When everything changes at once: finding a new normal after genome duplication

Abstract

Whole-genome duplication (WGD), which leads to polyploidy, is implicated in adaptation and speciation. But what are the immediate effects of WGD and how do newly polyploid lineages adapt to them? With many studies of new and evolved polyploids now available, along with studies of genes under selection in polyploids, we are in an increasingly good position to understand how polyploidy generates novelty. Here, I will review consistent effects of WGD on the biology of plants, such as an increase in cell size, increased stress tolerance and more. I will discuss how a change in something as fundamental as cell size can challenge the function of some cell types in particular. I will also discuss what we have learned about the short- to medium-term evolutionary response to WGD. It is now clear that some of this evolutionary response may ‘lock in’ traits that happen to be beneficial, while in other cases, it might be more of an ‘emergency response’ to work around physiological changes that are either deleterious, or cannot be undone in the polyploid context. Yet, other traits may return rapidly to a diploid-like state. Polyploids may, by re-jigging many inter-related processes, find a new, conditionally adaptive, normal.

Genome Size Covaries More Positively with Propagule Size than Adult Size: New Insights into an Old Problem

“…Assumption #5 is supported by many studies, showing that although increasing genome size (including polyploidy) is almost always associated with increased cell size [ 179 , 184 , 189 , 190 , 191 , 192 , 193 , 194 , 195 ], it usually has no or a negative relationship with cell number (as indicated by no or only small increases or decreases in body size [ 179 , 184 , 193 , 195 , 196 , 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 ] (see also Section 4.5 ; Table A2 ).…”

Polyploidy on Islands: Its Emergence and Importance for Diversification

“…It remains to be studied which aspects of polyploidy are critical for a given taxon and island and whether there is a more general aspect that allows polyploids to disperse, colonize, and/or diversify. Given advances in molecular biology, it seems feasible in the future to determine a propensity to form polyploid species ( Bomblies, 2020 ) and to detect ancient rounds of polyploidy ( Tiley et al, 2018 ). At the moment, polyploidy per se outside the island systems could not be considered in our analyses because of the difficulty to establish this in many cases (i.e., where the chromosome number of a sister lineage was unknown) and our observations that many of the lineages colonizing the island systems are already polyploid lineages of mainland taxa [e.g., Coprosma (Rubiaceae)].Where there is high species richness within a genus, it seems the polyploid lineage is the one that colonizes the island systems, but overall these examples remain few.…”

“…Our comparative study was limited to data that were available for the island systems under study and we were surprised that some of these “classic” island systems remain poorly known chromosomally and phylogenetically, especially the Galápagos. While genomic studies have revolutionized our ideas of polyploid genome dynamics (e.g., Bomblies, 2020 ), there is much value in continuing to generate chromosome numbers and dated phylogenies for native island endemics. Because island radiations are often young and/or rapid on an evolutionary timescale, in many cases acquiring a well-resolved phylogeny for a group of species based on single or few gene sequences has been challenging (e.g., Meudt and Simpson, 2006 ; Knope et al, 2012 ; Vitales et al, 2014 ).…”

Parallel adaptation in autopolyploidArabidopsis arenosais dominated by repeated recruitment of shared alleles

“…Autopolyploidy is expected to alter the selection and adaptation process in many ways, but a dearth of empirical data prevents synthetic evaluation. Besides immediate phenotypic [12][13][14] and genomic 10,11 changes following WGD, theory is unsettled regarding how adaptation proceeds as the autopolyploid lineage diversifies and adapts to novel challenges. On the one hand, autopolyploids can better mask deleterious alleles and accumulate cryptic allelic diversity 7 .…”