RESILIENCE ACROSS GENERATIONS: EXPLORING TRANSGENERATIONAL AND LARVAL ACCLIMATION TO THERMAL STRESS IN THE MARINE ANNELID HYDROIDES ELEGANS
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2024
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Temperature can have profound impacts on the reproductive and developmental aspects of marine ectotherms. I examined how varying temperatures impact egg size, energy content, larval survival, and settlement dynamics across generations in the marine annelid Hydroides elegans. This work aimed to highlight the adaptive mechanisms marine invertebrates may employ to cope with rapidly changing oceanic temperatures. Through a series of interconnected studies, I explored the phenotypic plasticity of egg characteristics, thermal tolerance of larvae, settlement, and oxygen consumption rates, focusing on the significance of transgenerational and within-generation thermal responses. My first study investigated the effects of maternal rearing temperature on egg size, fecundity, and energy content in the marine annelid Hydroides elegans, a free-spawning benthic annelid invasive to Hawai'i. Results demonstrated that parental rearing temperature significantly affects egg size and fecundity, with cooler temperatures favoring larger eggs and higher fecundity. Interestingly, while egg size typically decreased with increasing temperature, the energy content of the eggs exhibited an inverse relationship, with smaller eggs from warmer temperatures containing more energy as well as higher energy densities This finding challenges the common assumption that larger eggs contain more energy, suggesting that temperature-driven changes in egg size may not align with adaptive responses but rather represent physiological constraints. My second study explored the thermal tolerance and survival strategies in larval stages of the marine annelid Hydroides elegans under varying thermal conditions. We investigated the roles of larval acclimation and maternal effects at different rearing temperatures to understand potential adaptive responses to thermal stress. We found significant effects of larval rearing temperature on thermal tolerance, with higher rearing temperatures generally corresponding to lower LT50 values, suggesting decreased thermal tolerance in larvae that were raised at the highest temperature. Maternal rearing temperature and the interaction between larval and maternal temperatures showed less consistent impacts on larval survival, inconsistent with the hypothesis that transgenerational plasticity significantly enhances thermal tolerance in this species. My final study investigated the influence of transgenerational and larval environmental temperatures on the settlement dynamics and metabolic rates of Hydroides elegans larvae. Conducted across a temperature gradient of 21°C, 25°C, and 29°C, this study examines whether parental exposure to elevated temperatures affects settlement rates and oxygen consumption (proxy for metabolic rate) of offspring. Results indicate day post fertilization was the only factor affecting settlement rate but that larval rearing temperature significantly affects metabolic rates, with larvae at 29°C displaying higher oxygen consumption, suggesting an increase in energy expenditure per unit time. Conversely, parental temperature showed only a marginal influence on larval settlement, with no significant transgenerational effects on metabolic rates.
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Zoology, egg size, egg energy, larval survival, oxygen consumption, settlement, Temperature
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127 pages
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