Handedness and asymmetry in scale-eating cichlids: antisymmetries of different strength.

Individual symmetry is believed to be advantageous and reflecting developmental stability, but frequency-dependent selection can also maintain polymorphisms of asymmetric phenotypes. There are many examples of so-called antisymmetry, where mirror image morphs occur at equal frequencies. With very few exceptions, these are caused by nongenetic variation. One notable exception is handedness and mouth bending variation in the scale-eating cichlid Perissodus microlepis, which has been suggested to be an example of antisymmetry determined by a single genetic locus of large effect. Here, we report that this handedness and mouth bending asymmetry are not jointly and exclusively determined by a single major locus. We found no evidence of a major locus for asymmetry and some support for a major handedness locus. Also, asymmetry is plastic in this species: it can change in adults. We suggest that behavioral handedness in this system precedes and guides morphological asymmetry.