The effect of mirrors on African clawed frog (Xenopus laevis) larval growth, development, and behavior

Abstract

We examined the behavioral and developmental responses of Xenopus laevis larvae to their mirror images in three experiments. The mirrors allowed us to visually simulate increased density, without the tadpoles’ behavior being confounded by chemical cues from additional tadpoles. In the first experiment, we demonstrated that Xenopus tadpoles have a right eye preference for mirrors, contrary to the left eye preference of all other anuran species studied to date. This lateralized eye use disappeared, however, as tadpoles approached metamorphosis. Next, we examined how mirrored aquaria walls affected tadpole growth and development. We found that tadpoles raised in aquaria with partially mirrored walls showed depressed growth compared to tadpoles raised without mirrors, despite the fact that Xenopus larvae normally thrive when raised in visual contact with conspecifics. The tadpoles raised with mirrors had, though not significantly, proportionally larger bodies relative to their tail length (d = 0.51). This suggests that a phenotypically plastic response in body proportions was induced in these tadpoles solely by the sight of other tadpoles. The third experiment established that X. laevis tadpoles are more active in front of a mirror; i.e., they turn more often and spend more time in front of mirrored surfaces. We consider this increased activity to be an aberrant behavior of the tadpoles, which were attempting to school with their own images. We suggest that this extra activity reduced the amount of energy available for growth, accounting for the depressed growth seen in our second experiment.