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Diversification and speciation of Nassauvia subgenus Strongyloma (Asteraceae, Nassauvieae)

Dra. Marcela Viviana Nicola, postdoctoral fellow at the Instituto de Botánica Drawinion (IBODA, CONICET-ANCEFN; SI herbarium), San Isidro, Buenos Aires, Argentina.

Advisors: Dr. Leigh A. Johnson (BYU, Provo, Utah, USA), Dr. Raúl Pozner (IBODA), and Dra. Silvana M. Sede (IBODA).

The aim of our project was to examine the possible processes involved in the diversification and speciation of Nassauvia Comm. ex Juss. subgenus Strongyloma (DC) Cabrera and to contrast them with the known morphological and phylogeographic patterns of the group. The final result will also contribute to our understanding of the recent past history of the Patagonian biota.

The work I am pursuing builds upon my recent research. As background, Nassauvia subgenus Strongyloma is a well-defined group of small shrubs with a tendency toward heteroblastic development, subulate leaves with a vaginate base usually subtending brachyblasts with very small rosettes of minute leaves, and pubescent achenes. This subgenus includes five species characteristic of the Patagonian flora: N. axillaris (Lag. ex Lindl.) D. Don, N. fuegiana (Speg.) Cabrera, N. glomerulosa (Lag. ex Lindl.) D. Don, N. maeviae Cabrera, and N. ulicina (Hook. f.) Macloskie. They are sympatrically distributed mainly in the Patagonian steppe of Chile and Argentina to Tierra del Fuego, but one species extends through the Andes to southern Bolivia (Cabrera 1982). A morphometric study (Nicola et al. 2014a) showed that variation in morphological characters that have traditionally been used to differentiate these five species does not strictly follow species boundaries. In addition, a phylogeographic analysis (Nicola et al. 2014b) evidenced that haplotypes are shared by all the species of the subgenus and that distantly related haplotypes coexist within each of the species of subgenus Strongyloma.

The IAPT Research Improvement Grant for Plant Systematics 2013 gave me the financial support necessary to perform nuclear DNA cloning to provide data that is enabling me to compare topologies of phylogenies derived from nuclear DNA sequences and plastid DNA sequences to assess to what extent gene trees are a good estimation of species trees. This is based on that rationale that unresolved topologies may reflect recent origin and lack of enough useful phylogenetic signals, while incongruent topologies may reflect different evolutionary histories, revealing the existence of reticulation events or incomplete lineage sorting. The congruence between the variability of DNA sequences, the geographic distribution and the morphology, can clarify the presence of one or other events in the evolution of the genome (Nieto-Feliner & Roselló 2007).

I have obtained 38 clone samples where polymorphic nucleotide positions were detected for the ITS region of the ribosomal nuclear DNA. I have tested the monophyly of the subgenus through Bayesian and parsimony analyses, performed congruence tests amongst plastid and nuclear matrices and topologies, calculated the genealogical sorting index for each species, and estimated times of divergence. This work is producing some exciting results; we are preparing a manuscript for submission by the end of this year.

All funds received have been used to support the laboratory expenses associated with cloning and sequencing the nuclear DNA regions associated with this work. Specifically, funds contributed to the expense of cloning kits and associated expendables (petri dishes & nutrient agar), PCR amplification and purification of cloned colonies, and DNA sequencing of selected colonies.

Literature citations:

  • Cabrera, A.L. (1982) Revisión del género Nassauvia (Compositae). Darwiniana 24: 283-379.
  • Nicola, M.V.; L.A. Johnson & R. Pozner (2014a) Geographic variation among closely related, highly variable species with a wide distribution range: the South Andean-Patagonian Nassauvia subgenus Strongyloma (Asteraceae, Nassauvieae). Systematic Botany 39(1): 331-348.
  • Nicola, M.V.; S.M. Sede, L.A. Johnson & R. Pozner (2014b) Phylogeography and palaeodistribution modelling of Nassauvia subgenus Strongyloma (Asteraceae): exploring phylogeographical scenarios in the Patagonian steppe. Ecology and Evolution 4(22): 4270-4286.
  • Nieto Feliner, G. & J.A. Rosselló (2007) Better the devil you know? Guidelines for insightful utilization of nrDNA ITS in species-level evolutionary studies in plants. Molecular Phylogenetics and Evolution 44: 911-919.

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