Hybridization, polyploidy and speciation inSpartina(Poaceae)

Abstract

SummaryHybridization and polyploidy are well illustrated in the genus Spartina . This paper examines how recent molecular approaches have helped our understanding of the past and recent reticulate history of species, with special focus on allopolyploid speciation. Spartina species are tetraploid, hexaploid or dodecaploid perennials, most of them being native to the New World. The molecular phylogeny indicates an ancient split between the tetraploid and the hexaploid species, with S . argentinensis as sister to the hexaploid lineage. Recent hybridization and polyploidization events involved hexaploid species, resulting from introductions of the east-American S. alterniflora . In California, ongoing hybridizations with its sister species S. foliosa result in introgressant hybrid swarms. In Europe, hybridization with S. maritima resulted in S . × neyrautii (France) and S. × townsendii (England), with. S. alterniflora as the maternal parent. The allopolyploid S. anglica resulted from chromosome doubling of S . × townsendii. This young allopolyploid contains divergent homoeologous subgenomes that have not undergone significant changes since their reunion. Hybridization, rather than genome duplication, appears to have shaped the allopolyploid genome at both the structural and epigenetic levels.

Uniformity of the nuclear and chloroplast genomes of Spartina maritima (Poaceae), a salt-marsh species in decline along the Western European Coast

“…This lineage is composed of the Afro-European Atlantic S. maritima (2n ¼ 60), and the two sister species, the East American S. alterniflora (2n ¼ 62) and the West American S. foliosa (2n ¼ 60). These three species have nonoverlapping native distribution ranges but they maintain sufficient genetic relatedness to hybridize (Baumel et al, 2002a;Ainouche et al, 2004b). Since S. maritima is basal in this clade according to the phylogeny of genus Spartina (Baumel et al, 2002a), one can hypothesize that current populations of S. maritima actually represent a relic of an ancestral hexaploid species with a more widespread distribution.…”

“…Comparison of S. maritima to its most related species, S. alterniflora (Baumel et al, 2002a), reveals that the population genetics of these two species is very different (Ainouche et al, 2004b). The East-American S. alterniflora has been introduced to the Pacific coast of the US where it is now an invasive weed, most notably in the San Francisco Bay area (Daehler and Strong, 1997) and in Willapa Bay (Aberle 1993 in Daehler andStrong, 1997).…”

Variation of growth and functional traits of invasive knotweeds (Fallopia spp.) in Belgium

“…Such new hybrid taxa have increased genetic diversity compared to their parents, either because they combine their genetic pools, or because polyploidy restored fertility and allowed sexual reproduction which, in turn, increased genetic diversity (Soltis and Soltis 2000). This is the case in the genus Spartina (Ainouche et al 2003;Salmon et al 2005) or Senecio (Abbott and Lowe 2004).…”

Evolution of enhanced reproduction in the hybrid-derived invasive, California wild radish (Raphanus sativus)

“…Many well-known examples of interspecific hybrid invaders also exist. Spartina anglica in Britain is derived from the hybridization of an introduced species, S. alterniflora, with the native S. maritima, while the hybrid lineage between introduced S. alterniflora and the native S. foliosa is invading the West Coast of North America (Ainouche et al 2004;Ayres et al 2003).…”