Date of Award
Master of Science (M.S.)
Zachary R. Stahlschmidt
First Committee Member
Second Committee Member
The frequency, duration, and co-occurrence of several environmental stressors are increasing globally. Multiple stressors may have compounding or interactive effects on animals, resulting in either additive or non-additive costs, but animals may mitigate these costs through various strategies of resource conservation or shifts in resource allocation. Thus, through two related factorial experiments, I measured a range of traits—from those related to life history and behavior to underlying physiology— to investigate the nature of costs (additive, non-additive, or neither additive nor non-additive), cost-mitigating strategies (resource conservation or allocation), and life-history strategy related to multiple stressors. First, I leveraged life-history strategy differences in the sand field cricket, Gryllus firmus, to investigate the individual and interactive effects of food and water limitation on fitness-related traits. Gryllus crickets exhibit a wing dimorphism mediating two distinct life-history strategies—long-winged crickets invest into flight capability while short-winged crickets do not. My results indicate that traits vary in their sensitivity to environmental stressors and stressor-stressor interactions (e.g., flight muscle). I only found support for non-additive costs or single-stressor costs of water and food limitation to fitness-related traits. Water availability had a larger effect on traits than food availability, affected more traits than food availability (wing dimorphism), and mediated the effects of food availability. Second, I investigated the role of life-history strategy in cost-mitigating strategies and further examined the costs (additive or non-additive) of multiple stressors to fitness-related traits, physiology, and behavior. I used the variable field cricket, Gryllus lineaticeps, to examine the costs of a simulated heat wave and water limitation. These stressors resulted primarily in single-stressor or non-additive costs to important traits (e.g., survival, final body mass, and total water content), extensive shifts in resource allocation priorities (e.g., reduced prioritization of body mass), and a limited capacity to conserve resources (heat wave reduced energy use only when water was available). Further, life-history strategy influenced the emergency life history stage (ELHS) because wing morphology and stressor(s) interacted to influence gonad and body mass, boldness behavior, and immunocompetence. Together, these two studies demonstrate that water availability and life-history strategy should be incorporated into future studies integrating important conceptual frameworks of stress (multiple-stressor framework and ELHS) across a suite of traits—from survival and life history to behavior and physiology.
Padda, Sugjit S.. (2020). Stressed Out: Life-History Strategy and the Costs of Multiple Stressors in Gryllus Crickets. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/3702
Available for download on Sunday, September 25, 2022