Descending Dysploidy and Bidirectional Changes in Genome Size Accompanied Crepis (Asteraceae) Evolution

Abstract

The evolution of the karyotype and genome size was examined in species of Crepis sensu lato. The phylogenetic relationships, inferred from the plastid and nrITS DNA sequences, were used as a framework to infer the patterns of karyotype evolution. Five different base chromosome numbers (x = 3, 4, 5, 6, and 11) were observed. A phylogenetic analysis of the evolution of the chromosome numbers allowed the inference of x = 6 as the ancestral state and the descending dysploidy as the major direction of the chromosome base number evolution. The derived base chromosome numbers (x = 5, 4, and 3) were found to have originated independently and recurrently in the different lineages of the genus. A few independent events of increases in karyotype asymmetry were inferred to have accompanied the karyotype evolution in Crepis. The genome sizes of 33 Crepis species differed seven-fold and the ancestral genome size was reconstructed to be 1C = 3.44 pg. Both decreases and increases in the genome size were inferred to have occurred within and between the lineages. The data suggest that, in addition to dysploidy, the amplification/elimination of various repetitive DNAs was likely involved in the genome and taxa differentiation in the genus.

Keywords: chromosome number; flow cytometry; genome size; karyotype formula; phylogenetic analysis.

Figure 1

Phylogenetic relationships among the analysed Crepis species based on the nrITS and the cpDNA data sets. Bootstrap support values are indicated at each node. Names of the species that were recovered in different positions in the two datasets are indicated in colour. The trees were rooted with Picris hieracioides, Lactuca serriola, and Sonchus oleraceus.

Figure 2

Karyograms representing each of the karyotype formula distinguished among the analysed Crepis species: (A) Lapsana communis; (B) C. magellensis; (C) C. jacquinni; (D) C. paludosa; (E) C. succisifolia; (F) C. lyrate; (G) C. nicaeensis. Letters below each pair of chromosomes indicate the type of chromosome: m—metacentric; sm—submetacentric; and st—subtelocentric. The metaphase plates used to prepare the karyograms are presented in Figure S2. Scale bar = 5 µm.

Figure 3

Karyograms representing each of the karyotype formula distinguished among the analysed Crepis species: (A) C. pannonica; (B) C. foetida subsp. rhoaedifolia; (C) C. zacintha; (D) C. syriaca; (E) C. kotschyana; (F) C. vesicaria 2; (G) C. vesicaria 1; (H) C. leontodontoides; (I) C. oporinoides; (J) C. capillaris. Letters below each pair of chromosomes indicate the type of chromosome: m—metacentric; sm—submetacentric; and st—subtelocentric. The metaphase plates used to prepare the karyograms are presented in Figure S3. Scale bar = 5 µm.

Figure 4

Ancestral character state reconstruction of the chromosome base numbers of the analysed species of Crepis s.l. The chromosome base numbers have been mapped on the ML tree of concatenated cpDNA sequences using the maximum likelihood method implemented in ChromEvol 2.0 software [45]. The tree was rooted with Picris hieracioides, Lactuca serriola, and Sonchus oleraceus.

Figure 5

Karyotype evolution in the analysed species of Crepis s.l. Genome sizes were mapped on the ML tree of concatenated cpDNA sequences using the maximum likelihood method implemented in Phytools. Karyotype formulas (symbols preceding the species names) and the increases in karyotype asymmetry (black arrows) are indicated for all species. The genome sizes, karyotype formulas, and asymmetry indexes of each species are presented in Table 2. The figure includes only species for which all three datatypes (chromosome number, karyotype formula, and asymmetry index) were provided. The tree was rooted with Picris hieracioides, Lactuca serriola, and Sonchus oleraceus.