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, CMA/DAPI banding and FISH techniques were applied to metaphase chromosomes of 13 Jaborosa species plus Sclerophylax spinescens, and the resulting characters were reconstructed onto a dated phylogenetic tree. Jaborosa presents a distinctive evolutionary pathway at the chromosomal level in respect to its sister clades, the Hyoscyameae, Lycium and Sclerophylax. The divergence of the common ancestor of Jaborosa involved an increase in chromosome size, with a slight rise 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, such as duplications and transpositions. Contrasting evolution of the 5S and 18-5.8-26S rDNA seems to have occurred, with the 5S site being more stable than the 18-5.8-26S. 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 homoplastic, the combination of chromosome markers employed here allowed species discrimination.