Leaf-cutter Ant (\u3ci\u3eAtta cephalotes\u3c/i\u3e) Behavioral Ecology of Folivory in a Mixed-use Guyanan Lowland Rainforest

I studied the foraging ecology of a Neotropical leaf-cutter ant, Atta cephalotes, at CEIBA Biological Center, Guyana to elucidate diet choice and foraging strategy. These ants are serous agricultural pests because workers harvest leaves, flowers, fruits, and other plant organs of both cultivated and native plants. The plant materials are used to feed symbiotic fungi whose mycelia tips are the sole food of A. cephalotes larvae. Leaf-cutters were usually found in human disturbed habitats especially slash-and-burned forests cleared for farms, with their higher percentage of sun-exposure and lower plant stem diameters than second growth and primary forests. When given a choice of cultivated and wild plant leaves offered in a randomized smorgasbord test, leaf-cutters accepted significantly more cultivar leaves. These had lower concentrations of secondary compounds than wild plant leaves. In addition, leaf fragment size and thickness transported by returning foragers were related to the foragers’ body length, such that longer ants carried longer and thicker fragments compared to smaller ants. However, there was no relationship between travel distance to the nest and load size, recruitment and returning forager counts, or preference for cultivated plants as predicted by central place foraging theory. In summary, leaf-cutter ants at CEIBA Biological Center were found in human altered forest habitats, exhibited preferences for cultivated over wild plant organs, and did not conform to predictions of central place theory. Therefore, findings have implications for leaf-cutter ant behavioral ecology and agricultural management

QUALITATIVE CHEMICAL ANALYSIS OF INORGANIC SUBSTANCES AS PRACTICED IN GEORGETOWN COLLEGE, D. C. Pp. 61.

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The 4-Nitro-5-Methyl-2-Sulphobenzoic Acid and Some of Its Derivatives

The 4-nitro-5-methyl-2-sulphobenzoic acid has been investigated to a limited extent as one of the products formed when the 6-nitro-1, 3-dimethyl-4-sulphonic acid is oxidized by potassium permanganate in dilute alkaline solution. Previous to this research, the only record of its preparation was by Limpricht, in which case only a small amount of the neutral potassium salt was isolated. He gives this as occurring with one-half a molecule of water of crystallization, but does not state which of the two methyl groups of the original acid had been oxidized. The neutral potassium salt does not seem to contain any water of crystallization, however, and some doubt is cast upon the value of the observation as made by him

Liquid general anesthetics lower critical temperatures in plasma membrane vesicles

A large and diverse array of small hydrophobic molecules induce general anesthesia. Their efficacy as anesthetics has been shown to correlate both with their affinity for a hydrophobic environment and with their potency in inhibiting certain ligand gated ion channels. Here we explore the effects that n-alcohols and other liquid anesthetics have on the two-dimensional miscibility critical point observed in cell derived giant plasma membrane vesicles (GPMVs). We show that anesthetics depress the critical temperature (Tc) of these GPMVs without strongly altering the ratio of the two liquid phases found below Tc. The magnitude of this affect is consistent across n-alcohols when their concentration is rescaled by the median anesthetic concentration (AC50) for tadpole anesthesia, but not when plotted against the overall concentration in solution. At AC50 we see a 4{\deg}C downward shift in Tc, much larger than is typically seen in the main chain transition at these anesthetic concentrations. GPMV miscibility critical temperatures are also lowered to a similar extent by propofol, phenylethanol, and isopropanol when added at anesthetic concentrations, but not by tetradecanol or 2,6 diterbutylphenol, two structural analogs of general anesthetics that are hydrophobic but have no anesthetic potency. We propose that liquid general anesthetics provide an experimental tool for lowering critical temperatures in plasma membranes of intact cells, which we predict will reduce lipid-mediated heterogeneity in a way that is complimentary to increasing or decreasing cholesterol. Also, several possible implications of our results are discussed in the context of current models of anesthetic action on ligand gated ion channels.Comment: 16 pages, 6 figure

Invited Review Meeting Report: SMART Timing-Principles of Single Molecule Techniques Course at the University of Michigan 2014

ABSTRACT: Four days after the announcement of the 2014 Nobe

Uncovering Hidden Dynamics in Living Systems Using Bayesian Statistics and Single-Molecule Microscopy

Fluorescence microscopy is a powerful technique for understanding the organization, structure and dynamics of cells. Single-molecule imaging techniques extend our ability to probe cellular systems down to a range of only a few tens of nanometers. Observing the motion of single molecules inside living cells and tracking their behavior can give insight into the native biochemical and biophysical environment of the molecule. If certain conditions, such as the cell being in equilibrium, are met, we can relate the motion observed to the functional role of the molecule. However, biological systems are complex and single-molecule data can be noisy, so care must be taken when analyzing single-particle tracking data sets such that supervisory biases and other external constraints are not placed on the analysis. In this Thesis, I present my work on expanding the scope and quality of single-particle tracking analysis and, using this new method, present my investigations of the dynamics involved in several complex biological questions in both prokaryotes and eukaryotes. Chapter 2 proposes a new analysis method for single-particle tracking data based on a nonparametric Bayesian statistical framework that we call SMAUG. The accuracy and precision of this method, as well as its ability to uncover the true dynamics, is investigated using realistic simulations and in vitro experimental systems. This new method increases the information available from tracking experiments while not sacrificing accuracy or precision, thus allowing for more rigorous conclusions. In addition, this method is also applied to in vivo data from two relevant biological systems and the analysis identifies potential biological roles for the uncovered diffusive states. Chapter 2 demonstrates a method for improving the scope of single-molecule analysis by introducing a new analysis framework that increases the information available. Differential gene expression patterns are the basis of cellular biology. The markers that modulate which genes are active and which are silenced are called epigenetic markers. In Chapter 3, I use single-particle tracking and the SMAUG algorithm to investigate the dynamics behind epigenetic silencing in a fission yeast model system and uncover the hidden complexity of the system. I present the dynamics uncovered for the key protein in the pathway, Swi6, in otherwise wild-type cells. This measurement resolves four distinct biochemical states. Then, using targeted mutation studies, I investigate and assign a biological role to each of the four identified states, and I uncover the impact that DNA compaction has upon the system. Overall, my application of single-particle tracking and SMAUG analysis to this system provides an example of expanding the scope of single-particle imaging techniques to complex systems and using the information obtained to gain biological insight. Bacterial virulence is a complex pathway that requires precise timing and organization of the proteins involved to effect a response. In Chapter 4, I present my investigations deeper into the dynamics of Vibrio cholerae bacterial. I found three distinct biological states for the keystone protein, TcpP , in otherwise wild-type cells. Using mutation studies, I present the biological roles for the states uncovered and discuss future investigations into the system using more mutation studies. The work presented in this Thesis will have broad impact on the fields of biophysics and cell biology by expanding the scope and quality of the information gathered of single-particle tracking experiments and by answering specific questions about the dynamics of several biological pathways.PHDBiophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/151620/1/joshkars_1.pd