Introgression and Divergence in a Young Species Group

Area of Science:

• Evolutionary Biology
• Genomics
• Speciation Research

Background:

• Understanding species diversity requires studying gene flow and reproductive isolation in closely related species.
• The Formica rufa group (wood ants) provides a model system for investigating early-stage speciation.
• Previous studies have suggested polygenic species barriers in this group.

Purpose of the Study:

• To disentangle genomic patterns of divergence and introgression in five Formica rufa group wood ant species.
• To revise existing mitochondrial phylogenies with a nuclear genomic tree.
• To investigate the relationship between introgression, recombination, and genomic diversity in young species.

Main Methods:

• Resequencing data analysis of five Formica rufa group wood ant species.
• Construction of a nuclear genomic tree to complement mitochondrial phylogenies.
• Genome-wide correlation analyses of divergence, differentiation, diversity, and introgression.

Main Results:

• Introgression was confirmed, aligning with current natural hybridization observations.
• Genome-wide patterns align with theoretical expectations for young species, but lack expected correlations for polygenic barriers, possibly due to ancestral diversity.
• No strong positive correlation between introgression and recombination was found, suggesting introgression is not always deleterious; low diversity in high introgression regions may indicate selection.
• Gene flow was observed to cross multiple species boundaries, even without direct interbreeding.

Conclusions:

• Early-stage speciation in wood ants is characterized by complex introgression patterns that influence genomic structure.
• The findings challenge simple models of polygenic species barriers and highlight the role of ancestral diversity.
• Introgression may be shaped by selection and can facilitate gene flow across species boundaries, with potential long-term evolutionary benefits and costs.