Master of Science / Department of Biology / John M. Briggs / Woody encroachment has altered the vegetative structure of grasslands worldwide and represents a potentially irreversible shift in grassland dynamics and biodiversity. Clonal woody species appear to be one of the greatest contributors to the shift from graminoid to woody dominance in the tallgrass prairie. Part of the high success rate of clonal species may be attributed to an ability to circumvent recruitment filters through the integration of environmental heterogeneity and acropetal translocation of resources from mother to daughter ramets. The clonal shrub Cornus drummondii persists in a tension zone of the graminoid-dominated tallgrass prairie, where the dominance structure is primarily maintained through the direct and indirect effects of fire. The competitive displacement of native herbaceous vegetation associated with the establishment and expansion of C. drummondii causes a major alteration in the fuel dynamics responsible for the propagation and sustainment of fire, potentially contributing to biofeedback mechanisms that facilitate shrub expansion. The goal of this research was to quantify fire behavior parameters (temperature, intensity, rate of spread, and heat flux) in relation to C. drummondii invasions and to test physiological integration as a mechanism driving encroachment, using manipulation experiments at the Konza Prairie Biological Station. We observed a significant decrease in fireline intensity associated with the encroachment of C. drummondii, which was amplified by the effects of stem density and shrub island area. This alteration in fire behavior also led to reduced heat flux at stems within shrub islands, reducing the likelihood of tissue necrosis and top-kill. With additional fuel, temperatures and fire intensities were higher, similar to open grasslands. In severing rhizomes, and effectively severing the integration of clonal ramets, we observed a higher risk of mortality of daughter ramets. These rhizome severed ramets were more water stressed, had lower photosynthetic rates, and lower woody and foliar biomass production. These results indicate that C. drummondii significantly alters fire behavior, releasing ramets from the fire trap of successive top-killing, while the integration of intraclonal ramets allows daughter ramets to survive mid-summer drought and increases the likelihood of successful establishment and further clonal reproduction.

Sexual selection drives the evolution of male morphology, life history, physiology, and behaviour across taxa. Here I examine the mechanisms of sexual selection that arise at various stages in mating interactions to identify congruence or conflict between the traits selected by choice and competition. I first examine plasticity of developing male Australian redback spiders (Latrodectus hasselti) and show that male metabolic rates vary adaptively to facilitate the scramble to reach virgins. Next, I show that females cease sex pheromone production after mating and re-advertise receptivity later in their reproductive season effectively creating two windows in which males may compete. I show that females discriminate against males that do not meet a threshold courtship duration suggesting that courtship is the trait selected through choice. However, male-male competition leads to reductions in courtship effort provided to females. During the first window paternity is split equally if rival males mate in quick succession with a virgin female. However, if the second mating is delayed, there is a strong bias in the paternity of the second male. A delay in the second mating is beneficial to females as it reduces longevity costs of polyandry. However, delays in the initial mating decrease female longevity, likely because of elevated metabolic rates of virgins. My research shows that the trait favoured by female choice is in opposition to selection via male-male competition. Females’ sex pheromone production yields windows during which mating will optimize female, but not male, fitness. Studies that isolate the mechanisms of sexual selection are valuable in that they can identify the traits under selection. However, my research shows that considering these processes in isolation can lead to incorrect inferences about the net effect of sexual selection.

Genomic organization of the major histocompatibility complex (MHC) can profoundly influence gene function and multigene family evolution. Situated at the interface of individual genetic variation and the adaptive immune response, MHC class I and II loci are intensively studied for disease associations and used as markers of adaptive genetic variation in evolutionary ecology research. Genomic sequence of MHC-containing cosmid clones from the red-billed gull (Larus scopulinus, Charadriiformes: shorebirds, gulls, and allies) was obtained for comparative analysis of avian MHC evolution. MHCI polymorphism was further investigated using cDNA library screening and locus-specific genotyping protocols. This first information regarding MHC organization and MHCI variation in charadriiforms suggests a complex evolutionary history to MHC architecture in birds. Duplication of MHCIIα loci in tandem MHCIIα/β pairs and their proximity to MHC-region gene COL11A2 are similar to arrangements in nonavian vertebrates, and contrast with the “minimal essential” MHC of the chicken (Gallus gallus, Galliformes: gamebirds). MHCI–TAP2 organization is shared with Galloanserae (gamebirds + waterfowl), as is a proposed major classical function for this MHCI gene. In contrast, the placement of MHCI genes adjacent to sequence from chromosomes 3, 5, and 22 of the chicken and zebra finch (Taeniopygia guttata, Passeriformes: perching birds) indicates interchromosomal rearrangements in birds and the possible genomic dispersal of nonclassical MHCI genes in the red-billed gull. Screening for avian malaria, genetic parentage tests, and field data from red-billed gulls at Kaikoura Peninsula, New Zealand were combined with MHCI genotypes to investigate relationships with disease and reproduction. Plasmodium infection was confirmed in red-billed gulls, and breeding condition was negatively associated with malarial infection and positively related to variation at the putative major MHCI locus. A low rate of extrapair paternity was identified across thirteen breeding seasons. Partners without extrapair young (EPY) had greater MHCI dissimilarity than was expected by chance, whereas lower individual MHCI variation and elevated hatching failure existed for pairs with EPY. In addition to contributing to studies of MHC evolution, sexual selection, and disease dynamics in the New Zealand avifauna, this research will facilitate studies of MHC genes in related charadriiforms, many of which are of conservation concern.

The flyingfishes (Teleostei: Exocoetidae) are a family of 53 epipelagic marine species distributed throughout tropical and subtropical surface waters. They form a key mid-trophic link between zooplankton and predators, and have evolved special adaptations to survive in the open ocean. However, little is known about their basic evolutionary history and ecology. Here, I apply a multidisciplinary approach to better understand the evolution and ecology of flyingfishes. I propose the first species-level phylogenetic hypothesis for the group, based on nuclear and mtDNA sequences, and show that the most speciose genus (Cheilopogon) is paraphyletic. Gliding evolved progressively from two- to four-wing strategies, and habitat preference is correlated with species range size. I also analyzed patterns of genetic diversity within the most abundant genus, Exocoetus, and found no evidence of cryptic species. Instead, I found that this genus likely consists of three genetically distinct species (in contrast to the five currently recognized) and two indistinct species that diverged very recently. Population genetic analysis of Exocoetus volitans (266 samples from 97 localities) indicates a single, circum-tropical population that is well connected; yet the Isthmus of Panama and an Equatorial barrier limit gene flow. Finally, I investigated species abundance, richness, diversity, and distributions within the eastern tropical Pacific Ocean (11,125 specimens). My results provide critical updates on species distributions and habitat preferences. Predictive modeling indicates that sea surface temperature is important for defining flyingfish habitat. This thesis addresses central issues concerning both evolution and ecology in the epipelagic zone, and highlights the need for better understanding remote marine regions and organisms.

Immune thrombocytopenic purpura (ITP) is an autoimmune disease characterized by autoantibody-mediated platelet destruction. To test the efficacy of novel sulfur compounds as alternative treatments for ITP, we used a mouse model of passive immune thrombocytopenia (PIT). Using this model, the platelet nadir could not be maintained, with platelet counts rising after day 4, despite daily anti-platelet antibody administration. We examined reticulated platelet counts by flow cytometry, and found increased thrombopoiesis in the bone marrow to be at least partially responsible for this platelet rebound. Consequentially, two improved mouse models of PIT were developed, where the platelet rebound is circumvented. The first model employs sublethal total body gamma-irradiation in combination with daily antibody administration, while the second model employs gradual escalation of the daily antibody dose. Finally, we show that none of the tested candidate compounds show efficacy in elevating platelet counts in vivo, likely due to their limited solubility.

Analysis of the genome of Anabaena sp. PCC7120 reveals that it lacks the gene, ccaA, which encodes the bonafide carboxysomal, β-class carbonic anhydrase (CA) CcaA. However, the carboxysome enriched fraction of Anabaena PCC7120 exhibits CA activity. Bioinformatic analysis reveals that the N-terminal region of the carboxysome protein CcmM has high sequence and structural similarity to the γ-class CA of Methanosarcina thermophila. Recombinantly expressed CcmM is found to be inactive in in-vitro CA assays. E. coli cell extracts containing an overexpressed form of CcmM comprised of the N-terminal 209 amino acids (CcmM209) are also inactive. However, CcmM209 displays CA activity after incubation with the thiol oxidizing agent diamide or when bound to an affinity matrix. It appears that CcmM is indeed a functional γ-CA which is active under oxidizing condition. It is hypothesized that the C-terminal RbcS like domain in CcmM may regulate activity by allowing CcmM activation only when sequestered within the carboxysome.

Starch-derived bioplastics are an inexpensive, renewable and environmentally-friendly alternative to traditional petroleum-based plastics. Proteins secreted by Ophiostoma ulmi, were investigated for their application in bioplastic product. Proteins were isolated from fungal cultures by anion exchange chromatography and used to treat starch. Subsequently, plastic films were generated by solution casting, with glycerol as plasticizer. Tensile strength of the films was found to increase significantly compared to the control. The relative water holding capacity of the treated starch also decreased dramatically. Attempts to identify fungal proteins by MALDI-TOF MS/MS did not result in positive matches, mainly due to lack of fungal sequence information. Additionally, the effect of non-specific proteins resulted in a modest increase in tensile strength and a slightly greater effect on water absorption. Proteins secreted by O. ulmi were therefore implicated in improving properties of starch-based plastics. Investigation into the role of an extracellular polysaccharide is also suggested.

Rosiglitazone (RSG) is an insulin-sensitizing drug used to treat Type 2 Diabetes Mellitus (T2DM). Clinical trials show that women taking RSG experience more limb fractures than patients taking other T2DM drugs. The purpose of this study is to understand how RSG (3mg/kg/day and 10mg/kg/day) and the bisphosphonate alendronate (0.7mg/kg/week) alter bone quality in the male, female and female ovariectomized (OVX) Zucker fatty rat model over a 12 week period. Bone quality was evaluated by mechanical testing of cortical and trabecular bone. Microarchitecture, bone mineral density (BMD), cortical bone porosity, bone formation/resorption and mineralization were also measured. Female OVX RSG10mg/kg rats had significantly lower vertebral BMD and compromised trabecular architecture versus OVX controls. Increased cortical porosity and decreased mechanical properties occurred in these rats. ALN treatment prevented these negative effects in the OVX RSG model. Evidence of reduced bone formation and excess bone resorption was detected in female RSG-treated rats.

In an attempt to identify agents that specifically target neuroblastoma (NB) tumour-initiating cells (TIC) we performed drug screens using libraries of bioactive compounds. Cardiac glycosides (CGs) were the largest class of drugs identified with antitumour activity. At high CG doses inhibitory effects on the Na+/K+-ATPase induce cardiotoxicity; therefore, CG analogues were designed in an attempt to separate the effects on NB cells from cardiotoxicity. We identified RIDK34 as our lead compound from a structure-activity-relationship analysis (IC50 8 nM). RIDK34 contains a unique oxime group and shows increasing potency against NB TICs. The Na+/K+-ATPase is a target for the apoptotic activity of digoxin and RIDK34, whereby a signaling cascade involving Src and ERK may induce apoptosis. Furthermore, we predict that signaling activation does not require inactivation of the Na+/K+-ATPase and subsequent deregulation of [Na+]i and [K+]I gradients. Thus CGs and particularly RIDK34 may be expected to display diminished cardiotoxicity and greater therapeutic potential.

Gastrulation is a highly complex series of cellular rearrangements that leads to the internalization of the mesoderm and endoderm. The cellular behaviors that underlie morphogenesis are dependent upon changes in cell motility and polarity. Eph receptors belong to a family of receptor tyrosine kinases that are involved in a variety of developmental processes. This study is the first to examine the role EphA4 during Xenopus gastrulation. Morpholino oligonucleotide (MO) mediated knockdown of EphA4 resulted in attenuated mesoderm involution and reduced the expression of the posterior mesoderm marker brachyury (Xbra). Expression of EphA4 in the blastocoel roof was sufficient to promote ectopic Xbra expression. I show that EphA4 can regulate Xbra expression and involution movements by signaling through PAK1. Temporal regulation of Xbra was sufficent to rescue EphA4 induced gastrulation defects. This study has uncovered a novel EphA4/PAK1 pathway which is required for mesoderm involution and Xbra expression during Xenopus gastrulation.