Optimal Foraging By Bacteriophages Through Host Avoidance

Optimal foraging theory explains diet restriction as an adaptation to best utilize an array of foods differing in quality, the poorest items not worth the lost opportunity of finding better ones. Although optimal foraging has traditionally been applied to animal behavior, the model is easily applied to viral host range, which is genetically determined. The usual perspective for bacteriophages ( bacterial viruses) is that expanding host range is always advantageous if fitness on former hosts is not compromised. However, foraging theory identifies conditions favoring avoidance of poor hosts even if larger host ranges have no intrinsic costs. Bacteriophage T7 rapidly evolved to discriminate among different Escherichia coli strains when one host strain was engineered to kill infecting phages but the other remained productive. After modifying bacteria to yield more subtle fitness effects on T7, we tested qualitative predictions of optimal foraging theory by competing broad and narrow host range phages against each other. Consistent with the foraging model, diet restriction was favored when good hosts were common or there was a large difference in host quality. Contrary to the model, the direction of selection was affected by the density of poor hosts because being able to discriminate was costly.Integrative Biolog

Management Strategies for Beef Heifer Development

Four experiments were conducted to determine the impact of development systems, trace mineral source, and trace mineral supplementation on beef heifers. Experiment 1 utilized 300 Angus-based, spring-born heifers to evaluate postweaning heifer development systems on gain, reproductive performance, and feed efficiency as a pregnant heifer. Heifers were blocked by BW and randomly assigned to graze corn residue, upland range, or were fed 1 of 2 diets in a drylot differing in energy levels: high or low. Heifer development system did not impact AI or final pregnancy rates. Development cost per pregnant heifer was not different among treatments. Furthermore, pregnant heifer feed efficiency was not impacted by development system. In Experiment 2, March-born and May-born crossbred heifers were stratified by BW and randomly assigned to 1 of 2 postweaning treatments from mid-January to mid-April: (1) ad libitum meadow hay and 1.64 kg/d of a 32% CP supplement (HAY) or (2) grazed meadow and 0.41 kg/d of supplement (MDW). March and May-born HAY heifers experienced greater ADG during the treatment period. During the summer period, however, MDW heifers had greater ADG than HAY heifers, likely due to compensatory gain. Heifer development system did not impact pregnancy rate in the March or May replacement heifers; however, March-born heifer pregnancy rate was greater than May-born. The lower pregnancy rate in May heifers may be due to declining forage quality during the late-summer breeding season. In Experiment 3, heifers were synchronized with a 14-d CIDR-prostaglandin F2α protocol and either injected with a trace mineral or received no injection at CIDR insertion. Prior to synchronization, heifers were range developed and offered free-choice mineral. Mineral status prior to mineral treatment did not differ among heifers. The proportion of heifers pregnant within the first 21 d and 33 d of the breeding season was not different nor was overall pregnancy rates. In summary, injectable trace mineral at CIDR insertion 33 d before artificial insemination did not influence reproductive performance in heifers with adequate trace mineral status. In a final study, beef heifers previously managed on 3 separate development systems were stratified by previous development treatment and BW and allocated into 1 of 8 pens per yr. Pens were randomly assigned to 1 of 2 mineral sources, hydroxy (HD) or sulfate (CON). Mineral status was analyzed via two liver biopsies prior to and following the 68-d mineral treatment. Heifer BW, ADG, and reproductive performance was not different in heifers receiving either mineral source treatments. Mineral source treatment did not affect final Mn or Zn concentrations. Liver Cu concentrations were greater for CON than HD heifers at the end of the trace mineral trial; however, all heifers maintained adequate status throughout the study. The difference in Cu status may be due to ruminally insoluble hydroxy Cu allowing thiomolybdate absorption, thus reducing hepatic Cu stores and resulting in decreased Cu status. Advisors: Rick N. Funston and Andrea S. Cup

Page 10, Last Photo

Black and white photograph of the end of the list of names in the previous photo, along with the last photo of Jose Cantu.https://scholarworks.utrgv.edu/kbormemorialalbum/1009/thumbnail.jp

Page 08, Funeral

Black and white photographs of Jose Cantu\u27s funeral.https://scholarworks.utrgv.edu/kbormemorialalbum/1007/thumbnail.jp

Page 02, Programa Popular

Black and white photographs of Programa Popular Christmas event.https://scholarworks.utrgv.edu/kbormemorialalbum/1001/thumbnail.jp

Page 01, Cover

Color photograph of the front and back covers of the album.https://scholarworks.utrgv.edu/kbormemorialalbum/1000/thumbnail.jp

Mechanical and Chemical Effects in Adhesion of Thin Shell Structures with Applications in Wafer Bonding and Adhesion of Living Cells

A theoretical model is analyzed to investigate the adhesion of thin shell structures to both rigid and deformable substrates under a variety of surface conditions. The thermodynamic forces driving the adhesive process are determined from an interfacial free energy, which is described within a classical thermodynamics framework. Deformations of the thin, elastic shells are studied using a geometrically nonlinear shell theory. Finite-range adhesive tractions, chemical segregation, substrate compliance, and substrate topography all are considered over a wide range of geometric and material parameters. Equilibrium adhesion states are characterized by a shell flatness parameter, the contact radius, and the adhesive and elastic energies. The nonlinear, coupled differential equations governing mechanical and chemical equilibrium are studied using finite differences and numerical continuation methods. The analysis has applications in wafer bonding and the adhesion of living cells