Bridging the gap

Sensory information necessarily informs decision-making, but both sensory information and the biological structures that receive and process it are subject to inherent limitations and uncertainty. Both these factors degrade an animal’s capacity to make informed, adaptive decisions in a complex and ever-changing world. How is it that animals manage these constraints? In this thesis, I set out to examine multiple cue use and decision-making in a highly derived marine teleost: the Picasso or lagoon triggerfish, Rhinecanthus aculeatus. The use of multiple cues represents an integrative solution to the problem of informational uncertainty; however, it remains poorly understood outside of a narrow range of species and behaviours, largely mammalian. This thesis begins to address the question of how the processes of cue integration are accomplished in other vertebrate taxa. I approached this through two complementary sets of experiments, addressing related questions of decision-making in relation to information use. In Chapter 2 I examined whether triggerfish are capable of sensory updating, i.e., weighting their prior estimates with incoming information to inform their decision-making. In Chapter 3, I re-examined the same data set and performed a modified replicate to dissect multiple factors contributing to decision-making, focusing on task learning and how subjects might have taken advantage of low-level heuristics to solve the problems presented to them. I placed this discussion in an integrated associative learning framework. For Chapter 4, I was curious as to how aquatic environments, which are highly labile and may favour different sensory channels in different contexts, might affect learning style in triggerfish. To examine this, I tested how triggerfish learn to discriminate objects with multiple competing cues in an environment where cue quality is subject to varying environmental transmission quality. I approached all these questions through the framework of associative learning, using conditioning techniques to train triggerfish to discriminate between sets of stimuli with different properties and examine how they make decisions under different conditions. Fishes are not only taxonomically distant to more typically studied models of decision-making such as mammals, but also represent an ecological contrast, moving with relative freedom in a three-dimensional environment that exerts radically different pressures on their movement, sensory, and decision ecology. The findings presented in this thesis increase our understanding of information use within fishes and expand our understanding of the evolution and ecology of decision-making within the vertebrates.