Origin and genetic diversity of Spartina anglica (Poaceae) using nuclear DNA markers

Spartina alterniflora, introduced into the UK in the 1800s. was the seed pa rent in an interspecific hybridization with S. maritima. The sterile F1 hyb rid S. xtownsendii gave rise to the fertile allopolyploid S. anglica by chr omosomal doubling. Previous chromosome, isozyme, and cpDNA surveys did not reveal notable genetic variation within either the parental or the hybrid s pecies. We used nuclear DNA markers (random amplified polymorphic DNA ([RAP D]) and inter-simple sequence repeats (ISSR) to further explore the origin, diversity, and parentage of S. anglica. We found DNA fragments in S. xtown sendii were the aggregate of diagnostic DNA fragments from S. maritima and S. alterniflora, thus confirming its hybrid origin. The S. xtownsendii geno type was identical to most of the S. anglica individuals analyzed, establis hing the genetic concordance of these two taxa. We found widespread genetic variation within S. anglica. This could indicate that S. anglica arose sev eral times. from different S. maritima sires. Alternatively. alleles could have been lost through recombination and/or through loss of entire chromoso mes in S. anglica. Finally. all but one S. anglica individual had a S. alte rniflora component that was indistinguishable from a S. alterniflora plant extant in Marchwood, UK, leaving open the possibility that this plant is th e actual seed parent of S. anglica.