Effects of Early Ontogenetic Sensitive Periods on the Generalization of Risk and Safety Information in Wood Frog Tadpoles (Lithobates sylvaticus)

Abstract

Environments often change within an organism’s lifetime. The ability to react and adapt to these changes is referred to as plasticity. Periods of development with heightened plasticity are called sensitive periods. Events experienced during sensitive periods can have disproportionate effects later in life across multiple phenotypes, a phenomenon called phenotypic resonance. Originally based on the phenomenon of phenotypic resonance, the phenomenon of cognitive resonance is described as the disproportionate effect a sensitive period has on the way information is used by an individual. Cognitive resonance has been studied using risk and safety information, but not on other cognitive processes such as generalization. This thesis focused on the effects of sensitive periods on the generalization of safety and risk related information. Wood frog tadpoles (Lithobates sylvaticus) were chosen as the model system and embryonic development as the sensitive period. In the first experiment, tadpoles were trained to recognize brook trout as a predator using a pairing with conspecific alarm cues, which are innately recognized as indicating risk. Tadpoles were then exposed to one of the following test odours to form a generalization gradient based on phylogenetic relatedness: brook trout, splake, tiger trout, rainbow trout, or goldfish. Tadpoles trained as embryos that brook trout was risky partially generalized risk to splake, tiger trout, and rainbow trout, which are all members of Salmonidae, but not to the distantly related goldfish. Tadpoles trained that brook trout was risky as larvae only generalized risk to splake and tiger trout, both of which are hybrids of brook trout. The second experiment followed similar procedures to the first. However, tadpoles were trained to recognize brook trout odour as safe through a process of repeated unpaired exposures called latent inhibition. Each tadpole was then taught one of the aforementioned test odours as risky through one paring with alarm cues. Tadpoles trained as embryos that brook trout was safe generalized safety partially to splake, tiger trout, and rainbow trout, but not to goldfish. Tadpoles trained that brook trout was safe as larvae only generalized to splake, the intra-genus hybrid with brook trout. These two studies indicate that embryonically exposed tadpoles generalize to more species than do larval tadpoles for both safety and risk related information. My research is among the first studies to delve into the effects of cognitive resonance and could help to further understand the effects of early development on cognitive abilities. This thesis also has implications for fields where knowledge of early development might make a difference, such as behavioural conservation and human cognitive development.