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Title: The green sea turtle : adaptation and resilience to climate change
Author: Tilley, D.
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2019
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Sea turtles are a globally distributed migratory species that use a range of habitats during their life cycle, including both land and sea. As egg laying ectotherms they are particularly susceptible to variation in temperature, especially during clutch incubation. Climate change models predict increasing temperatures over the course of the century, along with sea level rise, and changes in weather patterns. Understanding how these factors impact the environment and such ectothermic species is key to their survival. The green sea turtle, Chelonia mydas, is one of the best studied sea turtle species, and like all seven species they are of conservation concern, thus understanding the impact of climate change on this group is of importance for their conservation. In this thesis I seek to investigate the impacts of temperature on offspring sex ratios and hatching success, two key parameters in the reproductive biology of sea turtles, using the Ascension Island rookery as model population. This will infer knowledge on adaptation and resilience to climate change. I first carry out a literature review (Chapter 2) to evaluate the existing knowledge of current primary sex ratios, and find that despite nearly four decades of work on the topic, little progress has been made. Indeed, only four studies have been published on sex determining temperatures in laboratory conditions, and a range of varying methods have been used. I then carried out a laboratory-based study to establish the pivotal temperature, the temperature at which an equal proportion of male and females are produced, (29.3°C) for the Ascension Island green turtle rookery (Chapter 3) and carry out a translocation experiment to determine whether maternal philopatry confers any form of advantage to incubating clutches through localised adaptation (Chapter 4). Neither under laboratory conditions, nor in-situ do I find any evidence of localised thermal adaptation; hatching success drops with increasing temperatures, and clutches from different thermal backgrounds produce equivalent proportions of males and females. Finally, I use this information to evaluate island wide sex ratios and offspring output, based on different climate projection scenarios (Chapter 5). I find that the primary sex ratio will likely be extremely female biased (> 90%) by the end of the century, with hatching success starting to decrease in the most extreme scenarios, especially at the darker beaches where temperatures will exceed thresholds for successful incubation. The geographic isolation of Ascension Island means that there are limited opportunities for dispersal. A full assessment of the impacts of climate change on sea level rise, coastal erosion and changes in weather patterns may provide more information on the treats and opportunities that this population faces. In the meantime, a change in nesting seasonality or nesting distribution within the beaches of Ascension may provide critical to mitigate the impacts of increasing temperatures.
Supervisor: Broderick, A. ; Godley, B. ; Weber, S. Sponsor: Natural Environment Research Council (NERC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available