Agroecosystems produce insects in great abundance, with episodic irruptions in time, and patchy distributions in space. In the industrial scale agroecosystems of south-central Texas, millions of Brazilian free-tailed bats (Tadarida brasiliensis) consume these insect pests. In the past decade, growers in Texas have planted transgenic Bt (Bacillus thuringiensis) crops on a large scale, which may reduce populations of target insect species by up to 95%. To investigate potential impacts of this evolving agricultural landscape on insectivorous bats, I examined the response of foraging bats to emergences of insects from replicate Bt and non-Bt fields of corn and cotton in the Winter Garden region of south-central Texas. I quantified bat activity using ultrasonic detectors deployed simultaneously in Bt and non-Bt fields. I measured insect activity using pheromone traps and video imaging. Professional crop consultants scouted fields to determine dates of insect emergence. We recorded 92% more echolocation calls, 62% more AnaBat files, and 257% more feeding buzzes over agricultural fields during periods of local insect emergence. During these insect emergence periods, bat activity was correlated with the abundance of moths and negatively related to the distance between foraging sites and roosting sites. In general, Bt crops did not have a measurable impact on the activity of bats except at one site where moths were more abundant over non-Bt crops versus Bt crops. Foraging bats showed a delayed response to moth abundance, which is consistent with the hypothesis that roosts serve as information centers that enhance foraging efficiency. The ability of millions of bats to exploit localized patches of prey across a large area provides further evidence of their pest control service. This economically important pest control service extends beyond growers in Texas, as the populations of moths produced in agroecosystems in Texas influence agricultural production on a continental scale.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 176-213). Also available in print.

Similar forces of selection operating on multiple taxa can cause convergent evolution of quantitative traits. When those same forces of selection occur across an environmental gradient a phenotypic cline may evolve. I have conducted an experiment in central Texas to test whether seed oil melting points and proportions of saturated fatty acids have repeatedly evolved to germinate as predicted by theory. Species with lower seed oil melting points and proportions of saturated fatty acids are expected to germinate at cooler temperatures than ones that germinate at warmer temperatures. Field observations were conducted at two sites for one year to characterize germination temperatures of sixteen species. Gas chromatography was utilized to describe the fatty acid compositions and melting points of those species’ triacylglycerol (oil) stores. The field sites produced conflicting results. At one site, all analyses supported the theory. Whereas evidence from the other site either contradicted expectation or was equivocal. Likewise there was some evidence that plants with annual life histories are under stronger selection to evolve melting points that approximate germination temperature than species with perennial life histories. Finally, evidence was found that a higher level of variation in seed oil melting point and percent of saturated fatty acids is maintained in species that were observed to germinate at low temperatures relative to species observed to germinate at higher temperatures. / text

Not available / text

The ability of traits to adapt in response to change is one of the most fundamental aspects of evolution. Optimality models used to predict adaptation frequently make simplifying assumptions about the ability of traits to evolve freely within simple tradeoffs. However, we frequently have little understanding of genomic mechanisms underlying phenotypic evolution. Genetic constraints clearly limit phenotypic change, but the extent to which they do so is unclear. I will explore molecular and phenotypic responses to genomic and environmental perturbations through experimental evolution in T7 bacteriophage. First, I studied evolutionary robustness of the lysis time phenotype when lysin gene lysozyme was deleted. This deletion profoundly delayed lysis and thus decreased fitness. Evolved phages recovered much of the lost fitness and mostly restored lysis timing. The recovery was mediated by changes in a tail fiber gene (gene 16) with muralytic activity that is generally used in genome entry. Next, I extended the work on lysozyme to observe the effect of increasing constraint on evolutionary recovery. The effects of various combinations of deletions of lysozyme, 17.5 (which plays a role in lysis) and 16 suggested that another gene played a role similar to 17.5 in lysis. The phage defective in both lysozyme and 16 did not lyse hosts thoroughly even after long periods of infection, suggesting that these were the only effective lysin genes. Adaptation of this phage on cells expressing the essential gp16 constrained the primary adaptive pathway of recovery from lysozyme deletion. A mutually exclusive alternative pathway involving a variety of different genes evolved. The line recovered the ability to lyse normal hosts, by a mechanism involving multiple mutations. Finally, I tested the ability of T7 to adapt to an optimum lysis time. Based on empirical results from other phages, mature phage virions accumulate linearly inside the cell over time. This assumption underlies a model suggesting that availability of hosts determines optimal lysis time. While adaptation to different host densities caused the expected qualitative evolutionary changes, adaptation to conditions expected to select for slow lysis did not lead to the quantitative optimum. This is probably due to nonlinear virion accumulation.

The discoglossoid Frogs (Discoglossidae and Leiopelmatidae) are generally considered to be the most primitive of the living frogs. Previous authors have grouped them on the basis of common possession of a limited number of primitive features of little phylogenetic significance, leaving the question of intra-discoglossoid relationships uncertain. The present study is a re-examination df the supraspecific relationships in the superfamily using computer-aided cladistic analyses of a large set of osteological data - specifically 95 characters (153 binary characters) in 21 modern discoglossoid taxa. Where possible, characters are assigned a polarity, principally using urodeles as the outgroup. Evolutionary relationships are inferred from the congruence of cladograms generated from compatibility and parsimony analyses of the data set. In an introductory section, modern approaches to systematic analysis and classification are reviewed and a justification for the chosen method is provided. The concepts of natural taxa and natural classifications are discussed, criteria for hypothesizing character polarities and accounts of compatibility and parsimony analysis methods are given • •A. remarkable degree of congruence' between the cladograms produced from a Le Quesne compatibility analysis and a Wagner parsimony analysis is evident. Results suggest:- (a) The leiopelmatid genera Ascaphus and Leiopelma are a sister pair but are probably only weakly related. (b) The modern DiBcoglossidae is a monophyletic group in which Alytes is sister to Bombina + Barbourula + Discoglossus. (c)Discoglossus is sister to Bombina + Barbourula. (d)Bombina and Barbourula are a sister pair. (e)All the discoglossoid genera are monophyletic. (f)Bombina comprises two species groups: small (B. bombina - B variegata - B orientalis) and large species (B maxima and B microdeladigitora). Comparisons are made with previous work and an overview hypothesis of the historical zoogeography of the discoglossoid frogs is presented.

Effective population size is one of the fundamental parameters in many population genetic models. It provides a common currency to compare populations by reference to an analytically tractable ideally behaving population. Different values of this parameter can have very significant effects on rates and modes of evolution. Sewall Wright's shifting balance theory stresses the importance of drift interacting with selection and dispersal in the process of evolution. For this process to work requires effective deme sizes of no more than a few hundred. Errors of only one order of magnitude can seriously distort our view of the mechanisms of evolution underlying a population structure. Methods exist for dealing with some of the obvious departures from the ideal population. Natural populations seldom conform to other assumptions about population structure made to calculate effective deme size. One such assumption is that individuals are uniformly distributed over area. Much work shows that this is often far from the case. Computer simulations were used to investigate the effects of different spatial distributions of individuals, in combination with various dispersal regimes, on the scale and degree of genetic differentiation. The model consists of diploid individuals arranged according to a spatial distribution with various dispersal regimes imposed upon them. Generations are discrete and the model is allowed to run for 120 to 200 generations. Wright's F-statistics are used as one measure of genetic differentiation. F-statistics do well at reflecting the overall level of differentiation but do not give any idea of spatial structure. Spatial autocorrelation techniques are used to examine the spatial scale and temporal continuity of gene frequency differentiation. Significant effects of the spatial distribution of individuals are found that are not visible through F-statistics. Stable features on the gene frequency surfaces are found to be much larger than the calculated neighborhood sizes. Very different scales of structure can result from different distributions of individuals even though they result in similar estimates of effective deme size. I conclude that it is necessary to have detailed information on a population's structure to be able to predict the effects of genetic drift on the scale of genetic differentiation.

This thesis examines the evolutionary divergence between northern European and Italian populations of Chorthippus parallelus. Several differing approaches were taken, which identified the inception of various components of the speciation process between these parapatric populations which meet in the Alps. Firstly, partial post-zygotic reproductive isolation was demonstrated using hybrid crosses. The male hybrid offspring of both reciprocal crosses were sterile, displaying severe testicular dysfunction, while the female hybrids showed no deleterious effects of hybridisation. In this grasshopper the males are the heterogametic sex, possessing a single X chromosome, and so this pattern of hybrid sterility conforms to Haldane's rule. Secondly, investigation of the calling song of the male grasshopper, a component of the mate recognition system, suggested the presence of pre-mating reproductive isolation. Males from the different races were found to sing calling song of a significantly different structure. Finally, examination of DNA sequence divergence in a mitochondrial DNA marker demonstrated Significant levels of genetic differentiation between the races. This population divergence and incipient reproductive isolation parallels that found between the north European and Iberian populations of this grasshopper, and provides further evidence that the divergent geographical races have resulted from allopatric divergence while in isolated refugial populations during the glacial periods of the Pleistocene Epoch. These approaches were repeated to investigate genetic divergence between localised populations within the Italian peninsula. No hybrid dysfunction was observed between these populations, suggesting that they are recently derived from one continuous population. This was probably the refugial population of the last ice-age. Additionally, investigation with the mtDNA marker gave preliminary evidence for population expansion from the south to the north of Italy. Interestingly, the male calling song was Significantly different in populations from the north and the south of Italy, suggesting that a component of pre-mating reproductive isolation may have evolved prior to post-mating isolation in allopatric populations of C. parallelus.

No description available.

All animals progress through a series of functionally discrete life stages from fertilization through adulthood and often into senescence. Reproduction in the adult stage can only occur after maturation--the final life history transition during ontogeny--from juvenile to adult. Despite a robust literature that predicts the optimal body size and development time at which this transition should occur, the ontogenetic factors that are responsible for determining metamorphosis and the manner in which they are translated into the hormonal mechanisms regulating maturation remain unresolved in most species. In this dissertation, I first review the theoretical context and importance of understanding maturation from both life history and physiological/developmental perspectives. Then I review the literature that describes various ontogenetic factors thought to determine the onset of maturation in insects. Finally, I present four studies that examine two of the major hypotheses that have been proposed to explain the onset of metamorphosis in insects using Manduca sexta larvae (Lepidoptera: Sphingidae) as a model organism. In the first study, I show that physical thresholds are unlikely to be the factor that determines maturation in larval M. sexta because larval insects do not seem to be growth constrained in the manner assumed in the literature. Next, I present three chapters that examine the possibility that attainment of a resource storage threshold is the determining factor for the onset of metamorphosis. In the first of these studies, I show that there is a hemolytic factor present after metamorphic commitment that can induce precocious metamorphosis in larval M. sexta, indicating that maturation can be coordinated at least partially from developing tissues throughout the body. The following study examines resource storage during metamorphic commitment in the final larval instar of M. sexta. I show that resource storage is of critical importance during the final period of larval growth in terms of mass allocation. Even with environmentally-induced variability in resource storage, growing M. sexta appear to have a target amount of stored resources near the body weight at which metamorphic commitment occurs. Individuals reared on reduced quality diet store proportionally more resources with a higher caloric value than individuals reared on in terms of fat growth, which is consistent with a decrease in the body weight at metamorphic commitment observed in other studies. Individuals reared at different temperatures invest differently in resource storage during growth; however, resource storage content tends to converge at the critical weight, which may explain invariance of the critical weight in response to rearing temperature found in other studies. Finally, I examine resource storage in the context of allocation tradeoffs with growth and metabolic rate. I demonstrate that storage increases substantially as growth rate declines in the final larval instar of M. sexta.