North Rim Research Articles

Using integrated step selection to determine effects of predation risk on bison habitat selection and movement

AbstractAnimal movement is a fundamental mechanism that shapes communities and ecosystems. Ungulates alter the ecosystems they inhabit and understanding their movements and distribution is critical for linking habitat with population dynamics. Predation risk has been shown to strongly influence ungulate movement patterns, such that ungulates may select habitat where predation risk is lower (refugia), adjust movement rates, temporal patterns, or selection of cover variables in areas with greater predation risk. We evaluated potential predation avoidance behavior in a population of plains bison inhabiting the north rim of Grand Canyon National Park (GRCA) and adjacent Kaibab National Forest (KNF). The KNF has year‐round hunting managed by Arizona Game and Fish Department, whereas hunting is not allowed in GRCA. Human‐maintained water sources on the KNF are particularly important resources for bison wherein they may be exposed to higher predation risk to access these resources. We used 2‐h GPS locations for three years from 31 bison (n = 9 males; n = 22 females), and integrative step selection analysis to test four hypotheses about the potential for bison to reduce their risk from human predation by avoiding areas of high predation risk; moving faster in areas with high predation risk; entering high‐risk areas at night when risk is reduced; and entering high‐risk areas in habitats that provide cover (coniferous forest). The highest performing model indicated bison movement was 1.3 times faster per 2‐h step interval than in areas with no hunting across all vegetation classes (coniferous forest, shrub, quaking aspen, grass‐forb meadow) and across all topography classes (valley, slope, ridge). Bison moved more slowly in grass‐forb meadows than all other vegetation types, and in valleys relative to slopes and ridges. Several radio‐collared individuals had no GPS locations in KNF for the duration of the study. Bison avoided predation risk using two strategies: moving faster while in the KNF, and fully avoiding high‐risk areas by remaining within GRCA. Management that manipulates or reduces timing of hunting seasons may reduce perceived predation risk and encourage bison to distribute into the KNF and across a broader range of available habitat.

Hydrotectonics of Grand Canyon Groundwater

The Grand Canyon provides a deeply dissected view of the aquifers of the Colorado Plateau and its public and tribal lands. Stacked sandstone and karst aquifers are vertically connected by a network of faults and breccia pipes creating a complex groundwater network. Hydrochemical variations define structurally controlled groundwater sub-basins, each with main discharging springs. North Rim (N-Rim), South Rim (S-Rim), and far-west springs have different stable isotope fingerprints, reflecting different mean recharge elevations. Variation within each region reflects proportions of fast/slow aquifer pathways. Often considered perched, the upper Coconino (C) aquifer has a similar compositional range as the regional Redwall-Muav (R-M) karst aquifer, indicating connectivity. Natural and anthropogenic tracers show that recharge can travel 2 km vertically and tens of kilometers laterally in days to months via fracture conduits to mix with older karst baseflow. Six decades of piping N-Rim water to S-Rim Village and infiltration of effluent along the Bright Angel fault have sustained S-Rim groundwaters and likely induced S-Rim microseismicity. Sustainable groundwater management and uranium mining threats require better monitoring and application of hydrotectonic concepts. ▪Hydrotectonic concepts include distinct structural sub-basins, fault fast conduits, confined aquifers, karst aquifers, upwelling geothermal fluids, and induced seismicity.▪N-Rim, S-Rim, and far-west springs have different stable isotope fingerprints reflecting different mean recharge elevations and residence times.▪The upper C and lower R-M aquifers have overlapping stable isotope fingerprints in a given region, indicating vertical connectivity between aquifers.▪S-Rim springs and groundwater wells are being sustained by ∼60 years of piping of N-Rim water to S-Rim, possibly inducing seismicity.

Data Fusion for Satellite-Derived Earth Surface: The 2021 Topographic Map of Etna Volcano

We present a new automatic procedure for updating digital topographic data from multi-source satellite imagery, which consists in the production of Digital Surface Models (DSMs) from high resolution optical satellite images, followed by a context-aware fusion that exploits the complementary characteristics of the multi-source DSMs. The fused DSM minimizes blunders and artifacts due to occlusions (e.g., the presence of clouds, snow or ash plumes) in the source images, resulting in improved accuracy and quality versus those that are not merged. The procedure has been tested to produce the 2021 digital topography of Mt Etna, whose summit area is constantly changing and shows the new peak of 3347 m on the north rim of the South East Crater. We also employ the 2021 DSM to measure the volcanic deposits emplaced in the last five years, finding about 120 million cubic meters, with a yearly average volume of about 24 million cubic meters in agreement with the large eruptive rates registered at Mt Etna since the nineteen seventies. The flexibility and modularity of the presented procedure make it easily exportable to other environmental contexts, allowing for a fast and frequent reconstruction of topographic surfaces even in extreme environments.

Interdecadal Change of Ural Blocking Highs and Its Atmospheric Cause in Winter during 1979–2018

The Ural blocking (UB) high is a weather system closely related to the cold air process during winter, which could trigger extreme cold events in East Asia. By retrieving five single blocking indexes, including accumulation frequency, central latitude, blocking intensity, mean duration and north rim, it is found that the UB in winter occurs more frequently, grows stronger, lasts longer and is located more northward after 2002, compared with 1985–2001. In order to describe the UB comprehensively, a new comprehensive blocking index (CBI) is developed based on the above five blocking indexes. The CBI can also reflect the interdecadal change of UB synthetically. Analysis on the corresponding atmospheric circulation shows that the relationship between the UB and atmospheric circulation, such as the polar vortex and jet, is closer in 2002–2018 than in 1985–2001. Compared with the atmospheric circulation in 1985–2001, the most prominent feature in 2002–2018 is that the intensity of the polar vortex is weaker at 100 hPa, and that the subtropical jet moves northward. Meanwhile, the East Asian trough downstream of the Urals deepens at 500 hPa and the Siberian high strengthens, indicating that the East Asia winter monsoon is stronger during 2002–2018. Further analysis on atmospheric waves and baroclinicity demonstrates that the meridional circulation of planetary waves strengthens, especially the 2-waves, which may increase the frequency of the UB and shift its location northward after 2002. Additionally, the baroclinicity (−∂T/∂y) in the mid-high latitudes is weakened during winter since 2002, which is also beneficial for the establishment of meridional circulation, causing a stronger intensity and longer duration of the UB.

Singaway: Working and Playing for the National Parks, 1923–1972

The first time I saw a picture of the swimming pool in front of the Zion Lodge, I couldn't believe it. I have been to Zion National Park at least annually for nearly forty years, and despite the crowds, the park is still a symbol to me (and millions more) of natural wonder and wilderness solitude. The image of that swimming pool, which was decommissioned and buried in the 1970s, hinted at a secret past—a hidden side to the national park experience that has largely disappeared, one that emphasized convenience, culture, and collective entertainment.Singaway opens the door to that hidden history. In its large-format, richly illustrated pages, the book traces the human experience at Zion, Bryce Canyon, Cedar Breaks, and the North Rim of Grand Canyon as seen through the eyes of Utah Parks Company employees. For five decades, the UPC (a subsidiary of the Union Pacific Railroad) provided a luxurious, all-inclusive vacation to well-healed vacationers, catering to their every need and want from the moment they stepped off the train in dusty Lund, Utah, and traveled to the lavish El Escalante Hotel in Cedar City, and all along the way during their “grand circle tour.” This was not camping; it was a “glamorous adventure” featuring elegant dinners with formal dress, live bands, and fine china (xxi).The book opens with an introductory essay giving background to railroad boosterism, national parks concessions, and UPC employment opportunities, which ranged from cooks and housekeepers to waitstaff and “gearjammers,” the tour bus drivers who also functioned as in-transit entertainers. Over its fifty-year life span, the UPC “employed more than 40,000 young men and young women ages 16 to 26, mostly college students” (v). Many of these employees came from nearby southern Utah communities, of course, but the company recruited from across the nation, giving employees exposure to new people and lifestyles. Though the photographs clearly show a lack of racial diversity among the staff, more than one interviewee pointed out opportunities they had to overcome prejudice, and another stated that “the Parks Company was at the forefront of hiring people with disabilities” in the 1950s and 1960s (144). Regardless of what an employees’ day job was, he or she often participated in entertaining the visiting “dudes,” including evening programs and the “singaways,” where the whole staff gathered in front of the lodge to sing humorous and nostalgia-inducing songs as the tour buses left for the next park.The majority of the text comprises excerpts from oral histories and memoirs by former employees. Each chapter focuses on a different aspect of the employee experience, from recruiting and job duties to dorm life and social activities. Two of my favorite sections were “Dude Stories,” filled with tales of the clueless things city folk say and do in national parks, and “Pranks and Practical Jokes,” which will remind many readers of their own teenage years. The topical arrangement was the best choice for the book, though a downside is that quotes and sections are sometimes repetitive, and it is hard to follow how things changed over the decades since excerpts are not arranged chronologically.What stand out are the funny and poignant stories, heartwarming instances of summer romances blossoming into decades of marriage, and reflections on growing up and learning the first lessons of adulthood. The illustrations are an absolute delight, and every time I looked for a photograph of something described in an interview, there was a photograph. All the material comes from the extensive Utah Parks Company Collection at SUU's Sherratt Library, and much of that collection is digitized and available online.This book will certainly appeal to anyone who worked for the UPC or took the grand circle tour, but beyond that, it is a memorable and detailed look at a unique place and time in Utah history. Readers gain insights into prices, technology, transportation, and ways of life in mid-twentieth-century southern Utah, and there are fascinating asides about local history, such as the pumphouse at Roaring Springs that for decades provided electricity and fresh water to the North Rim Lodge, 3,800 feet above. Along the way there are hints at the larger stories of these decades, from World War II to the downwind effects of nuclear testing.

Replacement of the Typical artedi Form of Cisco Coregonus artedi in Lake Huron by Endemic Shallow‐Water Ciscoes, Including Putative Hybrids

AbstractVarious ecomorphs of the shallow‐water Cisco Coregonus artedi were the dominant fish planktivores in each of the Great Lakes until invasive species and overfishing resulted in extirpations and extinctions. In this paper, we describe the present morphological diversity and distribution of shallow‐water Ciscoes in each of Lake Huron’s three basins: the main basin, Georgian Bay, and the North Channel. Typical artedi, a formerly widespread ecomorph that had supported the lake’s largest fishery, appears to have been extirpated from all three basins. Three types of shorthead cisco, a recently described and variable ecomorph, were extant. One type was morphologically robust and abundant along the north rim of the lake. The second type was large bodied, terete (streamlined), short finned, and collected at only one location in the main basin. The third type consisted of putative shorthead cisco × typical artedi hybrids, which were widespread in Georgian Bay and the North Channel. Only the putative hybrids were regularly collected in midwater trawls, suggesting that they were more pelagic, which we attribute to an inferred partial ancestry with typical artedi. The putative shorthead cisco × typical artedi hybrids of Georgian Bay and the North Channel have replaced typical artedi to some degree, while shorthead ciscoes in the main basin, though possibly more abundant now than in the past, have not measurably replaced typical artedi. Even with the apparent extirpation of typical artedi, Lake Huron has a greater diversity of shallow‐water Ciscoes than any of the other Great Lakes, which we attribute to its more complex topography.

The role of conformational epitopes in the evolutionary divergence of enterovirus D68 clades: A bioinformatics-based study.

Enterovirus D68 (EV-D68), as one of the major pathogens of paediatric respiratory disease, has been widely spread in the population in recent years. As the basis of virus antigenicity, antigenic epitopes are essential to monitoring the transformation of virus antigenicity. However, there is a lack of systematic studies on the antigenic epitopes of EV-D68. In this study, a bioinformatics-based prediction algorithm for human enteroviruses was used to predict the conformational epitopes of EV-D68. The prediction results showed that the conformational epitopes of EV-D68 were clustered into three sites: site 1, site 2, and site 3. Site 1 was located in the "north rim" region of the canyon near the fivefold axis; site 2 was located in the "puff" region near the twofold axis; and site 3 consisted of two parts, one in the "knob" region on the south rim of the canyon and the other in the threefold axis region. The predicted epitopes overlapped highly with the binding regions of four reported monoclonal antibodies (mAbs), indicating that the predictions were highly reliable. Phylogenetic analysis showed that amino acid mutations in the epitopes of the VP1 BC loop, DE loop, C-terminus, and VP2 EF loop played a crucial role in the evolutionary divergence of EV-D68 clades/subclades and epidemics. This finding indicated that the VP1 BC loop, DE loop, C-terminus, and VP2 EF loop were the most important epitopes of EV-D68. Research on the epitopes of EV-D68 will contribute to outbreak surveillance and to the development of diagnostic reagents and recombinant vaccines.

Comparison of Aerial Thermal Infrared Imagery and Helicopter Surveys of Bison (Bison bison) in Grand Canyon National Park, USA.

Aerial thermal infrared (TIR) surveys are an attractive option for estimating abundances of large mammals inhabiting extensive and heterogeneous terrain. Compared to standard helicopter or fixed-wing aerial surveys, TIR flights can be conducted at higher altitudes translating into greater spatial coverage and increased observer safety; however, monetary costs are much greater. Further, there is no consensus on whether TIR surveys offer improved detection. Consequently, we performed a study to compare results of a TIR and helicopter survey of bison (Bison bison) on the Powell Plateau in Grand Canyon National Park, USA. We also compared results of both surveys to estimates obtained using a larger dataset of bison helicopter detections along the entire North Rim of the Grand Canyon. Observers in the TIR survey counted fewer individual bison than helicopter observers (101 to 127) and the TIR survey cost was 367% higher. Additionally, the TIR estimate was 18.8% lower than the estimate obtained using a larger dataset, while the comparative helicopter survey was 9.3% lower. Despite our small sample size, we found that helicopter surveys are currently the best method for estimating bison abundances in dense canopy cover sites due to ostensibly more accurate estimates and lower cost compared to TIR surveys. Additional research will be needed to evaluate the efficacy of these methods, as well as very high resolution satellite imagery, for bison populations in more open landscapes.

Post-eruption evolution of maar lakes and potential instability: The Lake Pavin case study, French Massif Central

Few studies have focused on the post-eruption evolution of maar craters and associated lake level changes, although breaching of the crater rim poses mass-flow and flood hazards long after the initial eruption. Lake Pavin is a maar lake in the French Massif central formed by an eruption c. 6700 years ago. The maar is perched on the edge of a glacially-shaped valley and the rim overlooks the surrounding subdued landscape. The rim is breached to the north by an overflow channel, and to the south the maar has cut into the flank of the Montchal scoria cone and lava flows. Incision of the lake outlet led to the growth of an alluvial fan that pushed the Couze Pavin River towards the north side of the Gelat valley.Two lake terraces within the crater are used to determine stages in the evolution of the lake. The highstand Stage 1 terrace +18 m above the current lake level indicates that the post-eruption lake surface and volume was 15% and 38% larger than the present-day lake, respectively, prior to the 5-7th Century CE. The poorly preserved Stage 2 bench, +4.35 m on the west side of the natural dam, indicates that incision paused between Stage 1 and achievement of present lake level (Stage 3) before the 18th Century. Four units of streamflow deposits (c. 0.087 km2 in area and 0.14–0.18 km3 in volume) that formed the fan at the mouth of the outlet in the Gelat valley have been 14C dated to between the 9th and 16th Century. From the fan sedimentology, we infer that the lake level dropped slowly between highstand Stages 1 and 2, when the outlet cut down through the rim saddle. The lake level drop accelerated between Stage 2 and Stage 3 before the 14th Century, inducing small debris flows. The latter may have resulted from heavy rainstorms, but there is no evidence for catastrophic events. Stepwise downcutting of the north rim saddle was also governed by contrasted properties of the deposits forming the dam. The current lake level has been stable since at least the early 18th Century, but the long-term stability of the dam is at risk.

Billion-year exposure ages in Gale crater (Mars) indicate Mount Sharp formed before the Amazonian period

The erosion rates and mechanisms operating on Mount Sharp in Gale crater, Mars were assessed via experiments performed by the SAM instrument to determine the cosmogenic noble gas contents of Murray mudstone formation samples Mojave 2 and Quela. Previous measurements of samples from the Aeolis Palus depression between Mount Sharp and the north rim of Gale crater indicate that scarp retreat-generated surfaces formed within the last 100 Ma. In contrast, Mojave 2 yielded exposure ages of 1,320±240 (3He), 910±420 (21Ne), and 310±60 Ma (36Ar). Quela gave a 3He age of 1,460±200 Ma; 21Ne and 36Ar from this sample could not be quantified due to isobaric interferences. The discordant and young 36Ar exposure age in Mojave 2 is likely the result of interaction with water which dissolved the chlorine-bearing host phases of this nuclide. The most probable exposure scenario is that both Mojave 2 and Quela have been at the surface for the most recent ∼1 Ga after the overlying few meters of rock were removed in a geologically rapid exhumation episode. Based on local geomorphology, scarp retreat is the most likely mechanism for the exposure at these two sites. The exposure ages measured throughout Curiosity's traverse indicate that the net removal of rock has proceeded more recently on Aeolis Palus than on the lower slopes of Mount Sharp. The implied differential erosion rate is insufficient to explain how Mount Sharp formed, even over billions of years. Instead, given that the surfaces on Mount Sharp have existed for >1 Ga, the mountain must have formed early, likely during the Hesperian. This study provides direct quantitative support for inferences based on crater counts that Mount Sharp had eroded to close to its current form before onset of the Amazonian.

Serotype specific epitopes identified by neutralizing antibodies underpin immunogenic differences in Enterovirus B

Echovirus 30 (E30), a serotype of Enterovirus B (EV-B), recently emerged as a major causative agent of aseptic meningitis worldwide. E30 is particularly devastating in the neonatal population and currently no vaccine or antiviral therapy is available. Here we characterize two highly potent E30-specific monoclonal antibodies, 6C5 and 4B10, which efficiently block binding of the virus to its attachment receptor CD55 and uncoating receptor FcRn. Combinations of 6C5 and 4B10 augment the sum of their individual anti-viral activities. High-resolution structures of E30-6C5-Fab and E30-4B10-Fab define the location and nature of epitopes targeted by the antibodies. 6C5 and 4B10 engage the capsid loci at the north rim of the canyon and in-canyon, respectively. Notably, these regions exhibit antigenic variability across EV-Bs, highlighting challenges in development of broad-spectrum antibodies. Our structures of these neutralizing antibodies of E30 are instructive for development of vaccines and therapeutics against EV-B infections.

Conference report: Large Meteorite Impacts and Planetary Evolution VI

Conference report: Large Meteorite Impacts and Planetary Evolution VI

Ceramic Production and Exchange among the Virgin Anasazi, 30 Years Later

At the 1988 SAA annual meeting in Phoenix, Margaret Lyneis presented a paper with the title Ceramic Production and Exchange among the Virgin Anasazi. In that paper, she presented evidence that much of the pottery found on archaeological sites in the Moapa Valley of southeastern Nevada was in fact produced 70–100 km to the east. This pottery was made from distinctive raw materials found near the north rim of the western Grand Canyon. That 1988 SAA paper inspired much subsequent research, including my doctoral dissertation, which examined ceramic distributions across the western part of the Virgin region. In this paper, I update and expand on my earlier study. This analysis adds detail to Lyneis's original arguments, but demonstrates that she was largely correct. From about AD. 1050–1125, small-scale Virgin region settlements were linked by intensive ceramic exchange networks that crossed long distances and rugged terrain.

Recent cryovolcanism in Virgil Fossae on Pluto

The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae troughs or channels and in the surrounding terrain are exposures of H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 μm of NH3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. Model calculations of NH3 destruction in H2O ice by galactic cosmic rays suggest that the maximum lifetime of NH3 in the uppermost meter of the exposed surface is ~109 years, while considerations of Lyman-α ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 10000. Thus, 109 y is taken as an upper limit to the age of the emplacement event, and it could be substantially younger.The red colorant in the ammoniated H2O in Virgil Fossae and surroundings may be a macromolecular organic material (tholin) thought to give color to much of Pluto's surface, but probably different in composition and age. Owing to the limited spectral range of the New Horizons imaging spectrometer and the signal precision of the data, apart from the H2O and NH3 signatures there are no direct spectroscopic clues to the chemistry of the strongly colored deposit on Pluto. We suggest that the colored material was a component of the fluid reservoir from which the material now on the surface in this region was erupted. Although other compositions are possible, if it is indeed a complex organic material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside Pluto.A planet-scale stress pattern in Pluto's lithosphere induced by true polar wander, freezing of a putative interior ocean, and surface loading has caused fracturing in a broad arc west of Sputnik Planitia, consistent with the structure of Virgil Fossae and similar extensional features. This faulting may have facilitated the ascent of fluid in subsurface reservoirs to reach the surface as flows and as fountains of cryoclastic materials, consistent with the appearance of colored, ammoniated H2O ice deposits in and around Virgil Fossae. Models of a cryoflow emerging from sources in Virgil Fossae indicate that the lateral extent of the flow can be several km (Umurhan et al., 2019). The deposit over the full length (>200 km) of the main trough in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of ~2.5 km, suggests that it debouched from multiple sources, probably along the length of the strike direction of the normal faults defining the graben. The source or sources of the ammoniated H2O are one or more subsurface reservoirs that may or may not connect to the global ocean postulated for Pluto's interior. Alternatives to cryovolcanism in producing the observed characteristics of the region around Virgil Fossae are explored in the discussion section of the paper.

Assessing the Relationship between Forest Structure and Fire Severity on the North Rim of the Grand Canyon

While operational fire severity products inform fire management decisions in Grand Canyon National Park (GRCA), managers have expressed the need for better quantification of the consequences of severity, specifically forest structure. In this study we computed metrics related to the forest structure from airborne laser scanning (ALS) data and investigated the influence that fires that burned in the decade previous had on forest structure on the North Rim of the Grand Canyon in Arizona. We found that fire severity best explains the occurrence of structure classes that include canopy cover, vertical fuel distribution, and surface roughness. In general we found that high fire severity resulted in structure types that exhibit lower canopy cover and higher surface roughness. Areas that burned more frequently with lower fire severity in general had a more closed canopy and a lower surface roughness, with less brush and less conifer regeneration. In a random forests modeling exercise to examine the relationship between severity and structure we found mean canopy height to be a powerful explanatory variable, but still proved less informative than the three-component structure classification. We show that fire severity not only impacts forest structure but also brings heterogeneity to vegetation types along the elevation gradient on the Kaibab plateau. This work provides managers with a unique dataset, usable in conjunction with vegetation, fuels and fire history data, to support management decisions at GRCA.

Genetic analyses of Astragalus sect. Humillimi (Fabaceae) resolve taxonomy and enable effective conservation.

Astragalus sect. Humillimi is distributed across the southwestern United States and contains two endangered taxa, A. cremnophylax var. cremnophylax and A. humillimus. The former was originally described from the South Rim of the Grand Canyon. Analysis of individuals discovered on the North Rim of the Grand Canyon yielded some evidence that the population represented a distinct species. To enable effective conservation, we clarify the group's taxonomy and characterize the genetic diversity of A. cremnophylax and A. humillimus. We used AFLPs to genotype most species in sect. Humillimi, focusing on the two endangered forms. We examined patterns of genetic diversity using complementary analytical approaches. Our results demonstrate that North Rim populations group with A. c. var. cremnophylax. We found low levels of genetic diversity at certain localities and strong differentiation among populations. Astragalus humillimus, which has suffered recent and severe population declines, exhibits weak differentiation among and low diversity within populations. Our results clarify the taxonomy of sect. Humillimi and define the boundaries of A. c. var. cremnophylax, which is shown to inhabit both rims of the Grand Canyon. This clarification, and detailed analysis of genetic variation within both endangered taxa, may advance ongoing efforts to conserve these taxa. Our results suggest that range-wide genetic analysis of A. humillimus may inform recovery strategies for this taxon.

Genome-wide markers reveal a complex evolutionary history involving divergence and introgression in the Abert\u2019s squirrel (Sciurus aberti) species group

BackgroundGenetic introgression between divergent lineages is now considered more common than previously appreciated, with potentially important consequences for adaptation and speciation. Introgression is often asymmetric between populations and patterns can vary for different types of loci (nuclear vs. organellar), complicating phylogeographic reconstruction. The taxonomy of the ecologically specialized Abert’s squirrel species group has been controversial, and previous studies based on mitochondrial data have not fully resolved the evolutionary relationships among populations. Moreover, while these studies identified potential areas of secondary contact between divergent lineages, the possibility for introgression has not been tested.ResultsWe used RAD-seq to unravel the complex evolutionary history of the Abert’s squirrel species group. Although some of our findings reinforce inferences based on mitochondrial data, we also find significant areas of discordance. Discordant signals generally arise from previously undetected introgression between divergent populations that differentially affected variation at mitochondrial and nuclear loci. Most notably, our results support earlier claims (disputed by mitochondrial data) that S. aberti kaibabensis, found only on the north rim of the Grand Canyon, is highly divergent from other populations. However, we also detected introgression of S. aberti kaibabensis DNA into other S. aberti populations, which likely accounts for the previously inferred close genetic relationship between this population and those south of the Grand Canyon.ConclusionsOverall, the evolutionary history of Abert’s squirrels appears to be shaped largely by divergence during periods of habitat isolation. However, we also found evidence for interbreeding during periods of secondary contact resulting in introgression, with variable effects on mitochondrial and nuclear markers. Our results support the emerging view that populations often diversify under scenarios involving both divergence in isolation and gene flow during secondary contact, and highlight the value of genome-wide datasets for resolving such complex evolutionary histories.

Domal, thrombolitic, microbialite biostromes and associated lithofacies in the Upper Albian Devils River Trend along the northern, high-energy margin of the Maverick Basin

The Lower Cretaceous Devils River Trend on the northeast margin of the Maverick Basin in southwest Texas contains unique deposits of large domal, thrombolitic, microbial biostromes that have not been identified elsewhere in the Albian of the onshore Gulf of Mexico. These microbial biostromes are overlain by microbial-dominated, moderate-energy grainstones to mud-free rudstones. Above the grainstone to rudstone section is a hiatus (the Albian-19, high-frequency-sequence maximum flooding surface), and above this hiatus are large caprinid rudist bioherms. The overall setting for these carbonate deposits is the moderate- to high-energy north rim of the intraplatform Maverick Basin that is approximately 150 mi (240 km) behind the Stuart City Reef Trend. Four levels of description are necessary to describe the biostromes: (1) megalevel (overall external form)—domal biostromes, (2) macrolevel (larger internal form or layering)—sinuous convex-up layers within domes, (3) mesolevel (basic growth morphology—clotted thrombolites [subvertical to vertical]), and (4) microlevel (microbialite basic texture)—microbial peloids and mesoclots (clots of microbial-mediated material—mainly packed clusters of dark, micritic peloids). The thrombolitic peloids and mesoclots are arranged in digitate to randomly branching growth forms. The thrombolites are very microporous. Growth-framework cavities with sediment fill are common and are filled with mesoclots, peloids, clasts, miliolids, ostracods, echinoid fragments, bivalve fragments, and gastropods. The microbial biostrome is not continuous but has gaps (channels) filled with microbial-dominated grainstone and mud-free rudstones. The microbial-dominated grainstone and mud-free rudstone strata above the microbial biostrome are continuous, although irregularly bedded, with some beds being cross-stratified, and they are composed of fossiliferous, peloidal, mesoclot grainstone with abundant biota encrusted in a microbial coating. The domal, thrombolitic, microbialite biostrome is interpreted to have been deposited on a moderate-energy, semirestricted intraplatform rim at the northeast edge of the Maverick Basin during a higher order transgression. The microbial-dominated strata may have been associated with high nutrient concentrations and initial low sedimentation rates, followed by low to moderate sedimentation rates. The microbial-dominated grainstones and mud-free rudstones above were laid down in a moderate-energy environment during continued transgression. A sharp break exists with the shelf-interior, high-frequency highstand cycle above, which contains abundant rudist bioherms but no microbialites. Most of the primary megapores (growth-framework cavities and interparticle pores) are cemented with equant calcite. Nano- and micropores are extremely abundant within the microbial-related strata. These deposits would make good microporous reservoirs in the subsurface.

Spectral Properties of the Galactic Supernova Remnant Vela Jr. (G266.2-1.2) Using Chandra

An X-ray nonthermal spectral investigation of the galactic shell-type supernova remnant (SNR) Vela Jr. using archival data from Chandra for the northern and northwestern rims of the SNR is presented. Spectra were extracted from four emission regions in these rims (three in the northwestern rim and one in the northern). The X-ray spectra of the northwestern rim were well reproduced by a single power-law and the synchrotron model srcut , and for the north rim, the spectra were fitted by a single and a broken power-law , respectively. The spectra of both rims show no line emission. Each spectrum was fit by subtracting the modeled and nonmodeled background spectra, and statistically acceptable fits to all regions were derived using each model. Slight variations in derived fit parameters (such as photon index and roll-off frequency) with the background modeling method are also reported.

Bison on the Southwest Colorado Plateau: Conservation at the Edge

Cross-cutting multidisciplinary evidence sufficiently demonstrates that wild, free-ranging bison (Bison bison) that occupy portions of the House Rock Valley and Grand Canyon North Rim in northern Arizona are native wildlife at the southwest edge of their historical range. Wildlife at the edge of historical range can play an important role in the conservation of species after declines in distribution and abundance. Very low density bison likely approximate long-term prehistoric and historic conditions on the southwestern Colorado Plateau. Small, low-density bison herds managed as free-ranging wildlife could approximate these historic conditions, coexist with sensitive landscape and cultural resources, and contribute to a bison metapopulation, thereby contributing to the continental conservation of this species.