Purging due to self-fertilization does not prevent accumulation of expansion load

Area of Science:

• Evolutionary Biology
• Genetics
• Ecology

Background:

• Species range expansions expose colonizing populations to new environments and mating challenges.
• Self-fertilization (selfing) is common at range edges, potentially aiding mate acquisition and purging genetic load.
• Genetic load, the accumulation of deleterious mutations, can hinder population establishment and persistence.

Purpose of the Study:

• To investigate how selfing influences genetic load accumulation and colonization speed during range expansions.
• To differentiate inbreeding effects from demographic factors versus selfing itself.
• To compare simulation predictions with empirical data from the plant Arabis alpina.

Main Methods:

• Population genetics simulations to model range expansion with varying selfing rates.
• Analysis of whole-genome sequences from outcrossing and selfing populations of Arabis alpina.
• Comparison of simulated genetic load patterns with empirical genomic data.

Main Results:

• Selfing populations exhibit faster range expansion rates.
• Both selfing and outcrossing populations accumulate genetic load during expansion.
• Higher selfing rates effectively purge large-effect recessive mutations, but smaller-effect alleles accumulate.
• Empirical data from Arabis alpina support simulation findings of expansion load and purging in selfing populations.

Conclusions:

• Selfing facilitates faster colonization during range expansions.
• While selfing can purge severe mutations, it does not prevent the overall accumulation of genetic load.
• Purging via selfing is a partial benefit, but insufficient to fully counteract expansion-driven genetic load.
• Understanding mating system evolution is crucial for predicting species' responses to environmental change and range shifts.