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Individuals often differ in their ability to cope with challenging environmental and social conditions. Evidence from model systems suggests that patterns of DNA methylation are associated with variation in coping ability. These associations could arise directly if methylation plays a role in controlling the physiological response to stressors by, among other things, regulating the release of glucocorticoids in response to challenges. Alternatively, the association could arise indirectly if methylation and resilience have a common cause, such as early life conditions. In either case, methylation might act as a biomarker for coping ability. At present, however, relatively little is known about whether variation in methylation is associated with organismal performance and resilience under natural conditions. We studied genome-wide patterns of DNA methylation in free-living female tree swallows (Tachycineta bicolor) using methylated DNA immunoprecipitation (MeDIP) and a tree swallow genome that was assembled for this study. We identified areas of the genome that were differentially methylated with respect to social signal expression (breast brightness) and physiological traits (ability to terminate the glucocorticoid stress response through negative feedback). We also asked whether methylation predicted resilience to a subsequent experimentally imposed challenge. Individuals with brighter breast plumage and higher stress resilience had lower methylation at differentially methylated regions across the genome. Thus, widespread differences in methylation predicted both social signal expression and the response to future challenges under natural conditions. These results have implications for predicting individual differences in resilience, and for understanding the mechanistic basis of resilience and its environmental and social mediators.
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Warming global temperatures are affecting a range of aspects of wild populations, but the exact mechanisms driving associations between temperature and phenotypic traits may be difficult to identify. Here, we use a 36-year data-set on a wild population of red deer to investigate the causes of associations between temperature and two important components of female reproduction: timing of breeding and offspring size. By separating within- versus between-individual associations with temperature for each trait, we show that within-individual phenotypic plasticity (changes within a female’s lifetime) was entirely sufficient to generate the observed population-level association with temperature at key times of year. However, despite apparently adequate statistical power, we found no evidence of any variation between females in their responses (i.e. no ‘IxE’ interactions). Our results suggest that female deer show plasticity in reproductive traits in response to temperatures in the year leading up to calving, and that this response is consistent across individuals, implying no potential for either selection or heritability of plasticity. We estimate that the plastic response to rising temperatures explained 24% of the observed advance in mean calving date over the study period. We highlight the need for comparable analyses of other systems to determine the contribution of within-individual plasticity to population-level responses to climate change.
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Wild quantitative genetic studies have focused on a subset of traits (largely morphological and life-history), with others, such as behaviors, receiving much less attention. This is because it is challenging to obtain sufficient data, particularly for behaviors involving interactions between individuals. Here, we explore an indirect approach for pilot investigations of the role of genetic differences in generating variation in parental care. Variation in parental genetic effects for offspring performance is expected to arise from among-parent genetic variation in parental care. Therefore, we used the animal model to predict maternal breeding values for lamb growth and used these predictions to select females for field observation, where maternal and lamb behaviors were recorded. Higher predicted maternal breeding value for lamb growth was associated with greater suckling success, but not with any other measures of suckling behavior. Though our work cannot explicitly estimate the genetic basis of the specific traits involved, it does provide a strategy for hypothesis generation and refinement, that we hope could be used to justify data collection costs needed for confirmatory studies. Here results suggest that behavioral genetic variation is involved in generating maternal genetic effects on lamb growth in Soay sheep. Though important caveats and cautions apply, our approach may extend the ability to initiate more genetic investigations of difficult-to-study behaviours and social interactions in natural populations.
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An experimental study on ordered pyrochlore structured Gd1.5Ce0.5Ti2O7 (Fd-3m) was carried out up to 45 GPa by synchrotron radiation X-ray diffraction and Raman spectroscopy. Experimental results show that Gd1.5Ce0.5Ti2O7 transfers to a disordered cotunnite-like phase (Pnma Z=4) at ~42 GPa. Compared with the end member Gd2Ti2O7, the substitution of Ce3+ for Gd3+ increases the transition pressure and the high-pressure stability of the pyrochlore phase. This pressure-induced structure transition is mainly controlled by cationic order-disorder modification, and the cationic radius ratio rA/rB may also be effective for predicting the pyrochlore oxides’ high-pressure stability. In addition, two isostructural transitions of Gd1.5Ce0.5Ti2O7 are observed at 6.5 GPa and 13 GPa, and their unit-cell volumes as a function of pressure demonstrate that the compression behavior is rather complex.
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Spatial environmental heterogeneity coupled with dispersal can promote ecological persistence of diverse metacommunities. Does this premise hold when metacommunities evolve? Using a 2-resource competition model, we studied the evolution of resource-uptake specialization as a function of resource type (substitutable to essential) and shape of the trade-off between resource uptake affinities (generalist- to specialist-favoring). In spatially homogeneous environments, evolutionarily stable coexistence of consumers is only possible for sufficiently substitutable resources and specialist-favoring trade-offs. Remarkably, these same conditions yield comparatively low diversity in heterogeneous environments, because they promote sympatric evolution of two opposite resource specialists that, together, monopolize the two resources everywhere. Consumer diversity is instead maximized for intermediate trade-offs and clearly substitutable or clearly essential resources, where evolved metacommunities are characterized by contrasting selection regimes. Taken together, our results present new insights on resource-competition-mediated evolutionarily-stable diversity in homogeneous and heterogeneous environments, which should be applicable to a wide range of systems.
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Carnivorous wasps of the family Vespidae are known to seek out and disperse the diaspores of at least two North American and two Asian plant species. Attraction of the wasps to the diaspores is likely due to the release of volatile compounds that signal availability of an eliaiosome rich in protein and fat, which the wasps remove before releasing the diaspore. It is thought that this interaction between carnivorous wasps and plants is rare, occurring in just a few plant species. Here, we present our findings on dispersal of spicebush (Calycanthus occidentalis Hook. & Arn.) achenes by carnivorous wasps of the genus Vespula. Observations and experiments were performed with the goals of discovering: how geographically widespread this interaction is; what the reward system is, if any; and, how wasps detect the achenes. Eight populations of C. occidentalis in northern California were used to observe wasps and plants, and to perform experiments on wasp attraction to the achenes. In all examined populations, workers of western yellowjacket (Vespula pensylvanica [de Saussure, 1857]) were observed entering mature Calycanthus receptacles, removing achenes, taking flight with them, and successfully transporting achenes through the air. Receptacles were found to open upward at an average angle of 45° (SD = 29°), preventing the achenes from falling to the ground when mature. No animals other than wasps were observed visiting the receptacles during the observations. Experiments suggest that wasps are attracted to an elaiosome-like organ of the achene. Nutritional analysis shows that this organ is high in fat and protein. Further experiments using solvent extracts of the achenes suggest that the attraction is likely mediated by volatile compounds.
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Hunters often target species that require resource investment disproportionate to associated nutritional rewards. Costly signalling theory provides a potential explanation, proposing that hunters target species that impose high costs (e.g. higher failure and injury risks, lower consumptive returns) because it signals an ability to absorb costly behaviour. If costly signalling is relevant to contemporary ‘big game’ hunters, we would expect hunters to pay higher prices to hunt taxa with higher perceived costs. Accordingly, we hypothesized that hunt prices would be higher for taxa that are larger-bodied, rarer, carnivorous, or described as dangerous or difficult to hunt. In a data set on 721 guided hunts for fifteen North American large mammals, prices listed online increased with body size in carnivores (from approximately $550 to $1800 USD/day across the observed range). This pattern suggests that elements of costly signals may persist among contemporary non-subsistence hunters. Persistence might simply relate to deception, given that signal honesty and fitness benefits are unlikely in such different conditions compared with ancestral environments in which hunting behaviour evolved. If larger-bodied carnivores are generally more desirable to hunters, then conservation and management strategies should consider not only the ecology of the hunted but also the motivations of hunters.
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Due to its novelty and scale, the EMBER project is a key study within the prescribed burning evidence base. However, it has several significant but overlooked methodological flaws. In this paper, we outline and discuss these flaws. In doing so, we aim to highlight the current paucity of evidence relating to prescribed burning impacts on ecosystem services within the British uplands. We show that the results of the EMBER project are currently unreliable because: it used a correlative space‐for‐time approach; treatments were located within geographically separate and environmentally distinct sites; environmental differences between sites and treatments were not accounted for during statistical analysis; and, peat surface temperature results are suggestive of measurement error. Policy Implications. Given the importance of the EMBER project, our findings suggest that (a) government agencies and policymakers need to re‐examine the strengths and limitations of the prescribed burning evidence base; and, (b) future work needs to control for site‐specific differences so that prescribed burning impacts on ecosystem services can be reliably identified.
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Conodont elements, consisting of crown and basal tissue are the well-known fossilized hard parts of Conodonta (extinct marine chordates), but the taphonomic processes leading to decomposition or remineralization of the basal tissue are not well understood. Here we focus on the taphonomy of basal tissue, reviewing the published record and describing new material from Asia and Europe (248 occurrences globally). These include crown and basal tissue in conjunction, and isolated basal bodies showing different stages of preservation. Some isolated specimens resemble phosphate rings similar to those assigned to Phosphannulus universalis. High-resolution biostratigraphy indicates that the lamellar type of conodont basal tissue is found in all facies and depositional environments. Other basal tissue types, described in the literature as tubular, mesodentine, spherulitic or lamellar with canalules, are limited to the early Palaeozoic and found exclusively in siliciclastic deposits (with the exception of spherulitic tissue). Although the stratigraphic record of basal tissue spans the range of Euconodonta (Cambrian–Triassic), this study shows that most of the isolated plate and ring-like structures are derived from early Palaeozoic coniform conodonts. Basal tissue of platform-type elements has a much more fragile shape and is therefore rarely preserved as a recognizable isolated unit.
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Climate warming is contributing to increases in wildfire activity throughout the western U.S., leading to potentially long-lasting shifts in vegetation. The response of forest ecosystems to wildfire is thus a crucial indicator of future vegetation trajectories, and these responses are contingent upon factors such as seed availability, interannual climate variability, average climate (e.g., 30-year normals), and other components of the physical environment. To better understand variation in forest resilience to fire across vulnerable dry forests, we performed field surveys of conifer seedling abundance in 15 recent (1988-2010) wildfires and characterized temporal variation in seed cone production and seedling establishment. We then modeled post-fire seedling abundances for each species at a 30 m resolution using downscaled climate data, monthly water balance models, and canopy cover of surviving mature conifers. Widespread ponderosa pine (Pinus ponderosa) seed cone production occurred at least twice following each fire surveyed and pulses of conifer seedling establishment coincided with years of above-average moisture availability. Ponderosa pine and Douglas-fir (Pseudotsuga menziesii) seedling abundances were higher on more mesic sites and adjacent to surviving trees, though there were also important interspecific differences, likely attributable to drought- and shade-tolerance. We estimated that 41.8% (for ponderosa pine) and 68.5% (for Douglas-fir) of the total area burned did not meet tree density thresholds consistent with historical densities for each species. Spatial models demonstrated that the availability of seed trees (particularly in the interior of large, high-severity patches) limited seedling abundances in many areas, but 30-year average actual evapotranspiration and climatic water deficit also limited abundances on marginal sites. A better understanding of the limitations to post-fire recovery is likely to aid in developing adaptation and mitigation strategies through the improvement of models of future ecosystem change throughout the western U.S.
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