AINOUCHE, LILY M.1*, ALEX BAUMEL1, RANDALL J. BAYER2, RUSLAN KALENDAR3, and ALAN SCHULMAN3. 1UMR CNRS 6553 - University of Rennes1, Campus Scientifique de Beaulieu, 35042 Rennes Cedex France; 2CSIRO Plant Industry, Australian National Herbarium, GPO Box 1600, Canberra, ACT, 2601, Australia; 3Institute of Biotechnology, University of Helsinki, Plant Genomics Laboratory, Viikki Biocenter, PO Box 56, FIN-0014, Helsinki, Finland. - Hybridization, speciation and genome evolution in European Spartines (Poaceae).
Most Spartina species originate from the New World, and among
the four species which are native to the Old world, three are of
hybrid origin, being the result of the introduction of the East
American Spartina alterniflora in western-Europe, and its
subsequent hybridization with the indigenous Spartina maritima.
In England, hybridization resulted in a sterile hybrid, S. x
townsendii, which gave rise around 1890, to the new fertile
allopolyploid Spartina anglica. This species has since spread
into several continents, causing dramatic ecological changes. Another
sterile hybrid between S. alterniflora and S. maritima
has been reported at the end of the 19th century in southwest France,
which has been named S. x neyrautii. In order to analyze early
molecular changes affecting natural hybrid and allopolyploid species,
and their role in adaptation and stabilization of a new species,
molecular investigations have been undertaken on populations of
European spartines. All the species involved in the speciation process
are analyzed: the parents S. alterniflora and S.
maritima, the F1 sterile hybrids, and the allopolyploid S.
anglica. The latter species has been analyzed in both its native
range and in more recently colonized areas (Australia). Different
portions of the genome have been investigated using sequencing, RFLPs,
and retrotransposon based fingerprinting methods, and genetic
divergence between the parental species has been estimated. Our
results show that the parental species display consistent genetic
differentiation, and that both genomes remain unchanged when reunited
and duplicated in the same nucleus. Most populations of Spartina
anglica contain the same major genotype, which has been colonizing
different continents. This young species then represents a system
where genetic diversity is restricted to the intra-individual
(intergenomic) level, as a result of both genetic botteleneck at the
time of the species formation, and structural stasis of the homeologue
Key words: Allopolyploid, genome evolution, hybridization, Spartina