Examination of Wright's shifting balance theory of evolution as applied to animal breeding, detection of epistatic variance, and applications to insect pest management
Abstract
Wright's Shifting Balance Theory of Evolution (SBT) states that epistatic interactions are important in fitness trait evolution and that population structure influences development of epistatic interactions. Tribolium castaneum was used to model a subdivide/merge breeding scheme (based on SBT), followed by intense inbreeding, to study the efficacy of this system for improving selection response for fitness traits with large non-additive effects, and type of epistasis which developed due to interactions between selection and population structure. For increased offspring number, the subdivide/merge system showed no clear advantage over undivided population; however, the populations were dramatically different if inbreeding levels are considered in conjunction with selection response. While maintaining response levels comparable to the undivided population, the subdivided population underwent rapid inbreeding, relieved periodically by merge cycles, implying development of gene interaction systems which allowed both high levels of inbreeding and high offspring numbers. Upon inbreeding without selection, offspring number is expected to decline linearly, if predominantly governed by dominance. The subdivided population showed negative curvilinear decline, indicating underdominant epistasis resulting, in less severe inbreeding depression. The undivided population showed positive curvilinear decline indicating overdominant epistasis, resulting in greater inbreeding depression. Intense inbreeding without selection offers a simple method of estimating magnitude and direction of D x D epistatic interactions within a population. Tribolium castaneum was also used as a model organism with which to examine control of pesticide resistance development rate through application of quantitative genetic theory. A simple two-generation procedure was developed that allowed estimation of cross-resistance potential, resistance development rate due to pesticide application order, fitness cost to resistance and resistance reversion rate. The procedure was tested using deltamethrin and malathion, pesticides of known differing actions. Change in population resistance level was predicted using tandem pesticide application. Asymmetrical genetic correlations led to significant differences in predicted resistance development, depending upon pesticide order. Fitness cost of resistance is important for the success of rotation application schemes, so that resistance reverts when pesticide application stops. Deltamethrin resistance had no significant fitness cost. Malathion resistance had a significant fitness cost, but predicted reversion was extremely slow, making future use of malathion impractical.
Degree
Ph.D.
Advisors
Stuart, Purdue University.
Subject Area
Genetics|Livestock|Agronomy
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