The evolutionary history of the white-rayed species of Melampodium (Asteraceae) involved multiple cycles of hybridization and polyploidization.
OBJECTIVE
Polyploidy plays an important role in race differentiation and eventually speciation. Underlying mechanisms include chromosomal and genomic changes facilitating reproductive isolation and/or stabilization of hybrids. A prerequisite for studying these processes is a sound knowledge on the origin of polyploids. A well-suited group for studying polyploid evolution consists of the three species of Melampodium ser. Leucantha (Asteraceae): M. argophyllum, M. cinereum, and M. leucanthum.


METHODS
The origin of polyploids was inferred using network and tree-based phylogenetic analyses of several plastid and nuclear DNA sequences and of fingerprint data (AFLP). Genome evolution was assessed via genome size measurements, karyotype analysis, and in situ hybridization of ribosomal DNA.


RESULTS
Tetraploid cytotypes of the phylogenetically distinct M. cinereum and M. leucanthum had, compared to the diploid cytotypes, doubled genome sizes and no evidence of gross chromosomal rearrangements. Hexaploid M. argophyllum constituted a separate lineage with limited intermixing with the other species, except in analyses from nuclear ITS. Its genome size was lower than expected if M. cinereum and/or M. leucanthum were involved in its origin, and no chromosomal rearrangements were evident.


CONCLUSIONS
Polyploids in M. cinereum and M. leucanthum are of recent autopolyploid origin in line with the lack of significant genomic changes. Hexaploid M. argophyllum also appears to be of autopolyploid origin against the previous hypothesis of an allopolyploid origin involving the other two species, but some gene flow with the other species in early phases of differentiation cannot be excluded.
Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria.
Carolin A
CA
Rebernig
Hanna
H
Weiss-Schneeweiss
Cordula
C
Blöch
Barbara
B
Turner
Tod F
TF
Stuessy
Renate
R
Obermayer
Jose L
JL
Villaseñor
Gerald M
GM
Schneeweiss
D054458:Amplified Fragment Length Polymorphism Analysis; D019659:Asteraceae / Q000145:classification / Q000235:genetics*; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D018745:Genome, Plant / Q000235:genetics; D005843:Geography; D006824:Hybridization, Genetic; D017404:In Situ Hybridization, Fluorescence; D059785:Karyotype; D008800:Mexico; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D011123:Polyploidy; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013781:Texas
D018744:DNA, Plant; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D010940:Plant Proteins