On hidden heterogeneity in directional asymmetry – can systematic bias be avoided?
Article first published online: 3 OCT 2005
Journal of Evolutionary Biology
Volume 19, Issue 2, pages 492–499, March 2006
How to Cite
STIGE, L. C., DAVID, B. and ALIBERT, P. (2006), On hidden heterogeneity in directional asymmetry – can systematic bias be avoided?. Journal of Evolutionary Biology, 19: 492–499. doi: 10.1111/j.1420-9101.2005.01011.x
- Issue published online: 3 OCT 2005
- Article first published online: 3 OCT 2005
- Received 18 July 2005; accepted 22 July 2005
- Abatus cordatus;
- case study;
- developmental stability;
- directional asymmetry;
- fluctuating asymmetry;
Directional asymmetry (DA) biases the analysis of fluctuating asymmetry (FA) mainly because among-individual differences in the predisposition for DA are difficult to detect. However, we argue that systematic bias mainly results from predictable associations between signed right–left asymmetry and other factors, i.e. from systematic variation in DA. We here demonstrate methods to test and correct for this, by analysing bilateral asymmetry in size and shape of an irregular sea urchin. Notably, in this model system, DA depended significantly on body length and geographic origin, although mean signed asymmetry (mean DA) was not significant in the sample as a whole. In contrast to the systematic variation in DA, undetectable, random variability in the underlying DA mainly leads to reduced statistical power. Using computer simulations, we show that this loss of power is probably slight in most circumstances. We recommend future studies on FA to routinely test and correct for not only as yet for mean DA, but also for systematic variation in DA.