EPR of Cu\u3csup\u3e2+\u3c/sup\u3e Prion Protein Constructs at 2 GHz Using the \u3cem\u3eg\u3c/em\u3e\u3csub\u3e⊥\u3c/sub\u3e Region to Characterize Nitrogen Ligation

A double octarepeat prion protein construct, which has two histidines, mixed with copper sulfate in a 3:2 molar ratio provides at most three imidazole ligands to each copper ion to form a square-planar Cu2+ complex. This work is concerned with identification of the fourth ligand. A new (to our knowledge) electron paramagnetic resonance method based on analysis of the intense features of the electron paramagnetic resonance spectrum in the g⊥ region at 2 GHz is introduced to distinguish between three and four nitrogen ligands. The methodology was established by studies of a model system consisting of histidine imidazole ligation to Cu2+. In this spectral region at 2 GHz (S-band), g-strain and broadening from the possible rhombic character of the Zeeman interaction are small. The most intense line is identified with the MI = +1/2 extra absorption peak. Spectral simulation demonstrated that this peak is insensitive to cupric Ax and Ay hyperfine interaction. The spectral region to the high-field side of this peak is uncluttered and suitable for analysis of nitrogen superhyperfine couplings to determine the number of nitrogens. The spectral region to the low-field side of the intense extra absorption peak in the g⊥ part of the spectrum is sensitive to the rhombic distortion parameters Ax and Ay. Application of the method to the prion protein system indicates that two species are present and that the dominant species contains four nitrogen ligands. A new loop-gap microwave resonator is described that contains ∼1 mL of frozen sample

Temporal Variability and cooperative Breeding: Testing the Bet-Hedging Hypothesis in the Acorn Woodpecker

Cooperative breeding is generally considered an adaptation to ecological constraints on dispersal and independent breeding, usually due to limited breeding opportunities. Although benefits of cooperative breeding are typically thought of in terms of increased mean reproductive success, it has recently been proposed that this phenomenonmay be a bet-hedging strategy that reduces variance in reproductive success (fecundity variance) inpopulations living inhighly variable environments. We tested this hypothesis using long-term data on the polygynandrous acorn woodpecker (Melanerpes formicivorus). In general, fecundity variance decreased with increasing sociality, at least when controlling for annual variation in ecological conditions. Nonetheless, decreased fecundity variance was insufficient to compensate for reduced per capita reproductive success of larger,more social groups, which typically suffered lower estimatedmean fitness.We did, however, find evidence that sociality in the form of larger group size resulted in increased fitness in years following a small acorn crop due to reduced fecundity variance. Bet-hedging, although not the factor driving sociality in general, may play a role in driving acorn woodpecker group living when acorns are scarce and ecological conditions are poor

The Criticality of Defense-Focused Technical Education

The United States Air Force is a service born of technology, and throughout its history, technology has remained central to its identity and power. From the start, visionary leaders realized the importance of technologically focused education to advancing airpower. Consequently, through the years, institutions of higher learning such as the Air Force Institute of Technology AFIT, as well as the civilian institution program it administers, have continued the meaningful work of developing the technology and organic human capital to sustain the Air Forces edge as a fighting force. As advances in technology have led the Air Force into the new domains and challenges of space and cyberspace, the role of delivering defenseoriented technical education has become even more critical. In this process, leveraging our network of science and technology partners to produce technically educated and operationally focused Airmen has proved as significant as the advances themselves. Because demand for these graduates continues to increase, deliberate investment in science, technology, engineering, and mathematics STEM education must also increase. Today, as yesterday, experienced Air Force leaders with a defense-focused technical education are essential to maintaining our military supremacy, and AFIT continues to meet that need--as it has since its inception in 1919

Testing Alternative Hypotheses for the Cause of Population Declines: The Case of the Red-Headed Woodpecker

The Red-headed Woodpecker (Melanerpes erythrocephalus) has experienced strong population declines during the past 3 decades. Using North American Breeding Bird Survey (BBS) and Audubon Christmas Bird Count (CBC) data, we investigated 4 hypotheses that may explain this decline, including: (1) interspecific competition with native Red-bellied Woodpeckers (Melanerpes carolinus) and nonnative European Starlings (Sturnus vulgaris); (2) predation by Cooper\u27s Hawks (Accipiter cooperii) and Sharp-shinned Hawks (Accipiter striatus); (3) climate change; and (4) changes in forested area within their range. In analyses of both the breeding and overwintering periods, our results indicated a role of increased accipiter populations in driving Red-headed Woodpecker declines through increased predation. We also found evidence for significant effects of warmer winter temperatures and increased forest cover, both directly and indirectly through their effects on enhancing accipiter populations. In contrast, our results failed to support the hypothesis that interspecific competition with either Red-bellied Woodpeckers or European Starlings has played a role in Red-headed Woodpecker declines. Despite considerable evidence for nest-site competition and aggression between Red-headed Woodpeckers and both Red-bellied Woodpeckers and European Starlings, these interactions do not appear to be limiting Red-headed Woodpecker populations

Habitat Saturation Results in Joint-Nesting Female Coalitions in a Social Bird

Joint nesting by females and cooperative polyandry—cooperatively breeding groups with a male-biased breeder sex ratio—are little-understood, rare breeding systems. We tested alternative hypotheses of factors potentially driving these phenomena in a population of joint-nesting acorn woodpeckers (Melanerpes formicivorus). During periods of high population density and thus low independent breeding opportunities, acorn woodpecker females formed joint-nesting coalitions with close kin. Coalitions were typically associated with groups with a male bias. We found strong evidence for both inter- and intrasexual conflict, as joint nesting conferred a fitness benefit to some males, a significant fitness cost to females, and no gain in per capita reproductive output for either sex. Such conflict, particularly the cost to females, may be an important reason why joint nesting is rare among cooperatively breeding taxa

Territory Inheritance and the Evolution of Cooperative Breeding in the Acorn Woodpecker

There are two main hypotheses for why offspring in cooperatively breeding taxa delay dispersal and remain on their natal territory rather than disperse. First, ecological constraints may force offspring to remain on their natal territory until a reproductive opportunity presents itself in an otherwise saturated habitat. Alternatively, delaying dispersal and helping kin may increase an offspring\u27s inclusive fitness. One means by which offspring might enhance their direct fitness by delaying dispersal is by inheriting breeding status on their natal territory. Such territory inheritance regularly occurs in acorn woodpeckers, Melanerpes formicivorus, a species whose social groups consist of a cooperatively polygynandrous breeding core along with nonbreeding helpers of both sexes that are offspring from prior breeding efforts. Here we examine the life-history differences and the fitness consequences of birds attaining breeder status by either inheriting their natal territory or dispersing to a new territory. Despite significant differences in life history, including the mean territory quality on which individuals bred and mean co-breeder coalition size of breeders, we found no statistical differences in either direct or kin-selected (indirect) fitness benefits for breeders that inherited and dispersed. The incidence of birds engaging in both strategies, inheriting their natal territory and later dispersing, or dispersing but later returning to inherit their natal territory, further reduces the potential direct fitness benefits of inheritance relative to dispersal, since neither precludes the other. Territory inheritance is an important, alternative means of achieving breeding status in this population. However, ecological constraints to dispersal and kin-selected fitness benefits as a helper likely play larger roles driving the acorn woodpecker\u27s extraordinary social system

Unraveling a Paradox of Habitat Relationships: Scale-Dependent Drivers of Temporal Occupancy-Abundance Relationships in a Cooperatively Breeding Bird

Context Spatial occupancy and local abundance of species often positively covary, but the mechanisms driving this widespread relationship are poorly understood. Resource dynamics and habitat changes have been suggested as potential drivers, but long-term studies relating them to abundance and occupancy are rare. In this 34-year study of acorn woodpeckers (Melanerpes formicivorus), a cooperatively breeding species, we observed a paradoxical response to changes in habitat composition: despite a reduction in the availability of high-quality breeding habitat, the population increased considerably. Objectives We investigated the role of annual variation in food availability and long-term changes in habitat composition as predictors of population dynamics. Methods Using model selection, we contrasted competing hypotheses on the effects of changing resource availability on occupancy and social group size across three spatial scales: territory, neighborhood, and landscape. Results The increase in abundance was largely determined by the formation of new social groups, driven by a landscape-level expansion of canopy cover and its interaction with neighborhood-level acorn abundance, indicative of long-term increases in overall acorn productivity. Group size increased with neighborhood acorn crop two years earlier but groups were smaller in territories with more canopy cover. Conclusions Our results indicate that scale-dependent processes can result in paradoxical relationships in systems with spatial and temporal resource heterogeneity. Moreover, the findings support the role of resources in driving changes in abundance and occupancy at a landscape scale, suggesting that colonization of marginal habitat drives the positive occupancy-abundance relationship in this cooperatively breeding species

The Octarepeat Domain of the Prion Protein Binds Cu(II) with Three Distinct Coordination Modes at pH 7.4

The prion protein (PrP) binds Cu2+ in its N-terminal octarepeat domain. This unusual domain is comprised of four or more tandem repeats of the fundamental sequence PHGGGWGQ. Previous work from our laboratories demonstrates that at full copper occupancy, each HGGGW segment binds a single Cu2+. However, several recent studies suggest that low copper occupancy favors different coordination modes, possibly involving imidazoles from histidines in adjacent octapeptide segments. This is investigated here using a combination of X-band EPR, S-band EPR, and ESEEM, along with a library of modified peptides designed to favor different coordination interactions. At pH 7.4, three distinct coordination modes are identified. Each mode is fully characterized to reveal a series of copper-dependent octarepeat domain structures. Multiple His coordination is clearly identified at low copper stoichiometry. In addition, EPR detected copper−copper interactions at full occupancy suggest that the octarepeat domain partially collapses, perhaps stabilizing this specific binding mode and facilitating cooperative copper uptake. This work provides the first complete characterization of all dominant copper coordination modes at pH 7.4