Patterns of chromosomal evolution in Solanaceae: a phylogenetic approach

ACOSTA M. C.; MOSCONE E. A.; COCUCCI A. A.

Guarujá, Sao Paulo

Conferencia; IV Simposio Latino-Americano de Citogenética y Evolución; 2013

Sociedade Brasileira de Genética

Interspecific phylogenies allow the understanding of species diversification processes and distribution patterns. In addition, phylogenetic trees are necessary to understand patterns of morphological and chromosome evolution, and allow ancestral characters and ancestral karyotype reconstructions. Here, we used a nuclear and chloroplast Nierembergia DNA phylogeny in order to reveal patterns of chromosomal evolution. Nierembergia is a New World genus of Solanaceae which includes 21 species indigenous to South America and one species native to Mexico. The genus is diverse in growth form, ranging from rhizomatous, tuber-bearing, or prostrate herbs to small shrubs, and is unusual in that instead of nectar, oils from elaiophores inside the corolla limb act as pollinator attractants. We mapped on the phylogeny one set of chromosomal data from 21 samples belonging to 17 species and 6 varieties of Nierembergia, Bouchetia, Leptoglossis and Petunia obtained by conventional staining, AgNOR-, C- and fluorescent chromosome banding and fluorescent in situ hybridization with the aims of reconstructing ancestral karyotypes and understanding the chromosomal evolution. In addition, we used karyological data to reconstruct chromosomal phylogeny and a Bayesian Molecular Relaxed Clock to estimate divergence times between species. Nierembergia shows two major divergent clades: a lowland species group with asymmetrical karyotypes, small chromosomes, two chromosomes pairs with nucleolar organizing regions and centromeric heterochromatin bands, and a montane species group with symmetrical karyotypes, large chromosomes, only one NOR, and without centromeric heterochromatin. Molecular dating on the DNA phylogeny revealed that both groups diverged during Late Miocene when an Atlantic marine ingression called the “Paranean Sea” probably confined onto the ancestors of these species to refuges on not flooded highlands. Thus, the superimposition of chromosomal information onto chronogram allows the construction of hypotheses about chromosomal evolution and speciation processes.