Cleistogamous capitulum in Centaurea melitensis (Asteraceae): heterochronic origin

Area of Science:

• Evolutionary biology
• Developmental biology
• Plant morphology

Background:

• Cleistogamous capitula in Centaurea melitensis show distinct morphological and functional changes compared to chasmogamous capitula.
• The evolution of cleistogamy within the Asteraceae family lacks comprehensive study.
• Understanding the developmental mechanisms behind cleistogamy is crucial for evolutionary insights.

Purpose of the Study:

• To investigate the heterochronic processes underlying the morphological changes in cleistogamous capitula of Centaurea melitensis.
• To determine if early onset, altered growth rates, or early offset of development contribute to cleistogamy.
• To analyze the role of these processes in the evolution of self-fertilization strategies.

Main Methods:

• Bivariate allometric analyses were employed to compare cleistogamous and chasmogamous capitula.
• Gould's clock models were used to graphically represent changes in size, shape, and age of capitulum and floret structures.
• Comparative morphological analysis of floral development stages was conducted.

Main Results:

• Cleistogamous capitula exhibit a partially paedomorphic appearance relative to chasmogamous capitula.
• Three heterochronic processes were identified: early onset of floral development (predisplacement), decreased growth rate (except gynoecium width), and early offset time (progenesis).
• Progenesis, or early offset of development, was found to be the most significant factor in the origin of the cleistogamous capitulum.

Conclusions:

• The morphological divergence of cleistogamous capitula in Centaurea melitensis is significantly shaped by heterochronic developmental changes.
• Progenesis plays a primary role in the evolutionary origin of cleistogamy in this species.
• These findings contribute to understanding the evolution of reproductive strategies and developmental plasticity in Asteraceae.