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Quantitative Analyses of Coupling in Hybrid Zones
Thomas J Firneno1, Georgy Semenov2, Erik B Dopman3
1Department of Biology, University of Denver, Denver, Colorado 80208, USA.
Cold Spring Harbor Perspectives in Biology
|September 22, 2023
Summary
The coupling coefficient quantifies how selection and recombination affect linked genes in hybrid zones. This study reveals a continuum of gene flow barriers, suggesting gradual evolution of reproductive isolation.
Area of Science:
- Evolutionary Biology
- Population Genetics
- Speciation Research
Background:
- Hybrid zones are crucial for understanding speciation and the evolution of reproductive isolation.
- The degree to which genetic loci influencing hybrid fitness are linked (coupled) is theoretically important but rarely quantified.
- The coupling coefficient, reflecting the ratio of selection to recombination, is key to understanding coupled vs. uncoupled selection.
Purpose of the Study:
- To characterize the relationship between the coupling coefficient and the variance in genetic clines across multiple loci.
- To empirically quantify the extent of genetic coupling in natural hybrid zones.
- To test theoretical predictions about the transition between uncoupled and coupled systems.
Main Methods:
- Utilized computer simulations to model the relationship between coupling coefficients and cline variances.
- Reanalyzed 25 existing hybrid zone datasets using the developed simulation framework.
- Estimated coupling coefficients and cline variances from empirical genetic data.
Main Results:
- Found that cline variances and estimated coupling coefficients form a continuous spectrum, from high variance/weak coupling to low variance/strong coupling.
- Observed a smooth transition rather than a sharp threshold between uncoupled and coupled genetic systems.
- Results align with scenarios of low hybridization rates and strong genome-wide barriers when the coupling coefficient exceeds 1.
Conclusions:
- The extent of genetic coupling in hybrid zones is variable and exists on a continuum.
- Strong barriers to gene flow may be approached gradually, not abruptly.
- Findings provide empirical support for theoretical models of selection on linked loci during speciation.
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