Artificial selection on laterality in the teleost fish Girardinus falcatus

We performed five generations of artificial selection on laterality of eye preference in Girardinus falcatus using a detour test. Two lines were selected for right turning when encountering a potential predator, two for left turning, one for no turning bias and one unselected line was used as control. We observed a prompt response to directional selection in all lines and the response was approximately symmetrical in left and right turning lines. However, the response to selection ceased after the first or the second generation and unexpectedly in all lines the average laterality score slowly decreased in subsequent generations. After selection was suspended for three generations, no significant variation in mean laterality was observed in most cases, indicating that natural selection was not actively opposing artificial selection during the experiment. After five generations, selected lines maintained substantial additive variance as evidenced by the possibility of rapidly reversing the direction of laterality bias in just one generation of counter-selection.