Saudi Cultural Missions Theses & Dissertations
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Item Restricted Exploring Evolutionary History and Climate Adaptation in a Freeze-tolerant VertebrateSkelly, David(Saudi Digital Library, 2025-05) Alshwairikh, Yara; Skelly, DavidAs we consider the future of species in a changing climate, it is critical that evolutionary perspectives become part of the grounding for conservation planning. Responses to changing climate will undoubtedly vary among species, and for ectotherms, temperature plays a crucial part in many aspects of their biology such as reproduction, growth, and overwintering. Adaptation may be critical for species surviving the effects of climate change, and understanding the evolutionary history for species is an essential baseline for uncovering their adaptive potential and predicting their evolutionary trajectory. My research focuses on the wood frog (Rana sylvatica=Lithobates sylvaticus) – a cold adapted, freeze-tolerant amphibian that is simultaneously the most widely distributed amphibian in North America, and highly vulnerable to human modifications to its environment. In this dissertation, I disentangle how lineage diversification within wood frogs proceeded following the Last Glacial Maximum (LGM). I investigate how wood frog genomes adapted to environmental conditions experienced over a 32-year period and identify regions of the genome as candidates for environmental adaptation. Lastly, I perform a freeze-thaw experiment to uncover the gene-expression profile of the complex and quick freeze-thaw process, and identify candidate genes for their role in freeze- tolerance adaptation.16 0Item Restricted Drivers of C4 evolution in the grasses(The University of Sheffield, 2024-06) Alenazi, Ahmed Salem; Dunning, LukeBiologists have long been fascinated by the biological complexity that exists today, with organisms displaying a remarkable diversity of adaptations that have enabled them to thrive in almost every environment. Many of the most impressive adaptations would be classified as complex traits, with structural and metabolic elements working in synergy. To evolve, multiple elements need to be rewired, which can be achieved by incremental modifications over successive generations. Understanding evolutionary steps leading to the emergence of a complex trait can help solve the evolutionary complexity puzzle. The C4 photosynthetic pathway is a complex adaptation involving multiple biochemical and anatomical changes that have allowed certain plant lineages to succeed in specific environmental conditions, including warm and arid climates. Here, we aimed to investigate the evolutionary modifications required to construct the C4 cycle, a complex trait. I initially focused on examining the remarkable photosynthetic variation in the grass Alloteropsis semialata, a species unique in having both C4 and non-C4 photosynthetic genotypes. In my research, I conducted a comparative analysis to identify leaf traits associated with the proportion of carbon fixed using the C4 cycle. The findings revealed that plants with higher C4 activity generally have a greater ratio of photosynthetically active bundle sheath tissue. Subsequently, I employed a genome-wide association study (GWAS) to identify several candidate genes associated with the strength of the C4 cycle and enhancing the proportion of bundle sheath tissue. Finally, in the final chapter of my research, I adopted a more comprehensive perspective to investigate the genetic precursors that may have enabled the repeated evolution of C4 photosynthesis in the PACMAD grasses. I found that genes associated with cell wall modifications and stomatal aperture were duplicated at the base of the PACMAD clade, potentially facilitating the repeated convergent evolution of Kranz anatomy. Collectively, all three data chapters highlight the importance of anatomical modifications in the emergence of the C4 cycle. Overall my thesis identifies several key changes required for C4 evolution, and the results may be relevant to engineering C4 in C3 species, such as rice.12 0