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

Abstract

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.

Quantitative genetics approaches to study evolutionary processes in ecotoxicology; a perspective from research on the evolution of resistance

“…Heritability estimates were obtained from various parent-offspring regressions (offspring on father, offspring on mother, offspring on midparent). The estimates ranged from -0.43 ± 0.43 to 0.55 ± 0.50, but none were statistically different from zero and estimates averaged only 0.09 (Klerks and Moreau 2001). Laboratory selection experiments with these fish and contaminants similarly failed to detect a consistent increase in resistance (unpublished data).…”

“…Consequently, many heritability estimates suffer inherently from low precision (i.e., have a large standard error). For example, the parent/offspring based heritability estimates in the previously mentioned study in the sheepshead minnow C. variegatus had standard errors averaging 0.37 (with the heritability estimates averaging 0.09) in spite of the use of 20-30 families for each estimate (Klerks and Moreau 2001). This situation can be improved by optimizing the experimental design and increasing the sample size, but can easily reach the point where it is not feasible from a logistical standpoint.…”

“…Using half-sib families makes for a more complicated design (e.g., a number of males is each mated to multiple females) and more complex analysis, but enables the quantification of not only the additive genetic variation, but also the dominance variation and maternal effects (Falconer and Mackay 1996). Examples of studies estimating heritabilities from resemblances in laboratory-reared families, are provided here for studies with the oligochaete L. hoffmeisteri (Klerks and Levinton 1993) and the sheepshead minnow Cyprinodon variegatus (Klerks and Moreau 2001). For the oligochaete, worms were raised in pairs, offspring removed regularly and raised separately, and resistance quantified in both parents and offspring once offspring were maturewith resistance measured as time-to-death when exposed individually to an aqueous solution with a mixture of cadmium, nickel and cobalt.…”

Toxicity and bioaccumulation of TNT in marine fish in sediment exposures

“…Fish were maintained in 20 psu reconstituted seawater (RSW, Crystal Sea s , Marine Enterprises International, Essex, MD) at 23 1C throughout culturing and experimental procedures. Sheepshead minnows are abundant in estuaries along the southeastern and eastern coast of the United States and are widely used in routine toxicity testing of whole effluent and receiving waters (ASTM, 1999) as well as in ecotoxicological research (e.g., Manning et al, 1999;Klerks and Moreau, 2001;Lytle et al, 2003;Jonsson et al, 2004).…”

Understanding interactive effects of climate change and toxicants: Importance of evolutionary processes

“…Some empirical evidence on heritable variation, also termed adaptive potential, indicates that as the number of stressors increases, adaptive potential decreases although there is still considerable uncertainty regarding the generality of this response (Hoffman and Merila 1999). However, Klerks and Moreau (2001) showed that as the number of contaminants in an exposure mixture increased, the heritability of resistance decreased suggesting adaptive potential was reduced. Thus, populations may experience decreased ability to adapt to novel environmental stressors when exposed to multiple co‐occurring stressors.…”