EFFECT OF ENVIRONMENTAL TEMPERATURE ON ASPECTS OF THE DEVELOPMENTAL ECOPHYSIOLOGY OF THE SEMI-TERRESTRIAL AMPHIPOD ORCHESTIA GAMMARELLUS
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Ecophysiological responses vary during development in ways that may determine the ecological and evolutionary consequences of climate change. How temperature alters processes vital to organismal homeostasis (e.g. cardiac and gastro-intestinal (GI) behaviour) and survival (e.g. thermal tolerance) at different developmental stages is underdeveloped. Consequently, my thesis investigated key aspects of the thermal biology (specifically cardiac output, the ontogeny of GI behaviour and upper thermal limits) of an ecologically-important, brooded species, the semi-terrestrial amphipod Orchestia gammarellus. Little is known of the earliest embryonic responses, particularly with respect to direct developing brooded species. This is in-part due to a lack of high-throughput technologies capable of visualising stages of early development. This was achieved by firstly developing a platform for autonomous image acquisition and analysis, Embryophenomics, subsequently used to investigate effects of temperature on the ecophysiology of O. gammarellus. The thermal history of embryos in situ was recorded during the reproductive period and used to inform incubation temperatures. A relatively small increase in temperature (5 °C) greatly increased the rate of GI movement and yolk usage throughout development, supporting the hypothesis that the gut is an engine for yolk dispersal. However, there was little support for the hypothesis that GI movement was stimulated by hypoxia and therefore the gut does not appear to have the precardiac function found in other crustacean embryos. This is the first qualitative and quantitative investigation of changes in GI behaviour with ontogeny in any crustacean, adding to previous descriptions of development generally. Despite being in a thermally stable environment in situ there are profound changes in upper thermal limits of embryos throughout development. This does not fit the current paradigm that thermal tolerance is necessarily governed by selection pressure. Overall the ecophysiological responses to temperature of O. gammarellus would not have been predictable based on the life history and thermal environment of the embryos.
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