Heritability of resistance to individual contaminants and to contaminant mixtures in the sheepshead minnow (Cyprindon variegatus).

Resistance heritability (the additive genetic variance out of the total phenotypic variance, signifying a population's potential to genetically adapt to detrimental levels of contamination) was quantified in the sheepshead minnow (Cyprinodon variegatus). Heritability was estimated for tolerance to individual contaminants (phenanthrene, zinc) and to contaminant mixtures (phenanthrene plus zinc, and a complex mixture with three metals and three polycyclic aromatic hydrocarbons). Estimates were obtained from resemblances between relatives, both parent-offspring pairs, and families of sibs and half-sibs. Heritabilities determined from parent-offspring regressions averaged only 0.08 (scale, 0-1), whereas resemblance among full sibs yielded heritabilities averaging 0.85. The half-sib analysis yielded heritabilities of -0.01 (sire component) and 0.77 (dam component). This pattern in the magnitude of heritabilities indicates that heritabilities for the resistance of C. variegatus to these chemicals are low (with the high resemblances among sibs being due to common environmental and dominance genetic variation rather than additive genetic variation). The parent-offspring regressions provide evidence that heritabilities may be lower if more contaminants are involved. Our results mean, then, that C. variegatus in contaminated environments is not likely to become resistant to these contaminants very rapidly, and that resistance may develop even more slowly as more contaminants become involved.