Introgression despite minimal hybridization: mating system modulates phenotypic associations with introgression in...

Area of Science:

• Evolutionary Biology
• Speciation Research
• Population Genetics

Background:

• Understanding how trait divergence restricts gene flow is crucial for studying speciation.
• Mating system transitions are common during speciation and involve phenotypic changes, but their impact on gene flow is unclear.

Purpose of the Study:

• To quantify introgression between selfing and outcrossing sister Clarkia taxa in four contact zones.
• To investigate the influence of mating systems and phenotypic variation on gene flow and hybrid formation during early speciation.

Main Methods:

• Genomic analysis of 410 individuals to quantify introgression.
• Common garden experiments and geospatial data to assess hybrid frequency and phenotypic associations.
• Analysis of chloroplast DNA to infer patterns of hybridization.

Main Results:

• Substantial admixture was observed, but no early-generation hybrids were detected.
• Introgression was consistently asymmetric, favoring the selfing mating system.
• The selfing species showed spatially structured introgression associated with phenotypic traits, like flower color, potentially reducing hybridization.

Conclusions:

• Premating isolation mechanisms minimize hybridization despite recent divergence and historical introgression.
• Mating systems play a consistent role in modulating introgression direction.
• Phenotypic variation influences backcrossing dynamics after initial hybridization events.