The independence of enzyme heterozygosity and life-history traits in natural populations of salvelinus fontinalis (brook trout)

The relationship was examined between allozyme heterozygosity at six polymorphic loci and several life-history traits (age and size at maturity, egg size, fecundity, proportional allocation of body tissue to gonads) within five natural, unexploited populations of brook trout (Salvelinus fontinalis) on Cape Race, Newfoundland, Canada. We tested two predictions of the hypothesis that increased allozyme heterozygosity enhances fitness. We found little or no support for the predictions that single or multilocus heterozygosity is (i) positively associated with the phenotypic value of life-history traits, and is (ii) negatively associated with trait variances. Neither single nor multilocus heterozygosity was positively associated with a life-history trait in 67 within-population analyses. Trait variance decreased significantly with increased multilocus heterozygosity in only 1 of 25 cases. We conclude that trade-offs, non-directional selection, relatively high environmental variation in life-history traits, and conflicting selection pressures on the same trait (in different stages of life) may combine to reduce the likelihood of detecting significant correlations between heterozygosity and those traits most closely related to fitness in natural populations.