The evolutionary importance of genetic constraints has always been recognized by biologists, but very little data is available to quantitatively assess the role of constraints in shaping the biology of organisms. The field of quantitative genetics provides the tools necessary to study evolutionary constraints, mainly through the estimation of the matrix of additive genetic variance and covariance (the G matrix). The main goals of this Ph.D. dissertation were to study the persistence of constraints across environments and across species, to explore the consequences of constraints on species divergence, and to try to understand some morphological and life history characteristics of field crickets in light of genetic variation. Populations of seven wing-dimorphic cricket species from the genera Gryllus and Teleogryllus were sampled from the wild and reared in the laboratory. Using multiple statistical approaches to the comparison of G matrices, results revealed little variation in G matrices across species. Moreover, the relatively small effect of rearing environment and of the two wing morphologies on G were shown to be of the same magnitude as variation between species, therefore confirming the general constancy of genetic constraints through evolutionary time scales. Mean trait values, selection regimes and phylogenetic distances were all shown not to be predictors of G matrix variation. In agreement with the constraint hypothesis of quantitative genetic theory, morphological divergence between species was shown to be predictable from a reconstructed ancestral G matrix. In addition, information on genetic variation was used to explain various patterns relating to size, ovipositor length, wing morphology and diapause occurrence in field crickets. Overall, we suggest that genetic constraints, as described by quantitative genetics, have played a major role in shaping the observed biological diversity of field cricket species, a conclusion tha

Maize (Zea mays L.) inbred lines for hybrid breeding are usually developed within distinct heterotic groups. Breeders impose strong selection and maintain relatively small population sizes that are adapted to local environments, where the aim is to identify the desired recombinant types in the progeny. However, linkages between loci that control a trait may not permit breeders to obtain the desirable genetic recombination in these populations. It is hypothesized that different favorable and unfavorable alleles accumulate within the lines from different heterotic groups. In addition, within each inbred line, favourable alleles are linked with unfavourable alleles. Two early-season maize inbreds, CG60 (Iodent) and CG102 (Stiff Stalk), were used to develop a selfed recombinant inbred line (SRIL) and an intermated recombinant inbred line (IRIL) populations. Furthermore, individuals from within these populations were testcrossed with an inbred tester from the Lancaster Sure Crop heterotic group, to give rise to selfed SRIL testcross (SRIL-TC) and IRIL testcross (IRIL-TC) populations. The inbred and inbred-testcross populations were evaluated for trait variation and QTL mapping. The genetic variance was high in inbred populations (SRIL and IRIL) with transgressive segregation for flowering time and agronomic traits. However, genetic variances and correlation coefficients did not significantly differ between the inbred populations. Results suggested that pleiotropic genes were prevalent for these traits. In addition, linkages between the loci that control these traits were not common within parental genomes. Genetic linkage maps developed from the IRIL population were larger than those of the SRIL population. In the inbred-testcross populations (SRIL-TC and IRIL-TC) high means and high levels of trait variation were observed for all traits. The genetic variances and correlation coefficients of hybrid traits did not significantly differ between the SRIL-TC and IRIL-TC populations. Twenty five significant small to moderate QTL were detected, but only one, for grain moisture, was shared between inbred-testcross populations. Overall, the two inbred parents from different heterotic groups have many distinct alleles that contribute to traits. The recombinant inbred line populations had high means and variances for grain yield and related traits, which opens the possibility of utilizing these lines for hybrid breeding.

Laboratory experiments, genetic simulation, and theoretical analyses were performed to address several objectives related to the use of genetic markers in plant breeding programs. Two software packages were developed: GREGOR provides flexible and efficient computer algorithms for performing genetic simulation experiments, and KIN provides improved methods for estimating coancestry from known pedigrees. Random amplified polymorphic DNA (RAPD) markers were investigated in elite barley lines, and estimates of genetic distance based on RAPD markers were compared to estimates based on coancestry. Both types of estimate can provide information that is useful to breeders and geneticists. Genetic simulation was used to investigate the power, accuracy and precision of several methods that are available for analyzing quantitative trait loci (QTL). In most cases, simplified methods of QTL analysis based on linear regression were similar or superior to more complex methods based on mixture models. Methods for genetic analysis using selective genotyping and pooled DNA were also investigated. These methods may allow precise estimates of the positions of markers and QTL to be made.

Inheritance studies have previously been undertaken at the South African Sugar Association Experiment Station (SASEX) under irrigated conditions. Since most sugarcane is grown in South Africa under dryland (raingrown) conditions, heritability estimates were calculated under these conditions in this study and compared to those previously obtained under irrigated conditions. A sugarcane population consisting of 12 crosses, 32 offspring in each cross, and their parents were planted in the first two selection stages of the SASEX selection programme to ascertain which stage provided the most useful information when selecting parent cultivars. Data collected from Stage 2 was more reliable than data collected from Stage 1. Variance components, narrow and broad sense heritabilities, correlations among traits, and clonal repeatabilities between seasons were determined for 11 sugarcane traits at Stages 1 and 2. These traits studied included: stalk population; stalk diameter; stalk height; cane mass; dry matter % cane; fibre % cane; brix % cane; brix % dry matter; purity; pol % cane; and ers % cane. Narrow sense heritabilities of the sugarcane traits were estimated by mid-parent offspring regression . Alternative heritability estimates were obtained through restricted maximum likelihood (REML) analysis of the unbalanced North Carolina design II at Stage 2. Although narrow sense heritabilities determined by mid-parent-offspring regression were comparable with those previously determined at SASEX and by other workers, REML was more efficient than regression. Use of REML enabled additive and non-additive genetic variance components to be estimated by allocating degrees of freedom to treatments and the interactions between the different treatments. Heritability estimates varied for different traits and compared favourably with those obtained under irrigated conditions and by other workers. Additive genetic variance was more important than non-additive genetic variance for some characters, but not for stalk population, cane mass, and dry matter % cane, for which both variances were important. Selection of parent cultivars for all sucrose-related traits, fibre % cane, and stalk diameter should be as successful under raingrown as under irrigated conditions, provided that the environmental variation is determined efficiently under raingrown conditions. Environmental correlations were observed between some traits, particularly between the yield related traits, and may have influenced heritability estimates for those traits determined by mid-parent offspring regression. Stalk diameter, fibre % cane, and brix % dry matter were the most repeatable traits between seasons. Cane mass was the least repeatable trait between Stages 1 and 2 but was highly repeatable between plant (-P) and ratoon (-R) crops of Stage 2. Stalk diameter was positively correlated with brix % dry matter (0.457-P and 0.623-R) and strongly negatively correlated with stalk population (-0.790-P and -0.711-R) and fibre % cane (-0.628-P and -0.651-R). Cane mass was strongly positively correlated with brix % dry matter (0.638-P and 0.679-R). By selecting for brix % dry matter and stalk diameter, indirect selection for cane mass would be possible. Brix % dry matter was determined as the most reliable trait on which to base parental and commercial cultivar selection because it was highly heritable, highly repeatable and highly positively correlated with stalk diameter and cane mass. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

A modification of bulked segregant analysis was used to raise the density of markers in a 34.5 cM region between Ugp2 and Ugp1, on chromosome 3 of the Harrington x TR306 barley Hordeum vulgare L.) cross. A computer program was used to select pools contrasting for parental alleles at the target site. Of 257 RAPD primers tested on DNA pools, one, UBC 508, detected a polymorphic DNA fragment (UBC508(C)). It mapped 10.2 cM distal to Ugp2. Two additional DNA polymorphisms, (UBC508(A) and UBC508(B)), mapped on chromosome 2. An additional marker, BCD 1796B, mapped 4.9 cM proximal to Ugp1. Both strands of the UBC508(C) fragment were sequenced. They were 588 bp long and had some homology to a region of the DNA that regulates transcription of the H. vulgare pazx gene encoding protein Zx. The effect of adding new marker(s) on the QTL analysis of agronomic and quality traits of barley, was investigated. For extract beta-glucan, a new peak was identified in the analysis when only UBC508(C) or when both UBC508(C) and BCD1796B were added. For fine-coarse difference a QTL x E interaction peak was detected when only BCD 1796B was added or when both UBC508(C) and BCD 1796B were added.

The difference in evolutionary interests of males and females can select for traits that favour an individual??s fitness at the expense of their mate??s lifetime fitness. Despite the widespread occurrence of this sexual conflict over reproductive interactions, however, research to date has largely focused on the fitness costs imposed on females by manipulative males. Empirical evidence is particularly sparse for how mating can also be costly for males, the genetic structure of traits involved in reproductive interactions, and how sexual conflict can modify sexual selection in general. My aim was to explore the broader evolutionary consequence of sexual conflict and male-female interactions. In the nuptial-feeding Australian ground cricket, Pteronemobius sp., I used an experimental evolution approach to explore how diet and sexual conflict interact to determine the costs of mating. In the Australian black field cricket, Teleogryllus commodus, I used molecular and quantitative genetic approaches to characterise the fitness consequences and genetic basis of spermatophore attachment, a trait at the centre of inter-locus sexual conflict, and then related this to both condition and male attractiveness. Finally, in T. commodus, I quantified how sexual conflict alters the sexual selection acting on male sexual traits and how this in turn shapes genetic architecture and the persistence of additive genetic variance. My results demonstrate the complex nature of reproductive interactions between males and females. Importantly, I show that diet can mediate the expression of sexual conflict in a mating system and shape the evolution of male life-span. I also show that reproductive interactions influence the fitness benefits that both male and females obtain from mating in ways that are not predicted by current theory and that much of the potential for such traits to co-evolve is via a common genetic association with condition. Finally, I demonstrate that sexual conflict can profoundly modify the process and outcome of sexual selection, thereby influencing how additive genetic variation is maintained in a suite of male sexual traits. These results highlight the need for a greater integration of sexual conflict and sexual selection theory as the evolutionary potential and significance of sexual conflict may currently be underestimated.

Thesis (D. Sc.)--University of Adelaide, 1987. / Title from container. Includes bibliographies and indexes.

Thesis (Ph.D.)-- University of Adelaide, Dept. of Plant Science, 2001. / Includes bibliographical references (leaves 192-211).

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 72-79). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 72-79). Also available on the Internet.