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Evidence of Host Behavioral Photoregulation Of PHOTOSMOREGULATION: EVIDENCE OF HOST BEHAVIORAL PHOTOREGULATION OF AN ALGAL ENDOSYMBIONT BY THE ACOEL CONVOLUTRILOBA RETROGEMMA AS A MEANS OF NON-METABOLIC OSMOREGULATION by THOMAS SHANNON III (Under the Direction of William K. Fitt) ABSTRACT This study examines the photobehaviors of the acoel Convolutriloba retrogemma, the factors affecting these behaviors, their regulatory functions, and how they affect or are affected by the acoel’s algal endosymbiont. The first behavior detailed is a step-up, photophobic response to sudden increases in light. The variable response is blue-light-mediated and triggered by visual, photic stimuli. The second behavior detailed is a phototactic-photoaccumulative behavior responsible for observed mass basking formations. The photoaccumulative behavior is regulated by the photosynthetic activity of the algal endosymbiont. It is not exhibited by aposymbiotic animals. The effects of holozoic starvation are examined, particularly as they apply to host phototactic and photoaccumulative behavior. The data show that contrary to expected behavior, acoels denied prey for over 20 days do not seek out areas of high intensity light, but instead retreat to areas of lower intensity or to shadows. The results of this study support a hypothesis that the basking behaviors of these acoels serve as methods of photoregulating their algal endosymbionts. The results further suggest that starved acoels have diminished capabilities for processing translocated algal photosynthates and that under high-light conditions a build-up of these compounds results in hyposmotic stress in the animals. It is suggested that the photoregulatory basking behaviors of C. retrogemma may function as a method of host osmoregulation and that intercellular change in osmotic pressure resulting from photosynthesis is the photoregulatory stimulus. The term “photosmoregulation” is offered to describe the process. Presented is a novel method for detecting the movements of photosynthate in vivo in C. retrogemma utilizing differential weight change in animals subjected to light and dark treatments without holozoic feeding. Though successful in yielding desired results, the method was decidedly labor-intensive and an alternative method is suggested. Also presented is a refined method for the separation of algal symbionts from host tissue, and a method for determining accurate wet-weight of this and other soft-bodied, invertebrate species. Lastly, contained herein is a monograph describing a new species of acoel, Convolutriloba macropyga. INDEX WORDS: Convolutriloba retrogemma, Convolutriloba macropyga, acoel, alga, symbiont, zoochlorellae, photosynthate, translocation, wet weight, photomovements, behavior, photoregulation, osmoregulation, photosmoregulation, nutrition, response, light emitting diode, halo PHOTOSMOREGULATION: EVIDENCE OF HOST BEHAVIORAL PHOTOREGULATION OF AN ALGAL ENDOSYMBIONT BY THE ACOEL CONVOLUTRILOBA RETROGEMMA AS A MEANS OF NON-METABOLIC OSMOREGULATION by THOMAS SHANNON III B.A., Saint Mary’s College of Maryland, 2000 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2007 © 2007 Thomas Shannon III All Rights Reserved PHOTOSMOREGULATION: EVIDENCE OF HOST BEHAVIORAL PHOTOREGULATION OF AN ALGAL ENDOSYMBIONT BY THE ACOEL CONVOLUTRILOBA RETROGEMMA AS A MEANS OF NON-METABOLIC OSMOREGULATION by THOMAS SHANNON III Major Professor: William K. Fitt Committee: Mark A. Farmer Walter I. Hatch James W. Porter Gregory W. Schmidt Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2007 For Tink iv TABLE OF CONTENTS Page LIST OF FIGURES ....................................................................................................................... vi CHAPTER 1 INTRODUCTION .........................................................................................................1 2 LITERATURE REVIEW: AN OVERVIEW OF OSMOREGULATION IN ANIMALS AND THE POTENTIAL OSMOTIC IMPLICATIONS OF ALGAL- INVERTEBRATE SYMBIOSES ................................................................................11 3 A NOVEL METHOD FOR THE DETERMINATION OF PHOTOSYNTHATE TRANSLOCATION IN AN ALGAL-ACOEL SYMBIOTIC SYSTEM: A QUALITATIVE APPROACH.....................................................................................41 4 PHOTOMOVEMENTS OF CONVOLUTRILOBA RETROGEMMA .........................67 5 PHOTOREGULATION AS A METHOD OF OSMOREGULATION IN THE SYMBIOTIC SYSTEM OF CONVOLUTRILOBA RETROGEMMA .........................93 6 CONVOLUTRILOBA MACROPYGA SP. NOV., AN UNCOMMONLY FECUND ACOEL (ACOELOMORPHA) DISCOVERED IN TROPICAL AQUARIA..........122 7 CONCLUSION AND FUTURE DIRECTION.........................................................158 v LIST OF FIGURES Figure 1.1. Photomicrograph of live Convolutriloba spp. Shown are representatives of the four described species: C. retrogemma, C. hastifera, C. longifissura, and C. macropyga. Specimens were viewed on a Wild M3Z stereomicroscope and photographed with a Sony DSC-P71 digital still camera.......................................................................................................................................9 Figure 1.2. Comparative photomicrograph of live, sexually-immature Convolutriloba spp. A. Convolutriloba retrogemma B. Convolutriloba hastifera C. Convolutriloba longifissura D. Convolutriloba macropyga. Specimens were viewed on a Wild M3Z stereomicroscope and photographed with a Sony DSC-P71 digital still camera. .............................................................10 Figure 3.1. Schematic representation of the dewatering device used for the non-disruptive, vacuum-assisted, removal of water (external medium) from live acoels prior to weighing the animals. The device was fabricated from common PVC pipe and fittings...................................60 Figure 3.2. Photograph of apparatus used for removing water (external medium) from live acoels. A. Vacuum-assisted dewatering device. Vacuum source connects to barbed fitting. Valve allows for fine control of suction at the dewatering stage (top of device). B. Chamber used to hold acoels for PAM fluorometry. C. Underside of chamber designed to connect to dewatering stage to remove water from acoels. Center hole covered with 14 micron plankton net to support acoels during dewatering and fluorometry processes. D. Chamber connected to PAM fiber-optic cable. ............................................................................................................................61 Figure 3.3. Effective quantum yield of photosystem II in the zoochlorellae endosymbionts (in vivo) of Convolutriloba retrogemma, determined by PAM fluorometry, as a function of DCMU concentration in the external medium. Error bars represent 95% confidence intervals. ..............62 Figure 3.4. Percent weight change (loss) of Convolutriloba retrogemma kept in total darkness for 7 days as a function of DCMU concentration in the external medium compared to control group (no DCMU). Error bars represent 95% confidence intervals. ............................................63 Figure 3.5. Percent weight loss of Convolutriloba retrogemma subjected to 4 treatments (Light, Light with DCMU, Dark, and Dark with DCMU). Light was provided at an irradiance of 70 -2 -1 µmole·m ·s , [DCMU]=0.1 µM, nLC=37, nLD=46, nDC=46, nDD=45. Error bars represent 95% confidence intervals. Results indicate positive photosynthetic carbon fixation and net transfer of photosynthate from algae to host. ..................................................................................................64 vi Figure 3.6. Percent weight loss of Convolutriloba retrogemma subjected to 4 treatments. Same as previous figure, but with non-photosynthetic effects of DCMU removed from the data corresponding to the treatments utilizing DCMU. Error bars represent 95% confidence intervals. Data clearly show significantly higher weight loss in acoels kept in the dark and those treated with DCMU, indicating a net translocation of photosynthate from symbiont to host...................65 Figure 3.7. Post-test zoochlorellae densities in Light and Dark Control group acoels used in the carbon-translocation experiment. Density was measured as algal cells per milligram of host tissue. Error bars represent 95% confidence intervals..................................................................66 Figure 4.1. Characteristic halo-formation resulting from the photoaccumulative behavior of basking Convolutriloba retrogemma. Aggregations, 2–5 cm wide, of the acoel generally form between 1 and 6 cm surrounding objects on flat substrate. ...........................................................83 Figure 4.2. Schematic representation of light chamber and time-lapse photography apparatus utilized in the photomovement experiments..................................................................................84 Figure 4.3. Transmittance spectra of the filters used in determining and defining the short-term response of Convolutriloba retrogemma to a step-up, sudden increase in light intensity. These filters were used in conjunction with a halogen, fiber-optic light source......................................85 Figure 4.4. Photographs of light chamber used in photomovement experiments. A. Chamber with camera and LED light-source attached. Thin tubing at top supplies moisture-saturated air, lower penetrations are cooling-water supply and return lines. Inset
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