1、INTERACTIONS AMONG OLIGOCHAETES AND A MYXOZOAN PARASITE, MYXOBOLUS CEREBRALISbyLeah Candace SteinbachA thesis submitted in partial fulfillment of the requirements for the degree ofMaster of ScienceinBiological SciencesMONTANA STATE UNIVERSITYBozeman, MontanaNovember 2003iiAPPROVALof a thesis submitt
2、ed byLeah Candace SteinbachThis thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies.Dr. Billie Keran
3、s _ _(Signature) DateApproved for the Department of EcologyDr. Scott Creel _ _(Signature) DateApproved for the College of Graduate StudiesDr. Bruce McLeod _ _(Signature) DateiiiSTATEMENT OF PERMISSION TO USEIn presenting this thesis in partial fulfillment of the requirements for a masters degree at
4、Montana State University, I agree that the Library shall make it available to borrowers under the rules of the Library.If I have indicated my intention to copyright this thesis by including a copyright notice page, copying is allowable only for scholarly purposes, consistent with “fair use” as presc
5、ribed in the U. S. Copyright Law. Only the copyright holder may grant requests for permission for extended quotation from or reproduction of this thesis in whole or in parts.Signature _Date _ivACKNOWLEDGEMENTSThis research was funded by the National Partnership on Management of Wild and Native Coldw
6、ater Fisheries and I am appreciative of their financial support for such ecological research. I would like to give thanks to my committee, Dr. Billie Kerans, Dr. Charlotte Rasmussen and Dr. Cathy Zabinski for their support and guidance. Thanks to Russell Elwell for keeping me smiling. Also everyone
7、who contributed to the editing process: Dr. Bob Garrott, Eric Bergman, Katie Brown, Chelsea Cada, Patty Hernandez, Adam Messer, David Richards, Jessie Salix, Lew Stringer, Jeff Warren and Julie Zickovich. Thanks to Jasper Buchbauer for laboratory assistance. A much appreciated thanks to Julie Zickov
8、ich for her excellent laboratory assistance. Also, a most appreciative thanks to Cal Frasier for his assistance and help in the laboratory. And a special thank you to Dr. Billie Kerans for providing me with so much of her personal energy, effort and friendship. vTABLE OF CONTENTSPageLIST OF TABLES.v
9、ii LIST OF FIGURES .viiiABSTRACT.ix1. INTRODUCTION .1THE LIFE CYCLE OF MYXOBOLUS CEREBRALIS.3TUBIFEX TUBIFEX AND MYXOBOLUS CEREBRALIS.4TUBIFEX TUBIFEX, LIMNODRILUS HOFFMEISTERI AND MYXOBOLUS CEREBRALIS .82. OBJECTIVE 1: INTERACTIONS AMONG TWO STRAINS OF TUBIFEX TUBIFEX AND MYXOBOLUS CEREBRALIS .12IN
10、TRODUCTION .12METHODS .17Experimental Procedures .17Molecular Analyses .23Statistical Analyses .25RESULTS .26DISCUSSION.323. OBJECTIVES 2 AND 3: INTERACTIONS AMONG TWO TUBIFICID SPECIES AND A MYXOZOAN PARASITE, AND THRESHOLD INFECTION DOSE.39INTRODUCTION .39METHODS .42Experiment 1: Threshold infecti
11、on dose.44Experiment 2: Interactions between oligochaetes.45RESULTS .48Experiment 1: Threshold infection dose.48Experiment 2: Interactions between oligochaetes.49DISCUSSION.554. CONCLUSIONS.64viTABLE OF CONTENTS CONTINUEDPAGEREFERENCES CITED.70APPENDICES .81Appendix A: ANOVA Tables from Chapter 2 .8
12、2Appendix B: Total triactinomyxon production from Chapter 2 .84Appendix C: Strain A and strain B progeny identified from Chapter 2 .86Appendix D: Infection prevalence from Experiment 1, Chapter 3.88Appendix E: Triactinomyxon production from Chapter 3.90viiLIST OF TABLESTable Page2.1. Analysis of var
13、iance results on the effects of oligochaete combination and myxospore dose on biomass response variables .272.2 Triactinomyxon variables of total triactinomyxons produced per day, infection prevalence and triactinomyxons produced by an individual per day for each oligochaete combination.30 3.1. Anal
14、ysis of variance results of the effects of oligochaete combination and myxospore dose on biomass response variables .51viiiLIST OF FIGURESFigure Page1.1 The life cycle of Myxobolus cerebralis. .52.1 The effects of Tubifex tubifex strains and densityand Myxobolus cerebralis on the total biomass, adul
15、t growthand progeny biomass production .292.2 Randomly amplified polymorphic DNA gel identifying each strain of T. tubifex and possible hybrid progeny .313.1 The relationship between level of myxospore exposure and the percentage of Tubifex tubifex releasing triactinomyxons.493.2 The effects of olig
16、ochaete species and density and Myxobolus cerebralis infection on total biomass, adult growth and progeny biomass production.523.3 The effect of oligochaete density and composition on the proportion of Tubifex tubifex releasing triactinomyxons .533.4 The average triactinomyxon production of an indiv
17、idual Tubifex tubifex.54ixABSTRACTMyxobolus cerebralis, the causative agent of salmonid whirling disease, has caused the decline of two populations of wild rainbow trout (Oncorhynchus mykiss) on the Madison River MT and the Colorado River CO. The life cycle of Myxobolus cerebralis alternates between
18、 two hosts: various salmonid species and one aquatic oligochaete species, Tubifex tubifex. The objectives of this study were to determine the threshold myxospore dose needed to achieve complete infection within Tubifex tubifex and the influence that interactions among oligochaetes and M. cerebralis
19、had on oligochaete fitness and the success of M. cerebralis. I examined the threshold myxospore dose of two T. tubifex strains experimentally and using nine myxospore doses. I determined that a dose of 50 myxospores per individual T. tubifex achieved complete infection in the susceptible strain of T
20、. tubifex. Interactions were examined in two response surface competition design experiments using two strains of T. tubifex, two species of oligochaetes and various doses of myxospores. The interactions among strains of resistant and susceptible T. tubifex were density dependent. The infection prev
21、alence and the proliferation of the parasite (triactinomyxon production) within treatments containing resistant and susceptible individuals were comparable to treatments containing only susceptible individuals. The interactions among susceptible T. tubifex and Limnodrilius hoffmeisteri and the infec
22、tion prevalence of T. tubifex were density dependent. Tubifex tubifex had greater infection prevalence in treatments with L. hoffmeisteri, but had variable triactinomyxon production. In both interaction experiments, susceptible T. tubifex had greater adult growth when interacting with resistant T. t
23、ubifex or L. hoffmeisteri and when exposed to myxospores. This suggests that susceptible T. tubifex may have benefited from a low dose of myxospores. The results of these experimental interactions must be now be contrasted with interactions in natural systems. Further, the next task is to characteri
24、ze oligochaete communities by strain of T. tubifex and species of oligochaete, which has the potential to increase our understanding of host-parasite dynamics. 1CHAPTER 1INTRODUCTIONMyxobolus cerebralis (Myxozoa: Myxosporea/ Actinosporea), the cause of salmonid whirling disease (El-Matbouli et al. 1
25、992), was discovered in 1893 in Germany (Nickum 1996). Initially M. cerebralis was a serious pathogen of hatchery trout, however modifications in hatchery practices reduced its damaging effects. Throughout the 1980s, it was widely accepted that the parasite was not a threat to wild trout populations
26、 (Nickum 1996). However, recent evidence suggest that M. cerebralis has caused declines of wild trout (Oncorhynchus mykiss) populations in the Intermountain West (USA) (Nehring and Walker 1996, Vincent 1996). The life cycle of M. cerebralis involves two obligatory hosts: various salmonid species and
27、 an aquatic oligochaete, Tubifex tubifex (Oligochaeta: Tubificidae)(Wolf and Markiw 1984). Because the ecology of the salmonid and T. tubifex hosts are linked by M. cerebralis, investigations of both hosts are required to fully understand interaction dynamics among all three species (Kerans and Zale
28、 2002, Gilbert and Granath 2003). Studies examining the interactions between salmonids and M. cerebralis have revealed important facets of the whirling disease problem. For example, infection in salmonids varies with species, age and environmental variables (Halliday 1973, Markiw 1992, Hedrick et al. 1998, Zendt and Bergersen 2000, Ryce et al. 2001, Krueger 2002, MacConnell and Vincent 2002, Ryce 2003). Research on M. cerebralis has focused on
