Ecological determinants of host resistance to parasite infectioninmonarch butterflies Público
Lindsey, Elizabeth Anne (2008)
Published
Abstract
Ecological determinants of host resistance to parasite infection in monarch butterflies By Elizabeth A. Lindsey
Heterogeneity in host resistance to infection is common in wild populations despite the obvious fitness benefits of resistance. This variation can be maintained by evolutionary processes and should also be crucially affected by ecological factors. The central goal of my dissertation is to examine how ecological factors influence observed variation in host resistance, focusing specifically on monarch butterflies Danaus plexippus and an obligate protozoan parasite Ophryocystis elektroscirrha. All populations of monarch butterflies examined to date are infected with this parasite, and parasite prevalence varies with host migratory status. Resistance here was defined broadly to include the ability of an individual to either counter infection or survive and reproduce in the presence of infection. Ecological variables examined included host sex, rearing density and environmental temperature. Initial results showed that host resistance and immunity differed between male and female monarchs in a direction consistent with sex-based tradeoffs between the demands of reproduction and costly immune defenses. Effects of larval rearing density on monarch-parasite interactions included an increase in infection probability and stronger negative effects of parasite infection with increasing density, consistent with predictions that crowding induces greater physiological stress and susceptibility among hosts. Global changes in temperature have been predicted to increase the intensity and prevalence of infection in many host-parasite systems. Effects of temperature reported here showed that infected monarchs in warmer temperatures suffered greater levels of wing deformity and incurred lower parasite loads. Thus, hot temperatures appear to have detrimental consequences for the host and parasite, an effect that could effectively lower parasite prevalence owing to reduced transmission at the population level. Across all studies, unparasitized butterflies showed greater (darker) wing melanism than parasitized monarchs, an observation that could be caused by condition-dependent melanin synthesis or by trade-offs in melanin produced for parasite defense versus wing coloration. Overall, results reported here demonstrate a difference in immune defenses between male and female monarchs, and significant effects of larval density and temperature on host resistance and parasite replication and potential transmission.
Table of Contents
TABLE OF CONTENTS INTRODUCTION...1
REFERENCES...10
CHAPTER 1
SEX DIFFERENCES IN IMMUNE DEFENSES AND RESPONSE TO PARASITISM IN MONARCH BUTTERFLIES...18 ABSTRACT...19 INTRODUCTION...21 METHODS AND MATERIALS...25 RESULTS...30 DISCUSSION...34 ACKNOWLEDGEMENTS...38 REFERENCES...39
CHAPTER 2
CROWDING AND DISEASE: EFFECTS OF HOST DENSITY ON RESPONSE TO INFECTION IN A BUTTERFLY-PARASITE INTERACTION...53 ABSTRACT...54 INTRODUCTION...56 METHODS AND MATERIALS...59 RESULTS...67 DISCUSSION...71 ACKNOWLEDGEMENTS...77 REFERENCES...78
CHAPTER 3
WARMER TEMPERATURES LIMIT HOST AND PARASITE FITNESS: EXPERIMENTAL EVIDENCE FROM A BUTTERFLY-PARASITE SYSTEM...98 ABSTRACT...99 INTRODUCTION...101 METHODS AND MATERIALS...104 RESULTS...111 DISCUSSION...116 ACKNOWLEDGEMENTS...122 REFERENCES...123
TABLES AND FIGURES CHAPTER 1
TABLE 1. LINDSEY AND ALTIZER. TABLE 1. ANALYSIS OF VARIANCE SHOWING EFFECTS OF PARASITE TREATMENT, SEX, AND HEMOCYTE CONCENTRATION OF PARASITE LOAD, ADULT LONGEVITY, AND MORPHOLOGICAL CHARACTERISTICS...49
FIGURE LEGENDS. LINDSEY AND ALTIZER 50
FIGURE 1. LINDSEY AND ALTIZER. FIGURE 1. EFFECTS OF PARASITE TREATMENT AND SEX ON (A) HEMOCYTE CONCENTRATION OF LARVAE (CELLS PER μL OF HEMOLYMPH, SQUARE-ROOT TRANSFORMED), (B) ADULT BODY LENGTH (IN MM), (C) ADULT FOREWING AREA (IN MM2), AND (D) ADULT LONGEVITY (IN DAYS)...51 FIGURE 2. LINDSEY AND ALTIZER. FIGURE 2. RELATIONSHIP BETWEEN HEMOCYTE CONCENTRATION OF LARVAE (SQUARE-ROOT TRANSFORMED) AND ADULT BODY LENGTH FOR (A) FEMALES AND (B) MALES...52
CHAPTER 2
TABLE 1. LINDSEY, MEHTA ,ET AL. TABLE 1. NUMBER OF MONARCHS USED TO INITIATE THE EXPERIMENT, AND PERCENT SURVIVING TO ADULT ECLOSION, SHOWN SEPARATELY FOR EACH PARASITE TREATMENT AND LARVAL REARING DENSITY...88 TABLE 2. LINDSEY, MEHTA, ET AL. TABLE 2. ANALYSIS OF VARIANCE SHOWING EFFECTS OF PARASITE TREATMENT, LARVAL REARING DENSITY, AND SEX ON PUPAL MASS AND ADULT FOREWING MORPHOLOGY...89
FIGURE LEGENDS. LINDSEY, MEHTA ET AL...90
FIGURE 1. LINDSEY, MEHTA ET AL. FIGURE 1. FIFTH INSTAR MONARCH LARVAE FEEDING ON ASCLEPIAS SYRIACA (COMMON MILKWEED) IN A FIELD NEAR FORESTPORT, NEW YORK, USA, DURING THE SUMMER OF 2007 (PHOTOGRAPH: MAUREEN CLARK)...93 FIGURE 2. LINDSEY, MEHTA ET AL. FIGURE 2. RELATIONSHIP BETWEEN THE AVERAGE DENSITIES OF MONARCH BUTTERFLY LARVAE BY REGION AND PHASE...94 FIGURE 3. LINDSEY, MEHTA ET AL. FIGURE 3. EFFECTS OF LARVAL REARING DENSITY AND PARASITE TREATMENT ON A) PUPAL MASS (GRAMS) AND B) DEVELOPMENT TIME (DAYS)...95 FIGURE 4. LINDSEY, MEHTA ET AL. FIGURE 4. EFFECTS OF LARVAL REARING DENSITY AND PARASITE TREATMENT ON ADULT LONGEVITY (IN DAYS)...96 FIGURE 5. LINDSEY, MEHTA ET AL. FIGURE 4. EFFECTS OF LARVAL REARING DENSITY AND PARASITE TREATMENT ON A) ADULT FOREWING AREA (MM) AND B) PROPORTION OF BLACK PIGMENTATION ON ADULT FOREWINGS...97
CHAPTER 3
TABLE 1. LINDSEY, VALIN ,ET AL. TABLE 1. TARGETED TEMPERATURE SETTINGS, REALIZED AVERAGE MAXIMUM AND MINIMUM TEMPERATURES (IN °C), AND AVERAGE MAXIMUM AND MINIMUM RELATIVE HUMIDITY VALUES FOR COLD, MODERATE, AND HOT TEMPERATURES...132 TABLE 2. LINDSEY, VALIN, ET AL. TABLE 2. ANALYSIS OF VARIANCE SHOWING EFFECTS OF PARASITE TREATMENT, TEMPERATURE, AND SEX ON DEVELOPMENT TIME, PARASITE SPORE LOAD, ADULT MASS, FOREWING AREA, AND MELANISM...133
FIGURE LEGENDS. LINDSEY, VALIN, ET AL...134
FIGURE 1. LINDSEY, VALIN ET AL. FIGURE 1. PROPORTION OF MONARCHS SURVIVING FROM INOCULATION TO THE ADULT STAGE UNDER COLD, MODERATE, AND HOT TEMPERATURES...136 FIGURE 2. LINDSEY, VALIN ET AL. FIGURE 2. EFFECT OF TEMPERATURE AND PARASITE TREATMENT ON DEVELOPMENT TIME (DAYS LOG-TRANSFORMED)...137 FIGURE 3. LINDSEY, VALIN ET AL. FIGURE 3. EFFECT OF TEMPERATURE AND PARASITE TREATMENT ON PARASITE SPORE LOAD...138 FIGURE 4. LINDSEY, VALIN ET AL. FIGURE 4. EFFECTS OF TEMPERATURE AND PARASITE TREATMENT ON A) PROPORTION OF DEFORMED ADULT MONARCHS AND B) ADULT LONGEVITY (IN DAYS)...139 FIGURE 5. LINDSEY, VALIN ET AL. FIGURE 5. EFFECTS OF TEMPERATURE AND PARASITE TREATMENT ON THE PROPORTION OF BLACK ON MONARCH FOREWINGS FOR A) MALES AND B) FEMALES...140
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