The immediate effects of polyploidization of Spirodela polyrhiza change in a strain-specific way along environmental gradients

Interspecific transfer of genetic information through polyploid bridges

Hybridization blurs species boundaries and leads to intertwined lineages resulting in reticulate evolution. Polyploidy, the outcome of whole genome duplication (WGD), has more recently been implicated in promoting and facilitating hybridization between polyploid species, potentially leading to adaptive introgression. However, because polyploid lineages are usually ephemeral states in the evolutionary history of life it is unclear whether WGD-potentiated hybridization has any appreciable effect on their diploid counterparts. Here, we develop a model of cytotype dynamics within mixed-ploidy populations to demonstrate that polyploidy can in fact serve as a bridge for gene flow between diploid lineages, where introgression is fully or partially hampered by the species barrier. Polyploid bridges emerge in the presence of triploid organisms, which despite critically low levels of fitness, can still allow the transfer of alleles between diploid states of independently evolving mixed-ploidy species. Notably, while marked genetic divergence prevents polyploid-mediated interspecific gene flow, we show that increased recombination rates can offset these evolutionary constraints, allowing a more efficient sorting of alleles at higher-ploidy levels before introgression into diploid gene pools. Additionally, we derive an analytical approximation for the rate of gene flow at the tetraploid level necessary to supersede introgression between diploids with nonzero introgression rates, which is especially relevant for plant species complexes, where interspecific gene flow is ubiquitous. Altogether, our results illustrate the potential impact of polyploid bridges on the (re)distribution of genetic material across ecological communities during evolution, representing a potential force behind reticulation.

Neopolyploidy-induced changes in giant duckweed (Spirodela polyrhiza) alter herbivore preference and performance and plant population performance

PREMISE

Polyploidy is a widespread mutational process in angiosperms that may alter population performance of not only plants but also their interacting species. Yet, knowledge of whether polyploidy affects plant-herbivore dynamics is scarce. Here, we tested whether aphid herbivores exhibit preference for diploid or neopolyploid plants, whether polyploidy impacts plant and herbivore performance, and whether these interactions depend on the plant genetic background.

METHODS

Using independently synthesized neotetraploid strains paired with their diploid progenitors of greater duckweed (Spirodela polyrhiza), we evaluated the effect of neopolyploidy on duckweed's interaction with the water-lily aphid (Rhopalosiphum nymphaeae). Using paired-choice experiments, we evaluated feeding preference of the herbivore. We then evaluated the consequences of polyploidy on aphid and plant performance by measuring population growth over multiple generations.

RESULTS

Aphids preferred neopolyploids when plants were provided at equal abundances but not at equal surface areas, suggesting the role of plant population surface area in driving this preference. Additionally, neopolyploidy increased aphid population performance, but this result was dependent on the plant's genetic lineage. Lastly, the impact of herbivory on neopolyploid vs. diploid duckweed varied greatly with genetic lineage, where neopolyploids appeared to be variably tolerant compared to diploids, sometimes mirroring the effect on herbivore performance.

CONCLUSIONS

By experimentally testing the impacts of polyploidy on trophic species interactions, we showed that polyploidization can impact the preference and performance of herbivores on their plant hosts. These results have significant implications for the establishment and persistence of plants and herbivores in the face of plant polyploidy.

Duplicated gene networks promote 'hopeful' phenotypic variation

The consequences of whole-genome duplication (WGD) remain elusive. A new study by Ebadi et al. simulating duplicated gene networks predicts that WGD immediately generates autopolyploids with extreme phenotypes and increases phenotypic variance. Such theoretical work calls for new experimental studies addressing to what extent WGD may be beneficial under environmental changes.

The duplication of genomes and genetic networks and its potential for evolutionary adaptation and survival during environmental turmoil

The importance of whole-genome duplication (WGD) for evolution is controversial. Whereas some view WGD mainly as detrimental and an evolutionary dead end, there is growing evidence that polyploidization can help overcome environmental change, stressful conditions, or periods of extinction. However, despite much research, the mechanistic underpinnings of why and how polyploids might be able to outcompete or outlive nonpolyploids at times of environmental upheaval remain elusive, especially for autopolyploids, in which heterosis effects are limited. On the longer term, WGD might increase both mutational and environmental robustness due to redundancy and increased genetic variation, but on the short-or even immediate-term, selective advantages of WGDs are harder to explain. Here, by duplicating artificially generated Gene Regulatory Networks (GRNs), we show that duplicated GRNs-and thus duplicated genomes-show higher signal output variation than nonduplicated GRNs. This increased variation leads to niche expansion and can provide polyploid populations with substantial advantages to survive environmental turmoil. In contrast, under stable environments, GRNs might be maladaptive to changes, a phenomenon that is exacerbated in duplicated GRNs. We believe that these results provide insights into how genome duplication and (auto)polyploidy might help organisms to adapt quickly to novel conditions and to survive ecological uproar or even cataclysmic events.

Survival Strategies of Duckweeds, the World's Smallest Angiosperms

Duckweeds (Lemnaceae) are small, simply constructed aquatic higher plants that grow on or just below the surface of quiet waters. They consist primarily of leaf-like assimilatory organs, or fronds, that reproduce mainly by vegetative replication. Despite their diminutive size and inornate habit, duckweeds have been able to colonize and maintain themselves in almost all of the world's climate zones. They are thereby subject to multiple adverse influences during the growing season, such as high temperatures, extremes of light intensity and pH, nutrient shortage, damage by microorganisms and herbivores, the presence of harmful substances in the water, and competition from other aquatic plants, and they must also be able to withstand winter cold and drought that can be lethal to the fronds. This review discusses the means by which duckweeds come to grips with these adverse influences to ensure their survival. Important duckweed attributes in this regard are a pronounced potential for rapid growth and frond replication, a juvenile developmental status facilitating adventitious organ formation, and clonal diversity. Duckweeds have specific features at their disposal for coping with particular environmental difficulties and can also cooperate with other organisms of their surroundings to improve their survival chances.

Sixth International Conference on Duckweed Research and Applications Presents Lemnaceae as a Model Plant System in the Genomics and Postgenomics Era

The 6th International Conference on Duckweed Research and Applications (6th ICDRA) was organized at the Institute of Plant Genetics and Crop Plant Research (IPK) located in Gatersleben, Germany, from 29 May to 1 June 2022. The growing community of duckweed research and application specialists was noted with participants from 21 different countries including an increased share of newly integrated young researchers. The four-day conference focused on diverse aspects of basic and applied research together with practical applications of these tiny aquatic plants that could have an enormous potential for biomass production.