Selection in two-sex stage-structured populations: Genetics, demography, and polymorphism

Area of Science:

• Evolutionary biology
• Population genetics
• Demography

Background:

• Natural selection outcomes depend on birth, death, and development rates.
• Understanding genetic polymorphism requires considering demographic factors.
• Sex-specific differences in demography are often overlooked in evolutionary models.

Purpose of the Study:

• To derive conditions for protected polymorphism in populations with age- or stage-dependent demography and two sexes.
• To investigate the role of sexual dimorphism in eco-evolutionary dynamics.
• To model the impact of sex-specific selection on survival, growth, and fertility.

Main Methods:

• Developed a novel two-sex matrix population model.
• Incorporated Mendelian genetics (one locus, two alleles, random mating).
• Analyzed eigenvalues of the linearized model at homozygote boundary equilibria.

Main Results:

• In the absence of sexual dimorphism, protected polymorphism requires heterozygote superiority.
• Sexual dimorphism can allow invasion by inferior heterozygotes.
• This invasion can reduce population growth rate and lead to extinction (evolutionary suicide).

Conclusions:

• Sexual dimorphism is crucial for understanding extinction risk and eco-evolutionary processes.
• Sex- and stage-specific demographic structures can lead to alleles favoring selection while driving populations to extinction.
• The model integrates ecological and evolutionary timescales without assuming separation.