ABSTRACT PREY SIZE SELECTIVITY IN UTRICULARIA VULGARIS Bladderwort are a genus of carnivorous plants that traps zooplankton of submillimeter size by active suction. They are among the smallest suction feeders, with gapes ranging from 0.2 to 0.9 mm in the species Utriculria vulgaris. Other suction feeders of similar size (larval fish) are relatively ineffective feeders, in contrast to adult fish. Even though small suction feeders such as larval fish are ineffective suction feeders, we wanted to explore if that principle applies to other small suction feeders such as aquatic carnivorous plants. The aim of this study is to explore the prey size selectivity and feeding morphology of bladderwort. Despite the hydrodynamic theory, suction feeding is ineffective in smaller predators, bladderworts were found to be effective suction feeders even due to their microscopic size. Furthermore, previous hydrodynamic theory studies suggest that there is a minimum gape length (lower limit) required to be able to suction feed prey successfully. We found that the traps of U. vulgaris range over one order of magnitude from 0.3 to 3 mm and with gape shape closely isometric with trap size (scaling coefficient 0.95). To explore prey size selectivity, we conducted laboratory feeding trials with ostracods (size range 0.07 to 0.7 mm). We found that larger bladderwort traps catch larger and a wider size range of prey, consistent with findings in fish. Despite their microscopic size, bladderworts are able to overcome the hydrodynamic theory prediction and suction feed prey near the lower size limit. Rayhan Kabir May 2017 PREY SIZE SELECTIVITY IN UTRICULARIA VULGARIS by Rayhan Kabir A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Biology in the College of Science and Mathematics California State University, Fresno May 2017 APPROVED For the Department of Biology: We, the undersigned, certify that the thesis of the following student meets the required standards of scholarship, format, and style of the university and the student's graduate degree program for the awarding of the master's degree. Rayhan Kabir Thesis Author Ulrike Müller (Chair) Biology Otto Berg Chemistry David Lent Biology For the University Graduate Committee: Dean, Division of Graduate Studies AUTHORIZATION FOR REPRODUCTION OF MASTER’S THESIS X I grant permission for the reproduction of this thesis in part or in its entirety without further authorization from me, on the condition that the person or agency requesting reproduction absorbs the cost and provides proper acknowledgment of authorship. Permission to reproduce this thesis in part or in its entirety must be obtained from me. Signature of thesis author: ACKNOWLEDGMENTS I would like to acknowledge and give great thanks to my mentor and advisor, Dr. Ulrike Müller. Her guidance and support throughout this project has been invaluable. I would also like to thank my committee members Dr. Otto Berg and Dr. David Lent with helping me navigate my thesis project in the right direction. In addition, I would like to thank all the graduates and undergraduates students who have helped me on this research project for the previous two semesters: Nolan Avery, Fatima Hidalgo, Jennifer Espinoza, Magaly Herrera, Jasleen Kaur, Cory Mayfield, Eduardo Meza, Ronnie Odia, Andrea Ramirez, Ricardo Ramirez, and Juan Villalobos. Lastly, I would like to thank the Biology Department for FSSRA funding, graduate travel grants, and IRA funding to help fund this project and/or support me during this project. TABLE OF CONTENTS Page LIST OF TABLES ................................................................................................ viii LIST OF FIGURES ................................................................................................. ix INTRODUCTION .................................................................................................... 1 Motile Aquatic Suction Feeders (Fish) ............................................................. 2 Non-Motile Aquatic Suction Feeders (Bladderwort) ........................................ 3 Bladderwort Trap Mechanism .......................................................................... 3 Predator/Prey Interaction (Bladderwort) ........................................................... 4 Determining Prey Size Selectivity .................................................................... 6 Scientific Questions .......................................................................................... 6 Project Objectives ............................................................................................. 7 HYPOTHESIS AND SPECIFIC AIMS ................................................................... 9 Hypotheses ........................................................................................................ 9 Aims ................................................................................................................ 9 METHODOLOGY ................................................................................................. 10 Aquatic Carnivorous Plant Husbandry ........................................................... 10 Prey Culture Cultivation ................................................................................. 10 Predator/Prey Experiments ............................................................................. 11 Image Analysis: Analyzing the Images Scanned ............................................ 13 Data Analysis .................................................................................................. 14 Methods to Address Aims 1a & 1b ................................................................. 15 Methods to Address Aims 2a, 2b, and 2c ....................................................... 16 RESULTS ............................................................................................................... 17 Mechanisms of Selectivity .............................................................................. 17 vii vii Page Quantification of Selectivity ........................................................................... 18 DISCUSSION ......................................................................................................... 20 Mechanisms of Selectivity .............................................................................. 20 Quantification of Selectivity ........................................................................... 21 Conclusion ....................................................................................................... 22 Future Work .................................................................................................... 22 FIGURES ............................................................................................................... 24 TABLES ................................................................................................................. 45 REFERENCES ....................................................................................................... 48 LIST OF TABLES Page Table 1: Date of experiments, total prey available, prey captures, and percentage of captures per experiment .................................................... 45 Table 2: U. vulgaris body normality statistics....................................................... 46 Table 3: U. vulgaris body normality statistics....................................................... 47 LIST OF FIGURES Page Figure 1: Confocal image of individual U. vulgaris (Bladderwort) using a confocal microscope. .............................................................................. 24 Figure 2. Scanned image (via Canon CanoScan 8600F Flatbed Scanner) of U. vulgaris bladders attached to branches, which are attached to different nodes on a single strand ........................................................... 25 Figure 3. Phantom v12.1 digital high-speed camera (left) and color microscope (right) images of U. vulgaris with loaded (ready to be triggered) bladder can be triggered by using cat whiskers as shown above. ...................................................................................................... 26 Figure 4. After the loaded bladderwort, has been triggered the bladderwort sucks in water causing the (unloaded) bladder itself to inflate shown above in 2 different images; Phantom v12.1 digital high-speed camera (left) & color microscope (right). ............................................... 26 Figure 5. Image captured via color microscope of a bladderwort that has suction fed its prey which is trapped inside the bladder with no escape possible due to the tight seal of the trap. ..................................... 27 Figure 6. Image of 20 gallon U. vulgaris growth tank filled with deionized water, kept at room temperature (21 °C) and is pH slightly below 7.0 to replicate boggy conditions. ................................................................. 28 Figure 7. Image of Ostracod cultivation with the 1-liter mason glass jar filled pond water from the CSU Fresno greenhouse pond. .............................. 29 Figure 8. Color microscope image of the ostracod species used in the predator/prey experiments. ..................................................................... 30 Figure 9. Image of the TetraMin Tropical Granules Fish Food used to provide nutrients for the Ostracod cultivation jar in figure 7. ............................. 31 Figure 10. Using the Canon CanoScan 8600F