The role of phenotypic plasticity in threespine stickleback (Gasterosteus aculeatus) adaptation to thermally variable habitats
Date
2024-12-06
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Abstract
Phenotypic plasticity, the ability of a genotype to give rise to multiple phenotypes dependent on environmental cues, is a well-established phenomenon that allows organisms to rapidly modify their phenotype in response to environmental change. It has been recommended that phenotypic plasticity be included in predicting population and species’ response to climate change. However, there remains substantial debate regarding its role in population persistence, adaptation, and evolutionary theory. While phenotypic plasticity occurs at all biological levels, it is largely driven by changes in gene regulation, and it has been suggested that resolving these molecular mechanisms will facilitate its integration into studies of adaptation and evolution. In this thesis, I use threespine stickleback (Gasterosteus aculeatus) to investigate how evolution has shaped reversible (i.e., phenotypic flexibility) and irreversible (i.e., developmental plasticity) plastic responses to temperature, a key abiotic environmental variable. To do so, I first tested if local adaptation to freshwater habitats has altered plasticity within key biological pathways by comparing gene expression of freshwater and marine ecotypes acclimated to cold or warm temperatures. Using Weighted Gene Co-expression Network Analysis, I found evolutionary conserved and divergent responses between the ecotypes, with freshwater stickleback having evolved increased thermal plasticity in several gene modules. I then determined that marine stickleback exhibit substantial developmental plasticity induced by egg temperature that persists into adulthood, over a year after the thermal stressor was removed. The effect of developmental temperature was found in both liver and muscle tissue, however, each tissue type exhibited distinct patterns of gene expression and thermal plasticity. At the whole organism level, egg developmental temperature was found to significantly alter the lower critical thermal limit in all families in the direction cued (i.e., eggs developed at cool temperatures had decreased lower critical thermal limit). The upper critical thermal limit showed inconsistent patterns of plasticity across families but was found to already be higher than temperatures predicted under climate change scenarios. Collectively, these data illustrate that organisms exhibit thermal plasticity from the molecular to whole organism level and that these responses have been shaped by evolution to generate the current patterns of plasticity that will underlie species’ response to future conditions.
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Keywords
Phenotypic plasticity, Developmental plasticity, Phenotypic flexibility, Gene expression, Thermal tolerance, Climate change
Citation
Stanford, B. (2024). The role of phenotypic plasticity in threespine stickleback (Gasterosteus aculeatus) adaptation to thermally variable habitats (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.