Plant genome diversity and evolution in response to environmental N and P
Professor Andrew Leitch, Queen Mary University of London, UK
Dr Ilia Leitch, Royal Botanic Gardens, Kew, UK
Angiosperm genome sizes (GS) range c. 2,400-fold, but are strongly skewed towards small values despite having an abundance of repetitive DNA and, in most lineages, multiple rounds of polyploidy in their ancestry. Such observations suggest selection against large GSs. One potential source of selection is nutrient availability, particularly phosphorous (P) and nitrogen (N), since large genomes are costly to build in terms of N and P needed to make nucleic acids, elements that are frequently limiting. To test the hypothesis that N and P availability limits GS, we analysed the impact of different nutrient regimes on the above-ground biomass of angiosperm species with different GS, ploidy level, and Grime’s C-S-R plant strategies growing in the world’s longest running ecological experiment, Park Grass (Rothamsted, UK), established 1856. The biomass-weighted GS of species growing on plots where both N and P were added in fertilizer treatments were significantly higher than plants growing on control plots and plots where either N or P (but not both) were added. Polyploids with a large GS and a strong C (competitor) strategy increased most significantly when both N and P were added together. These results are consistent with the long-term Rengen Grassland experiment recently published by Šmarda et al. (2013) and are consistent with the hypothesized effect of N and P limiting biomass on plots in species dependant on GS. The data also point to polyploids with large genomes being strong competitors but only in the presence of both N and P. Overall these data support the suggestion that nucleic acids are indeed biochemically costly, influencing plant community and ecosystem composition. In addition to the Park Grass plots, we have analysed the Silwood Park (UK) field experiment, set up over the last 24 years. These plots were also established to see the effects of fertilizer and pH on species composition, but with a design that enables a much greater power of statistical analysis. In addition, they allow the effects of rabbit, insect and mollusc herbivory on biomass to be investigated. We will therefore present the impact of GS in relation to the plants growing on these plots as well.
Evolutionary ecology of phosphorus use in a freshwater zooplankter
Professor Puni Jeyasingh, Oklahoma State University, USA
Professor Lawrence Weider, University of Oklahoma, USA
Compared to producers, we know little about the physiological and evolutionary consequences of variation in phosphorus (P) supply in consumers. Because consumers impart strong control on P supply, information on the physiological and evolutionary consequences of altered P supply is needed for a better understanding of ecosystem responses to nutrient pollution (i.e. eutrophication). Work on the keystone freshwater consumer, Daphnia, has revealed complex physiological and evolutionary consequences to altered inorganic P supply. There is substantial variation in genotype X P-environment interactions in Daphnia P-use. Such G x E interactions appear to be largely driven by differential expression of pathways mitigating the biochemical responses of algae to altered P supply. By exploiting the unique biology of daphniids that produce diapausing “resting eggs”, we compared eggs laid before and after the onset of cultural eutrophication. We reconstructed not only the population genetic history by analyzing resting egg DNA over a ~1600-year-period, but also the transcriptomic and physiological differences on a few experimentally hatched (“resurrected”) eggs. Striking shifts in frequency of neutral markers, transcriptomes, and P-use were closely correlated with the onset of anthropogenic eutrophication. Radiotracer assays revealed unique effects of ancient and extant genotypes on the quality and quantity of algae via differential recycling. Such effects are unlikely to be a simple function of differences in P-recycling, because we found significant differences between ancient and extant genotypes in the content of several other elements (e.g., potassium, iron).
Consequences of polyploidy for a New Zealand snail
Dr Maurine Neiman, University of Iowa, USA
Maurine will start by surveying some of the potential costs and benefits associated with polyploidy and will then explain why her New Zealand “mud snail” system is such a great model for the study of ploidy elevation (and sex!). After a brief foray into the genomic consequences of polyploidy, she will then consider whether phenotypic costs associated with polyploidy can help to explain why diploidy generally prevails in animals. Maurine will present data from her snail system indicating that while these phenotypic costs are likely to exist, they might only be evident under stressful conditions. She will focus on evaluating connections between costs of polyploidy associated with building additional chromosomes when the environmental availability of the nutrients (e.g., phosphorus) of which nucleic acids are comprised is low.
P selection and genome size variation in plants
Dr Petr Šmarda, Masaryk University, Czech Republic
DNA in the cell nuclei is very rich in phosphorus (P) and therefore it is expected that organisms with large genome (nuclei) sizes may be selectively disadvantaged (limited in growths and occurrence) in the phosphorus limited environments. During the past four years we have made several observational and manipulative experiments testing this hypothesis. In one experiment we observed differences in genome sizes spectra of species in a vegetation that have established on plots with different nitrogen (N) and P treatment in a >70-years continuing grassland fertilizer experiment. In other experiments we have compared genome size spectra of species in eight radiating genera of the Cape flora adapted for soils that sharply differ in the total-rock and the plant-available N and P contents and in plots with various nutrient contents in Svalbard, a high arctic area known for extraordinarily high frequency of polyploids. In several manipulative experiments we have observed effects of increased N and P on differences in germination speed, germination and emergence success, and total biomass between polyploids and their diploid progenitors (12–14 pairs). Our results allow to detect some effect of increased or low nutrients on the success of polyploids and species with increased genome size, though neither P nor N seem to be the primary reasons for their success in a particular habitat or environment. Maybe a better understanding on the role of nutrients on success of species with different genome size could be obtained with exact knowledge of their genome size-associated nutrient demands.