The use of fluctuating asymmetry as a measure of environmentally induced developmental instability: A meta-analysis

Random and subtle deviations from bilateral symmetry (fluctuating asymmetry) have long been of interest to biologists who wish to study the susceptibility of organisms to changes in environmental quality. However, the reliability of FA as a biomarker has come under question due to inconsistent results in the literature. We conducted a meta-analysis of published literature to test the hypothesis that FA is a reliable biomarker of environmental stress in insects and identify possible sources of variation amongst studies. We expected studies to detect larger, positive magnitudes of effect on FA in lab populations due to the lack of confounding effects from other environmental factors compared to wild populations. Additionally, we predicted that studies that used geometric morphometric approaches to FA in shape and size would be more sensitive to changes in environmental quality compared to linear and meristic measures and thus show larger effects on FA. We also expected anthropogenic stressors to generate significantly larger effects on FA compared to naturally occurring stressors due to the organisms’ inability to buffer developmental pathways against a novel stressor. Finally, we predicted comparatively larger magnitudes of effect in studies that verified the environmental factor acting on the organism was a stressor by detecting negative effects on fitness-related traits. Overall, we found that FA is a sensitive biomarker of environmental stress. Environmental stressors explained 36% of the variation of effect on FA across studies. Studies that demonstrated a negative effect of the stressor on fitness-related traits showed significantly larger, positive magnitudes of effect on FA compared to studies that did not detect an effect from the environmental stressor. Additionally, studies conducted under laboratory conditions detected significantly larger, effects on FA compared to field-based studies. The kind of trait measured and the novelty of the stressor did not significantly account for differences amongst studies. Thus, the use of FA as a biomarker of environmental stress is a legitimate tool particularly when studies verify the biological relevance of stressors for the study organism.