Abstract
Polyploidy contributes massively to the taxonomic and genomic diversity of angiosperms, but certain aspects of polyploid evolution are still enigmatic. The establishment of a new polyploid lineage following whole-genome duplication (WGD) is a critical step for all polyploid species, but this process is difficult to identify and observe in nature. Mathematical models offer an opportunity to study this process by varying parameters related to the populations, habitats, and organisms involved in the polyploid establishment process. While several models of polyploid establishment have been published previously, very few incorporate spatial factors, including spatial relationships between organisms, habitat shape, or population density. This study presents a stochastic, spatial model of polyploid establishment that shows how factors such as habitat shape and dispersal type can influence the fixation and persistence of nascent polyploids and modulate the effects of other factors. This model predicts that narrow, constrained habitats such as roadsides and coastlines may enhance polyploid establishment, particularly in combination with frequent clonal reproduction, limited dispersal, and high population density. The similarity between this scenario and the growth of many invasive or colonizing species along disturbed, narrow habitats such as roadsides may offer a partial explanation of the prevalence of polyploidy among invasive species.
Highlights
Polyploid evolution is impossible to understand without knowing how and under what conditions new polyploid populations become established
While polyploid fixation is another measure of polyploid success in this study, rapid fixation will likely favor the production of genetically uniform polyploid populations that may be less adaptable in the long term
Offspring lost to dispersal outside of the suitable habitat would not affect the size of the population, as reproduction would still proceed until the population reached carrying capacity during each generation
Summary
Polyploid evolution is impossible to understand without knowing how and under what conditions new polyploid populations become established. Broad comparisons of diploid and polyploid taxa show minor or inconsistent associations between self-incompatibility, mating system and ploidy (Mable, 2004; Barringer, 2007), and phylogenetic studies of mating system and polyploidy in Solanaceae (Robertson et al, 2011; Zenil-Ferguson et al, 2019) have shown that self-compatibility is more likely to evolve prior to polyploidy than in concert with it This trait is frequently variable within species or even populations, which further complicates any inference performed at the species level. This paper describes a new spatial, stochastic polyploid establishment model that addresses these questions This model includes parameters for population size (K), reproductive assurance (Ra) through selfing or clonality, lifespan (annual vs perennial), and habitat shape (square vs narrow). The model does not incorporate any trait or fitness differences between cytotypes (aside from the fact that they are reproductively isolated from each other, which can lead to reproductive interference when mating occurs between cytotypes), and each simulation is compared to a non-spatial control with the same starting conditions
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