No support for fluctuating asymmetry as a biomarker of chemical residues in livestock dung

Abstract

AbstractFluctuating asymmetries (FAs) are small random deviations between left- and right-side measurements of normally symmetrical traits in a given organism. Changes in FA have frequently been proposed as biomarkers for organisms exposed to stress during development and may have value for detecting low levels of chemical residues or other stressors in the environment. We tested this hypothesis in three replicated laboratory experiments and failed to find any effect of chemical residues (ivermectin) in cattle dung on levels of FAs (wing and leg traits) for the dung-breeding fly Scathophaga stercoraria L. (Diptera: Scathophagidae). In trying to resolve this discrepancy with previous reports, we found that many studies failed to replicate measurements of FA traits within an experiment, which increases the likelihood of spurious positive results. Furthermore, experiments were rarely replicated either within or between studies, so the repeatability of positive results has usually gone untested. These issues have been raised by others, but are still not being adequately addressed. Discussions regarding the value of FAs as biomarkers will not advance until this is done.