Individual Xenopus Tadpoles Display Distinct and Consistent Visual Preferences

Xenopus tadpoles begin displaying several innate visually guided behaviors by developmental stage 48-just 10 days postfertilization. These behaviors include a preference for green over light, and light over dark. Until now, these preferences have been studied by measuring the behavior of groups of tadpoles. The overall behavior of the group, however, does not necessarily reflect the behavior of individuals. Therefore, here we studied visual preferences displayed by individual tadpoles. Our data show that individual tadpoles display varied behavior relative to one another: some tadpoles displayed a strong preference for light over dark while others preferred dark over light; some displayed a strong preference for green over light while others preferred light over green. While preferences varied across tadpoles, preferences displayed within individuals were stable over time (i.e., consistent). Also, previous work on groups of tadpoles shows that visual preferences are shaped by the neuromodulator serotonin (5-HT). At the single tadpole level, we found that inhibiting 5-HT weakened the preference for light displayed by most individuals, and that enhancing endogenous serotonin transmission strengthened the preference for light displayed by most individuals. However, through this, we also identified a small subset of tadpoles that displayed an exceptionally strong preference for light which appeared to be insensitive to experimentally altered levels of 5-HT activity.