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 SpartinaTable 1: Inter-individual molecular variation in native and introduced Spartina anglica populations investigated using three multilocus methods:RAPD (Random Amplification <strong>of</strong> Polymorphic DNA, 14 primers), ISSR (Inter Simple Sequence Repeats, 4 primers), IRAP (Inter-Retrotransposon Amplified Polymorphism, 7 primer pairs), REMAP (Retrotransposon Microsatellite Amplified Polymorphism, 4 primer pairs).The mean individual number sampled per population = 10. N= number <strong>of</strong> samples analyzed per region; pm = polymorphic markers; m=number<strong>of</strong> markers recorded; mg = number <strong>of</strong> genotypes that differ from <strong>the</strong> “major” genotype identified by Baumel et al. (2001) and identical to S. xtownsendii.RAPD ISSR IRAP/REMAPN pm/ m mg/N N pm/m mg/N N pm/m mg/NEngland &Ireland45 3/146 2/45 20 0/1440 b 3/920/204/40 40 b 10/296 9/40France129 a 6/146 6/12920129 a 2/921/142/201/1295 2/296 2/5Australia 20 0/146 0/20 160 0/21 0/160 - - -a = data from Baumel et al. (2001); b = data from Baumel et al. (2002b).Intermediate, morphologically variable individuals may beencountered (Guenegou and Levasseur, personalcommunication), but no genetic exchange was foundbetween <strong>the</strong> two species according to cytological, allozyme(M.T. Misset and G. Allard, unpublished data) andmolecular (Baumel et al. 2001) data.In Australia, 160 samples were collected in various sitesfrom Victoria (Corner Inlet including <strong>the</strong> mouth <strong>of</strong> <strong>the</strong>Albert River and Anderson Inlet, Gippsland) and Tasmania(Franklin River in Port Sorell Bay, Duck River nearSmithton, Perkins Bay, Tamar River and Little Swanportestuary). In Victoria, various attempts at eradication havebeen performed using <strong>the</strong> herbicide Fusillade; we havesampled non-treated zones and also collected rare survivingplants from treated areas. Morphological variation is alsoencountered in <strong>the</strong> Australian populations where two distinctphenotypes (short plants <strong>of</strong> 10 – 20 cm high on <strong>the</strong> one handand taller plants measuring up to 30 cm on <strong>the</strong> o<strong>the</strong>r hand)were collected in <strong>the</strong> Albert River (Victoria). In LittleSwanport, 20 seedlings have been collected in order toanalyse samples resulting unambiguously from sexualreproduction. We found that all <strong>the</strong> individuals investigated inAustralia and Tasmania display <strong>the</strong> same multilocus RAPD orISSR genotype (Table 1), which is identical to <strong>the</strong> majorgenotype encountered in Europe and to S. x townsendii.It appears that populations <strong>of</strong> S. anglica in both itsnative range and more recently colonized areas are mainlycomposed <strong>of</strong> <strong>the</strong> major genotype that is identical to <strong>the</strong> firstgeneration hybrid S. x townsendii. Some variation may beencountered, however, that result from a few mutationsoccurring in local populations and corresponding in mostcases to fragment loss. Ayres and Strong (2001) also notedfragment loss in S. anglica. They encountered variation inRAPD and ISSR analyses including samples <strong>of</strong> S. anglicafrom England and Australia, and observed variable bandlossat five S. maritima-specific loci. However, Salmon et al.(2005) have reported preferential fragment loss <strong>of</strong> S.alterniflora-specific markers using AFLP (AmplifiedFragment Length Polymorphism) in both S. x townsendii andS. anglica. It should be noted that <strong>the</strong> estimation <strong>of</strong> diversitymay be ei<strong>the</strong>r underestimated or overestimated according toboth sampling (number <strong>of</strong> individuals analysed and number<strong>of</strong> markers examined over <strong>the</strong> genome) and <strong>the</strong> techniqueused: We can see (Table 1) that although globally limited,more variation can be detected from ISSR and IRAP–REMAP markers, that target repetitive (Simple SequenceRepeats and Retrotransposons), potentially more variable,parts <strong>of</strong> <strong>the</strong> genome. Moreover, considering that <strong>the</strong>se PCRbasedmarkers are dominant, variation resulting fromsegregating heterozygous genotypes cannot be ruled out.Ano<strong>the</strong>r potential source <strong>of</strong> variation is <strong>the</strong> structuraldynamic that may affect recently formed allopolyploidgenomes (Wendel 2000), but in <strong>the</strong> case <strong>of</strong> S. anglica, thisdynamic does not seem to affect <strong>the</strong> genotype initiallyformed in England to <strong>the</strong> extent that was reported in <strong>the</strong>literature in o<strong>the</strong>r allopolyploid model systems (Baumel etal. 2002b; Ainouche et al. 2004b).We have recently explored <strong>the</strong> epigenetic alterationsthat may affect <strong>the</strong> allopolyploid genome <strong>of</strong> S. anglica(Salmon et al. 2005). Epigenetic mechanisms causeexpression changes that do not result from <strong>the</strong> modification<strong>of</strong> <strong>the</strong> DNA sequence, and have been shown to result fromvarious, non-exclusive processes including DNA or histonemethylation, histone acetylation, and chromatin compaction-18-