Patterns of chromosomal evolution in the florally diverse Andean clade Iochrominae (Solanaceae)

Abstract

Iochrominae is a largely Andean clade known for its remarkable diversity of floral forms and colors. Although knowledge of chromosomal changes can provide insights into the processes underlying speciation, such data in Iochrominae are scant. We performed cytogenetic analyses to characterize chromosome number and morphology, CMA/DAPI heterochromatic bands, and distribution of rDNA sites in Iochrominae. Ancestral karyotypes were reconstructed on a newly-estimated molecular phylogeny in order to test congruence between karyotype evolution and clade differentiation. We found that, compared with its closest relatives, Iochrominae comprises species with highly symmetrical karyotypes, with no changes in base chromosome number. The common ancestor of Iochrominae was inferred to be a diploid with 2n = 24, with a karyotype with 0-2 submetacentric chromosomes and the rest metacentric, an arm ratio ca. 1.30, one locus of 45S or NORs, and one locus of 5S. Using phylogenetic comparative methods, we estimated the number of changes for these chromosomal traits, and found the highest for 5S loci. Patterns of character change are largely homoplastic, although combinations of traits can be useful to identify groups within Iochrominae. Asymmetry was the only character that allow us to differentiate this clade among its relatives. Overall, our study suggests that the diversification of Iochrominae has not been accompanied by the formation of strong chromosomal barriers, which may help to explain the crossability of many species and even genera within the group. Highlights • Iochrominae is a largely Andean clade known for its remarkable floral diversity • Ancestral karyotypes were reconstructed into a molecular phylogeny • Chromosomal changes are homoplastic, although combinations of traits identify groups within Iochrominae • Iochrominae comprises species with highly symmetrical karyotypes, mostly 2n = 24 • Diversification of Iochrominae has not been accompanied by strong chromosome barriers 2 Key Words asymmetry, chromosome, evolution, Iochrominae, karyotype, Solanaceae 1. Introduction The tomato family Solanaceae includes a diversity of economically important species, such as potatoes, chili peppers, eggplants and tobacco. All of these crops belong to a major lineage within the family informally called the "x = 12 clade" (Olmstead et al., 2008). Its roughly 2300 species share chromosome numbers based on 12 pairs, including the giant genus Solanum, with c. 1000-1500 species (Bohs, 2005). The conservation of this base chromosome number suggests that the diversification of this clade across all continents (except Antarctica) over roughly 20.921 million years ago (mya; Dupin et al., 2017;De-Silva et al., 2017) was not coupled with significant cytological evolution. Nonetheless, detailed cytological studies remain few, especially for diverse and poorly studied Neotropical groups. For example, there are only c. 52 chromosome counts for the entire tribe of tomatillo and its allies (Physalideae), comprising 29 genera and more than 200 spec...

Comparative Plastomics of Ashwagandha (Withania, Solanaceae) and Identification of Mutational Hotspots for Barcoding Medicinal Plants

“…There is no consensus on the positions of the small clades related to Withania, while its closest relatives are also debated. In our analysis, Withania resembles Physalis, which is similar to the results of Deanna et al [77], although this branching is supported by only weak bootstrap values.…”

Comparative Plastomics of Ashwagandha (Withania, Solanaceae) and Identification of Mutational Hotspots for Barcoding Medicinal Plants

“…The phylogenetic relationships within the genus are poorly known, and the biology, chromosome numbers, and the exact number of species are also lacking. Chromosome counts showed that most species of Withania are polyploids with 2n = 2x = 48 [82], derived from the x = 12 haploid chromosome number typical for the majority of Solanaceae species. In addition to the currently accepted Withania taxa, there are 35 unresolved botanical names that need further investigation to clarify the taxonomy of the genus.…”

Repeated evolution of a morphological novelty: a phylogenetic analysis of the inflated fruiting calyx in the Physalideae tribe (Solanaceae)

“…Starting with the monophyletic and well‐studied Iochrominae, only three out of six genera are monophyletic, even after recent nomenclatural changes (Shaw, , b). The crossability among genera, high convergence in traits used to delimitate generic taxonomy, and the comparative lack of karyological variation (Smith and Baum, ; Smith et al., ; Deanna et al., ; Shaw, ) suggest that combining the genera into a single monophyletic Iochroma may be the most stable solution. During the past 20 years, 19 new species of Iochroma and one Saracha have been described (e.g., Leiva Gonzalez et al., ; Leiva González and Lezama, ; Lezama Escobedo et al., ; Fernandez‐Hilario and Smith, ), but no key for the entire group has been proposed, increasing the necessity of a full taxonomic revision.…”

“…Thus, genetic changes that modify these hormonal signals, MPF2 expression, or MPF2 function could all contribute to variation in calyx inflation (Riss, ). Comparative molecular and developmental studies to date implicate both regulatory and structural mutations in MPF2 ‐like genes (Hu and Saedler, ; Khan et al., ; Riss, ), coupled with shifts in copy number due to the many ploidy changes in the tribe (Iqbal and Datta, ; Deanna et al., ).…”