| Summary: | This thesis investigates the interactions between some different elements of colour in group-living freshwater fishes, oddity in groups and the effects of these on observed behaviour. In the early chapters (2-4), I address the rapid colour change of which such fishes are capable. I investigate how social and habitat preferences interact with this morphological change, showing that physiological colour change can be as a direct result of changing habitat colour, and that the resulting body colour influcences social and habitat choice. I reveal a second function to this colour change, in dominance signalling, and discuss the social and other costs associated with physiological melanic colour change. The later chapters are focussed on some other aspects of oddity and risk in social behaviour of freshwater fishes. In chapter 5 I test a model predicting mixed phenotype grouping, concluding that prey animals must balance the relative risks of oddity and conspicuousness in their social decisions, potentially leading to the evolution of mixed phenotype grouping as a response to predation risk alone. Chapter 6 further investigates body size-oddity in the Trinidadian guppy, revealing body-size differences in social preferences. I elaborate on this finding in chapter 7 by discovering that large prey are at greater risk than small prey, given their oddity in a group, and that the differing social preferences are as a result of 'poor' decision makers being more easily captured and removed from the population by predators, leaving only 'good' decision makers to grow large .
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