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Abstract
Environmental temperature plays a critical role in the survival and geographic distribution of most organisms, as it can directly influence the rate of all biochemical and physiological reactions. Recent climate models show that seasonal variation and the average sea surface temperature are predicted to increase across the globe in the coming decades. This will have a significant impact on many species, limiting the geographic range at which many organisms can survive, and potentially leading to the extinction of thermosensitive species. Previous research has shown that acute changes in temperature can result in severe stress responses in which organisms show increased expression of stress-related genes, and even a small degree of thermal stress, whether from increased or decreased temperatures, can have a significant physiological effect on an organism. My research used two independent experiments to investigate thermal variation and stress across a wide range of temperatures to provide insight into how a coastal marine organism, the sea anemone Nematostella vectensis, may be affected by this predicted shift in average high and low environmental temperature.First, to investigate the relationship between geographic origin and thermal tolerance, four female N. vectensis from three locations (Nova Scotia (NS10.1, NS5.2), Maryland (MD4), Florida (F1)) were bred with two males from two locations (Maryland (MD1.5) and Florida (FL3)) to create a diverse set of hybrid crosses. Larvae resulting from each cross were placed under an acute thermal stress regime, wherein larvae were heated along a thermal gradient for six hours. The LT50, or temperature at which 50% of the larvae die, was calculated from the results of several trials of the heat stress regime for each hybrid cross created. The LT50s were compared between crosses and to geographic baselines defined by previous literature. Statistically significant differences were found for nearly every baseline comparison, with Florida – Nova Scotia crosses showing the highest statistically significant differences when compared to baselines for either parent. Between-cross comparisons revealed that the LT50 of Maryland hybrids closely resembled the thermal tolerance of the non-Maryland parent in all instances. These results suggest that thermal tolerance may be influenced by location of origin for the parents, with some locations having a stronger effect. For the second experiment, I investigated the transcriptional response of adult N. vectensis to cold temperature stress. Transcriptional data was collected from adults exposed to three temperature treatments (0°C, 10°C, 20°C) for either an acute (24 hours) or prolonged (7 days) period. RNA from adults was then sequenced using a 3’ Taq-seq protocol, and genes with significant differences in expression were identified for all pairwise comparisons as well as multivariate analyses. I found that in short-term cold stress conditions, a moderate decrease in environmental temperature may elicit a stronger response than more severe drop in temperature. When compared to the control, the 10°C temperature treatment resulted in over 12x as many differentially expressed genes (124 DEGs) after a 24-hour period than the 0°C treatment (10 DEGs). This study will widen the understanding of marine estuarine organisms’ ability to tolerate, acclimate and adapt to predicted changes in the environmental temperatures resulting from climate change.