Chromosomal changes and recent diversification in the Andean genus Jaborosa (Solanaceae)

Abstract

With the purpose of discussing the evolutionary dynamics of the karyotypes and their relationship with key geological events, chromomycin A3/4′,6-diamidino-2-phenylindole (CMA/DAPI) banding and fluorescence in situ hybridization (FISH) techniques were applied to metaphase chromosomes of 13 Jaborosa spp. and Sclerophylax spinescens, and the resulting characters were reconstructed onto a dated phylogenetic tree. Jaborosa shows a distinctive evolutionary pathway at the chromosomal level with respect to its sister clades, Hyoscyameae, Lycium and Sclerophylax. The divergence of the common ancestor of Jaborosa involved an increase in chromosome size, with a slight increase in the amount of heterochromatin and chromosomal asymmetry, all these changes taking place at the diploid level. Variation in the number and position of rDNA sites showed profuse chromosomal rearrangements, including duplications and transpositions. Contrasting evolution of the 5S and 18S-5.8S-26S rDNA seems to have occurred, with the 5S site being more stable than 18S-5.8S-26S. The diversification of Jaborosa seems to be correlated with the most recent uplifts in the Andes in central South America and the establishment of the Patagonian steppe: the genus colonized these biomes and, at the same time, underwent a remarkable chromosomal and morphological differentiation. Although some characters were seen to be homoplasious, the combination of chromosome markers employed here allowed species discrimination.