UVM Theses and Dissertations
Format:
Print
Author:
Tucker, Thomas M.
Dept./Program:
Biology
Year:
2004
Degree:
M.S.
Abstract:
Gaining a better understanding of host and parasite co-evolution involves synthesizing knowledge from the fields of medicine, agriculture, wildlife management, and parasitology and how ecology and evolution applies to each of these disciplines. Most studies of host and parasite co-evolution focus on one aspect of either the host or the parasite. Due to the differences in physical size, generation times, and general ecology between interacting hosts and parasites, holistic views of how hosts and parasites simultaneously evolve in response to one another are too complex and cumbersome to yield much real meaning. With the latest improvements in computer speed and power, previously impossible analyses have become possible. In this thesis, I analyze the co-evolution between arthropod pests and parasites that are commonly used to reduce their population sizes, with a focus on how co-evolution is maintained.
The first part of the thesis is an ecological study between Japanese beetles (Popillia japonica) and microbial parasites that are used to control them (Paenobacillus popilliae japonica). Specifically, I investigate whether or not variation in parasite defense exists between exposed and unexposed beetle populations. The defense trait that is measured is the level of phenoloxidase (PO) production. This study shows that variation in PO production does exist according to exposure to microbial control agents, that PO is correlated with increased resistance to parasites, and that there is a fitness cost associated with PO production. The second part of the thesis investigates how six parameters affect the co-evolution between hosts and parasites. The parameters are host recombination rate, parasite recombination rate, cost of host resistance, cost of parasite virulence, parasite prevalence, and the mechanism of virulence (either quantitative or qualitative). The focus of this chapter is that for co-evolution to occur there must be genetic variation in host and parasite population.When either hosts or parasites become genetically fixed, co-evolution cannot occur. The parameters and their effects are investigated by simulating an ecologic interaction between populations of hosts and parasites using techniques from the field of evolutionary computation. The results show that all six parameters have significant effects on the maintenance of genetic variation in a host and parasite system. The results from this thesis can be used in predicting the outcome of applying a saprophytic parasite to an area where arthropod pests are a problem. By measuring certain quantities from the natural populations such as the prevalence of the parasite (a direct result of how much bio-control agent is applied), resistance and virulence costs, and determining the genetic linkage between the genes for resistance and virulence, one may determine how long the hosts and parasites will apply selection pressures upon each other.
The first part of the thesis is an ecological study between Japanese beetles (Popillia japonica) and microbial parasites that are used to control them (Paenobacillus popilliae japonica). Specifically, I investigate whether or not variation in parasite defense exists between exposed and unexposed beetle populations. The defense trait that is measured is the level of phenoloxidase (PO) production. This study shows that variation in PO production does exist according to exposure to microbial control agents, that PO is correlated with increased resistance to parasites, and that there is a fitness cost associated with PO production. The second part of the thesis investigates how six parameters affect the co-evolution between hosts and parasites. The parameters are host recombination rate, parasite recombination rate, cost of host resistance, cost of parasite virulence, parasite prevalence, and the mechanism of virulence (either quantitative or qualitative). The focus of this chapter is that for co-evolution to occur there must be genetic variation in host and parasite population.When either hosts or parasites become genetically fixed, co-evolution cannot occur. The parameters and their effects are investigated by simulating an ecologic interaction between populations of hosts and parasites using techniques from the field of evolutionary computation. The results show that all six parameters have significant effects on the maintenance of genetic variation in a host and parasite system. The results from this thesis can be used in predicting the outcome of applying a saprophytic parasite to an area where arthropod pests are a problem. By measuring certain quantities from the natural populations such as the prevalence of the parasite (a direct result of how much bio-control agent is applied), resistance and virulence costs, and determining the genetic linkage between the genes for resistance and virulence, one may determine how long the hosts and parasites will apply selection pressures upon each other.