Effects of milkweed species on monarch butterflies and their parasites Open Access
Hoang, Kevin Ming-Kong (2016)
Published
Abstract
Parasites contribute to much of the species diversity and cover a wide range of hosts and environments. By definition, parasites induce fitness reductions in hosts, whether it is through reduction in host size, immune defense, lifespan, or fecundity. The intricate host-parasite relationship is affected by a number of factors, such as host diet, nutrition, and immune system. For example, the monarch butterfly (Danaus plexippus), which can be infected with the protozoan parasite Ophryocystis elektroscirrha, exhibits oviposition preferences when infected. Infected females, which spread the parasite during oviposition, seek out medicinal milkweeds (Asclepias spp.) to lay their eggs upon in order to alleviate the effects of O. elektroscirrha in the next generation. These medicinal milkweeds differ in their toxic chemical contents and reduce parasite loads as well as increase lifespans of infected monarchs compared to those reared on non-medicinal milkweeds. Here, we explore how different milkweed species affect the host-parasite interaction between the monarch butterfly and its parasite. Specifically, we compare Morrenia odorata, a member of the milkweed family, as a host plant for monarchs with more common milkweed species (Asclepias spp.). We found that M. odorata can be used to rear monarch larvae to adulthood but that the lifespans of these monarchs are generally lower than those reared on Asclepias milkweeds. Additionally, M. odorata does not appear to have any medicinal effects on infected monarchs. On top of this, female monarchs significantly preferred to oviposit on Asclepias milkweeds over M. odorata when given a choice. A separate experiment we conducted was to study the effects of different monarch larval diets on parasite morphology. Here, we found a significant relationship between larval diet and parasite size. The toxic chemicals within milkweeds significantly reduced parasite size, a hidden benefit of medicinal milkweeds on O. elektroscirrha. Not only do these milkweeds reduce parasite loads, but they also reduce parasite sizes, another possible mechanism to lower parasite fitness. In the future, additional studies on the effects of M. odorata and monarch larvae diets on monarch-parasite interactions need to be conducted to further expand our knowledge on this intricate and alluring host-parasite relationship.
Table of Contents
Chapter 1 Effects of Morrenia odorata on monarch fitness and parasite infection
ABSTRACT 1
INTRODUCTION 1
MATERIALS AND METHODS 5
Host and Parasite sources 5
Plant sources 6
Experiment 1 6
Experiment 2 9
Statistical tests 9
RESULTS 10
Experiment 1 10
Summer 2015 10
Fall 2015 11
Experiment 2 11
DISCUSSION 11
FIGURES 14
Chapter 2 Host diet affects the morphology of a butterfly pathogen
ABSTRACT 22
INTRODUCTION 22
MATERIALS AND METHODS 26
Host and Parasite sources 26
Plant sources 26
Experimental design 27
Parasite morphology analysis 29
Statistical tests 29
RESULTS 30
DISCUSSION 31
REFERENCES 34
TABLES 40
FIGURES 43
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