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Aim. Understanding the forces that drive range shifts in forest landscapes is imperative for predicting species distributions under anthropogenic climate and land use change. However, empirical studies exploring how these components jointly influence critical early-life stages of mountain tree species across environmental gradients are scarce. We used the high-mountain tree Polylepis australis as model species to investigate the relative importance of altitude and associated climatic conditions, land use for livestock and microsite characteristics on early-life performance. Location. Córdoba Sierras, central Argentina. Methods. We set up an extensive in situ sowing experiment with a robust split-plot design that integrated spatial scales ranging from 0.4 m2 subplots at the microsite level (associated with vegetative and micro-topographic structures), to livestock exclosure and enclosure plots of several hectares, to an altitudinal gradient of 1000 m. Components of early-life performance were monitored across two subsequent growing seasons. Results. Microsite characteristics played a fundamental role in P. australis establishment, whereby interactions with altitude and/or land use suggested alternate mechanisms: facilitation (likely reduced desiccation) dominated at low altitude while at high altitude abiotic stress (likely intensive frost and radiation) overruled any microsite effects. At mid altitude benefits of competition release prevailed over facilitation and microsite effects gained importance under livestock presence. Inconsistencies between pre- and post- emergence responses illustrated potential tradeoffs between beneficial and detrimental effects of microsite conditions upon performance throughout early life: a favorable location for seeds may abruptly turn adverse for seedlings. Main conclusions. We unravel how changes in altitude, anthropogenic disturbances and microsite characteristics jointly modulate P. australis performance across stages of early establishment. Such information is fundamental when categorizing specific microhabitats as “safe sites” for tree regeneration especially in mountain environments with high spatiotemporal heterogeneity.
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Top predators cause avoidance behaviours in competitors and prey, which can lead to niche partitioning and facilitate coexistence. We investigate changes in partitioning of the temporal niche in a mammalian community in response to both the rapid decline in abundance of a top predator and its rapid increase, produced by two concurrent natural experiments: 1) the severe decline of the Tasmanian devil due to a transmissible cancer, and 2) the introduction of Tasmanian devils to an island, with subsequent population increase. We focus on devils, two mesopredators, and three prey species, allowing us to examine niche partitioning in the context of intra- and inter-specific competition, and predator-prey interactions. The most consistent shift in temporal activity occurred in devils themselves, which were active earlier in the night at high densities, presumably because of heightened intraspecific competition. When devils were rare, their closest competitor, the spotted-tailed quoll, increased activity in the early part of the night, resulting in increased overlap with the devil’s temporal niche and suggesting release from interference competition. The invasive feral cat, another mesopredator, did not shift its temporal activity in response to either decreasing or increasing devil densities. Shifts in temporal activity of the major prey species of devils were stronger in response to rising than to falling devil densities. We infer that the costs associated with not avoiding predators when their density is rising (i.e., death) are higher than the costs of continuing to adopt avoidance behaviours as predator densities fall (i.e., loss of foraging opportunity), so rising predator densities may trigger more rapid shifts. The rapid changes in devil abundance provide a unique framework to test how the non-lethal effects of top predators affect community-wide partitioning of temporal niches, revealing that this top-predator has an important but varied influence on the diel activity of other species.
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Premise of the research. The disjunct distribution of plant genera between eastern Asia (EA) and eastern North America (ENA) has long attracted the attention of biologists and biogeographers. For most genera that have been studied, there are more species in EA than ENA and the diversity anomaly may have resulted from the greater physiographical heterogeneity in conjunction with climate and sea level changes in EA than in ENA. However, few empirical studies have explicitly tested the association between species diversity and allopatric speciation events. The genus Stewartia (Theaceae) displays this diversity anomaly with two species in ENA and 21 species in EA, but the phylogeny of this group has not been resolved due to insufficient data. Methodology. Here, we sampled 15 species of Stewartia (65%) and generated data from over 500 nuclear loci using the anchored phylogenomic approach to produce a robust phylogeny of Stewartia. In addition, biogeographical analyses were performed to elucidate the natural history of Stewartia including estimated times of divergence, ancestral areas, and speciation patterns. Pivotal results. Our parsimony, Bayesian, and species tree analyses produced congruent phylogenies with high resolution of the interspecific relationships within Stewartia. Speciation in Asia was mostly allopatric between the Japanese islands and the Asian continent during the Miocene and early Pliocene, while the two ENA species represent lineages from different times with S. malacodendron being the first lineage to split off from the remaining species and S. ovata coming later sister to the deciduous species of Asian Stewartia. Conclusions. The results provide direct evidence for the importance of allopatry in the differential diversity between EA and ENA.
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The Chihuahuan Desert includes many endemic angiosperm species, some having very restricted geographic ranges. One of these species is Oreocarya crassipes (I. M. Johnst.) Hasenstab & M. G. Simpson, an endangered distylous gypsophile from the Trans-Pecos region in southern Brewster County, Texas, USA. The species is known from 10 populations, and this small number of populations, human development in the area, a distylous breeding system, and edaphic requirements threaten the long-term viability of the species. Using both hundreds of single nucleotide polymorphisms identified via tunable genotyping-by-sequencing (tGBS) and 10 microsatellite loci, patterns of genetic diversity, demography, selection, and migration were examined for 192 individuals from four populations of O. crassipes. From the sampled individuals, two populations (clusters) were identified via multiple methodologies and with both types of data. With SNP data, population substructure was further resolved among one of these populations to identify two distinct groups of individuals. Multiple individuals recognized as having mixed ancestry, along with Fst values and AMOVA results, provide evidence of genetic exchange among populations, which is less common for gypsophiles than non-gypsophiles, and the rate of migration among populations has been increasing recently. The Fst values for O. crassipes are more similar to those of other rare species than to other gypsophiles. Additionally, while distyly specifically does not necessarily impact the population genetics of the species, allogamy, which is facilitated by distyly, seems to have played a role in the genetic structure of O. crassipes.
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Invasive species may quickly colonize novel environments, which could be attributed to both phenotypic plasticity and an ability to locally adapt. Reproductive traits are expected to be under strong selection when the new environment limits reproductive success of the invading species. This may be especially important for external fertilizers, which release sperm and eggs into the new environment. Despite adult tolerance to high salinity, the invasive fish Neogobius melanostomus (round goby) is absent from fully marine regions of the Baltic Sea, raising the possibility that its distribution is limited by tolerance during earlier life-stages. Here, we investigate the hypothesis that the spread of N. melanostomus is limited by sperm function in novel salinities. We sampled sperm from two invasion fronts with higher and lower salinities in the Baltic Sea and tested them across a range of salinity levels. We found that sperm velocity and percentage of motile sperm declined in salinity levels higher and lower than those currently experienced by the Baltic Sea populations, with different performance curves for the two fronts. Sperm velocity also peaked closer to the home salinity conditions in each respective invasion front, with older localities showing an increased fit to local conditions. By calculating how the sperm velocity has changed over generations, we show this phenotypic shift to be in the range of other fish species under strong selection, indicating on-going local adaptation or epigenetic acclimation to their novel environment. These results show that while immigrant reproductive dysfunction appears to at least partly limit the distribution of invasive N. melanostomus in the Baltic Sea, local adaptation to novel environments could enable future spread beyond their current boundaries.
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1. Plantation silviculture is increasing globally and is particularly intensive in temperate coniferous forests, where densely planting trees requires practices common to non-conifer systems that can alter forest floor microhabitat, and potentially threaten amphibian persistence. Most declining amphibian species depend on specific forest microhabitats as terrestrial refugia, but amphibian extirpation associated with tree harvest alone appears unlikely, suggesting that impacts of planting forests on groundcover might better predict recent declines in amphibian occupancy. 2. We repeatedly sampled larval presence or absence of 10 amphibian species native to temperate coniferous forest in the Southeastern United States for one year at 62 isolated wetlands located in either naturally regenerating or planted forest (plantation) to assess three direct ways that planted forests might reduce amphibian breeding site occupancy by: 1) increasing conifer densities, 2) decreasing groundcover, and 3) an indirect pathway, whereby increased tree densities at plantations might reduce groundcover and thus amphibian site occupancy. 3. After controlling for wetland traits and accounting for differences in detection, breeding site occupancy for 8/10 amphibian species was dependent upon whether forests were planted surrounding wetlands (within 300 m). Herbaceous groundcover, not canopy, most commonly influenced occupancy and increased occupancy for declining surface active or fossorial amphibians. 4. Path analyses showed that, by directly and indirectly reducing groundcover (via conifer densities), plantations had significantly lower occupancy of two declining surface active or fossorial frog species, whereas two common aquatic frog species were tolerant to planting conifers. Among declining species, salamanders showed a greater reduction in occupancy than anurans, likely because of greater vulnerability to the drier forest floor conditions of plantation than naturally regenerating forests. 5. Synthesis and applications: Direct negative impacts of coniferous plantation on amphibians can be addressed by limiting groundcover and soil impacts, including switching from high intensity practices, such as mechanical chopping vegetation or bedding soil, to lower intensity site preparation treatments that are less likely to significantly disturb groundcover. Indirect negative effects of dense canopy cover at planted forests could be lowered by periodically thinning canopies prior to final harvest, thus increasing intact forest groundcover and the conservation of both common and declining amphibians.
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Visually hunting predators must overcome the challenges that prey groups present. One such challenge is the confusion effect where an overburdened visual system means predators are unable to successfully target prey. A strategy to overcome confusion is the targeting of distinct, or odd, individuals (the oddity effect). In live prey experiments, manipulation of group member phenotypes can be challenging and prey may differ on more than the single feature one intends to define as odd. The use of highly controllable computerized stimuli to study predator-prey interactions is increasingly popular in the field of behavioral ecology. However, to our knowledge, the validity of computerized stimuli to study the oddity effect has not been established. Predator choice experiments were conducted using naive stickleback predators to ascertain whether the oddity effect could be demonstrated in the absence of live prey. We found evidence for both the oddity effect and preferential targeting of group edges and low density regions, as would be predicted if predators targeted prey individuals to minimize confusion. The oddity effect was evident at a low threshold, above which dots were no longer perceived as odd, and no longer attacked more often than expected by chance. We conclude that computerized stimuli are an improved, practical method for studying oddity effects while further validating the use of similar methods for studying other aspects of visual predation. In addition to higher control of ‘prey’ appearance, the replacement of live prey animals with digital stimuli is ethically beneficial and reusing code improves experimental efficiency.
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The airway epithelium is critical for maintaining innate and adaptive immune responses, and occupational exposures that disrupt its immune homeostasis may initiate and amplify airway inflammation. In our previous study, we demonstrated that silver nanoparticles (AgNP), which are engineered nanomaterials used in multiple applications but primarily in the manufacturing of many antimicrobial products, induce toxicity in organotypic cultures derived from murine tracheal epithelial cells (MTEC), and those differentiated toward a “Type 2 [T2]-Skewed” phenotype experienced an increased sensitivity to AgNP toxicity, suggesting that asthmatics could be a sensitive population to AgNP exposures in occupational settings. However, the mechanistic basis for this genotype × phenotype interaction (G×P) has yet to be defined. In the present study, we conducted transcriptional profiling using RNA-sequencing (RNA-seq) to predict the enrichment of specific canonical pathways and upstream transcriptional regulators to assist in defining a mechanistic basis for G×P effects on AgNP toxicity. Organotypic cultures were derived from MTEC across two genetically inbred mouse strains (A/J and C57BL/6J mice), two phenotypes (“Normal” and “T2-Skewed”), and one AgNP exposure (an acute 24 h exposure) to characterize G×P effects on transcriptional response to AgNP toxicity. The “T2-Skewed” phenotype was marked by increased pro-inflammatory T17 responses to AgNP toxicity, which are significant predictors of neutrophilic/difficult-to-control asthma and suggests that asthmatics could be a sensitive population to AgNP exposures in occupational settings. This study highlights the importance of considering G×P effects when identifying these sensitive populations, whose underlying genetics or diseases could directly modify their response to AgNP exposures.
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Objective: To determine whether ascending arousal network (AAN) connectivity is reduced in patients presenting with traumatic coma. Methods: We performed high angular resolution diffusion imaging (HARDI) in 16 patients with acute severe traumatic brain injury who were comatose on admission and in 16 matched controls. We used probabilistic tractography to measure the connectivity probability (CP) of AAN axonal pathways linking the brainstem tegmentum to the hypothalamus, thalamus and basal forebrain. To assess the spatial specificity of CP differences between patients and controls, we also measured CP within four subcortical pathways outside the AAN. Results: Compared to controls, patients showed a reduction in AAN pathways connecting the brainstem tegmentum to a region of interest encompassing the hypothalamus, thalamus, and basal forebrain. Examining each pathway individually, brainstem-hypothalamus and brainstem-thalamus CPs, but not brainstem-forebrain CP, were significantly reduced in patients. Only one subcortical pathway outside the AAN showed reduced CP in patients. Conclusions: We provide initial evidence for the reduced integrity of axonal pathways linking the brainstem tegmentum to the hypothalamus and thalamus in patients presenting with traumatic coma. Our findings support current conceptual models of coma as being caused by subcortical AAN injury. AAN connectivity mapping provides an opportunity to advance the study of human coma and consciousness.
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Idelalisib is a phosphatidylinositol 3-kinase inhibitor highly selective for the delta isoform that has shown good efficacy in treating chronic lymphocytic leukemia and follicular lymphoma. In clinical trials, however, idelalisib was associated with rare, but potentially serious liver and lung toxicities. In this study, we used the Collaborative Cross (CC) mouse population to identify genetic factors associated with the drug response that may inform risk management strategies for idelalisib in humans. Eight (8) male mice (4 matched pairs) from 50 CC lines were treated once daily for 14 days by oral gavage with either vehicle or idelalisib at a dose selected to achieve clinically-relevant peak plasma concentrations (150 mg/kg/day). The drug was well tolerated across all CC lines, and there were no observations of overt liver injury. Differences across CC lines were seen in drug concentration in plasma samples collected at the approximate Tmax on study Days 1, 7, and 14. There were also small but statistically significant treatment-induced alterations in plasma total bile acids and microRNA-122, and these may indicate early hepatocellular stress required for immune-mediated hepatotoxicity in humans. Idelalisib treatment further induced significant elevations in the total cell count of terminal bronchoalveolar lavage fluid, which may be analogous to pneumonitis observed in the clinic. Genetic mapping identified loci associated with interim plasma idelalisib concentration and the other three treatment-related endpoints. Thirteen (13) priority candidate quantitative trait genes identified in CC mice may now guide interrogation of risk factors for adverse drug responses associated with idelalisib in humans.
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