Comparative Study on Memory Phases in the Parasitic Wasps Cotesia Glomerata and Cotesia Rubecula
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Department of Zoology Laboratory of Entomology Institute of animal ecology Dr. Hans Smid Prof. Dr. Johannes Steidle University of Wageningen University of Hohenheim (220c) The Netherlands Stuttgart, Germany Comparative study on memory phases in the parasitic wasps Cotesia glomerata and Cotesia rubecula Diploma Thesis This work was financially supported by the Herzog-Carl-Foundation, University of Hohenheim Submitted by Silja Tribuhl (07.05) Hohenheim, Stuttgart, March 2007 Faculty of Agricultural Sciences Table of contents I Table of contents Comparative study on memory phases in the parasitic wasps Cotesia glomerata and Cotesia rubecula Listof figures III Listof tables IV 1.Summary 1 2.Introduction 2 2.1 Insects and learning......................................................................................................2 2.2 Associative learning.....................................................................................................2 2.3 Learning and memory formation.................................................................................3 2.4 Cotesia glomerata and Cotesia rubecula.....................................................................5 2.5 Memory phases in Cotesia glomerata and Cotesia rubecula......................................7 3.Material and Methods 11 3.1 Insects.........................................................................................................................11 3.2 Plants..........................................................................................................................11 3.3 Odour source..............................................................................................................12 3.4 Wind tunnel................................................................................................................12 3.5 Experimental design...................................................................................................13 3.6 Wind tunnel assay......................................................................................................14 3.7 Statistical analysis......................................................................................................15 4.Results 15 4.1 Results of different learning trials in Cotesia glomerata...........................................15 4.2 Results of single learning trials in C. glomerata and C. rubecula after 4 hours........17 5.Discussion 20 5.1 Cotesia glomerata......................................................................................................20 5.2 Cotesia rubecula........................................................................................................21 5.3 Variations in learning during the experiments...........................................................22 5.4 Costs and benefits of learning....................................................................................24 5.5 Cotesia glomerata and Cotesia rubecula – why are they so different in learning?...25 6.References 28 Table of contents II Appendix: Transition from solitary to gregarious development in parasitic wasps 1.Introduction 32 1.1 Solitary and gregarious development.........................................................................32 1.2 Transition from solitary to gregarious development..................................................34 1.3 Cotesia glomerata and Cotesia rubecula...................................................................34 2.Material and Methods 35 2.1 Experimental setup.....................................................................................................35 2.2 Statistical analysis......................................................................................................36 3.Results 36 4.Discussion 39 5.References 43 List of figures III List of figures Comparative study on memory phases in the parasitic wasps Cotesia glomerata and Cotesia rubecula Fig.1: Putative pathway of memory formation. 4 Fig.2: Putative pathway of memory formation. 5 Fig.3: Life cycle of parasitic wasps. 6 Fig. 4: Memory retention in C. glomerata and C. rubecula. 8 Fig. 5a: Memory retention in C. rubecula afterthree spaced trials. 9 Fig. 5b: Memory retention in C. glomerata after three spaced trials. 9 Fig. 6: Memory retention in C. glomerata and C. rubecula 4 hours after single training. 10 Fig. 7: Wind tunnel set-up. 13 Fig.8: Wind tunnel. 14 Fig. 9: Cotesia glomerata: Choice for cabbage or nasturtium after no, one single or threespaced learning trials. 16 Fig. 10: C. glomerata and C. rubecula: Choice for nasturtium depending on the treatment. 18 Appendix: Transition from solitary to gregarious development in parasitic wasps Fig. 1: Mean numbers of twisting and folding in mymariform larvae of the solitary A. victus and the gregarious A. listronoti. 35 Fig. 2: Mean numbers of lateral bending of the solitary C. rubecula and the gregarious C. glomerata. 37 Fig. 3: Larvae of C. glomerata and C. rubecula 6 days after oviposition. 37 Fig. 4: Mouthparts of larvae of C. glomerata and C. rubecula 5 to 8 days after oviposition. 38 Fig.5: The evolution of gregariousness. 41 List of tables IV List of tables Comparative study on memory phases in the parasitic wasps Cotesia glomerata and Cotesia rubecula Table 1: C. glomerata: Choice for nasturtium after different learning trials. 17 Table 2: C. glomerata: Choice for nasturtium 4 hours after one learning trial. 19 Table 3: C. rubecula: Choice for nasturtium 4 hours after one learning trial. 19 Appendix: Transition from solitary to gregarious development in parasitic wasps Table 1: Mean numbers of bending in C. glomerata and C. rubecula. 37 1. Summary 1 Comparative study on memory phases in the parasitic wasps Cotesia glomerata and Cotesia rubecula 1. Summary The parasitic wasps Cotesia glomerata and Cotesia rubecula are closely related and live in the same habitat in the Netherlands. The wasps lay their eggs in caterpillars of Pieris butterflies. To find their hosts the wasps are innately attracted by volatiles emitted by infested cabbage plants. If hosts are encountered on plants different than cabbage the wasps learn to associate the odour of this plant species with the presence of suitable hosts. Although the wasps are closely related, clear differences in learning and memory formation occur. C. glomerata forms long-term memory (LTM) already after one successful egg laying experience whereas C. rubecula needs three spaced experiences. Former experiments assumed that after three spaced conditioning trials LTM is consolidated directly out of anesthesia sensitive memory (ASM) in C. glomerata and no anesthesia resistant memory (ARM) is present. In C. rubecula two memory traces coexist after three spaced trials, ARM and LTM. To test if ARM is present in C. glomerata a classical conditioning setup is used, in combination with cooling to inhibit ASM and with a translation inhibitor (anisomycin) that blocks LTM. Both species were tested with one conditioning trial. In C. glomerata both, cooling and anisomycin inhibited 4 hour memory retention, which shows that ARM seems to be absent in C. glomerata after 4 hours. ASM is directly consolidated into LTM in this species suggesting that LTM induction prevents formation of ARM. In C. rubecula there was no effect of cooling on 4 hour memory retention, and previous results showed that 4 hour memory retention in this species cannot be inhibited by anisomycin. This shows that 4 hour memory retention is constituted exclusively by ARM. Looking at learning and memory formation in the context of the natural behaviour of the wasps, it becomes clearer why these differences in memory formation might occur. For C. glomerata finding a host on a special plant species is reliable information due to the egg laying performance of its host P. brassicae which chooses a stand of plants of the same species. If C. glomerata associates the odour of the new encountered plant with the presence of suitable hosts it can be sure to find enough hosts for its offspring. Therefore new memory is stored directly into LTM. For C. rubecula finding a host is not reliable information because 2. Introduction 2 its host P. rapae spreads its eggs widely on different host plants. For the wasp it would be maladaptive to change its innate behaviour and search for the new encountered plant species. Still associations are formed in C. rubecula but this memory is stored in ASM and ARM which wane within one day and are a form of “low cost” memories, demanding less energetic costs than the formation of LTM which requires new gene expression. 2. Introduction 2.1 Insects and learning When you think of insects you think of tiny little animals flying or crawling around maybe disturbing you. The idea that these little insects are able to learn and that they react in a flexible way to their environment would maybe never come to your mind. “Do insects have a brain?” is a frequently asked question when I tell people about my research. Of course the brains of insects look a little bit different than brains in higher animals or humans but the way they function is not very different. Insects are able to learn and this fact has been of great interest for a lot of researchers all over the world. Are there any advantages for the insects if they are able to learn? Do they all learn in the same way, with the same speed? How long are they able to remember learned information? Which genes are involved in memory formation? Especially the fruit fly Drosophila has been well-investigated concerning