Flow cytometry and GISH reveal mixed ploidy populations and Spartina nonaploids with genomes of S. alterniflora and S. maritima origin.
BACKGROUND
The genus Spartina exhibits extensive hybridization and includes classic examples of recent speciation by allopolyploidy. In the UK there are two hexaploid species, S. maritima and S. alterniflora, as well as the homoploid hybrid S. x townsendii (2n = 60) and a derived allododecaploid S. anglica (2n = 120, 122, 124); the latter two are considered to have originated in Hythe, southern England at the end of the 19th century.


METHODS
Genomic in situ hybridization (GISH) and flow cytometry were used to characterize the genomic composition and distribution of these species and their ploidy levels at Eling Marchwood and Hythe, both near Southampton, southern England.


RESULTS
GISH identified approx. 60 chromosomes each of S. maritima and S. alterniflora origin in S. anglica and 62 chromosomes from S. alterniflora and 30 chromosomes from S. maritima in a nonaploid individual from Eling Marchwood, UK. GISH and flow cytometry also revealed that most (94 %) individuals examined at Hythe were hexaploid (the remaining two individuals (6 %) were dodedcaploid; n = 34), whereas hexaploid (approx. 36 % of plants), nonaploid (approx. 27 %) and dodecaploid (approx. 36 %) individuals were found at Eling Marchwood (n = 22).


CONCLUSIONS
Nonaploid individuals indicate the potential for introgression between hexaploid and dodecaploid species, complicating the picture of polyploid-induced speciation within the genus. Despite the aggressive ecological habit of S. anglica, it has not out-competed S. x townsendii at Hythe (homoploid hybrids at a frequency of 94 %, n = 34), despite >100 years of coexistence. The success of GISH opens up the potential for future studies of polyploid-induced genome restructuring in this genus.
Renny-Byfield
Simon
S
Queen Mary University of London, School of Biological and Chemical Sciences, London E1 4NS, UK.
Ainouche
Malika
M
Leitch
Ilia J
IJ
Lim
K Yoong
KY
Le Comber
Steven C
SC
Leitch
Andrew R
AR
D002467:Cell Nucleus / Q000378:metabolism; D005434:Flow Cytometry; D018745:Genome, Plant / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007211:Indoles / Q000378:metabolism; D008677:Metaphase / Q000235:genetics; D018517:Plant Roots / Q000166:cytology / Q000235:genetics; D011003:Ploidies; D006109:Poaceae / Q000235:genetics*; D011418:Prophase / Q000235:genetics; D013194:Staining and Labeling
D007211:Indoles; C007293:DAPI