Abstract
Coloration influences and is driven by many complex evolutionary relationships. Among these is the predator-prey arms race, at the heart of many crucial ideas about the evolution and ecology of coloration. As such, prey have evolved a wide range of anti-predator defenses, from camouflage and aposematism to toxic spines and aggressive behaviours.Looking through the lens of predator-prey interactions, crabs provide a wonderful study system for exploring ideas about the relationships between defensive behaviour and various ecological factors. There has yet to be a geographically wide-ranging study that looks at the evolution and ecology of defensive behaviour through phenotype-environment associations. In this thesis (chapter 2), I look at the anti-predator defenses of decapods, with a focus on behaviour. I have used simulated predation experiments conducted in the natural habitats of nine species of marine intertidal crabs from California, Zanzibar and Britain. In addition, I used calibrated photography to measure colour and luminance contrast, measured size and sex, and recorded the type of habitat occupied by individuals of these nine species. I sought to investigate the effects of body size, sex, habitat and contrast on anti-predator behaviour, and to look for general patterns across intertidal crabs. Broadly, I found that size was the most influential factor in crab defensive behaviour, with larger crabs being better defended by morphology. Habitat influenced the suite of defenses available to crabs, through substrate complexity and potential for refuge spots. There were few sex differences in defensive behaviour, although this remains to be tested with further sampling at different life stages and seasons. Colour and luminance contrast did not appear to influence behaviour as expected.
Building on the idea that colour, habitat and behaviour are inextricably linked, I also aimed to examine the effects of global anthropogenic changes to the environment on visual ecology (chapter 3). Natural habitats are increasingly affected by anthropogenically driven environmental changes resulting from habitat destruction, chemical and light pollution, and climate change. Organisms inhabiting such habitats are faced with novel disturbances that can alter their modes of signalling. Coloration is one such sensory modality whose production, perception and function is being affected by human-induced disturbances. To this end, I sought to describe, through a literature review, the wide ranging impacts of global environmental changes to habitats on animal coloration and propose ways in which colour can be used as an indicator of these changes and as a tool for conservation science.
| Date of Award | 23 Jan 2024 |
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| Original language | English |
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| Supervisor | Tim Caro (Supervisor) & Martin J How (Supervisor) |