Rhythmic natural selection over intertidal and brackish water genotypes: simple formulations for testing hypothesis.

Area of Science:

• Ecology
• Population Genetics
• Mathematical Biology

Background:

• Benthic habitats experience periodic environmental shifts (salinity, temperature) due to tidal cycles.
• These environmental changes impose natural selection pressures on benthic organisms.
• Classic population genetics highlights temporal selection's restrictive nature on genetic variance.

Purpose of the Study:

• To model continuous selection in asexual populations with sinusoidally fluctuating genotype fitness (wi).
• To investigate the impact of the ratio of tide period to generation time (h) on population dynamics.
• To analyze how genetic variance and mean fitness are affected by tidal selection.

Main Methods:

• Developed a replicator dynamics-based model for continuous selection.
• Simulated fluctuating genotype fitness (wi) as a sinusoid with a set amplitude.
• Defined the ratio (h) of tide period to generation time as a key parameter.

Main Results:

• If h > 1, advantageous genotype success is randomized, potentially decreasing mean population fitness (w¯) over time.
• If h < 1, genotype success is deterministic, dependent on minimum fitness (wmin), and limits co-dominance.
• Higher genotypic diversity buffers the decay of genetic variance (σ(2)w), enhancing population cohesiveness.

Conclusions:

• The ratio of tide period to generation time critically determines the predictability and outcome of natural selection in tidally influenced environments.
• Genotypic diversity plays a crucial role in maintaining genetic variance and population stability under rhythmic selection.
• The model provides insights applicable to intertidal and brackish water organisms facing periodic environmental stress.