Prezygotic barriers effectively limit hybridization in a rapid evolutionary radiation

Area of Science:

• Evolutionary Biology
• Phylogenetics
• Plant Speciation

Background:

• Hybridization is a significant evolutionary mechanism across diverse taxa.
• Phylogenomic studies have revealed extensive hybridization, but factors limiting it remain unclear, especially in evolutionary radiations.
• Costus (Costaceae) represents a young radiation of tropical plants with high interfertility yet strong prezygotic isolation.

Purpose of the Study:

• To investigate patterns and drivers of introgression within the Costus evolutionary radiation.
• To understand how prezygotic reproductive isolation influences hybridization dynamics in a young plant radiation.

Main Methods:

• Phylogenomic analysis of 756 genes from 54 Costus species.
• Utilized complementary methods: D-statistics, gene-tree-based tests, and phylogenetic network analyses.
• Characterized introgression events across the evolutionary history of the Costus clade.

Main Results:

• Identified a moderate number of introgression events throughout Costus evolution.
• Detected a significant ancient introgression event at a deep divergence point within the radiation.
• Most introgression occurred between lineages sharing similar pollination syndromes (bee or hummingbird).

Conclusions:

• Prezygotic barriers, particularly pollinator specialization, play a crucial role in maintaining the balance between hybridization and reproductive isolation in Costus.
• Pollination syndromes act as key factors shaping introgression patterns in this tropical plant radiation.