Environmental and genetic effects on the asymmetry phenotype: Diazinon resistance in the Australian sheep blowfly, Lucilia cuprina.

The asymmetry phenotype of diazinon-resistant flies lacking a fitness/asymmetry Modifier (+/+; R/-) was dominant and independent of developmental temperature, larval density and diazinon concentration. Asymmetry score, pooled over three bristle characters, was approximately 50% greater for these phenotypes than for those of modified genotypes (M/+; +/+) and unmodified susceptibles (+/+; S/S) reared under standard laboratory conditions. Modified and susceptible phenotypes showed increased asymmetry score for temperatures and larval densities above and below standard rearing conditions; a positive correlation was observed between diazinon concentration and asymmetry score. Single and multiple environmental stresses resulted in similar scores that approached, but never exceeded, those of unmodified resistant phenotypes. Irrespective of the developmental conditions anti-symmetry and fluctuating asymmetry were typically observed for each bristle character of unmodified resistant and the modified and susceptible phenotypes, respectively. Thus while similar asymmetry scores could arise from genetic or environmental effects, asymmetry pattern was genetically based. Population cage analyses at different temperatures and larval densities showed a negative association between mean asymmetry and relative fitness.