“…The occupation of arctic habitats was frequently considered to be associated with polyploidy (Brochmann and Steen, 1999;Brochmann et al, 2004;Jordon-Thaden and Koch, 2008). In Artemisia and Ranunculus diploid and polyploid species occur in the Arctic.…”

Two Beringian Origins for the Allotetraploid Fern Polystichum braunii (Dryopteridaceae)

“…This pattern may be driven by cycles of glaciation and deglaciation in boreal regions (Stebbins 1950). Especially in northern regions, the fixed-heterozygote genomes of allopolyploids may counter inbreeding and genetic drift during periglacial climate change (Brochmann et al 2004). Ferns present an array of polyploids with patterns suggesting this history, from those with highly localized populations and widespread progenitors to those with continent-wide distributions and missing progenitors.…”