Evolutionary trends in Iridaceae: new cytogenetic findings from the New World

Abstract

With the present work, we aim to provide a better understanding of chromosome evolutionary trends among southern Brazilian species of Iridoideae. Chromosome numbers and genome sizes were determined for 21 and 22 species belonging to eight genera of Tigridieae and two genera of Trimezieae, respectively. The chromosome numbers of nine species belonging to five genera are reported here for the first time. Analyses of meiotic behaviour, tetrad normality and pollen viability in 14 species revealed regular meiosis and high meiotic indexes and pollen viability (> 90%). The chromosome data obtained here and compiled from the literature were plotted onto a phylogenetic framework to identify major events of chromosome rearrangements across the phylogenetic tree of Iridoideae. Following this approach, we propose that the ancestral base chromosome number for Iridoideae is x = 8 and that polyploidy and dysploidy events have occurred throughout evolution. Despite the variation in chromosome numbers observed in Tigridieae and Trimezieae, for these two tribes our data provide support for an ancestral base number of x = 7, largely conserved in Tigridieae, but a polyploidy event may have occurred prior to the diversification of Trimezieae, giving rise to a base number of x2 = 14 (detected by maximum‐parsimony using haploid number and maximum likelihood). In Tigridieae, polyploid cytotypes were commonly observed (2x, 4x, 6x and 8x), whereas in Trimezieae, dysploidy seems to have been the most important event. This feature is reflected in the genome size, which varied greatly among species of Iridoideae, 4.2‐fold in Tigridieae and 1.5‐fold in Trimezieae. Although no clear difference was observed among the genome sizes of Tigridieae and Trimezieae, an important distinction was observed between these two tribes and Sisyrinchieae, with the latter possessing the smallest genome sizes in Iridoideae. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 177, 27–49.

Differentiation between two self-compatible cytotypes of Herbertia lahue (Iridaceae): evidence from genotypic and phenotypic variation

“…However, the diploid record is associated with plants characterized as H. aff. lahue by Goldblatt and Takei (1997), and notwithstanding extensive search for diploid plants of H. lahue, the current research recently confirmed the only occurrence of hexaploids (2n = 6x = 42) and octoploids (2n = 8x = 56) in southern Brazil (Moraes et al 2015).…”

“…Sampled populations of H. lahue were the same as previously characterized cytogenetically by Moraes et al (2015) ( Table 1). Drawing on cytogenetic characterization, cytotypes were identified preliminarily based on three floral criteria: (A) presence or absence of an uncinate apex in the outer tepals, (B) presence or absence of a constriction in the base from outer tepals, and (C) shape of inner tepals.…”

“…Indeed, recent genetic, genomic, and ecological studies illustrate that polyploidy is a highly dynamic process which can lead to increasingly intense habitat partitioning, with polyploid populations occupying habitats intermediate to those of their diploid progenitors. For H. lahue, the literature refers to three ploidy levels: diploid (Goldblatt and Takei 1997), hexaploid (Kenton and Heywood 1984;Goldblatt and Takei 1997;Baeza et al 2001;Moreno et al 2009;Moraes et al 2015), and octoploid (Goldblatt 1975;Kenton and Heywood 1984;Moreno et al 2009;Moraes et al 2015). However, the diploid record is associated with plants characterized as H. aff.…”

Detecting Mechanisms of Karyotype Evolution in Heterotaxis (Orchidaceae)

“…Some hypotheses have been proposed regarding the importance of fusion and fission in karyotype evolution: whereas some authors claim fusion as the most important type of rearrangement, since truly telocentric chromosomes either do not exist or are very rare [12]; others have suggested centric fission as the main process, as it minimizes the genetic risks due to deleterious reciprocal translocations, as postulated by the Minimal Interaction Theory [13–15]. So far, these hypotheses have rarely been tested in a phylogenetic framework (but see [11, 16]).…”

“…However, statistical approaches, as ancestral state reconstruction based on maximum likelihood, have recently been applied to infer karyotype evolution in a phylogenetic framework [11, 16, 26–28]. In such approaches, the phylogenetical proposals should present all species with karyotype data available and, when nuclear and chloroplast phylogenetic proposals are conflicting, both should be tested independently to reflect the more robust answer about karyotype evolution.…”