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1. Whole genome duplication does not promote common modes of reproductive isolation in Trifolium pratense

   https://doi.org/10.1002/ajb2.1466  

   Porturas, Laura D. ; Segraves, Kari A. ( April 2020 , American Journal of Botany)

   Although polyploidy has been studied since the early 1900s, fundamental aspects of polyploid ecology and evolution remain unexplored. In particular, surprisingly little is known about how newly formed polyploids (neopolyploids) become demographically established. Models predict that most polyploids should go extinct within the first few generations as a result of reproductive disadvantages associated with being the minority in a primarily diploid population (i.e., the minority cytotype principle), yet polyploidy is extremely common. Therefore, a key goal in the study of polyploidy is to determine the mechanisms that promote polyploid establishment in nature. Because premating isolation is critical in order for neopolylpoids to avoid minority cytotype exclusion and thus facilitate establishment, we examined floral morphology and three common premating barriers to determine their importance in generating reproductive isolation of neopolyploids from diploids.

   We induced neopolyploidy inTrifolium pratenseand compared their floral traits to the diploid progenitors. In addition to shifts in floral morphology, we examined three premating barriers: isolation by self‐fertilization, flowering‐time asynchrony, and pollinator‐mediated isolation.

   We found significant differences in the morphology of diploid and neopolyploid flowers, but these changes did not facilitate premating barriers that would generate reproductive isolation of neopolyploids from diploids. There was no difference in flowering phenology, pollinator visitation, or selfing between the cytotypes.

   Our results indicate that barriers other than the ones tested in this study—such as geographic isolation, vegetative reproduction, and pistil–stigma incompatibilities—may be more important in facilitating isolation and establishment of neopolyploidT. pratense.

    

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2. Polyploid plants obtain greater fitness benefits from a nutrient acquisition mutualism

   https://doi.org/10.1111/nph.16574  

   Forrester, Nicole_J ; Rebolleda‐Gómez, Maria ; Sachs, Joel_L ; Ashman, Tia‐Lynn ( May 2020 , New Phytologist)

   Polyploidy is a key driver of ecological and evolutionary processes in plants, yet little is known about its effects on biotic interactions. This gap in knowledge is especially profound for nutrient acquisition mutualisms, despite the fact that they regulate global nutrient cycles and structure ecosystems. Generalism in mutualistic interactions depends on the range of potential partners (niche breadth), the benefits obtained and ability to maintain benefits across a variety of partners (fitness plasticity). Here, we determine how each of these is influenced by polyploidy in the legume–rhizobium mutualism.

   We inoculated a broad geographic sample of natural diploid and autotetraploid alfalfa (Medicago sativa) lineages with a diverse panel ofSinorhizobiumbacterial symbionts. To analyze the extent and mechanism of generalism, we measured host growth benefits and functional traits.

   Autotetraploid plants obtained greater fitness enhancement from mutualistic interactions and were better able to maintain this across diverse rhizobial partners (i.e. low plasticity in fitness) relative to diploids. These benefits were not attributed to increases in niche breadth, but instead reflect increased rewards from investment in the mutualism.

   Polyploid plants displayed greater generalization in bacterial mutualisms relative to diploids, illustrating another axis of advantage for polyploids over diploids.

    

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3. Do water and soil nutrient scarcities differentially impact the performance of diploid and tetraploid Solidago gigantea (Giant Goldenrod, Asteraceae)?

   https://doi.org/10.1111/plb.13448  

   Walczyk, A. M. ; Hersch‐Green, E. I. ; Hawkesford, ed., M. ( July 2022 , Plant Biology)

   Plants require water and nutrients for survival, although the effects of their availabilities on plant fitness differ amongst species. Genome size variation, within and across species, is suspected to influence plant water and nutrient requirements, but little is known about how variations in these resources concurrently affect plant fitness based on genome size. We examined how genome size variation between autopolyploid cytotypes influences plant morphological and physiological traits, and whether cytotype‐specific trait responses differ based on water and/or nutrient availability.

   Diploid and autotetraploidSolidago gigantea(Giant Goldenrod) were grown in a greenhouse under four soil water:N+P treatments (L:L, L:H, H:L, H:H), and stomata characteristics (size, density), growth (above‐ and belowground biomass, R/S), and physiological (A_net,E,WUE) responses were measured.

   Resource availabilities and cytotype identity influenced some plant responses but their effects were independent of each other. Plants grown in high‐water and nutrient treatments were larger, plants grown in low‐water or high‐nutrient treatments had higherWUEbut lowerE, andA_netandErates decreased as plants aged. Autotetraploids also had larger and fewer stomata, higher biomass and largerA_netthan diploids.

   Nutrient and water availability could influence intra‐ and interspecific competitive outcomes. AlthoughS. giganteacytotypes were not differentially affected by resource treatments, genome size may influence cytogeographic range patterning and population establishment likelihood. For instance, the larger size of autotetraploidS. giganteamight render them more competitive for resources and niche space than diploids.

    

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4. Neopolyploidy causes increased nutrient requirements and a shift in plant growth strategy in H euchera c ylindrica

   https://doi.org/10.1002/ecy.4054  

   Anneberg, Thomas J. ; Segraves, Kari A. ( May 2023 , Ecology)

   Functional traits fall along a continuum from resource conservative to acquisitive and are powerful predictors of the ecological settings necessary for a species to persist and establish. As a consequence, a major problem that functional trait analysis could address is understanding the ecological contexts necessary for the persistence of polyploid plants, because early generation polyploids, or “neopolyploids,” are at a high extinction risk. Because neopolyploidy could increase nutrient limitation, growth strategies should shift to accommodate the increased need for resources, but this prediction is untested. To address this gap, we compared the functional trait responses of diploids, synthetic neotetraploids, and naturally occurring tetraploids ofHeuchera cylindrica, an herbaceous perennial plant, to nutrient manipulations in a greenhouse experiment. We found strong support for the hypothesis that neotetraploidy increases nutrient requirements, as evidenced by reduced productivity and increased tissue concentrations of nitrogen and phosphorus in neotetraploids. We also found that the repeated formation of independent origins of neotetraploidy led to differing responses to nutrient supply, but neotetraploidy generally shifted functional traits to be more resource acquisitive and inefficient. Taken together, our results suggest that shifts in functional trait responses may constrain the ability of neopolyploids to establish in nutrient‐poor habitats.

    

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5. Neopolyploidy increases stress tolerance and reduces fitness plasticity across multiple urban pollutants: support for the “general-purpose” genotype hypothesis

   https://doi.org/10.1093/evlett/qrad072  

   Turcotte, Martin M ; Kaufmann, Nancy ; Wagner, Katie L ; Zallek, Taylor A ; Ashman, Tia-Lynn ( January 2024 , Evolution Letters)

   Whole-genome duplication is a common macromutation with extensive impacts on gene expression, cellular function, and whole-organism phenotype. As a result, it has been proposed that polyploids have “general-purpose” genotypes that perform better than their diploid progenitors under stressful conditions. Here, we test this hypothesis in the context of stresses presented by anthropogenic pollutants. Specifically, we tested how multiple neotetraploid genetic lineages of the mostly asexually reproducing greater duckweed (Spirodela polyrhiza) perform across a favorable control environment and 5 urban pollutants (iron, salt, manganese, copper, and aluminum). By quantifying the population growth rate of asexually reproducing duckweed over multiple generations, we found that across most pollutants, but not all, polyploidy decreased the growth rate of actively growing propagules but increased that of dormant ones. Yet, when considering total propagule production, polyploidy increased tolerance to most pollutants, and polyploids maintained population-level fitness across pollutants better than diploids. Furthermore, broad-sense genetic correlations in growth rate among pollutants were all positive in neopolyploids but not so for diploids. Our results provide a rare test and support for the hypothesis that polyploids are more tolerant of stressful conditions and can maintain fitness better than diploids across heterogeneous stresses. These results may help predict that polyploids may be likely to persist in stressful environments, such as those caused by urbanization and other human activities. 

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