Does heterozygosity estimate inbreeding in real populations?

Area of Science:

• Population Genetics
• Evolutionary Biology
• Quantitative Genetics

Background:

• Recent studies link individual heterozygosity at neutral microsatellite markers to fitness components.
• Inbreeding depression is often cited as the mechanism, assuming marker heterozygosity reliably estimates inbreeding coefficients.

Purpose of the Study:

• To examine conditions under which heterozygosity and inbreeding are correlated using individual-based simulations.
• To assess the validity of using a small number of markers to estimate an individual's inbreeding coefficient.

Main Methods:

• Individual-based simulations were employed to model correlations between heterozygosity and inbreeding.
• Simulations explored various parameters including inbreeding frequency, severity, population structure, and mating systems.
• Marker correlations were analyzed within individuals using a large dataset (400 markers) from diverse human populations.

Main Results:

• Correlations between heterozygosity and inbreeding are only likely under narrow conditions: frequent and severe inbreeding (e.g., selfing, strong population structure, polygyny).
• Strong correlations require a large number of loci (~200) for heterozygosity estimation.
• With few markers, correlations are improbable except in extreme scenarios (e.g., 20 demes of 20 individuals with strong polygyny).
• Heterozygosity is weakly correlated among markers within individuals, even with 400 markers.

Conclusions:

• The assumption that a few markers reliably estimate inbreeding coefficients is questionable.
• If heterozygosity and inbreeding are generally uncorrelated, heterozygosity-fitness correlations may not be due to inbreeding depression.
• Alternative explanations, such as chance linkage to loci under balancing selection, are plausible.
• Current understanding may need revision regarding the prevalence of consanguineous mating or the role of polymorphisms in fitness.