In a heterogeneous environment where temperature influences fitness, individuals must navigate to a thermal optimum to maximize reproductive output and minimize physiological stress. However, the optimal temperature varies among individuals due to genetic and environmental contributions. The neural and genetic basis to such natural variation in behavior has remained elusive in most cases, as the high-throughput genomic, neurodevelopmental, and behavioral techniques were not developed. Using the nematode / 10000-01-01

Characterization of the determinants of economically important phenotypes showing complex inheritance should lead to more effective use of genetic resources. This study was conducted to determine the number, genome location and effects of QTLs determining malting quality and agronomic traits in the two North American barley quality standards. Using a doubled haploid population of 140 lines from the cross of Harrington x Morex, agronomic phenotype and malting quality data sets from nine and eight environments, respectively, and a 107-marker linkage map, QTL analyses were performed using simple interval mapping and simplified composite interval mapping procedures. Thirty five QTLs were associated either across environments or in individual environments, with five grain and agronomic traits (yield, kernel plumpness, test weight, heading date and plant height). Thirteen QTLs were associated with five malting quality traits (grain protein percentage, soluble/total protein ratio, ��-amylase activity, diastatic power and malt extract percentage). QTLs for multiple traits were coincident. The loci controlling inflorescence type [vrsl on chromosome 2 (2H) and int-c on chromosome 4 (4H)] were coincident with QTLs affecting all traits except heading date and malt extract percentage. The largest effect QTLs -for yield, kernel plumpness test weight, plant height grain protein percentage, S/T ratio, and diastatic power- were coincident with the vrsl locus. QTL analyses were conducted separately for each sub-population (six-rowed and two-rowed). Ten new QTLs were detected in the sub-populations. There were significant interactions between the vrsl and int-c loci for plant height, grain protein percentage, and SIT protein ratio. Positive transgressive segregants were found for all agronomic traits. They were more prevalent in the six-rowed sub-population, indicating that more favorable alleles were fixed in the two-rowed parent. Results suggest that this mating of two parents representing different germplasm groups caused a disruption in the balance of traits involved in malting quality, which resulted in no progeny carrying all favorable alleles and therefore surpassing the quality of either parent. This study describes some of the genetic determinants of agronomic and malting quality traits in a two-rowed x six-rowed cross and it is a first step toward the further characterization and manipulation of these determinants. / Graduation date: 2001

The evolution of mate choice remains one of the most controversial topics within evolutionary biology. In particular, the coevolutionary dynamics between ornaments and mating preferences has been extensively studied, but few generalizations have emerged. From a theoretical standpoint, the nature of the genetic covariance built up by the process of mate choice has received considerable attention, though the models still make biologically unrealistic assumptions. Empirically, the difficulty of estimating parameters in the models has hindered our ability to understand what processes are occurring in nature. Thus, it is the goal of this dissertation to contribute to the field both theoretically and empirically. I begin with a review of the evolution of mate choice and demonstrate how the lack of cross-talk between theoretical and empirical pursuits into studying mate choice has constrained our ability to extract basic principles. The review is followed by a new model of intersexual selection that relaxes some of the critical assumptions inherent in sexual selection theory. There are two empirical studies whose goal is to measure mating preference functions and genetic correlations in a way that can be related back to theory. Finally, I conclude by setting the stage for future endeavors into exploring the evolution of mate choice. The results presented herein demonstrate four things: (i) a lack of communication between theoretical and empirical studies of mate choice; (ii) genetic drift plays a much larger role in preference evolution than previously demonstrated; (iii) genetic correlations other than those explicitly modeled are likely to be important in preference evolution; and (iv) variation in mating preferences can eliminate intersexual selection altogether. From these four findings it can be concluded that a tighter link between theory and empiricism is needed, with a particular emphasis on the importance of measuring individual-level preference functions. Models will benefit from integrating the specific phenotypes measured by empiricists. Experimentation will be more useful to theory if particular attention is paid to the exact phenotypes that are measured. Overall, this dissertation is a stepping stone for a more cohesive and accurate understanding of mate choice evolution.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Quantitative genetics has traditionally been used to examine selection responses in domesticated organisms, but has recently been applied by evolutionary biologists to natural populations. Evolutionary biologists use quantitative genetics to model variation in traits related to fitness and, ultimately, to make predictions about the impact of natural selection on populations. However, there are few cases in which quantitative genetics has been used to predict changes in natural populations, and only two cases in which it has been used to predict a correlated response to natural selection. / I use a quantitative genetic model to predict the correlated response to natural selection in geographically distinct wild populations of the wing dimorphic sand cricket, Gryllus firmus. Three populations of G. firmus that naturally vary in proportion macroptery are used to qualitatively assess, for the first time, predictions from a quantitative genetic model postulating that an increase in proportion macroptery is correlated with a decrease in fecundity. Variation observed among the populations when raised in a common garden supports predictions and demonstrates that a difference in mean fecundity is the result of a response in fecundity within wing morphs in addition to a change in the proportion of macropterous females. My results indicate that the complexity behind evolutionary changes in traits genetically correlated with proportion macroptery can be modeled through quantitative genetics.

Recent scientific support for the involvement of genetic locus interaction in quantitative trait variation and the widespread use of quantitative trait locus (QTL) mapping has resulted in the need to examine those aspects concurrently. Computer software was written to simulate interacting quantitative trait loci (QTLs) in plant populations. Using this software, interacting QTLs were simulated to examine effects of epistasis on the detection of QTLs and the quality of QTL parameter estimates. Simulations involved doubled haploid populations exhibiting two non-epistatic traits and seven epistatic traits, each trait at four levels of heritability. Detection efficiency of QTL main and interaction effects decreased with decreasing heritability. At a given level of broad-sense heritability, traits differed with respect to the relative quality of main-effect detection and interaction-effect detection. Main-effect detection was notably poor for one epistatic locus that has a relatively small additive effect. Position estimates were accurate but their precision deteriorated with decreasing heritability. The quality of QTL effect estimates declined consistently with decreasing heritability, and loss in the accuracy was associated with losses in power of detection.

Identifying the genetic basis for phenotypic variation is a central question in evolutionary biology and can be studied in detail using model organisms. Fecundity variation in different isolates of C. briggsae has been observed previously, but the genetic causes of this variation are unclear. Crosses between C. briggsae advanced-intercross recombinant inbred lines (AI-RILs) and parental strains yield near isogenic line (NIL) strains, which I created to provide a powerful genetic resource to fine-map the basis for fecundity and other trait differences. Phenotypic analysis of the NILs shows the complexities of possible epistatic interactions on phenotypic expression. These NIL strains contribute a valuable genetic resource toward the long-term goal of identifying the genes responsible for differences in fecundity in this species. The elucidation of the basis for this trait variation will also contribute further into the mechanisms for how genotype and phenotype and environment all interact.

Identifying the genetic basis for phenotypic variation is a central question in evolutionary biology and can be studied in detail using model organisms. Fecundity variation in different isolates of C. briggsae has been observed previously, but the genetic causes of this variation are unclear. Crosses between C. briggsae advanced-intercross recombinant inbred lines (AI-RILs) and parental strains yield near isogenic line (NIL) strains, which I created to provide a powerful genetic resource to fine-map the basis for fecundity and other trait differences. Phenotypic analysis of the NILs shows the complexities of possible epistatic interactions on phenotypic expression. These NIL strains contribute a valuable genetic resource toward the long-term goal of identifying the genes responsible for differences in fecundity in this species. The elucidation of the basis for this trait variation will also contribute further into the mechanisms for how genotype and phenotype and environment all interact.

Thesis (M.S.)--University of North Carolina at Greensboro, 2005. / Title from PDF title page screen. Advisor: David L. Remington; submitted to the Dept. of Biology. Includes bibliographical references (p. 51-55).

Thesis (M.S.)--University of North Carolina at Greensboro, 2005. / Advisor: David L. Remington; submitted to the Dept. of Biology. Includes bibliographical references (p. 51-55).