The genetics of phenotypic plasticity I. Heritability

Abstract

Methods for estimating the genetic component of phenotypic plasticity are presented. In the general case of clonal replicates or full-sibs raised in several environments, the heritability of plasticity can be measured as the ratio of the genotype-environment interaction variance to the total phenotypic variance. In the special case of only two environments plasticity also can be measured as the difference among environments in genotype or family means. In that case, the heritability of plasticity can be measured as either a ratio of variance components or as the slope of a parent-offspring regression. The general measure suffers because no least-square standard errors have been developed, although they can be calculated by maximum-likelihood or bootstrapping techniques. For the other two methods least-square standard errors can be calculated but require very large experiments for statistical significance to be achieved. The heritability measures are compared using data on plasticity of thorax size in response to temperature in Drosophila melunogaster.The heritability estimates are all in close agreement. Models of the evolution of phenotypic plasticity have treated it as a trait in its own right and as a cross-environment genetic correlation. Although the first approach is the one used here, neither one is preferred.

Evolution of phenotypic plasticity: where are we going now?

“…As for the heritability of plasticity, Scheiner and Lyman [9] have introduced a formal way of calculating it, but such a measure has rarely been used in the literature because of logistical and conceptual reasons. Logistically, it is cumbersome to conduct experimental trials with a large enough number of genetically related families (raised in enough environments) to obtain estimates of heritability; moreover, the confidence intervals of such estimates usually span ranges that are large enough to make the effort not particularly informative.…”

Can individual variation in phenotypic plasticity enhance population viability?

“…Thus, individual plasticity is not fixed across generations. However, although the capacity to have a plastic response may be a heritable trait (Scheiner and Lyman, 1989), the occurrence of the plastic response is triggered by the state of a marmot and it is not heritable.…”

Genetics of phenotypic plasticity: QTL analysis in barley, Hordeum vulgare

“…In the epistatic model (Scheiner and Lyman, 1989), plasticity genes interact epistatically with, and thus regulate, the 'constitutive' loci that determine the mean value of the trait. In a limited number of modelsDrosophila melanogaster (Scharloo, 1991), tomato (Eshed and Zamir, 1996) and RNA viruses (Burch and Chao, 2004)there is evidence that canalization and phenotypic plasticity may be explained by epistatic mechanisms.…”

“…Three mechanisms were originally proposed to explain the genetic basis of phenotypic plasticity (see for synthesis Scheiner and Lyman, 1989). In the overdominance model, the degree of stability (or homeostasis) of a genotype is proportional to its degree of heterozygosity for relevant genes: an individual homozygous at these loci shows higher plasticity (Gillespie and Turelli, 1989).…”

“…In the pleiotropic model, it is the differential expression across environments of alleles at a locus that contributes to phenotypic plasticity (Via and Lande, 1985). In the epistatic model (Scheiner and Lyman, 1989), plasticity genes interact epistatically with, and thus regulate, the 'constitutive' loci that determine the mean value of the trait.…”