Structure and contingency determine mutational hotspots for flower color evolution.

Area of Science:

• Evolutionary genetics
• Developmental genetics
• Computational biology

Background:

• Genomic hotspots are known to concentrate phenotypic evolution, but the underlying theoretical basis and historical contingency are poorly understood.
• Flower color evolution, particularly anthocyanin pigmentation, provides a model system to study evolutionary trajectories and mutation patterns.

Purpose of the Study:

• To computationally investigate the theoretical basis for mutation concentration at genomic hotspots.
• To examine the role of historical contingency in the appearance of hotspots and the fixation of specific mutation types.
• To model flower color transitions (blue-to-purple and purple-to-red) to understand evolutionary pathways.

Main Methods:

• Utilized a computational approach to simulate evolutionary transitions in the anthocyanin pigmentation pathway.
• Focused on two common natural transitions: blue to purple and purple to red pigmentation.
• Analyzed the number, type (biochemical vs. regulatory), direction, and magnitude of mutations at key loci.

Main Results:

• Simulated transitions showed peaked evolutionary trajectories with large-effect mutations occurring early but not first.
• The types and direction of mutations were contingent on the specific color transition being modeled.
• Results largely mirrored natural flower color evolution, highlighting hotspot loci, but also indicated pleiotropic effects limiting natural trajectories.

Conclusions:

• The branching structure of the anthocyanin pathway predictably concentrates evolutionary change at hotspot loci.
• The specific types and order of mutations at these hotspots are contingent on the evolutionary context.
• Pleiotropic effects may further constrain evolutionary trajectories observed in nature.