*Stabilizing selection is a key evolutionary mechanism for which there is relatively little experimental evidence. To date, stabilizing selection has never been observed at the whole-genome level. *We tested the effect of selection on genome size in a field experiment using seeds collected in a population of Festuca pallens with a highly variable genome size. Using flow cytometry, we measured the genome size in germinating seedlings and juvenile plants grown with or without high intraspecific competition (908 individuals). Above-ground biomass and leaf number were used as measurements of individual vegetative performance. The possible confounding effect of seed weight was controlled for in a separate experiment. *Growth under high competition had a significant stabilizing effect on genome size. Because no relationship was observed between genome size and vegetative performance, we assume that the elimination of plants with extreme genome sizes was the result of decreased survival as a consequence of some unrecognized stress. *Our results indicate that genome size may be under direct selection. The equal disadvantaging of either large or small genomes indicates that the selection for optimum genome size in species may be fully context dependent. This study demonstrates the power of competition experiments for the detection of weak selection processes.

Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 2 CZ 61137 Brno Czech Republic

Komentář v

New Phytol. 2010 Sep;187(4):883-885. doi: 10.1111/j.1469-8137.2010.03412.x. PubMed

Zobrazit více v PubMed

Argueso JL, Westmoreland J, Mieczkowski PA, Gawel M, Petes TD, Resnick MA. 2008. Double-strand breaks associated with repetitive DNA can reshape the genome. Proceedings of the National Academy of Sciences, USA 105: 11845-11850.

Baucom RS, Estill JC, Leebens-Mack J, Bennetzen JL. 2009. Natural selection on gene function drives the evolution of LTR retrotransposon families in the rice genome. Genome Research 19: 243-254.

Beaulieu JM, Moles AT, Leitch IJ, Bennett MD, Dickie JB, Knight CA. 2007. Correlated evolution of genome size and seed mass. New Phytologist 173: 422-437.

Begon M, Townsend CR, Harper JL. 2006. Ecology: from individuals to ecosystem. Oxford, UK: Blackwell.

Bennett MD, Leitch IJ. 2005. Plant DNA C-values database (release 4.0, October 2005) ( http://data.kew.org/cvalues/ ).

Bennetzen JL, Ma J, Devos KM. 2005. Mechanisms of recent genome size variation in flowering plants. Annals of Botany 95: 127-132.

Black JN. 1958. Competition between plants of different initial seed sizes in swards of subterranean clover (Trifolium subterraneum L.) with particular reference to leaf area and the light microclimate. Australian Journal of Agricultural Research 9: 299-318.

Blomberg SP, Garland T Jr. 2002. Tempo and mode in evolution: phylogenetic inertia, adaptation and comparative methods. Journal of Evolutionary Biology 15: 899-910.

Brown MB, Forsythe AB. 1974. Robust tests for equality of variances. Journal of the American Statistical Association 69: 364-367.

Bureš P, Wang YF, Horová L, Suda J. 2004. Genome size variation in Central European species of Cirsium (Compositae) and their natural hybrids. Annals of Botany 94: 353-363.

Chrtek J, Zahradníček J, Krak K, Fehrer J. 2009. Genome size in Hieracium subgenus Hieracium (Asteraceae) is strongly correlated with major phylogenetic groups. Annals of Botany 104: 161-178.

Doležel J, Bartoš J. 2005. Plant DNA flow cytometry and estimation of nuclear genome size. Annals of Botany 95: 99-110.

Eilam T, Anikster Y, Millet E, Manisterski J, Feldman M. 2008. Nuclear DNA amount and genome downsizing in natural and synthetic allopolyploids of the genera Aegilops and Triticum. Genome 51: 616-628.

Eilam T, Anikster Y, Millet E, Manisterski J, Sagi-Assif O, Feldman M. 2007. Genome size and genome evolution in diploid Triticeae species. Genome 50: 1029-1037.

Eldredge N, Gould SJ. 1972. Punctuated equilibria: an alternative to phyletic gradualism. In: Schopf TJM, ed. Models in paleobiology. San Francisco, CA, USA: Freeman, Cooper and Co, 82-115.

Estes S, Arnold SJ. 2007. Resolving the paradox of stasis: models with stabilizing selection explain evolutionary divergence on all timescales. American Naturalist 169: 227-244.

Feldman M, Liu B, Segal G, Abbo S, Levy AA, Vega JM. 1997. Rapid elimination of low copy DNA sequences in polyploid wheat: a possible mechanism for differentiation of homoeologous chromosomes. Genetics 147: 1381-1387.

Felsenstein J. 1985. Phylogenies and the comparative method. American Naturalist 125: 1-15.

Fischer G, James SA, Roberts IN, Oliver SG, Louis EJ. 2000. Chromosomal evolution in Saccharomyces. Nature 405: 451-454.

Flavell RB, Bennett MD, Smith JB, Smith DB. 1974. Genome size and proportion of repeated nucleotide-sequence DNA in plants. Biochemical Genetics 12: 257-269.

Geber MA, Griffen LR. 2003. Inheritance and natural selection on functional traits. International Journal of Plant Sciences 164(Suppl. 3): S21-S41.

Gould SJ, Eldredge N. 1993. Punctuated equilibrium comes of age. Nature 366: 223-227.

Greilhuber J. 1998. Intraspecific variation in genome size: a critical reassessment. Annals of Botany 82(Suppl. A): 27-35.

Greilhuber J. 2005. Intraspecific variation in genome size in angiosperms: identifying its existence. Annals of Botany 95: 91-98.

Greilhuber J. 2008. Cytochemistry and C-values: the less-well-known world of nuclear DNA amounts. Annals of Botany 101: 791-804.

Greilhuber J, Temsch EM, Loureiro JCM. 2007. Nuclear DNA content measurement. In: Doležel J, Greilhuber J, Suda J, eds. Flow cytometry with plant cells. Weinheim, Germany: Willey-VCH, 67-101.

Grime JP, Jeffrey DW. 1965. Seedling establishment in vertical gradients of sunlight. Journal of Ecology 53: 621-642.

Gupta PK, Rees H. 1975. Tolerance of Lolium hybrids to quantitative variation in nuclear DNA. Nature 257: 587-588.

Hegarty MJ, Hiscock SJ. 2005. Hybrid speciation in plants: new insights from molecular studies. New Phytologist 165: 411-423.

Hutchinson J, Rees H, Seal AG. 1979. An assay of the activity of supplementary DNA in Lolium. Heredity 43: 411-421.

Janišová M. 1999. Population biology of Festuca pallens. PhD thesis, Institute of Botany, Slovak Academy of Sciences, Bratislava, Slovakia.

Johnson T, Barton N. 2005. Theoretical models of selection and mutation on quantitative traits. Philosophical Transactions of the Royal Society of London, Series B 360: 1411-1425.

Kingsolver JG, Hoekstra HE, Hoekstra JM, Berrigan D, Vignieri SN, Hill CE, Hoang A, Gibert P, Beerli P. 2001. The strength of phenotypic selection in natural populations. American Naturalist 157: 245-261.

Knight CA, Ackerly DD. 2002. Variation in nuclear DNA content across environmental gradients: a quantile regression analysis. Ecology Letters 5: 66-76.

Ku HM, Vision T, Liu J, Tanksley SD. 2000. Comparing sequenced segments of the tomato and Arabidopsis genomes: large-scale duplication followed by selective gene loss creates a network of synteny. Proceedings of the National Academy of Sciences, USA 97: 9121-9126.

Leitch AR, Leitch IJ. 2008. Genomic plasticity and the diversity of polyploid plants. Science 320: 481-483.

Leitch IJ, Beaulieu JM, Cheung K, Hanson L, Lysak MA, Fay MF. 2007. Punctuated genome size evolution in Liliaceae. Journal of Evolutionary Biology 20: 2296-2308.

Leitch IJ, Bennett MD. 2007. Genome size and its uses: the impact of flow cytometry. In: Doležel J, Greilhuber J, Suda J, eds. Flow cytometry with plant cells. Weinheim, Germany: Willey-VCH, 153-176.

Leitch IJ, Kahandawala I, Suda J, Hanson L, Ingrouille MJ, Chase MW, Fay MF. 2009. Genome size diversity in orchids: consequences and evolution. Annals of Botany 104: 469-481.

Linkies A, Graeber K, Knight C, Leubner-Metzger G. 2010. The evolution of seeds. New Phytologist 186: 817-831.

McDonald JH. 2009. Handbook of biological statistics, 2nd edn . Baltimore, MD, USA: Sparky House Publishing.

Michaels HJ, Benner B, Hartgerink AP, Lee TD, Rice S, Wilson MF, Bertin RI. 1988. Seed size variation: magnitude, distribution and ecological correlates. Evolutionary Ecology 2: 157-166.

Montgomery EA, Huang SM, Langley CH, Judd BH. 1991. Chromosome rearrangement by ectopic recombination in Drosophila melanogaster- genome structure and evolution. Genetics 129: 1085-1098.

Ozkan H, Levy AA, Feldman M. 2001. Allopolyploidy induced rapid genome evolution in the wheat (Aegilops-Triticum) group. Plant Cell 13: 1735-1747.

Ozkan H, Tuna M, Arumuganathan K. 2003. Nonadditive changes in genome size during allopolyploidization in the wheat (Aegilops-Triticum) group. Journal of Heredity 94: 260-264.

Pagel M. 1999. Inferring the historical patterns of biological evolution. Nature 401: 877-884.

Poggio L, Rosato M, Chiavarino AM, Naranjo CA. 1998. Genome size and environmental correlations in maize (Zea mays ssp. mays, Poaceae). Annals of Botany 82(Suppl. A): 107-115.

Rieseberg LH, Willis JH. 2007. Plant speciation. Science 317: 910-914.

SanMiguel P, Bennetzen JL. 1998. Evidence that a recent increase in maize genome size was caused by the massive amplification of intergene retrotransposons. Annals of Botany 82: 37-44.

Saverimuttu T, Westoby M. 1996. Seedling longevity under deep shade in relation to seed size. Journal of Ecology 84: 681-689.

Shindo C, Bernasconi G, Hardtke CS. 2008. Intraspecific competition reveals conditional fitness effect of single gene polymorphism at the Arabidopsis root growth regulator BRX. New Phytologist 180: 71-80.

Šmarda P, Bureš P. 2006. Intraspecific DNA content variability in Festuca pallens on different geographical scales and ploidy levels. Annals of Botany 98: 665-678.

Šmarda P, Bureš P. 2010. Understanding intraspecific genome size variation. Preslia 82: 41-61.

Šmarda P, Bureš P, Horová L. 2007. Random distribution pattern and non-adaptivity of genome size in a highly variable population of Festuca pallens. Annals of Botany 100: 141-150.

Šmarda P, Bureš P, Horová L, Foggi B, Rossi G. 2008a. Genome size and GC content evolution of Festuca: ancestral expansion and subsequent reduction. Annals of Botany 101: 421-433.

Šmarda P, Bureš P, Horová L, Rotreklová O. 2008b. Intrapopulation genome size dynamics in Festuca pallens. Annals of Botany 102: 599-607.

Travis J. 1989. The role of optimizing selection in natural populations. Annual Review of Ecology and Systematics 20: 279-296.

Webb CO, Ackerly DD, Kembel SW. 2008. Phylocom: software for the analysis of phylogenetic community structure and trait evolution. Bioinformatics 24: 2098-2100.

Wendel JF. 2000. Genome evolution in polyploids. Plant Molecular Biology 42: 225-249.

Westoby M, Jurado E, Leishman M. 1992. Comparative evolutionary ecology of seed size. Trends in Ecology and Evolution 7: 368-372.

Westoby M, Leishman M, Lord J. 1996. Comparative ecology of seed size and dispersal. Philosophical Transactions of the Royal Society of London, Series B 351: 1309-1318.

Wood JCS. 2009. Establishing and maintaining system linearity. Current Protocols in Cytometry 47: 1.4.1-1.4.14.

Zonneveld BJM, Duncan GD. 2006. Genome size for the species of Nerine Herb. (Amaryllidaceae) and its evident correlation with growth cycle, leaf width and other morphological characters. Plant Systematics and Evolution 257: 251-260.

Zuccolo A, Sebastian A, Talag J, Yu Y, Kim H, Collura K, Kudrna D, Wing RA. 2007. Transposable element distribution, abundance and role in genome size variation in the genus Oryza. BMC Evolutionary Biology 7: 152.

Small Genome Size Ensures Adaptive Flexibility for an Alpine Ginger