Stressful conditions may cause plant cells to invest more energy in metabolic regulation and elimination of toxins and therefore to invest less energy in stabilizing symmetrical development, resulting in an increase in developmental noise
(M0ller and Swaddle, 1997; Leung et al., 2000).
DI is defined as a suite of processes that tend to disrupt the precise development of bilateral traits in organisms and is believed to stem from various exogenous and endogenous stresses that collectively referred to as developmental noise
or perturbations [3,4].
When instability (occasionally referred to as developmental noise) occurs, it may be marked by relatively conspicuous morphological or behavioural errors, but more often by only minor random deviations from bilaterally symmetrical traits called fluctuating asymmetry (FA).
First, it measures minor genetically and environmentally induced departures from a perfectly designed developmental programme, and thus is provides a gauge of the organism's developmental noise, and indirectly of its viability fitness.
A quantitative-genetic model for selection on developmental noise
. Evolution 48:1478-1486.
It would appear illogical to expect the genetic mechanisms responsible for developmental stability to differ between the sexes given that both males and females need to be able to regulate and buffer character development against developmental noise
and environmental perturbation.
, and Yampolsky and Scheiner , for an analogous approach to quantifying developmental noise.) These alternative sources include genetic variance (Falconer 1989) in pupal period and one component of environmental variance, the "classical" phenotypic plasticity (deterministic reaction norm, or, synonymously, the systematic component of the nongenetic phenotypic variation sensu Bull  and Falconer ).
It provides, therefore, a candidate for random environmental variance (developmental noise or diverse parental effects), which represents the type of variance a diversified bet-hedging strategy can be based on.
Palmer (1994) Palmer and Strobeck (1992) assert that distributions of asymmetries within a population that do not meet these criteria may represent the effects of factors other than developmental noise and developmental stability, such as genetic predisposition (e.g., handedness) or [TABULAR DATA FOR TABLE 7 OMITTED] [TABULAR DATA FOR TABLE 8 OMITTED] ontogenetic interactions between sides.
Fluctuating asymmetry in Macaca fascicularis: a study of the etiology of developmental noise, Int.
Since the same genes code for proteins in each half of symmetrical traits, differences between halves is a measure of developmental noise
, and the organism's inability to correct for developmental noise
, or developmental instability (Mather 1953, Soule 1979, Parsons 1991, Palmer 1996).