Cytological and genome size data analyzed in a phylogenetic frame: Evolutionary implications concerning Sisyrinchium taxa (Iridaceae: Iridoideae).

Paula Burchardt,Lilian Eggers,José Marcello Salabert De Campos,Eliane Kaltchuk-Santos,Camila Dellanhese Inácio,Olivier Chauveau,Tatiana T Souza-Chies,Sidia M Callegari-Jacques,Sonja Siljak-Yakovlev,Lauís Brisolara-Corrêa

doi:10.1590/1678-4685-gmb-2017-0077

Abstract

Sisyrinchium is the largest genus of Iridaceae in the Americas and has the greatest amount of cytological data available. This study aimed at investigating how genomes evolved in this genus. Chromosome number, genome size and altitude from species of sect. Viperella were analyzed in a phylogenetic context. Meiotic and pollen analyses were performed to assess reproductive success of natural populations, especially from those polyploid taxa. Character optimizations revealed that the common ancestor of sect. Viperella was probably diploid (2n = 2x =18) with two subsequent polyplodization events. Total DNA content (2C) varied considerably across the phylogeny with larger genomes detected mainly in polyploid species. Altitude also varied across the phylogeny, however no significant relationship was found between DNA content changes and altitude in our data set. All taxa presented regular meiosis and pollen viability (> 87%), except for S. sp. nov. aff. alatum (22.70%), suggesting a recent hybrid origin. Chromosome number is mostly constant within this section and polyploidy is the only source of modification. Although 2C varied considerably among the 20 taxa investigated, the diversity observed cannot be attributed only to polyploidy events because large variations of DNA content were also observed among diploids.

Highlights

Iridaceae is one of the largest Asparagales families (APG IV, 2016), and chromosome number was determined for about 50% of the 2030 species included, mostly for taxa from the Northern Hemisphere and Africa (Goldblatt and Takei, 1997)
Chromosome counts for 17 taxa are presented here in Table 2; all but one (S. alatum) had their number determined for the first time
The smallest chromosomes were those of S. decumbens and S. wettsteinii (Figure 2A and H, respectively), and the largest chromosomes were found in S. macrocephalum subsp. giganteum (Figure 2E)

Summary

Introduction

Iridaceae is one of the largest Asparagales families (APG IV, 2016), and chromosome number was determined for about 50% of the 2030 species included, mostly for taxa from the Northern Hemisphere and Africa (Goldblatt and Takei, 1997). Knowledge about cytological characters has been especially helpful for genera circumscription and to understand species relationship in various genera (Goldblatt and Takei, 1997). In this family, there is great karyological variation, comprising karyotype features, basic chromosome number (x) and ploidy level. Chromosome heteromorphism and asymmetry are frequently found in several species (Alves et al, 2011) Such karyotypic variations are especially related to polyploidy and descending disploidy, both considered important events for the diversification of subfamily Iridoideae (Goldblatt and Takei, 1997; Moraes et al, 2015).

Objectives

Methods

Results

Discussion

Conclusion