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.
Highlights
Chromosomal changes, both numerical and structural, are acknowledged to be important mechanisms that accompany speciation and diversification in plants [1]
The aim of the study was to analyse the patterns of chromosome number and genome size evolution in Crepis s.l. species
The phylogenetic relationships of the 45 Crepis species and Lapsana communis were inferred from analyses of their nrITS sequences and four plastid regions
Summary
Chromosomal changes, both numerical and structural, are acknowledged to be important mechanisms that accompany speciation and diversification in plants [1]. The large variation in chromosome numbers in the plant kingdom is the result of two major mechanisms—polyploidy and dysploidy [2]. Polyploidisation (whole genome duplication) and subsequent diploidisation seem to play a greater role in the evolution of angiosperms than in other eukaryotes [3]. Dysploidy involves various types of structural rearrangements of chromosomes, which often result in decreases or increases in chromosome numbers [5,6]. The chromosome morphology can be altered by the amplification/loss of DNA sequences [7]. Accumulation and/or loss of DNA sequences (mainly repetitive DNA) are mechanisms that lead to changes in the total karyotype length and genome size [8,9]
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