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Description
The elaborate signals of animals are often costly to produce and maintain, thus communicating reliable information about the quality of an individual to potential mates or competitors. The properties of the sensory systems that receive signals can drive the evolution of these signals and shape their form and function. However, relatively little is known about the ecological and physiological constraints that may influence the development and maintenance of sensory systems. In the house finch (Carpodacus mexicanus) and many other bird species, carotenoid pigments are used to create colorful sexually selected displays, and their expression is limited by health and dietary access to carotenoids. Carotenoids also accumulate in the avian retina, protecting it from photodamage and tuning color vision. Analogous to plumage carotenoid accumulation, I hypothesized that avian vision is subject to environmental and physiological constraints imposed by the acquisition and allocation of carotenoids. To test this hypothesis, I carried out a series of field and captive studies of the house finch to assess natural variation in and correlates of retinal carotenoid accumulation and to experimentally investigate the effects of dietary carotenoid availability, immune activation, and light exposure on retinal carotenoid accumulation. Moreover, through dietary manipulations of retinal carotenoid accumulation, I tested the impacts of carotenoid accumulation on visually mediated foraging and mate choice behaviors. My results indicate that avian retinal carotenoid accumulation is variable and significantly influenced by dietary carotenoid availability and immune system activity. Behavioral studies suggest that retinal carotenoid accumulation influences visual foraging performance and mediates a trade-off between color discrimination and photoreceptor sensitivity under dim-light conditions. Retinal accumulation did not influence female choice for male carotenoid-based coloration, indicating that a direct link between retinal accumulation and sexual selection for coloration is unlikely. However, retinal carotenoid accumulation in males was positively correlated with their plumage coloration. Thus, carotenoid-mediated visual health and performance or may be part of the information encoded in sexually selected coloration.
ContributorsToomey, Matthew (Author) / McGraw, Kevin J. (Thesis advisor) / Deviche, Pierre (Committee member) / Smith, Brian (Committee member) / Rutowski, Ronald (Committee member) / Verrelli, Brian (Committee member) / Arizona State University (Publisher)
Created2011
Description
The goal of the present study was to investigate whether a rest period following the end of chronic stress would impact fear extinction. Past research has indicated that chronic stress leads to impairments in the learning and recall of fear conditioning extinction. Moreover, the effects of chronic stress can return to levels similar to controls when a post-stress “rest” period (i.e., undisturbed except for normal husbandry) is given prior to testing. Male rats underwent chronic restraint stress for 6hr/day/21days (STR-IMM). Some rats, underwent a post-stress rest period for 6- or 3-weeks after the end of stress (STR-R6, STR-R3). Control (CON) rats were unrestrained for the duration of the experiment. In Experiment 1, following the stress or rest manipulation, all rats were acclimated to conditioning and extinction contexts, fear conditioned with 3 tone-foot shock pairings, and then had two days of extinction training. All groups froze similarly to the tone across all training sessions. However, STR-R6/R3 froze less in the non-shock context than did STR-IMM or CON. During extinction training, STR-IMM showed high levels of freezing to the non-shock context, leading to a concern they may be generalizing across contexts. Consequently, a follow-up experiment tested for context generalization. In Experiment 2, STR-IMM rats underwent a generalization test in an environment that was either different or the same as the conditioning environment, using STR-R6 as a comparison. STR-IMM and STR-R6 showed similar relative levels of freezing to tone and context, regardless of their conditioning environment to reveal that STR-IMM did not generalize and instead, maybe expressing hypervigilance. Thus, the present study demonstrated the novel finding that a rest period from chronic stress can lead to reduced fear responsiveness in a non-shock environment.
ContributorsJudd, Jessica M (Author) / Conrad, Cheryl D. (Thesis advisor) / Sanabria, Federico (Committee member) / Smith, Brian (Committee member) / Arizona State University (Publisher)
Created2018