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

Resistance heritability (the additive genetic variance out of the total phe notypic variance, signifying a population's potential to genetically adapt to detrimental levels of contamination) was quantified in the sheepshead mi nnow (Cyprinodon variegatus). Heritability was estimated for tolerance to i ndividual contaminants (phenanthrene, zinc) and to contaminant mixtures (ph enanthrene plus zinc, and a complex mixture with three metals and three pol ycyclic aromatic hydrocarbons). Estimates were obtained from resemblances b etween relatives, both parent-offspring pairs, and families of sibs and hal f-sibs. Heritabilities determined from parent-offspring regressions average d only 0.08 (scale, 0-1), whereas resemblance among full sibs yielded herit abilities averaging 0.85. The half-sib analysis yielded heritabilities of - 0.01 (sire component) and 0.77 (dam component). This pattern in the magnitu de of heritabilities indicates that heritabilities for the resistance of C. variegatus to these chemicals are low (with the high resemblances among si bs 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 involve d. Our results mean, then, that C. variegatus in contaminated environments is not likely to become resistant to these contaminants very rapidly, and t hat resistance may develop even more slowly as more contaminants become inv olved.