Assembly of branched actin filaments produces dynamic structures required during membrane associated processes including cell motility and endocytosis. The Actin Related Protein 2/3 (Arp2/3) complex is the only known regulator capable of nucleating actin branches. To specify the sub cellular localization and timing of actin assembly the complex is tightly regulated. Canonical activation of the Arp2/3 complex by Wiskott-Aldrich Syndrome proteins (WASP), requires preformed actin filaments, ensuring the complex nucleates new actin filaments off the sides of preformed filaments. WASP proteins can therefore propagate branch formation but cannot initiate a Y-branch without performed filaments. A key question, then, is what is the source of preformed filaments that seed branched actin network formation in cells? It is unclear how activation of Arp2/3 by multiple regulators is balanced to specify actin filament architectures that are productive in vivo. In this dissertation, we identified WISH/DIP1/SPIN90 (WDS) family proteins as activators of the Arp2/3 complex that do not require preformed filaments, and evaluated whether WDS proteins seed branching nucleation. In chapter II, we dissected the biochemical properties of WDS proteins and found they activate the Arp2/3 complex using a non-WASP like mechanism. Importantly, we discovered WDS-mediated Arp2/3 activation produces linear, unbranched filaments, and this activity is conversed from yeast to mammals. These observations highlight that WDS proteins have the biochemical capacity to seed actin branches. In chapter III, we observed WDS-generated linear filaments can seed WASP-mediated branching directly using single molecule microscopy with fluorescently labeled Dip1. We find that WDS-mediated nucleation co-opts features of branching nucleation. In chapter IV, we investigated how WDS activity is balanced with WASP. We discovered WDS proteins use a single turnover mechanism to activate Arp2/3 and this is conserved during endocytosis. In contrast, WASP-mediated activation is multi-turnover, highlighting a crucial difference between WDS proteins and WASP. Our observations explain how Arp2/3 may limit linear filament production to initiate networks and favor branches during network propagation. Finally, we use fission yeast to show that increasing Dip1 is sufficient to cause defects in actin assembly and the timing of actin patches at sites of endocytosis.

A candidate protein from the venom gland of parasitoid wasp, Habrobracon hebetor, predicted to be responsible for the paralysis of lepidopteran caterpillars, was produced in baculovirus and bacterial expression systems. The function of both recombinant protein variants was confirmed by in vivo tests in Galleria mellonella larvae.

WASP-39b is a hot Saturn-mass exoplanet with a predicted clear atmosphere based on observations in the optical and infrared. Here, we complete the transmission spectrum of the atmosphere with observations in the near-infrared (NIR) over three water absorption features with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G102 (0.8-1.1 mu m) and G141 (1.1-1.7 mu m) spectroscopic grisms. We measure the predicted high-amplitude H2O feature centered at 1.4 mu m and the smaller amplitude features at 0.95 and 1.2 mu m, with a maximum water absorption amplitude of 2.4 planetary scale heights. We incorporate these new NIR measurements into previously published observational measurements to complete the transmission spectrum from 0.3 to 5 mu m. From these observed water features, combined with features in the optical and IR, we retrieve a well constrained temperature T-eq = 1030(20)(+30) K, and atmospheric metallicity 151(46) (+48) solar, which is relatively high with respect to the currently established mass-metallicity trends. This new measurement in the Saturn-mass range hints at further diversity in the planet formation process relative to our solar system giants.

We present an optical eclipse observation of the hot Jupiter WASP-12b using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. These spectra allow us to place an upper limit of A(g) < 0.064 (97.5% confidence level) on the planet's white light geometric albedo across 290-570 nm. Using six wavelength bins across the same wavelength range also produces stringent limits on the geometric albedo for all bins. However, our uncertainties in eclipse depth are similar to 40% greater than the Poisson limit and may be limited by the intrinsic variability of the Sun-like host star-the solar luminosity is known to vary at the 10(-4) level on a timescale of minutes. We use our eclipse depth limits to test two previously suggested atmospheric models for this planet: Mie scattering from an aluminum-oxide haze or cloud-free Rayleigh scattering. Our stringent nondetection rules out both models and is consistent with thermal emission plus weak Rayleigh scattering from atomic hydrogen and helium. Our results are in stark contrast with those for the much cooler HD 189733b, the only other hot Jupiter with spectrally resolved reflected light observations; those data showed an increase in albedo with decreasing wavelength. The fact that the first two exoplanets with optical albedo spectra exhibit significant differences demonstrates the importance of spectrally resolved reflected light observations and highlights the great diversity among hot Jupiters.

The determination of atmospheric structure and molecular abundances of planetary atmospheres via spectroscopy involves direct comparisons between models and data. While varying in sophistication, most model spectra comparisons fundamentally assume one-dimensional (1D) model physics. However, knowledge from general circulation models and of solar system planets suggests that planetary atmospheres are inherently three-dimensional in their structure and composition. We explore the potential biases resulting from standard "1D" assumptions within a Bayesian atmospheric retrieval framework. Specifically, we show how the assumption of a single 1D thermal profile can bias our interpretation of the thermal emission spectrum of a hot Jupiter atmosphere that is composed of two thermal profiles. We retrieve spectra of unresolved model planets as observed with a combination of the Hubble Space Telescope Wide Field Camera 3 (WFC3)+Spitzer Infrared Array Camera (IRAC) as well as the James Webb Space Telescope (JWST) under varying differences in the two thermal profiles. For WFC3+IRAC, there is a significantly biased estimate of CH4 abundance using a 1D model when the contrast is 80%. For JWST, two thermal profiles are required to adequately interpret the data and estimate the abundances when contrast is greater than 40%. We also apply this preliminary concept to the recent WFC3+IRAC phase curve data of the hot Jupiter WASP-43b. We see similar behavior as present in our simulated data: while the H2O abundance determination is robust, CH4 is artificially well-constrained to incorrect values under the 1D assumption. Our work demonstrates the need to evaluate model assumptions in order to extract meaningful constraints from atmospheric spectra and motivates exploration of optimal observational setups.

Mating system, mating behavior and the evolution thereof is the foundation of this study. More specifically the effect of inbreeding on the evolution of mating behavior is investigated. To this end the pollinating fig wasp, Platyscapa awekei, lends itself to inquiry about inbreeding and the effect on its behavior. A pollinating fig wasp female will lay her eggs inside a syconium, and all offspring will mate with each other. Interestingly the abovementioned pollinating wasp exhibits male dispersal, not commonly expected to occur in a haplodiploid species observed to inbreed frequently. Several theories attempt to explain the evolution of male dispersal in this case, but very little work has been done on the effect of inbreeding on the choice to disperse. In order to study the effects of inbreeding it was necessary to be able to measure the inbredness of individuals. For this reason I developed micro satellite markers both to determine the inbredness of individuals but also to derive parentage from offspring genotypes. With the inbreeding status in hand I had to correlate this with fitness measures in order to derive the effect of inbreeding on this species. Interestingly I found both inbreeding and outbreeding depression, with optimal fitness at some point between fully inbred and fully outbred status. I give some explanations for the occurrence of dispersal in this species but come to the conclusion that dispersal is merely part of a mixed mating system and that more detailed work need to be done to derive what the specific effect of dispersal is on fitness. / Dissertation (MSc(Agric))--University of Pretoria, 2009. / Genetics / unrestricted

The behaviour of sex allocation has been extensively studied in hymenopterans (ants, bees and wasps) as an adaptive trait with respect to intra-specific competition within the framework of kin selection theory. Mating in these organisms often takes place in patchy populations established by the offspring of a few foundresses. Typically, there is a bias in favour of female dispersal from these patches. Theory predicts that foundresses that oviposit alone will do best to produce just enough sons to mate all of their daughters so as to maximize the number of dispersing daughters, under conditions of what is referred to as Local Mate Competition (LMC) between brothers to mate their sisters. If foundresses co-found a patch with other foundresses, they are expected to invest more resources in sons insofar as opportunity to sire offspring with the daughters of the other foundresses presents itself. Among organisms with such a life histories are fig wasps, the insects that pollinate and lay their eggs in the flowers that grow inside young figs. There is thought to be strong selective pressure for foundresses to use information about clutch size differences in species where clutch sizes are small and low foundress numbers are frequently encountered. However, less rigorous modes of sex allocation are thought to suffice in species encountering intermediate foundress numbers. Theory thus predicts a positive relationship between the degree of structure within mating populations and the information utilized by foundresses with respect to intra-specific competition for resources and mating opportunities. This is being extensively tested across the diverse species range of fig wasps and their hosts with the larger objective in mind of contributing to a better understanding of the role of natural selection in accounting for variation observed of intra-specific behaviour. This dissertation reports on a study of the sex allocation behaviour of the pollinating fig wasp Platyscapa awekei, a species characterized by low foundress numbers and clutch size differences brought about by foundress competition over oviposition sites. Offspring collected from experimentally controlled twofoundress broods were fingerprinted using microsatellite genetic markers to assign maternity and work out clutch size differences. These data are used to test what information foundresses use when allocating sex. It is reported that foundresses appear to use information of clutch size differences in two foundress broods. This observation provides evidence of advanced information utilization in fig wasps. More generally, the findings add support to the hypothesis that natural selection can bring about subtle adaptive behaviour at the individual level, but simultaneously highlights the importance of accounting for the selective regime of the organism being studied when attempting to understand the role of natural selection in the evolution of fine scale adaptive traits. / Dissertation (MSc)--University of Pretoria, 2011. / Genetics / unrestricted

This report analyses accuracy of wind speed predictions using wind atlases for the application of wind farm project development. The report aims to compare publicly available New European Wind Atlas (NEWA) mesoscale model data with the NEWA microscale model data. Later, NEWA microscale predictions are checked with manual WindPro WAsP calculations, which use real wind statistics. 9 locations (3 surface roughness types and 3 distances to Baltic coast) are examined. The results show three key-findings: first, the NEWA mesoscale and microscale models are most consistent in coastal open-field locations. Second, NEWA microscale model is most consistent with WindPro WAsP calculations in coastal and mid-coastal forested areas. Lastly, WindPro WAsP calculations significantly reduced wind speed estimates for in-land locations.

The effects of food quantity on the morphology and development of the paper wasp Polistes metricus Say are studied, and experimental results are compared with predictions of the parental manipulation hypothesis. Food deprivation led to smaller female offspring. By hand feeding larvae we used a technique that counteracts the queen's hypothesized ability to restrict food provisioning. Hand feeding larvae did not result in larger offspring, but their abdomen was wider and heavier and the hand-fed wasps survived longer in a cold test. We infer that hand-fed colonies produced more gynes and fewer workers than did control colonies. Results of a restricted nourishment treatment do not support the differential feeding hypothesis, because in fasting colonies the emergence of all larvae was delayed by a month, and we did not detect discriminatory feeding of particular larvae for faster emergence. Although fasting colonies produced fewer offspring, the sex ratio did not show significant differences from the other groups. These data suggest that Polistes metricus colonies are partly able to respond to different nutritional conditions by allocating excess food to increase the number of gynes at the expense of workers.

No description available.