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

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.

Phylogenomics of the Caribbean melocacti: Cryptic species and multiple invasions

“…Species‐level resolution, as seen in parts of our plastome topology, although perhaps surprising given other reports of the lack of phylogenetic resolution in the genus (Taylor & al., 2014) and the presence of hybridization and polyploidy (Castro & al., 2019; Khan & al., 2020), may perhaps elucidate other biological processes not currently documented for most Caribbean species. Nassar & Ramírez (2004) uncovered autogamy in the widespread species Melocactus curvispinus in Venezuela, and Díaz Alvarez (2017) reported autogamy in populations of M. guitartii from Cuba.…”

“…Several population genetic studies of Brazilian species of Melocactus have provided evidence for species relationships, as well as frequent hybridization (Lambert & al., 2006; Bandhu & Mohanty, 2008; Khan & al., 2020). Chromosomal studies, likewise, have provided ample evidence that hybridization could be an underlying evolutionary force in the history of the genus, given that a number of polyploid taxa have been revealed from both Brazil and the Antilles (Das & al., 1998; Assis & al., 2003; Bandhu & Mohanty, 2008; Castro & al., 2019).…”

A New Approach Using Targeted Sequence Capture for Phylogenomic Studies across Cactaceae

“…Based on our results, it seems likely that using supercontigs, not just exons, as well as increasing taxon sampling of Cylindropuntieae may provide further support for these deep relationships, and we are currently testing this hypothesis with our more comprehensive dataset of these groups. Although high numbers of polyploids are well documented from all three tribes in Opuntioideae [ 51 ], there seems to be no reason to suspect that allopolyploidization is the reason for the congruence seen here, given that diploids also are common throughout those three clades. Thus, diploidy certainly is the ancestral state for Opuntioideae.…”

Ex Situ Conservation in the Brazilian Semiarid: Cactaceae Housed in the Collection of the Guimarães Duque Cactarium

“…The collection of the Cactarium is a resource for current and future studies about cacti biodiversity. The collection supports research carried out by INSA's Biodiversity group in the areas of Agroecology, Molecular Biology, Biochemistry, Cytogenetics, in vitro Cultivation, Ecology, Taxonomy and Systematics (Castro et al 2016;Batista et al 2018;Amaral et al 2020;Castro et al 2020;Marhold et al 2020a, b). In addition to the in vivo collection, the institute maintains an in vitro cactus collection, with about 3,000 specimens, representing 27 species (Batista et al 2018).…”