Evolutionary stasis in Euphorbiaceae pollen: selection and constraints

Area of Science:

• Evolutionary biology
• Plant reproductive biology
• Developmental genetics

Background:

• Evolutionary stasis is often attributed to stabilizing selection, but developmental constraints are less studied, especially in plants.
• Pollen ontogeny, specifically the last points of callose deposition (LPCD) pattern, influences adaptive pollen aperture patterns.
• The LPCD pattern shows low evolution in eudicots compared to monocots, suggesting stasis.

Purpose of the Study:

• To investigate the roles of developmental constraints versus selective pressures in the evolutionary stasis of the LPCD pattern in plants.
• To test hypotheses explaining the conserved LPCD pattern in eudicots, focusing on Euphorbiaceae s.s.
• To understand the evolutionary dynamics of microsporogenesis and its impact on pollen morphology.

Main Methods:

• Phylogenetic analysis of the LPCD pattern within Euphorbiaceae s.s.
• Comparative analysis of LPCD pattern evolution in eudicots and monocots.
• Investigation of microsporogenesis variation in relation to pollen aperture evolution.

Main Results:

• The LPCD pattern is highly conserved in Euphorbiaceae s.s.
• Selective pressures, rather than developmental constraints, are the primary drivers of LPCD pattern conservatism.
• A phylogenetic link exists between the loss of selection on pollen morphology and increased variation in microsporogenesis and LPCD patterns.
• Even under neutral conditions, microsporogenesis variation exhibits bias, favoring specific developmental and morphological outcomes.

Conclusions:

• Selective pressures play a dominant role in maintaining stasis of the LPCD pattern in plant pollen.
• The evolution of pollen aperture patterns is tightly linked to the conservation of underlying developmental processes.
• Biased variation in microsporogenesis suggests inherent developmental pathways influencing evolutionary trajectories, even without strong selection.