Date of Award

Summer 8-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Program/Concentration

Biology

Committee Director

Gloria Massamba N’Siala

Committee Member

Dan Barshis

Committee Member

Taylor Sloey

Abstract

Coastal ecosystems are increasingly exposed to unpredictable temperature fluctuations, potentially favoring strategies that buffer populations against environmental uncertainty. This study examines how phenotypic plasticity and diversified bet-hedging contribute to variation in life-history traits under differing thermal predictability in the marine annelid Ophryotrocha labronica. After three generations at 24 °C, broods were reared for three generations under four thermal regimes: constant 24 °C (C24), constant 27 °C (C27), predictable fluctuations (Fp), and unpredictable fluctuations (Fu). Survival was assessed before and after acclimation to evaluate selective pressure among regimes. Age at maturity, fecundity, and growth rate were used to quantify plasticity (trait means) and bet-hedging (CV). A second experiment similarly assessed standing genetic variation for plastic responses.

Survival patterns suggest stronger selection in constant regimes by F3 prior to acclimation, whereas post-acclimation mortality was highest at 27 °C, particularly in C27 during F1 and Fu during F3. Plasticity was generally absent and, when present, was regime- and generation-dependent, with maladaptive responses in F1 and adaptive plasticity in Fu for age at maturity by F3. Trait variability peaked in C27 during F1 and declined by F3, except for female age at maturity. Experiment two showed responses across all traits except fecundity, with similar patterns across regimes and inter-brood variation in plasticity for age at maturity. Overall, neither plasticity nor increased trait variability was a primary response to thermal unpredictability.

However, standing genetic variation for plasticity persisted in some traits despite multiple generations under constant conditions, indicating retained evolutionary potential.

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DOI

10.25777/9yvp-c622

ISBN

9798193216872

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