THE FITNESS CONSEQUENCES OF MULTIPLE-LOCUS HETEROZYGOSITY: THE RELATIONSHIP BETWEEN HETEROZYGOSITY AND GROWTH RATE IN...

Area of Science:

• Population genetics
• Quantitative genetics
• Evolutionary biology

Background:

• Positive correlations between heterozygosity and fitness are often observed.
• Inbreeding depression and overdominance are two main hypotheses explaining this.
• Distinguishing between these hypotheses has been challenging.

Purpose of the Study:

• To reanalyze previous data on pitch pine heterozygosity and growth rate.
• To contrast Smouse's overdominance model with an inbreeding depression analysis.
• To investigate the role of specific genotypes in determining growth rate.

Main Methods:

• Reanalysis of Ledig et al.'s (1983) pitch pine data using Smouse's (1986) overdominance model.
• Contrasting results with an inbreeding depression analysis.
• Utilizing an adaptive-distance model to assess genotype-fitness relationships.

Main Results:

• Reanalysis using individuals, not means, showed no significant heterozygosity-fitness correlations.
• The adaptive-distance model explained 15-50% of growth rate variation, significantly more than previous analyses.
• Significant correlations between adaptive distance and growth rate were found in four populations, with mixed results regarding the overdominance hypothesis.

Conclusions:

• Specific genotypes significantly influence growth rate in pitch pine.
• The relationship between growth rate and adaptive distance strengthens with population age.
• Simple heterozygosity-fitness correlations may not fully capture complex genetic influences on fitness.