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

Area of Science:

• Plant evolutionary biology
• Cytogenetics
• Genomics

Background:

• The genus *Crepis* exhibits significant diversity in karyotype and genome size.
• Understanding the evolutionary mechanisms driving these changes is crucial for plant speciation studies.

Purpose of the Study:

• To investigate the patterns of karyotype and genome size evolution in *Crepis*.
• To reconstruct the phylogenetic framework for inferring evolutionary trajectories.

Main Methods:

• Phylogenetic analysis using plastid and nrITS DNA sequences.
• Reconstruction of ancestral chromosome numbers and genome sizes.
• Analysis of karyotype asymmetry and genome size variation across 33 *Crepis* species.

Main Results:

• Five distinct base chromosome numbers (*x* = 3, 4, 5, 6, 11) were identified.
• Descending dysploidy (*x* = 6 ancestral) was inferred as the major evolutionary trend for chromosome numbers, with independent recurrent origins of lower numbers.
• Genome size varied seven-fold, with an inferred ancestral size of 1C = 3.44 pg, showing both increases and decreases.
• Karyotype asymmetry increased in several independent lineages.

Conclusions:

• Karyotype evolution in *Crepis* is characterized by descending dysploidy and recurrent changes in base chromosome number.
• Genome size evolution involved both increases and decreases, likely driven by amplification/elimination of repetitive DNA.
• These evolutionary processes, alongside dysploidy, contributed to genome and species differentiation in *Crepis*.