Fluctuating asymmetry of the yellow meadow ant along a metal-pollution gradient

• The increase of FA can be expected when the reduced traits are considered.
• FA in the reduced eyes of Lasius flavus does not increase in the metal-polluted area.
• FA in L. flavus eyes should not be used as metal-stress indicator.

Asymmetry in the morphological traits of bilateral organisms can be induced by environmental stress. As a result of released selection pressure, traits of low functional importance should demonstrate comparatively higher asymmetry in metal-polluted areas. In the present study we measured the size of the eyes of yellow meadow ant workers Lasius flavus. The eyes of this species are typically reduced due to underground life style. The ants were sampled from 48 wild colonies originating from 16 sites located along the metal pollution gradient established in a post-mining area in Poland. We found low intra-colonial variability of the asymmetry index describing the difference in the right and left eye. As a consequence, the asymmetry index was not associated with pollution levels at the sites of origin. The results indicate that although the eyes of L. flavus are reduced, metal pollution does not increase significantly asymmetry between the right and left eye. Power analysis estimated that the accuracy of the statistical analysis would have detected 18% decrease in FA along the pollution gradient. Thus, FA in L. flavus eyes should not be considered as an efficient metal-stress indicator. The mechanisms underlying the precision and symmetry between the right and left eye seem to still function during development.