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opencc-zeroOct 2020View details →

The strength and form of natural selection on transcript abundance in the wild

Gene transcription variation is known to contribute to disease susceptibility and adaptation, but we currently know very little about how contemporary natural selection shapes transcript abundance. Here, we propose a novel analytical framework to quantify the strength and form of ongoing natural selection at the transcriptome level in a wild vertebrate. We estimated selection on transcript abundance in a cohort of a wild salmonid fish (Salmo trutta) affected by an extracellular myxozoan parasite (Tetracapsuloides bryosalmonae) through mark-recapture field sampling and the integration of RNA-seq with classical regression-based selection analysis. We show, based on fin transcriptomes of the host, that infection by the parasite and subsequent host survival is linked to upregulation of mitotic cell cycle process. We also detect a widespread signal of disruptive selection on transcripts linked to host immune defence, host-pathogen interactions, cellular repair and maintenance. Our results provide insights about how selection can be measured at the transcriptome level to dissect the molecular mechanisms of contemporary natural selection driven by climate change and emerging anthropogenic threats. We anticipate that the approach described here will enable critical information on the molecular mechanisms and targets of natural selection to be obtained in real time.

opencc-zeroNov 2020View details →

Tree mycorrhizal type mediates the strength of negative density dependence in temperate forests

1. Recent plant-soil feedback experiments suggest that arbuscular mycorrhizal (AM) tree species experience stronger conspecific negative density dependence (CNDD) than ectomycorrhizal (EM) tree species. Yet how these findings inform our understanding of natural systems is limited because the roles of local soil conditions, light environments and tree species abundances in influencing CNDD for AM and EM species are not clear. 2. Here we examined seedling and sapling survival in two temperate old-growth forests (broadleaved pine and spruce-fir forests) in Northeast China, to evaluate the effects of both conspecific and heterospecific neighbour density, as well as the soil and light environments, on the survival of AM and EM-dependent trees at early life stages. 3. While light availability increased the survival of EM seedlings, soil organic resources increased EM sapling survival in the spruce-fir plot. AM seedlings suffered stronger CNDD than did EM seedlings in both plots. In the spruce-fir plot, soil factors and light availability mediated species CNDD but their effects differed for AM and EM species, and also between seedlings and saplings. For seedlings in both plots, we found that AM species exhibited a positive relationship between species abundance and CNDD strength, whereas this relationship was negative for EM species. 4. Synthesis. Our results provide one of the few tests of how fungal symbioses determine species responses to intra- and interspecific interactions and the direct effects of local environmental conditions on seedling and sapling survival. We show that mycorrhizal type mediates the strength of CNDD and its relationship with species abundance. These results suggest that tree mycorrhizal association can determine the strength of CNDD effects on both rare and common species, and these CNDD differences are likely to influence the community composition of temperate forests.

zenodo32/100

Probabilistic Approach for the Fatigue Strength Prediction of Polymers

The dominating factor in the fatigue of structures made from fiber reinforced polymers (FRP), for example wind turbine blades, is the polymer matrix. Traditionally, experimental stress-life data of polymers is approximated via a linear double-log Basquin model. Recently, the non-linear stress-life formulation by Stüssi was found to provide a better fit of the experimental data with a substantially reduced standard deviation. Moreover, a non-linear constant-life formulation, as proposed by Boerstra, for example, can enhance the representation of the mean stress effect compared to state-of-the-art linear models, i.e., the modified Goodman relation. To this end, we incorporated Stüssi’s model into the Boerstra relation to take account of the mean stress effects of an epoxy. This stress-life formulation was then enhanced with the Weibull probability function. The probabilistic-stress-life model provided a good approximation of the fatigue performance as a function of the stress ratio on the basis of an experimental data set. Finally, we suggested a step-wise engineering approach to derive the permissible stress-life with a view to practical design purposes. The procedure increased the reliability of the fatigue design evaluation compared to the state-of-the-art methodologies. Slides: <a href="https://doi.org/10.5281/zenodo.4443149">https://doi.org/10.5281/zenodo.4443149</a> Paper: <a href="https://doi.org/10.2514/6.2021-1289">https://doi.org/10.2514/6.2021-1289</a>

opencc-by-4.0Jan 2021View details →

opencc-zeroJun 2019View details →

Data from: A metadata approach to evaluate the state of ocean knowledge: strengths, limitations, and application to Mexico

Climate change, mismanaged resource extraction, and pollution are reshaping global marine ecosystems with direct consequences on human societies. Sustainable ocean development requires knowledge and data across disciplines, scales and knowledge types. Although several disciplines are generating large amounts of data on marine socio-ecological systems, such information is often underutilized due to fragmentation across institutions or stakeholders, limited standardization across scale, time or disciplines, and the fact that information is often not searchable within existing databases. Compiling metadata, the information which describes existing sets of data, is an effective tool that can address these challenges, particularly when metadata corresponding to multiple datasets can be combined to integrate, organize and classify multidisciplinary data. Here, using Mexico as a case study, we describe the compilation and analysis of a metadatabase of ocean knowledge that aims to improve access to information, facilitate multidisciplinary data sharing and integration, and foster collaboration among stakeholders. We also evaluate the knowledge trends and gaps for informing ocean management. Analysis of the metadatabase highlights that past and current research in Mexico focuses strongly on ecology and fisheries, with biological data more consistent over time and space compared to data on human dimensions. Regional imbalances in available information were also evident, with most available information corresponding to the Gulf of California, Campeche Bank and Caribbean and less available for the central and south Pacific and the western Gulf of Mexico. Despite existing knowledge gaps in Mexico and elsewhere, we argue that systematic efforts such as this can often reveal an abundance of information for decision-makers to develop policies that meet key commitments on ocean sustainability. Surmounting current cross-scale social and ecological challenges for sustainability requires transdisciplinary approaches. Metadatabases are critical tools to make efficient use of existing data, highlight and address strengths and deficiencies, and develop scenarios to inform policies for managing complex marine social-ecological systems.

opencc-zeroJan 2013View details →

Data from: Consumer interaction strength may limit the diversifying effect of intraspecific competition: a test in alewife (Alosa pseudoharengus).

Intraspecific competition is considered a principal driver of dietary variation, however, empirical studies provide mixed support for this mechanism. Here we link comparative and experimental work testing the effects of competition and resource availability on the dietary variation of alewife (Alosa pseudoharengus). Alewife, a consumer with extreme effects on its resources, are specifically utilized to additionally test the idea that that the strength of the interaction between a consumer and its resources may diminish the diversifying effect of competition. First, we compared the short- and long-term diet measures of from wild populations across a range of densities. Second, in a series of large-scale field mesocosm experiments we explored the influence of competition and interaction strength on alewife dietary variation. Results from the whole lake comparison and field experiments indicated that increasing competition was negatively correlated with population dietary variation. Further, altering the strength of the interaction between alewife and their prey via prey supplementation eliminated this negative relationship. Collectively, our results suggest that competitive interactions may not drive dietary diversification in highly effective consumers. Our results also suggest that further consideration of the strength of species interactions (and the consumer traits that underlie them) would improve our understanding of the link between intraspecific competition and variation

Data from: Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

Many arthropods and small vertebrates use adhesive pads for climbing. These biological adhesives have to meet conflicting demands: attachment must be strong and reliable, yet detachment should be fast and effortless. Climbing animals can rapidly and reversibly control their pads' adhesive strength by shear forces, but the mechanisms underlying this coupling have remained unclear. Here, we show that adhesive forces of stick insect pads closely followed the predictions from tape peeling models when shear forces were small, but strongly exceeded them when shear forces were large, resulting in an approximately linear increase of adhesion with friction. Adhesion sharply increased at peel angles less than ca 30°, allowing a rapid switch between attachment and detachment. The departure from classic peeling theory coincided with the appearance of pad sliding, which dramatically increased the peel force via a combination of two mechanisms. First, partial sliding pre-stretched the pads, so that they were effectively stiffer upon detachment and peeled increasingly like inextensible tape. Second, pad sliding reduces the thickness of the fluid layer in the contact zone, thereby increasing the stress levels required for peeling. In combination, these effects can explain the coupling between adhesion and friction that is fundamental to adhesion control across all climbing animals. Our results highlight that control of adhesion is not solely achieved by direction-dependence and morphological anisotropy, suggesting promising new routes for the development of controllable bio-inspired adhesives.

Data from: Asymmetric competitive effects during species range expansion: an experimental assessment of interaction strength between 'equivalent' grazer species at their range overlap

1. Biotic interactions are central to the development of theory and concepts in community ecology; experimental evidence has shown their strong effects on patterns of population and community organization and dynamics over local spatial scales. The role of competition in determining range limits and preventing invasions at biogeographic scales is more controversial, partly because of the complexity of processes involved in species colonization of novel habitats and the difficulties in performing appropriate manipulations and controls. 2. We examined experimentally whether competition is likely to affect poleward range expansion hindering or facilitating the establishment of the limpet Scurria viridula along the southeastern Pacific rocky shore (30°S, Chile) in the region occupied by the congeneric S. zebrina. We also assessed whether competition with the "invader" or range expanding species could reduce individual performance of the 'native' S. zebrina and depress local populations 3. Geographic field surveys were conducted to characterize the abundance and identity of limpets along the south-eastern Pacific coast from 18°S to 41°S, and the micro-scale (few cm) spatial distribution across the range overlap of the two species. Field-based competition experiments were conducted at the southern leading edge of the range of S. viridula (33°S) and at the northern limit of S. zebrina (30°S). 4. Field surveys showed poleward range expansion of S. viridula of ca. 210 km since year 2000, with an expansion rate of 13.1 km year -1. No range shift was detected for S. zebrina. The resident S. zebrina had significant negative effects on the growth rate of the invading juvenile S. viridula, while no effect of the latter was found on S. zebrina. Spatial segregation between species was found at the scale of cms. 5. Our results provide novel evidence of an asymmetric competitive effect of a resident species on an invader, which may hamper further range expansion. No negative effect of the invader on the resident species was detected. This study highlights the complexities of evaluating the role of species interactions in setting range limits of species, but showed how interspecific competition might slow the advance of an invader by reducing individual performance and overall population size at the advancing front.

Data from: Resource levels and prey state influence antipredator behavior and the strength of nonconsumptive predator effects

The risk of predation can drive trophic cascades by causing prey to engage in antipredator behavior (e.g. reduced feeding), but these behaviors can be energetically costly for prey. The effects of predation risk on prey (nonconsumptive effects, NCEs) and emergent indirect effects on basal resources should therefore depend on the ecological context (e.g. resource abundance, prey state) in which prey manage growth/predation risk tradeoffs. Despite an abundance of behavioral research and theory examining state-dependent responses to risk, there is a lack of empirical data on state-dependent NCEs and their impact on community-level processes. We used a rocky intertidal food chain to test model predictions for how resources levels and prey state (age/size) shape the magnitude of NCEs. Risk cues from predatory crabs (Carcinus maenas) caused juvenile and sub-adult snails (Nucella lapillus) to increase their use of refuge habitats and decrease their growth and per capita foraging rates on barnacles (Semibalanus balanoides). Increasing resource levels (high barnacle density) and prey state (sub-adults) enhanced the strength of NCEs. Our results support predictions that NCEs will be stronger in resource-rich systems that enhance prey state and suggest that the demographic composition of prey populations will influence the role of NCEs in trophic cascades. Contrary to theory, however, we found that resources and prey state had little to no effect on snails in the presence of predation risk. Rather, increases in NCE strength arose because of the strong positive effects of resources and prey state on prey foraging rates in the absence of risk. Hence, a common approach to estimating NCE strength – integrating measurements of prey traits with and without predation risk into a single metric – may mask the underlying mechanisms driving variation in the strength and relative importance of NCEs in ecological communities.

Data from: The strength of the association between heterozygosity and probability of interannual local recruitment increases with environmental harshness in blue tits

The extent of inbreeding depression and the magnitude of heterozygosity–fitness correlations (HFC) have been suggested to depend on the environmental context in which they are assayed, but little evidence is available for wild populations. We combine extensive molecular and capture–mark–recapture data from a blue tit (Cyanistes caeruleus) population to (1) analyze the relationship between heterozygosity and probability of interannual adult local recruitment and (2) test whether environmental stress imposed by physiologically suboptimal temperatures and rainfall influence the magnitude of HFC. To address these questions, we used two different arrays of microsatellite markers: 14 loci classified as neutral and 12 loci classified as putatively functional. We found significant relationships between heterozygosity and probability of interannual local recruitment that were most likely explained by variation in genomewide heterozygosity. The strength of the association between heterozygosity and probability of interannual local recruitment was positively associated with annual accumulated precipitation. Annual mean heterozygosity increased over time, which may have resulted from an overall positive selection on heterozygosity over the course of the study period. Finally, neutral and putatively functional loci showed similar trends, but the former had stronger effect sizes and seemed to better reflect genomewide heterozygosity. Overall, our results show that HFC can be context dependent, emphasizing the need to consider the role of environmental heterogeneity as a key factor when exploring the consequences of individual genetic diversity on fitness in natural populations.

opencc-zeroDec 2014View details →

Data from: A benign juvenile environment reduces the strength of antagonistic pleiotropy and genetic variation in the rate of senescence

1. The environment can play an important role in the evolution of senescence because the optimal allocation between somatic maintenance and reproduction depends on external factors influencing life expectancy. 2. The aims of this study were to experimentally test whether environmental conditions during early life can shape senescence schedules, and if so, to examine whether variation among individuals or genotypes with respect to the degree of ageing differs across environments. 3. We tested life-history plasticity and quantified genetic effects on the pattern of senescence across different environments within a reaction norm framework by using an experiment on the three-spined stickleback (Gasterosteus aculeatus, Linnaeus) in which F1 families originating from a wild annual population experienced different temperature regimes. 4. Male sticklebacks that had experienced a more benign environment earlier in life subsequently reduced their investment in carotenoid-based sexual signals early in the breeding season, and consequently senesced at a slower rate later in the season, compared to those that had developed under harsher conditions. This plasticity of ageing was genetically determined. Both antagonistic pleiotropy and genetic variation in the rate of senescence were evident only in the individuals raised in the harsher environment. 5. The experimental demonstration of genotype-by-environment interactions influencing the rate of reproductive senescence provides interesting insights into the role of the environment in the evolution of life-histories. The results suggest that benign conditions weaken the scope for senescence to evolve, and that the dependence on the environment may maintain genetic variation under selection.

Data from: Sperm competition and the evolution of precopulatory weapons: testis size and amplexus position, but not arm strength, affect fertilization success in a chorusing frog

Trade-offs between pre- and postcopulatory traits influence their evolution, and male expenditure on such traits is predicted to depend on the number of competitors, the benefits from investing in weapons, and the risk and intensity of sperm competition. Males of the chorusing frog Crinia georgiana use their arms as weapons in contest competition. Previously, we showed that increased numbers of rivals elevated the risk and intensity of sperm competition due to multimale amplexus, and caused a reversal in the direction of precopulatory selection on arm girth. Here we focused on the factors affecting postcopulatory fertilization success during group spawning, using paternity data from natural choruses. Competitive fertilization success depended on the time spent amplexed and amplexus position. Relative testes size but not arm girth, contributed to fertilization success, but the effect of testes size depended on amplexus position. Our findings offer within species empirical support for recent sperm competition models that incorporate precopulatory male-male competition, and show why an understanding of the evolution of animal weapons requires a consideration of both pre- and postcopulatory episodes of sexual selection.

opencc-zeroApr 2020View details →

Data from: Peak vertical jump power predicts radial bone strength better than hand grip strength in healthy individuals

Osteoporosis is considered a pediatric disease with geriatric consequences. However, measuring bone strength in children is complex and creates a practical problem for health professionals, teachers and parents. A non-invasive measure of muscle fitness that correlates to bone strength may provide a means to monitor bone strength throughout the lifespan. Therefore, the purpose of this study was to investigate the relationship between common muscle function tests (relative grip strength (RGS), peak vertical jump power (PP)) and bone strength in the radial diaphysis and epiphysis of a healthy population. Healthy participants (n=147 (81 female)) performed a bilateral grip strength test using a hand dynamometer, and a maximal vertical jump test. Peak vertical jump power was calculated from maximal jump height using the Sayer's equation. Moment of inertia (MoI), cortical area (CoA), cortical bone mineral density (cBMD), and polar strength-strain index (SSIp) were measured using peripheral Quantitative Computed Tomography (pQCT) to determine bone strength parameters at the 66% radial site (predominantly cortical bone). At the 4% site (trabecular bone site), bone mineral content (vBMC.tb), bone mineral density (vBMD.tb), total area (ToA.tb) and bone strength index (BSIc) were measured. Hierarchical multiple regression analyses determined the relationship of each muscle function test for each bone envelope (cortical and trabecular). For the cortical bone measurements: RGS, and PP were both significantly correlated with CoA, MoI, and SSIp. Peak vertical jump power predicted bone strength parameters to a greater extent compared to RGS. For the trabecular bone envelope, RGS was not a predictor of bone strength however peak power was a significant predictor of bone strength parameters. Peak vertical jump power was a significant predictor of bone strength at both trabecular and cortical radial sites. Interestingly PP, a lower limb measurement explained the most variance in the bone strength of the upper limb.

opencc-zeroDec 2018View details →

Data from: Netted crop covers reduce honey bee foraging activity and colony strength in a mass flowering crop

The widespread use of protective covers in horticulture represents a novel landscape-level change, presenting challenges for crop pollination. Honey bees (Apis mellifera L) are pollinators of many crops, but their behaviour can be affected by conditions under covers. To determine how netting crop covers can affect honey bee foraging dynamics, colony health, and pollination services, we assessed the performance of 52 nucleus honey bee colonies in five covered and six uncovered kiwifruit orchards. Colony strength was estimated pre- and post- introduction, and the foraging of individual bees (including pollen-, nectar-, and naïve foragers) was monitored in a subset of the hives fitted with RFID readers. Simultaneously, we evaluated pollination effectiveness by measuring flower visitation rates and the number of seeds produced after single honey bee visits. Honey bee colonies under cover exhibited both an acute loss of foragers and changes in the behaviour of successful foragers. Under cover, bees were four times less likely to return after their first trip outside the hive. Consequently, the number of adult bees in hives declined at a faster rate in these orchards, with colonies losing on average 1,057 ± 274 of their bees in under two weeks. Bees that did forage under cover completed fewer trips provisioning their colony, failing to re-enter after a few short-duration trips. These effects are likely to have implications for colony health and productivity. We also found that bee density (bees/thousand flowers) and visitation rates to flowers were lower under cover, however we did not detect a resultant change in pollination. Our findings highlight the need for environment-specific management techniques for pollinators. Improving honey bee orientation under covers and increasing our understanding of the effects of covers on bee nutrition and brood rearing should be primary objectives for maintaining colonies and potentially improving pollination in these systems.

opencc-zeroDec 2010View details →

Data from: Strong asymmetry in the relative strengths of prezygotic and postzygotic barriers between two damselfly sister species

One of the longest debates in biology has been over the relative importance of different isolating barriers in speciation. However, for most species, there are few data evaluating their relative contributions and we can only speculate on the general roles of pre- and postzygotic isolation. Here we quantify the absolute and cumulative contribution of 198 potential reproductive barriers between two sympatric damselfly sister species, Ischnura elegans and I. graellsii, including both premating (habitat, temporal, sexual and mechanical isolation) and postmating barriers (prezygotic: sperm insemination success and removal rate, oviposition success, fertility, fecundity; postzygotic: hybrid viability, hybrid sterility and hybrid breakdown). In sympatry, total reproductive isolation between I. elegans females and I. graellsii males was 95.2%, owing mostly to a premating mechanical incompatibility (93.4%), while other barriers were of little importance. Isolation between I. graellsii females and I. elegans males was also nearly complete (95.8%), which was caused by the cumulative action of multiple prezygotic (n=4, 75.4%) and postzygotic postmating barriers (n=5, 7.4%). Our results suggest that premating barriers are key factors in preventing gene flow between species, and that the relative strengths of premating barriers is highly asymmetrical between the reciprocal crosses.

Data from: The strength of migratory connectivity for birds en route to breeding through the Gulf of Mexico

The strength of migratory connectivity is a measure of the cohesion of populations among phases of the annual cycle, including breeding, migration, and wintering. Many Nearctic-Neotropical species have strong migratory connectivity between breeding and wintering phases of the annual cycle. It is less clear if this strength persists during migration when multiple endogenous and exogenous factors may decrease the cohesion of populations among routes or through time along the same routes. We sampled three bird species, American redstart (Setophaga ruticilla), ovenbird (Seiurus aurocapilla), and wood thrush (Hylocichla mustelina), during spring migration through the Gulf of Mexico region to test if breeding populations differentiate spatially among migration routes or temporally along the same migration routes and the extent to which within-population timing is a function of sex, age, and carry-over from winter habitat, as measured by stable carbon isotope values in claws (δ13C). To make quantitative comparisons of migratory connectivity possible, we developed and used new methodology to estimate the strength of migratory connectivity (MC) from probabilistic origin assignments identified using stable hydrogen isotopes in feathers (δ2H). We found support for spatial differentiation among routes by American redstarts and ovenbirds and temporal differentiation along routes by American redstarts. After controlling for breeding origin, the timing of American redstart migration differed among ages and sexes and ovenbird migration timing was influenced by carry-over from winter habitat. The strength of migratory connectivity did not differ among the three species, with each showing weak breeding-to-spring migration MC relative to prior assessments of breeding-wintering connectivity. Our work begins to fill an essential gap in methodology and understanding of the extent to which populations remain together during migration, information critical for a full annual cycle perspective on the population dynamics and conservation of migratory animals.

opencc-zeroDec 2016View details →

Data from: Induced defences alter the strength and direction of natural selection on reproductive traits in common milkweed

Evolutionary biologists have long sought to understand the ecological processes that generate plant reproductive diversity. Recent evidence indicates that constitutive antiherbivore defences can alter natural selection on reproductive traits, but it is unclear whether induced defences will have the same effect and whether reduced foliar damage in defended plants is the cause of this pattern. In a factorial field experiment using common milkweed, Asclepias syriaca L., we induced plant defences using jasmonic acid (JA) and imposed foliar damage using scissors. We found that JA-induced plants experienced selection for more inflorescences that were smaller in size (fewer flowers), whereas control plants only experienced a trend towards selection for larger inflorescences (more flowers); all effects were independent of foliar damage. Our results demonstrate that induced defences can alter both the strength and direction of selection on reproductive traits, and suggest that antiherbivore defences may promote the evolution of plant reproductive diversity.

Data from: The effects of rainforest fragment area on the strength of plant-pathogen interactions

Pathogenic interactions between fungi and plants facilitate plant species coexistence and tropical rainforest diversity. Such interactions, however, may be affected by forest fragmentation as fungi are susceptible to anthropogenic disturbance. To examine how fragmentation affects fungus-induced seed and seedling mortality, we sowed seeds of six plant species in soils collected from 21 forest fragments. We compared seedling establishment in unmanipulated soils to soils treated with fungicides. Fungicides increased germination of Toona ciliata seeds and decreased mortality of Syzygium rubicundum and Olea dioica seedlings. The fungus-induced mortality of one of these species, S. rubicundum, decreased with decreasing fragment size, indicating that its interactions with pathogenic fungi may weaken as fragments become smaller. We provide evidence that a potential diversity-maintaining plant-fungus interaction weakens in small forest fragments and suggest that such disruptions may have important long-term consequences for plant diversity. We, however, emphasize the need for further research across rainforest plant communities to better understand the future of diversity in fragmented rainforest landscapes.

Data from: Subgrain-controlled grain growth in laser melted 316L promoting strength at high temperatures

Stainless steel 316L prepared by laser melting consisted of hierarchical austenitic microstructure with micron sized (10-25 µm) grains containing fine 1µm subgrains with a cellular structure. At high temperature thermal treatments (≥ 1100 °C), merging and growth of the 1 µm subgrains into bigger subgrains restricted the rapid grain growth and microstructure coarsening. Partial phase transformation of austenite to ferrite at temperatures ≥ 1100 °C in combination with gradual and steady growth of subgrains inside the micron sized grains and nucleation of sigma phase have promoted the tensile strength of stainless steel 316L to 300 MPa at 1100 °C compared to conventionally made 316L counterparts with tensile strength of approximately 40 MPa. The grain growth mechanism of laser melted microstructure can change the application criteria for 316L and expand the application fields for 316L.