The evolutionary history of the white-rayed species of melampodium (Asteraceae) involved multiple cycles of hybridization and polyploidization

Abstract

Premise of the study: 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 polyploidy 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. Key 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. © 2012 Botanical Society of America.

Keywords

Allopolyploidy; Asteraceae; Autopolyploidy; Genome size; Hybridization; Melampodium; Polyploid evolution; RDNA

Published in

American Journal of Botany
2012, volume: 99, number: 6, pages: 1043-1057

SLU Authors

• Rebernig, Carolin

  • University of Vienna

UKÄ Subject classification

Botany
Biological Systematics

Publication identifier

• DOI: https://doi.org/10.3732/ajb.1100539

Permanent link to this page (URI)

https://res.slu.se/id/publ/132301