Experimental Avian Botulism Studies on Sewage Oxidation Ponds in Utah

The objective of this study was to field-test the microenvironment concept of avian botulism epizootiology. The microenvironment concept hypothesizes that aquatic invertebrate carcasses may serve both as a substrate for toxin production by Clostridium botulinum type C in nature and as a vehicle for toxin transmission to waterbirds. This concept has become the generally accepted, but inadequately tested, working hypothesis of type C botulism epizootiology. This study attempted to experimentally induce type C botulism in sentinel flocks of mallard ducks (Anas platyrhynchos) and American coots (Fulica americana) on sewage oxidation ponds in northern Utah. The three experimental oxidation ponds were inoculated with Cl. botulinum type C (strain X220B2) endospores in June, 1974. Aquatic invertebrate populations were monitored throughout the summer. Rotenone was used in August in two of the experimental ponds (one pond served as a control) to kill aquatic invertebrates and thereby provide a large amount of substrate for clostridial growth and toxin production. No botulism was detected among the sentinel birds even though they routinely ingested invertebrate carcasses. None of the samples of dead invertebrates collected from the experimental ponds contained detectable (in white mice) botulinum toxin. It was concluded that the microenvironment concept, as it now stands, cannot always be a sufficient explanation of how type C botulism epizootics are initiated in nature. Microbiological experiments designed to determine why the invertebrate carcasses collected from the study ponds contained no botulinum toxin were started and are now ongoing. Early results indicate that Cl. botulinum (X220B2) cells may not normally be able to effectively compete (at least in terms of toxin production) with other microorganisms present in the sewage ponds. It is suggested that the initiation of a type C botulism epizootic in nature may require the alleviation of the inhibitory effects of other putrefactive microorganisms upon clostridial metabolism and/ or toxin. This hypothesis is highly speculative and requires much further experimentation

Nesting Ecology of The Red-Winged Blackbird in North Central Minnesota

Reproductive success of a Red-winged Blackbird population nesting in marsh-like habitat In north central Minnesota was estimated. Territorial defense by males began in late April, and nest initiation occurred from mid-May through about mid-July. Nest-starts appeared to be divided into two categories: initial attempts which occurred in late May with a high degree of synchrony, and renesting attempts which occurred from about June 4-July 8, The nesting season lasted only about two months. A minimum of 20 percent of marked females renested on the study area, and others may have renested elsewhere. Three of the six females that renested switched male territories, moving as far as 230 m. An average of 2.6 young were fledged per male territory. A shortage of water adversely affected nesting habitat and probably lowered reproductive success

The role of topology and mechanics in uniaxially growing cell networks

In biological systems, the growth of cells, tissues, and organs is influenced by mechanical cues. Locally, cell growth leads to a mechanically heterogeneous environment as cells pull and push their neighbors in a cell network. Despite this local heterogeneity, at the tissue level, the cell network is remarkably robust, as it is not easily perturbed by changes in the mechanical environment or the network connectivity. Through a network model, we relate global tissue structure (i.e. the cell network topology) and local growth mechanisms (growth laws) to the overall tissue response. Within this framework, we investigate the two main mechanical growth laws that have been proposed: stress-driven or strain-driven growth. We show that in order to create a robust and stable tissue environment, networks with predominantly series connections are naturally driven by stress-driven growth, whereas networks with predominantly parallel connections are associated with strain-driven growth

Design of a Self-Resetting, Low-Maintenance, Long-Term Bait Station for Rodent Control

A low-maintenance, long-term bait station that resets itself after being triggered would be a very useful tool for controlling Richardson’s ground squirrels, or other problem rodent species, in remote locations. With collaborators, we developed and tested two such devices using lab rats in pen settings. The devices can be left in-situ for long periods of time without servicing, and requires only occasional bait and/or battery replacement. Squirrels would be unable to cache bait due to the integrated time-out mechanism. The devices use capacitive sensor or strain gauge systems for animal identification, making it very unlikely that smaller non-target species would be able to trigger the systems while the design precludes entry by larger non-target species. Further refinement and testing will be needed before a viable, commercial product can go into production. These refinements include increasing reliability, reducing power requirements, design features and triggering mechanisms tightly linked to the attributes of the targeted pest species, and reduction of production costs. The devices will also need to be tested in field settings for extended periods of time

Blocks and Cut Vertices of the Buneman Graph

Given a set \Sg of bipartitions of some finite set $X$ of cardinality at least 2, one can associate to \Sg a canonical $X$-labeled graph \B(\Sg), called the Buneman graph. This graph has several interesting mathematical properties - for example, it is a median network and therefore an isometric subgraph of a hypercube. It is commonly used as a tool in studies of DNA sequences gathered from populations. In this paper, we present some results concerning the {\em cut vertices} of \B(\Sg), i.e., vertices whose removal disconnect the graph, as well as its {\em blocks} or 2-{\em connected components} - results that yield, in particular, an intriguing generalization of the well-known fact that \B(\Sg) is a tree if and only if any two splits in \Sg are compatible

Evidence for Skyrmion crystallization from NMR relaxation experiments

A resistively detected NMR technique was used to probe the two-dimensional electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate $(1/T_{1})$ was extracted at near complete filling of the first Landau level by electrons. The nuclear spin of $^{75}$As is found to relax much more efficiently with $T\to 0$ and when a well developed quantum Hall state with $R_{xx}\simeq 0$ occurs. The data show a remarkable correlation between the nuclear spin relaxation and localization. This suggests that the magnetic ground state near complete filling of the first Landau level may contain a lattice of topological spin texture, i.e. a Skyrmion crystal