Sides and eyes: studies on laterality in anuran larvae

Although they don't have hands, tadpoles can nevertheless have handedness. For instance, tadpoles of most species typically turn about twice as often to their left than their right side when startled. Even more curious, tadpoles of many species (but not all) prefer to view themselves in mirrors with their left eye rather than their right. With NSERC support I plan to survey such "lateralized" behaviors from tadpoles of as many families and genera of frogs as possible. My overall goal is to understand the evolution of lateralized behaviors in these organisms. There is circumstantial evidence that turning bias in tadpoles is linked to asymmetry in the size of certain cells in their hindbrains. In order to elucidate this behavioural-neural link, I will examine the size of those cells in species with strongly lateralized behaviors. I will then test the hypothesis that handedness in tadpoles correlates with both the evolutionary relationships of the frogs and asymmetries in their brains. There are some recent data suggesting that predation risk influenced tadpole turning bias. I thus plan to investigate this in several species by recording tadpoles' turning biases while caged predators, such as fish, are nearby. Lastly, I have suggested that tadpoles might interpret their own image in a mirror as another tadpole and respond to their images as if they were crowded by other tadpoles. With NSERC support, I wish to test the hypothesis that different species will grow at different rates when raised in aquaria with mirrored walls depending on their propensity to live in dense groups (i.e., to school). Collectively this research should advance our understanding of the adaptive significance and evolution of lateralized behaviours in anurans and in other animals as well.