Graduation Semester and Year




Document Type


Degree Name

Master of Science in Biology



First Advisor

Matthew Walsh


In natural environments, organisms face multiple stressors that threaten their persistence. Aquatic organisms respond to a change in environmental conditions by adaptively modifying the expression of traits (i.e., phenotypic plasticity). Yet, our understanding of the interactive effects of multiple simultaneous stressors on the fitness of organisms is currently limited. This is because previous research has typically focused on the influence of environmental stressors in isolation thus ignoring the impacts that multiple variables may have on an organismal fitness. Here, I assessed the interactive effects of predator cues (Chaoborus) and low food quality (Cylindrospermopsis raciborskii) on key life-history traits in the invasive water flea Daphnia lumholtzi. Increasing concentrations of sub-optimal cyanobacteria resulted in delayed maturation, and declines in growth, size at maturation, and reproductive outputs (and slower rate of population growth). Yet, such declines were much smaller in the presence of predator cues. I thus observed significant predator x resource interactions for growth, size at maturation, clutch size, and intrinsic rate of increase. The opposite pattern was observed for the size of defense traits; Daphnia reared in the absence of predator cues maintained larger spines when fed a very low quality of food. Such results indicate that Daphnia exposed to predator cues preferentially allocate energy towards life history traits at the expense of defense characteristics when faced with severe food stress. Thus, a robust understanding of species responses to environmental stressors, such as global climate change, requires the robust manipulations of multiple key environmental variables.


Biology | Life Sciences


Degree granted by The University of Texas at Arlington

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