Karyotype characterization and evolution of chromosome number in Cactaceae with special emphasis on subfamily Cactoideae

Abstract

ABSTRACT Cactaceae species are karyotypically well-known with x = 11 and chromosome number variation due mainly to polyploidization. However, both assumptions are based on descriptive observations without taking an evolutionary framework of Cactaceae into account. Aiming to confirm these hypotheses in an evolutionary context, we obtained chromosome numbers for 20 species of Cactoideae, performed an extensive review of chromosome number for the family, and analyzed these data using a phylogenetic approach. The karyotypes presented here were characterized by CMA/DAPI banding, and for six species 5S and 45S rDNA sites were located. Our data, along with a survey of the literature, reinforce the long-standing hypothesis of a x = 11 as the base chromosome number for Cactaceae. They also reinforce the relevance of polyploidy in karyotype evolution of cacti, although polyploidy was important just after the diversification of subfamilies Maihuenioideae and Pereskioideae. Despite the homogeneous chromosome complements observed among cacti, chromosome banding and FISH techniques revealed informative characteristics, allowing the identification of chromosome synapomorphies, such as proximal CMA+ bands in Melocactus and proximal 5S rDNA in Pilosocereus, indicating the taxonomic potential of chromosome characterization in cacti.