The Association between Fluctuating Asymmetry, Trait Variability, Trait Heritability, and Stress: A Multiply Replicated Experiment on Combined Stresses in Drosophila melanogaster

Abstract

A number of hypotheses have been proposed about the association between developmental stability, phenotypic variability, heritability, and environmental stress. Stress is often considered to increase both the asymmetry and phenotypic variability of bilateral traits, although this may depend on trait heritability. Empirical studies of such associations often yield inconsistent results. This may reflect the diversity of traits and conditions used or a low repeatability of any associations. To test for repeatable associations between these variables, multiply replicated experiments were undertaken on Drosophila melanogaster using a combination stress at the egg, larval, and adult stages of reduced protein, ethanol in the medium, and a cold shock. Both metric and meristic traits were measured and levels of heritable variation for each trait estimated by maximum likelihood and parent-offspring regression over three generations. Trait means were reduced by stress, whereas among-individual variation increased. Fluctuating asymmetry (FA) was increased by stress in some cases, but few comparisons were significant. Only one trait, orbital bristle, showed consistent increases in FA. Changes in trait means, trait phenotypic variability, and developmental stability as a result of stress were not correlated. Extreme phenotypes tended to have higher levels of FA, but only the results for orbital bristles were significant. All traits had low to intermediate heritabilities except orbital bristle, which showed no heritable variation. Only traits with low heritability and high levels of phenotypic variability may show consistent increases in FA under stress. Overall, the independence of phenotypic variability, plasticity, and the developmental stability of traits extend to changes in these measures under stressful conditions.

An epistatic genetic basis for fluctuating asymmetry of tooth size and shape in mice

“…Fixation of the LG allele at the two loci shown in Figure 2a would increase molar size FA, for example, whereas if this occurred for the two loci shown in Figure 2b, molar shape FA would decrease. It has been increasingly recognized that FA responses to a given stressor generally are character specific (Woods et al, 1999;Indrasamy et al, 2000), and perhaps diversity in the epistatic combinations affecting FA levels in different characters contributes to this specificity.…”

Latitudinal gradient effect on the wing geometry of Auca coctei (Guérin)(Lepidoptera, Nymphalidae)

“…Wing morphology has been used as an indicator of changes in environmental conditions by measuring changes in developmental instability on the shape using fluctuating asymmetry (Woods et al 1999;Hoffmann et al 2002;2005;Takahashi et al 2011). Other factors that affect the stability are the decrease in temperature, atmospheric pressure, oxygen availability and increase in solar radiation leading to morphological changes in insects, e.g., compromising insect thermoregulation at high altitude and reducing convective heat loss of insects (Hodkinson 2005;).…”

A New Fluctuating Asymmetry Index, or the Solution for the Scaling Effect?

“…The theoretical argument that stressed individuals have greater DI is supported by some research showing a positive relationship between DI and the intensity of stress [4,[6][7][8][9][10][11][12]. However, empirical studies supporting its general adequacy for monitoring species or populations are generally lacking or contradictory [4,[13][14][15][16].…”