Proceedings of the Third International Conference on Invasive ...

Chapter 1: Spartina Biology<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive Spartinain different tissues <strong>of</strong> allotetraploid cotton (Gossypium),suggesting that sub-functionalization was consequent toallopolyploid formation. Over 2000 transcripts werescreened by cDNA AFLP (Adams et al. 2004) and about 5%<strong>of</strong> <strong>the</strong> duplicated genes were inferred to have been silencedor down-regulated in <strong>the</strong> experimentally re-syn<strong>the</strong>sizedallotetraploid Gossypium.SUMMARY AND CONCLUSIONSAllopolyploid species represent two important outcomes<strong>of</strong> hybridization and genome duplication that are critical for<strong>the</strong>ir evolutionary success: Hybridization leads to <strong>the</strong> merger<strong>of</strong> two more or less differentiated genomes that havepreviously evolved independently and polyploidizationentails an immediate duplication and functional redundancyat all loci. These events entail various molecular interactionsand adjustments that have received much attention in <strong>the</strong>recent literature, as <strong>the</strong>y are now considered as <strong>the</strong> keyprocesses that explain <strong>the</strong> evolutionary success <strong>of</strong> polyploidyin Eucaryotes (reviewed in Liu and Wendel 2003; Osborn etal. 2003). Heterosis and dosage effect in duplicated genomesare likely to increase <strong>the</strong> metabolic plasticity <strong>of</strong> <strong>the</strong>duplicated genes, <strong>the</strong>reby affecting <strong>the</strong> fitness <strong>of</strong> <strong>the</strong> newlyformed species (Riddle and Birchler 2003).The particularly successful Spartina anglica ischaracterised by morphological plasticity and largeecological amplitude, contrasting with a weak interindividualgenetic variation, but consistent epigenetic andexpression plasticity <strong>of</strong> <strong>the</strong> duplicated homeologousgenomes. Fur<strong>the</strong>r investigations and identification <strong>of</strong> <strong>the</strong>sequences that are affected by epigenetic regulation andexpression changes should deepen our understanding <strong>of</strong> <strong>the</strong>ecological success <strong>of</strong> this young species. Spartina <strong>of</strong>fersparticular opportunities to learn about <strong>the</strong> evolutionary andecological consequences <strong>of</strong> polyploid speciation andreticulate evolution at both <strong>the</strong> short term (in nascent speciessuch as S. anglica) and long term (in <strong>the</strong> parental, olderpolyploid species) <strong>of</strong> <strong>the</strong> evolutionary time scale.ACKNOWLEDGMENTSThis work is supported by CNRS funds (UMR CNRS6553 Ecobio), PICS 932 CNRS – CSIRO Canberra, NSF –CNRS funds (project 12 978), and by a postdoctoral grantfrom <strong>the</strong> French Ministry <strong>of</strong> Research to K. Fukunaga. Weare particularly grateful to Les Leunig and Paul Hedge for<strong>the</strong>ir assistance in sampling Australian populations <strong>of</strong> S.anglica in Victoria and Tasmania, respectively, to MikeMcCorry, for sending samples from Ireland, to TravisColumbus and Debra Ayres for sending various AmericanSpartina samples. Jonathan Wendel and Keith Adams (IowaState University, Ames) are thanked for helpful assistance in<strong>the</strong> cDNA AFLP approach and stimulating discussions onpolyploidy. Neil Bagnall (CSIRO Canberra) and SylvieBaloche (CNRS Rennes) are thanked for technical help.REFERENCESAbbott, R.J. and A.J. Lowe. 2004. Origins, establishment andevolution <strong>of</strong> two new polyploid species <strong>of</strong> Senecio in <strong>the</strong> BritishIsles. Biological Journal <strong>of</strong> <strong>the</strong> Linnean Society 82: 467-474.Adams, K.L., R. Cronn, R. Percifield, and J.F. Wendel. 2003.Genes duplicated by polyploidy show unequal contributions to<strong>the</strong> transcriptome and organ-specific reciprocal silencing.<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> National Academy <strong>of</strong> Sciences <strong>of</strong> <strong>the</strong> USA100, 4649–4654.Adams, K.L., R. Percifield, and J.F. Wendel. 2004. 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