Life Sciences Commons^™

The Ecological Importance Of Severe Wildfires: Some Like It Hot, Richard L. Hutto

Biological Sciences Faculty Publications

Many scientists and forest land managers concur that past fire suppression, grazing, and timber harvesting practices have created unnatural and unhealthy conditions in the dry, ponderosa pine forests of the western United States. Specifically, such forests are said to carry higher fuel loads and experience fires that are more severe than those that occurred historically. It remains unclear, however, how far these generalizations can be extrapolated in time and space, and how well they apply to the more mesic ponderosa pine systems and to other forest systems within the western United States. I use data on the pattern of distribution …

Ph-Induced Activation Of Arenavirus Membrane Fusion Is Antagonized By Small-Molecule Inhibitors, Joanne York, Dongcheng Dai, Sean M. Amberg, Jack H. Nunberg

Biological Sciences Faculty Publications

The arenavirus envelope glycoprotein (GPC) mediates viral entry through pH-induced membrane fusion in the endosome. This crucial process in the viral life cycle can be specifically inhibited in the New World arenaviruses by the small-molecule compound ST-294. Here, we show that ST-294 interferes with GPC-mediated membrane fusion by targeting the interaction of the G2 fusion subunit with the stable signal peptide (SSP). We demonstrate that amino acid substitutions at lysine-33 of the Junin virus SSP confer resistance to ST-294 and engender de novo sensitivity to ST-161, a chemically distinct inhibitor of the Old World Lassa fever virus. These compounds, as …

Recognition Of The Activated States Of Galpha13 By The Rgrgs Domain Of Pdzrhogef, Zhe Chen, William D. Singer, Shahab M. Danesh, Paul C. Sternweis, Stephen R. Sprang

Biological Sciences Faculty Publications

G12 class heterotrimeric G proteins stimulate RhoA activation by RGS-RhoGEFs. However, p115RhoGEF is a GTPase Activating Protein (GAP) toward Galpha13, whereas PDZRhoGEF is not. We have characterized the interaction between the PDZRhoGEF rgRGS domain (PRG-rgRGS) and the alpha subunit of G13 and have determined crystal structures of their complexes in both the inactive state bound to GDP and the active states bound to GDP*AlF (transition state) and GTPgammaS (Michaelis complex). PRG-rgRGS interacts extensively with the helical domain and the effector-binding sites on Galpha13 through contacts that are largely conserved in all three nucleotide-bound states, although PRG-rgRGS has highest affinity to …

Weed-Biocontrol Insects Reduce Native-Plant Recruitment Through Second-Order Apparent Competition, Dean E. Pearson, Ragan M. Callaway

Biological Sciences Faculty Publications

Small-mammal seed predation is an important force structuring native-plant communities that may also influence exotic-plant invasions. In the intermountain West, deer mice (Peromyscus maniculatus) are prominent predators of native-plant seeds, but they avoid consuming seeds of certain widespread invasives like spotted knapweed (Centaurea maculosa). These mice also consume the biological-control insects Urophora spp. introduced to control C. maculosa, and this food resource substantially increases deer mouse populations. Thus, mice may play an important role in the invasion and management of C. maculosa through food-web interactions. We examined deer mouse seed predation and its effects on …

Toxic Introns And Parasitic Intein In Coxiella Burnetii: Legacies Of A Promiscuous Past, Rahul Raghavan, Linda D. Hicks, Michael F. Minnick

Biological Sciences Faculty Publications

The genome of the obligate intracellular pathogen Coxiella burnetii contains a large number of selfish genetic elements, including two group I introns (Cbu.L1917 and Cbu.L1951) and an intervening sequence that interrupts the 23S rRNA gene, an intein (Cbu.DnaB) within dnaB and 29 insertion sequences. Here, we describe the ability of the intron-encoded RNAs (ribozymes) to retard bacterial growth rate (toxicity) and examine the functionality and phylogenetic history of Cbu.DnaB. When expressed in Escherichia coli, both introns repressed growth, with Cbu.L1917 being more inhibitory. Both ribozymes were found to associate with ribosomes of Coxiella and E. coli. In addition, ribozymes significantly …

Ric-8a Catalyzes Guanine Nucleotide Exchange On G Alphai1 Bound To The Gpr/Goloco Exchange Inhibitor Ags3, Celestine J. Thomas, Gregory G. Tall, Anirban Adhikari, Stephen R. Sprang

Biological Sciences Faculty Publications

Microtubule pulling forces that govern mitotic spindle movement of chromosomes are tightly regulated by G-proteins. A host of proteins, including Galpha subunits, Ric-8, AGS3, regulators of G-protein signalings, and scaffolding proteins, coordinate this vital cellular process. Ric-8A, acting as a guanine nucleotide exchange factor, catalyzes the release of GDP from various Galpha.GDP subunits and forms a stable nucleotide-free Ric-8A:Galpha complex. AGS3, a guanine nucleotide dissociation inhibitor (GDI), binds and stabilizes Galpha subunits in their GDP-bound state. Because Ric-8A and AGS3 may recognize and compete for Galpha.GDP in this pathway, we probed the interactions of a truncated AGS3 (AGS3-C; containing only …

No Evidence For Trade-Offs: Centaurea Plants From America Are Better Competitors And Defenders, Wendy M. Ridenour, Jorge M. Vivanco, Yulong Feng, Jun-Ichiro Horiuchi, Ragan M. Callaway

Biological Sciences Faculty Publications

The natural enemies hypothesis has led to a number of ideas by which invaders might evolve superior competitive ability. In this context, we compared growth, reproduction, competitive effect, competitive response, and defense capabilities between invasive North American populations of Centaurea maculosa and populations in Europe, where the species is native. We found that Centaurea from North America were larger than plants from European populations. North American Centaurea also demonstrated stronger competitive effects and responses than European Centaurea. However, competitive superiority did not come at a cost to herbivore defense. North American plants were much better defended against generalist insect …

I. Vh Gene Transcription Creates Stabilized Secondary Structures For Coordinated Mutagenesis During Somatic Hypermutation, Barbara E. Wright, Karen H. Schmidt, Michael F. Minnick, Nick Davis

Biological Sciences Faculty Publications

During the adaptive immune response, antigen challenge triggers a million-fold increase in mutation rates in the variable-region antibody genes. The frequency of mutation is causally and directly linked to transcription, which provides ssDNA and drives supercoiling that stabilizes secondary structures containing unpaired, intrinsically mutable bases. Simulation analysis of transcription in VH5 reveals a dominant 65nt secondary structure in the non-transcribed strand containing six sites of mutable ssDNA that have also been identified independently in human B cell lines and in primary mouse B cells. This dominant structure inter-converts briefly with less stable structures and is formed repeatedly during transcription, due …

Ii. Correlations Between Secondary Structure Stability And Mutation Frequency During Somatic Hypermutation, Barbara E. Wright, Karen H. Schmidt, Nick Davis, Aaron T. Hunt, Michael F. Minnick

Biological Sciences Faculty Publications

The role of secondary structures and base mutability at different levels of transcription and supercoiling is analyzed in variable region antibody genes VH5, VH94 and VH186.2. The data are consistent with a model of somatic hypermutation in which increasing levels of transcription and secondary structure stability correlate with the initial formation of successive mutable sites. Encoded differences exist in stem length and the number of GC pairs at low versus high levels of transcription in CDRs. These circumstances simplify the complexities of coordinating mutagenesis by confining this process to each mutable site successively, as they form in response to increasing …

Lositan: A Workbench To Detect Molecular Adaptation Based On A Fst-Outlier Method, Tiago Antao, Ana Lopes, Ricardo J. Lopes, Albano Beja-Pereira, Gordon Luikart

Biological Sciences Faculty Publications

Background: Testing for selection is becoming one of the most important steps in the analysis of multilocus population genetics data sets. Existing applications are difficult to use, leaving many nontrivial, error-prone tasks to the user.

Results: Here we present LOSITAN, a selection detection workbench based on a well evaluated F_st-outlier detection method. LOSITAN greatly facilitates correct approximation of model parameters (e.g., genome-wide average, neutral F_st), provides data import and export functions, iterative contour smoothing and generation of graphics in a easy to use graphical user interface. LOSITAN is able to use modern multi-core processor architectures by …

Phytotoxic Effects Of (+/-)-Catechin In Vitro, In Soil, And In The Field, Inderjit, Jarrod L. Pollock, Ragan M. Callaway, William E. Holben

Biological Sciences Faculty Publications

Background: Exploring the residence time of allelochemicals released by plants into different soils, episodic exposure of plants to allelochemicals, and the effects of allelochemicals in the field has the potential to improve our understanding of interactions among plants. Methodology/Principal Findings: We conducted experiments in India and the USA to understand the dynamics of soil concentrations and phytotoxicity of (+/-)-catechin, an allelopathic compound exuded from the roots of Centaurea maculosa, to other plants in vitro and in soil. Experiments with single and pulsed applications into soil were conducted in the field. Experimental application of (+/-)-catechin to soils always resulted in concentrations …

Protecting Migration Corridors: Challenges And Optimism For Mongolian Saiga, Joel Berger, Julie K. Young, Kim Murray Berger

Biological Sciences Faculty Publications

No abstract provided.

Effects Of Native Species Diversity And Resource Additions On Invader Impact, John L. Maron, Marilyn Marler

Biological Sciences Faculty Publications

Theory and empirical work have demonstrated that diverse communities can inhibit invasion. Yet, it is unclear how diversity influences invader impact, how impact varies among exotics, and what the relative importance of diversity is versus extrinsic factors that themselves can influence invasion. To address these issues, we established plant assemblages that varied in native species and functional richness and crossed this gradient in diversity with resource (water) addition. Identical assemblages were either uninvaded or invaded with one of three exotic forbs: spotted knapweed (Centaurea maculosa), dalmatian toadflax (Linaria dalmatica), or sulfur cinquefoil (Potentilla recta). To determine impacts, we measured the …

Is The Effect Of Forest Structure On Bird Diversity Modified By Forest Productivity?, Jacob P. Verschuyl, Andrew J. Hansen, David B. Mcwethy, Rex Sallabanks, Richard L. Hutto

Biological Sciences Faculty Publications

Currently, the most common strategy when managing forests for biodiversity at the landscape scale is to maintain structural complexity within stands and provide a variety of seral stages across landscapes. Advances in ecological theory reveal that biodiversity at continental scales is strongly influenced by available energy (i.e., climate factors relating to heat and light and primary productivity). This paper explores how available energy and forest structural complexity may interact to drive biodiversity at a regional scale.

We hypothesized that bird species richness exhibits a hump-shaped relationship with energy at the regional scale of the northwestern United States. As a result, …

Undetected Species Losses, Food Webs, And Ecological Baselines: A Cautionary Tale From The Greater Yellowstone Ecosystem, Usa, Joel Berger

Biological Sciences Faculty Publications

Large protected areas are often considered natural yet outside pressures may compromise ecological integrity. This paper points to a problem in assessing ecological baselines: what if species' extirpations go undetected? I present a data set spanning 130 years that demonstrates the loss of white-tailed jack rabbits Lepus townsendii from two National Parks in the well studied 60,000 km(2) Greater Yellowstone Ecosystem, USA. While these extirpations have been unnoticed until now, an ecological consequence may be elevated predation on juvenile ungulates. A critical challenge we face is how to apply better the concept of shifting baselines to the restoration of functional …

Transient Elevation Of Corticosterone Alters Begging Behavior And Growth Of White-Crowned Sparrow Nestlings, Haruka Wada, Creagh W. Breuner

Biological Sciences Faculty Publications

Developing animals may face a cost–benefit tradeoff during growth mediated through hormones such as glucocorticoids, as the hormone is essential for development but can have detrimental consequences. To investigate potential tradeoffs caused by brief, moderate elevations of corticosterone in avian young, we artificially elevated the hormone levels in two ways: feeding corticosterone-containing worms and applying corticosterone dermal patches. The former experiment tested the effects of an acute corticosterone elevation (25 min) on begging behavior, whereas the latter explored the effects of artificially elevated corticosterone for 24 to 48 h on growth. Corticosterone altered both begging behavior and growth of white-crowned …

An Invader Differentially Affects Leaf Physiology Of Two Natives Across A Gradient In Diversity, Pamela Kittelson, John L. Maron, Marilyn Marler

Biological Sciences Faculty Publications

Little is known about how exotics influence the ecophysiology of co-occurring native plants or how invader impact on plant physiology may be mediated by community diversity or resource levels. We measured the effect of the widespread invasive forb spotted knapweed (Centaurea maculosa) on leaf traits (leaf dry matter content, specific leaf area, leaf nitrogen percentage, leaf C:N ratios, and δ¹³C as a proxy for water use efficiency) of two co-occurring native perennial grassland species, Monarda fistulosa (bee balm) and Koeleria macrantha (Junegrass). The impact of spotted knapweed was assessed across plots that varied in functional diversity …

Novel Weapons: Invasive Plant Suppresses Fungal Mutualists In America But Not In Its Native Europe, Ragan M. Callaway, Don Cipollini, Kathryn Barto, Giles C. Thelen, Steven G. Hallett, Daniel Prati, Kristina Stinson, John Klironomos

Biological Sciences Faculty Publications

Why some invasive plant species transmogrify from weak competitors at home to strong competitors abroad remains one of the most elusive questions in ecology. Some evidence suggests that disproportionately high densities of some invaders are due to the release of biochemicals that are novel, and therefore harmful, to naïve organisms in their new range. So far, such evidence has been restricted to the direct phytotoxic effects of plants on other plants. Here we found that one of North America's most aggressive invaders of undisturbed forest understories, Alliaria petiolata (garlic mustard) and a plant that inhibits mycorrhizal fungal mutualists of North …

Extant Or Extinct? White-Tailed Jack Rabbits And Yellowstone's Food Web, Joel Berger

Biological Sciences Faculty Publications

No abstract provided.

Indirect Effects And Traditional Trophic Cascades: A Test Involving Wolves, Coyotes, And Pronghorn, Kim Murray Berger, Eric M. Gese, Joel Berger

Biological Sciences Faculty Publications

The traditional trophic cascades model is based on consumer - resource interactions at each link in a food chain. However, trophic-level interactions, such as mesocarnivore release resulting from intraguild predation, may also be important mediators of cascades. From September 2001 to August 2004, we used spatial and seasonal heterogeneity in wolf distribution and abundance in the southern Greater Yellowstone Ecosystem to evaluate whether mesopredator release of coyotes ( Canis latrans), resulting from the extirpation of wolves ( Canis lupus), accounts for high rates of coyote predation on pronghorn ( Antilocapra americana) fawns observed in some areas. Results of this ecological …

A Method To Determine 18 O Kinetic Isotope Effects In The Hydrolysis Of Nucleotide Triphosphates, Xinlin Du, Kurt Ferguson, Robert Gregory, Stephen R. Sprang

Biological Sciences Faculty Publications

A method to determine 18 O kinetic isotope effects (KIEs) in the hydrolysis of GTP that is generally applicable to reactions involving other nucleotide triphosphates is described. Internal competition, where the substrate of the reaction is a mixture of 18 O-labeled and unlabeled nucleotides, is employed, and the change in relative abundance of the two species in the course of the reaction is used to calculate KIE. The nucleotide labeled with 18 O at sites of mechanistic interest also contains 13C at all carbon positions, whereas the 16 O-labeled nucleotide is depleted of 13C. The relative abundance of the labeled …

Scientific Review For The Identification Of Critical Habitat For Woodland Caribou (Rangifer Tarandus Caribou), Boreal Population, In Canada, Mark Hebblewhite, Environment Canada

Biological Sciences Faculty Publications

Woodland Caribou (Rangifer tarandus caribou), Boreal Population (herein referred to as boreal caribou), are formally listed as Threatened under the federal Species at Risk Act (SARA). The Act requires the Minister of Environment to prepare a Recovery Strategy for the species that includes, to the extent possible and based upon the best available information, an identifi cation of its Critical Habitat and/or, if there is insuffi cient information available, a Schedule of Studies to determine that information. In August 2007, Environment Canada (EC) launched a science-based review with the mandate to identify Critical Habitat to the extent possible, using the …

What Constitutes A Natural Fire Regime? Insight From The Ecology And Distribution Of Coniferous Forest Birds In North America, Richard L. Hutto, Courtney J. Conway, Victoria A. Saab, Jeffrey R. Walters

Biological Sciences Faculty Publications

Bird species that specialize in the use of burned forest conditions can provide insight into the prehistoric fire regimes associated with the forest types that they have occupied over evolutionary time. The nature of their adaptations reflects the specific post-fire conditions that occurred prior to the unnatural influence of humans after European settlement. Specifically, the post-fire conditions, nest site locations, and social systems of two species (Bachman's sparrow [Aimophila aestivalis] and red-cockaded woodpecker [Picoides borealis]) suggest that, prehistorically, a frequent, low-severity fire regime characterized the southeastern pine system in which they evolved. In contrast, the patterns …