Chromosomes and Evolution in Melampodium (Asteraceae)

Changes in chromosome number have played an important role in the evolution of flowering plants. Duplication of entire genomes (eupolyploidy) and increase or decrease of single chromosomes (aneuploidy) are found in more than half of the quarter-million species. Many previous studies have attempted to understand chromosomal diversity within particular plant groups, often genera, and to correlate observed cytological differences with a known phylogeny. New molecular phylogenies, providing higher levels of confidence through larger amounts of data and statistical support, can now be generated within groups showing wide chromosomal variation for more precise understanding of mode and tempo of chromosomal change. The proposed research will examine chromosomal evolution within the genus Melampodium of the sunflower family (Asteraceae), which has a long series of haploid chromosome numbers of n = 9, 10, 11, 12, 18, 20, 23, 25 1, 27, 30, and 33. The genus contains 39 species distributed throughout the southwestern United States, Mexico, and Central America. The closely related genera are Acanthospermum (n = 11; 7 species), also from Latin America, and Lecocarpus (n = 11; 3 species), restricted to the Galapagos Islands. Previously published taxonomic papers, numerical phenetic and cladistic investigations, and perspectives on isolating mechanisms and modes of speciation in Melampodium, together provide many hypotheses on relationships and evolution that can be tested using new molecular phylogenetic and cytogenetic techniques. The first part of the integrated research project will use cytogenetic techniques, classical and molecular, to provide cytogenetic explanations for chromosomal diversity and evolution within the entire genus and within the white- rayed complex. DNA localizations will provide new data for comparing karyotypes among taxa for generating hypotheses on mechanisms of chromosome change, especially in allopolyploids, and origins of tetraploids within the range of diploids in the white-rayed complex. (This portion of the project has been already funded as port of a Hertha Firnberg award to Dr. Weiss-Schneeweiss.) The second part of the research project, and the part for which funding is requested in this proposal, will reconstruct the phylogeny of the eintire genus (plus related genera as outgroups) using nuclear and chloroplast DNA markers. Material will be DNA-sequenced and phylogenies constructed using a combination of parsimony, maximum likelihood, and Bayesian likelihood algorithms. A robust phylogenetic hypothesis will allow the course of chromosomal evolution within the genus to be traced. Special focus will be on determining origins of allopolyploids, which are difficult to unravel in a cladistic context. Mechanisms of diploid speciation in consort with ecological, breeding system, and distributional data, will also be examined. The proposed research also will analyze in a phylogeographic context, via DNA fingerprinting and chloroplast restriction-site data, relationships among populations of the white-rayed complex from northeastern Mexico and adjacent southwestern U.S.A. The three species of this complex (M. argophyllum, M. cinereum, and M. leucanthum) have nearly allopatric distributions that show ecological divergence. How these populations have derived from the rest of the genus and then migrated northward post-Pleistocene will be inferred from comparative populational AFLPs and cpDNA restriction-site data evaluated through quantitative analyses. Further, molecular data and field studies will examine the origins and mechanisms of maintenance of tetraploid cytotypes occurring within the diploid ranges of M. cinereum and M. leucanthum.

Changes in chromosome number have played an important role in the evolution of flowering plants. Duplication of entire genomes (eupolyploidy) and increase or decrease of single chromosomes (aneuploidy) are found in more than half of the quarter-million species. Many previous studies have attempted to understand chromosomal diversity within particular plant groups, often genera, and to correlate observed cytological differences with a known phylogeny. New molecular phylogenies, providing higher levels of confidence through larger amounts of data and statistical support, can now be generated within groups showing wide chromosomal variation for more precise understanding of mode and tempo of chromosomal change. The proposed research will examine chromosomal evolution within the genus Melampodium of the sunflower family (Asteraceae), which has a long series of haploid chromosome numbers of n = 9, 10, 11, 12, 18, 20, 23, 25 1, 27, 30, and 33. The genus contains 39 species distributed throughout the southwestern United States, Mexico, and Central America. The closely related genera are Acanthospermum (n = 11; 7 species), also from Latin America, and Lecocarpus (n = 11; 3 species), restricted to the Galapagos Islands. Previously published taxonomic papers, numerical phenetic and cladistic investigations, and perspectives on isolating mechanisms and modes of speciation in Melampodium, together provide many hypotheses on relationships and evolution that can be tested using new molecular phylogenetic and cytogenetic techniques. The first part of the integrated research project will use cytogenetic techniques, classical and molecular, to provide cytogenetic explanations for chromosomal diversity and evolution within the entire genus and within the white- rayed complex. DNA localizations will provide new data for comparing karyotypes among taxa for generating hypotheses on mechanisms of chromosome change, especially in allopolyploids, and origins of tetraploids within the range of diploids in the white-rayed complex. (This portion of the project has been already funded as port of a Hertha Firnberg award to Dr. Weiss-Schneeweiss.) The second part of the research project, and the part for which funding is requested in this proposal, will reconstruct the phylogeny of the eintire genus (plus related genera as outgroups) using nuclear and chloroplast DNA markers. Material will be DNA-sequenced and phylogenies constructed using a combination of parsimony, maximum likelihood, and Bayesian likelihood algorithms. A robust phylogenetic hypothesis will allow the course of chromosomal evolution within the genus to be traced. Special focus will be on determining origins of allopolyploids, which are difficult to unravel in a cladistic context. Mechanisms of diploid speciation in consort with ecological, breeding system, and distributional data, will also be examined. The proposed research also will analyze in a phylogeographic context, via DNA fingerprinting and chloroplast restriction-site data, relationships among populations of the white-rayed complex from northeastern Mexico and adjacent southwestern U.S.A. The three species of this complex (M. argophyllum, M. cinereum, and M. leucanthum) have nearly allopatric distributions that show ecological divergence. How these populations have derived from the rest of the genus and then migrated northward post-Pleistocene will be inferred from comparative populational AFLPs and cpDNA restriction-site data evaluated through quantitative analyses. Further, molecular data and field studies will examine the origins and mechanisms of maintenance of tetraploid cytotypes occurring within the diploid ranges of M. cinereum and M. leucanthum.