Re-evaluating Homoploid Reticulate Evolution in Helianthus Sunflowers

Area of Science:

• * Evolutionary biology
• * Plant genetics
• * Phylogenomics

Background:

• * Sunflowers (Helianthus) are key models for studying hybrid speciation.
• * Three species are well-known examples of homoploid hybrid speciation.
• * Previous research suggested specific hybridization events in Helianthus evolution.

Purpose of the Study:

• * To investigate the role of hybridization and gene flow in the radiation of annual sunflowers.
• * To conduct a phylogenomic analysis using whole-genome resequencing data.
• * To test for gene flow between Helianthus lineages.

Main Methods:

• * Whole-genome resequencing of annual sunflower species.
• * Phylogenomic analysis to reconstruct evolutionary relationships.
• * Admixture graph modeling to infer hybridization events and timing.

Main Results:

• * All tested annual sunflower species show evidence of admixture, indicating widespread hybridization.
• * Hybridization and introgression correlate with discordant phylogenetic signals.
• * Hybridization events are older than previously estimated, and two species likely originated from a single ancient event.
• * Introgression signals are pervasive across the entire Helianthus genus, including perennial species.

Conclusions:

• * Hybridization has played a significant and ancient role in the diversification of the Helianthus genus.
• * The genus Helianthus functions as a syngameon, with gene flow linking distinct species.
• * Findings challenge previous hypotheses on the origins of specific hybrid sunflower species.