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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Evidence that Polycyclic Aromatic Hydrocarbons in Two Carbonaceous Chondrites Predate Parent-Body Formation

Organic material in meteorites provides insight into the cosmochemistry of the early solar system. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the Allende and Murchison carbonaceous chondrites was investigated using spatially resolved microprobe laser-desorption laser-ionization mass spectrometry. Sharp chemical gradients of PAHs are associated with specific meteorite features. The ratios of various PAH intensities relative to the smallest PAH, naphthalene, are nearly constant across the sample. These findings suggest a common origin for PAHs dating prior to or contemporary with the formation of the parent body, consistent with proposed interstellar formation mechanisms.

Plows, F. L.↗
DOE OSTI2024

Methods of detecting predators in algal cultures

The present disclosure features methods of detecting crop damage in an algal culture. Such methods include detecting one or more carotenoids as a volatile organic compound in a sample obtained from a headspace of the algal culture.

Fisher, Carolyn Laura↗
DOE OSTI2020

Relative reproductive phenology and synchrony affect neonate survival in a nonprecocial ungulate

Abstract Degree of reproductive synchronization in prey is hypothesized as a predator defense strategy reducing prey risk via predator satiation or predator avoidance. Species with precocial young, especially those exposed to specialist predators, should be highly synchronous to satiate predators (predator satiation hypothesis), while prey with nonprecocial (i.e. altricial) young, especially those exposed to generalist predators, should become relatively asynchronous to avoid predator detection (predator avoidance hypothesis). The white‐tailed deer Odocoileus virginianus in North America is an example of a nonprecocial ungulate that uses the hider strategy early in life; its primary predator (coyote; Canis latrans ) is a generalist, making white‐tailed deer a good model species to test the predator avoidance hypothesis. We used birth dates and known fates of white‐tailed deer neonates ( n = 1,032) across nine study sites varying in relative synchrony and predator assemblages to test the predator avoidance hypothesis. We predicted that relative birthing asynchrony of the population would increase relative survival at the population level; therefore, at the individual scale, neonate birth date nearer to mean birthing date in a respective population would not influence individual survival. Coyotes were responsible for the majority of predation events, and survival of those neonates increased the closer the individual was born to peak birthing season in each respective population. Also, at the population level, reproductive asynchronization negatively affected survival. Contrary to the predator avoidance hypothesis, our data indicate patterns in neonate survival for white‐tailed deer better support the predator satiation hypothesis at the individual and population level. Additionally, coyotes may present a selective force great enough to shift reproductive synchrony such that predator satiation may become a feasible defense strategy for neonates at local spatial scales. Our results indicate that synchronizing reproduction may still be the most effective strategy to reduce individual predation risk from generalist predators, particularly when the window of heightened resource availability to the prey is narrow. A free Plain Language Summary can be found within the Supporting Information of this article.

Michel, Eric S.↗
DOE OSTI2021

Grazer-induced changes in molecular signatures of cyanobacteria

Algal biomass production is an emerging renewable source of fuels, nutrients, manufacturing materials, and pharmaceuticals. Industrial-scale production is predominantly performed in open raceway ponds that are inexpensive to build, operate, and maintain compared to closed bioreactors. However, these open pond systems suffer from increased opportunities for biological contamination from predators, pathogens, and competitors, which result in reduced biomass quality and yields and often the complete destruction of the crop over a short period of time. Early detection of contaminants is a necessary step of integrated pest management for triggering and informing interventions to prevent crop losses. To develop a sensitive method of detection utilizing mass spectrometry (MS), we used three methods – imaging mass spectrometry (imaging MS), liquid chromatography MS/MS (LC-MS/MS) combined with molecular networking, and gas chromatography MS/MS (GC–MS/MS) – to observe and identify molecular signatures from a model predator-prey system of the heterolobosean amoeba HGG1 preying on the filamentous cyanobacterium Anabaena sp. PCC 7120. Imaging MS enabled the association of molecules with the crop, the predator, or the activity of protozoan grazing, while LC-MS/MS-based molecular networking identified a subset of the grazing-specific signals as the chlorophyll breakdown products pyropheophytin, pheophorbide A, and pyropheophorbide. Application of MS techniques to other amoebacyanobacterial predator-prey pairs allowed categorization of grazing signatures as universal or specific to the species of prey, predator, or the prey-predator pairing, indicating that MS-based techniques can distinguish crops from competitors and potentially identify predators. Finally, GCMS/MS was shown to be capable of monitoring novel volatile organic compounds (VOCs), including those predicted to be released through chlorophyll breakdown, in the headspace over algal cultures under predation. Furthermore, these results demonstrate that the combination of multiple MS technologies creates a predictive framework to identify and catalog relevant molecular signatures for informing crop protection strategies.

09 BIOMASS FUELS↗
DOE OSTI2023

Assessing springtime vertebrate prey of sympatric mesopredators in the southeastern United States using metabarcoding analysis

Coyotes (Canis latrans) colonized the eastern United States over the last century and formed a 3-species predator guild with bobcats (Lynx rufus) and gray foxes (Urocyon cinereoargenteus) across much of the southeastern United States. Diets among the three species vary along with respective impacts on game species such as white-tailed deer (Odocoileus virginianus) and wild turkeys (Meleagris gallopavo). To determine predation impacts on vertebrate prey and dietary overlap in consumption of prey items, we assessed diets of coyote, bobcat, and gray fox during spring, coinciding with white-tailed deer fawning and wild turkey nesting and brood rearing. We sampled across three sites along the Savannah River in South Carolina from mid-May through mid-June of 2020–2021. We collected 180 scat samples along 295.9 kilometers (71.1–122.4 km/site) of unpaved secondary roads and used DNA metabarcoding to determine vertebrate diet items. We identified predator species of scat using DNA metabarcoding and species-specific mtDNA fragment analysis (153 were coyote, 20 bobcat, and seven gray fox). Overall, we found evidence that two species, coyote and bobcat, consumed deer while all three consumed turkeys. Frequency of deer in the diet varied across sites for coyotes from 62–86% and wild turkey was present with a frequency of occurrence of 9% for coyotes, 5% for bobcats, and 14% for gray fox. Vertebrate diet specialization was evident across predator species with high frequency of deer in coyote diets, rabbits and small mammals in bobcat diets, and herpetofauna in gray fox diets. During deer fawning and wild turkey nesting and brood rearing, dietary overlap appears to be mediated by disparate selection of prey items, which reduced competition among coyotes, bobcats, and gray foxes. Use of DNA metabarcoding may augment our understanding of dietary preferences within this predator guild by providing increased resolution of diet composition among important game species.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Analytical population dynamics underlying harmful algal blooms triggered by prey avoidance

A modified version of the NPZD ecosystem model is used to analytically examine the effects of predation avoidance, a possible mechanism for triggering harmful algal blooms (HAB). To resolve HAB development caused by predation avoidance, an additional phytoplankton functional group is considered, one that has slower nutrient uptake and better predation avoidance characteristics than the non-harmful phytoplankton group used in traditional NPZD models. Because the two phytoplankton groups (one non-harmful and one HAB) compete for only one resource within the same system, steady state (equilibrium) conditions cannot occur without the presence of zooplankton; only the non-harmful phytoplankton group, which defeats the HAB group in the resource competition, can survive in the equilibrium. The presence of sufficient zooplankton effectively acts to replenish the nutrient pool by consuming the non-harmful phytoplankton. When this occurs, two equilibrium states are found: one with both phytoplankton groups coexisting, and one that only includes the HAB group. Further, the condition required for equilibrium is that the total nitrogen within the system should be larger than a threshold determined by model coefficients. The threshold and feasibility of the equilibrium are sensitive to the relative HAB predation avoidance coefficient. If the coefficient is larger than the ratio of net growth rates between the HAB and non-harmful phytoplankton group, the threshold becomes infinite, and an equilibrium is not feasible. The time scale for the system to reach an equilibrium state that includes a HAB group is determined asymptotically. The dependence of a threshold condition as a controlling factor may explain the regime shift of dominant species causing HABs. The ecosystem model is fully implemented into the Regional Ocean Modeling System and applied to an idealized coastal embayment (with depths and geometry taken from San Francisco Bay) to show numerically the dominance of prey avoidance dynamics in a natural shallow water environment that includes advection and diffusion. The analytical results improve strategies for HAB modeling and provide guidance for setting model coefficients necessary to resolve a HAB event.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Müllerian mimicry and the coloration patterns of sympatric coral snakes

Abstract Coral snakes in the genus Micrurus are venomous, aposematic organisms that signal danger to predators through vivid coloration. Previous studies found that they serve as models to several harmless species of Batesian mimics. However, the extent to which Micrurus species engage in Müllerian mimicry remains poorly understood. We integrate detailed morphological and geographical distribution data to investigate if coral snakes are Müllerian mimics. We found that coloration is spatially structured and that Micrurus species tend to be more similar where they co-occur. Though long supposed, we demonstrate for the first time that coral snakes might indeed be Müllerian mimics as they show some convergence in coloration patterns. Additionally, we found that the length of red-coloured rings in Micrurus is conserved, even at large geographic scales. This finding suggests that bright red rings may be under more substantial stabilizing selection than other aspects of coloration and probably function as a generalized signal for deterring predators.

Evolutionary Biology↗
NASA NTRS2005

Reproductive Ecology Of The Florida Scrub-Jay (Aphelocoma Coerulescens) On John F. Kennedy Space Center/Merritt Island National Wildlife Refuge: A Long-Term Study

From 1988 to 2002 we studied the breeding ecology of Florida Scrub-Jays (Aphelocoma coerulescens) on John F. Kennedy Space Center/Merritt Island National Wildlife Refuge. We examined phenology, clutch size, hatching failure rates, fledgling production, nest success, predation rates, sources egg and nestling mortality, and the effects of helpers on these measures. Nesting phenology was similar among sites. Mean clutch size at Titan was significantly larger than at HC or T4. Pairs with helpers did not produce larger clutches than pairs without helpers. Fledgling production at T4 was significantly greater than at HC and similar to Titan. Pairs with helpers at HC produced significantly more fledglings than pairs without helpers; helpers did not influence fledgling production at the other sites. Nest success at HC and Titan was low, 19% and 32% respectively. Nest success at T4 was 48% and was significantly greater than at HC. Average predation rates at all sites increased with season progression. Predation rates at all sight rose sharply by early June. The main cause of nest failure at all sites was predation, 93%.

Carter, Geoffry M.↗
DOE OSTI2023

Pest suppression potential varies across 10 bioenergy cropping systems

Abstract Top‐down suppression of herbivores is a fundamental ecological process and a critical service in agricultural landscapes. Adoption of bioenergy cropping systems is likely to become an increasingly important driver causing loss or gain of this service in coming decades. We measured natural pest suppression potential in ten model bioenergy crops in a long‐term experimental array by deploying plasticine sentinel caterpillar mimics, which record imprints from predator attacks. Cropping systems included three intensive annual row crop systems and a range of simple perennial monocultures and more complex polycultures. We compared attack rates across the ten cropping systems and assessed differences over time within a growing season and between the ground level and canopy. We found strong differences in attack rates across cropping systems, usually with more attacks in perennial crops than annuals. However, outcomes varied in space and time, both within and among cropping systems. Birds and small mammals were responsible for most, and sometimes all, attacks in annual crops and were most important early in the season. Chewing arthropod attacks increased over the course of the growing season and were responsible for most attack events in perennial systems. In late summer there were almost no attacks in annual crop canopies, while attack rates in perennial canopies at the same time were quite high and were carried out almost entirely by chewing arthropods. Our results underscore the lack of trophic complexity in annual bioenergy cropping systems relative to perennials. They also illustrate the dramatic changes in predator activity and predation intensity that occur both seasonally and between the ground and plant canopy. Policies and practices that increase the footprint of annual crops for bioenergy are likely to cause a deficit in pest suppression services at local and landscape scales.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

No evidence of top–down effects by ants on litter decomposition in a temperate grassland

Ants play multiple roles in ecosystems, but their ability to affect decomposition processes in temperate grasslands is relatively unknown. We investigated whether the suppression of ant populations influenced litter decomposition in grasslands via predation of some decomposers (e.g., mites and springtails) and/or microbial activity and composition. We performed two successful ant suppression treatments (seven weeks, 37% suppression, year 1, 10 weeks, 70% suppression, year 2) over the course of a 59-week experiment. We then assayed the effects of ant suppression using coarse- and fine-mesh litterbags and evaluated litter chemistry, microbial and arthropod communities, and microbial enzyme activity. Ant suppression efforts reduced ant abundance and altered ant, arthropod decomposer, and non-ant predator community composition. However, ant suppression did not affect decomposer arthropod abundance, litter mass loss, microbial composition, or enzyme activity in litterbags. Litterbag mesh size did not alter microbial composition, perhaps due to a failure to exclude decomposers, as mites and springtails were more or equally abundant in fine-mesh bags. Nevertheless, mesh size did change litter chemistry, suggesting that mesh size-mediated microenvironments affect decomposition environment regardless of invertebrate exclusion. Coarse-mesh litterbags had higher concentrations of microbial sugars, lignin, and N and lower concentrations of litter C and crystalline cellulose than fine-mesh litterbags. Litterbag mesh size may alter decomposition processes irrespective of invertebrate abundance. We found no evidence that ant predation was an important driver of decomposer populations or decomposition in these systems, and we suspect redundancy at the top of the detrital food web dilutes the role of ants.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Food web dynamics drive variation in Smallmouth Bass Micropterus dolomieu mercury contamination in protected Southern Appalachian streams

Mercury is a global pollutant that threatens otherwise protected aquatic ecosystems. Mercury food web dynamics are not well understood in streams with no point sources of contamination but have the potential to concentrate this dangerous pollutant in upper trophic level consumers. A 2016 study revealed that mercury concentrations of Smallmouth Bass Micropterus dolomieu varied between three streams in Great Smoky Mountains National Park (GSMNP), Tennessee, USA. We tested the hypothesis that food web interactions drive spatial variation in mercury concentrations of the apex predator of protected stream ecosystems. We measured carbon and nitrogen stable isotope ratios, and mercury concentrations of eight food web components of GSMNP streams including basal resources, intermediate consumers, and Smallmouth Bass, the apex predator. Mean THg concentrations of basal resources did not differ between streams, but the spatial pattern of concentrations of intermediate consumers mirrored Smallmouth Bass. Relationships between organismal contaminant concentrations and trophic level were positive in all three streams, indicating biomagnification is occurring in the protected streams of GSMNP. Furthermore, our findings indicate that mercury dynamics in intermediate trophic levels, rather than differences in basal resource concentrations, may drive differences in mercury contamination of apex predators of the protected stream ecosystems of GSMNP.

Bioaccumulation↗
DOE OSTI2022

Resolving the structure of phage–bacteria interactions in the context of natural diversity

Microbial communities are shaped by viral predators. Yet, resolving which viruses (phages) and bacteria are interacting is a major challenge in the context of natural levels of microbial diversity. Thus, fundamental features of how phage-bacteria interactions are structured and evolve in the wild remain poorly resolved. Here we use large-scale isolation of environmental marine Vibrio bacteria and their phages to obtain estimates of strain-level phage predator loads, and use all-by-all host range assays to discover how phage and host genomic diversity shape interactions. We show that lytic interactions in environmental interaction networks (as observed in agar overlay) are sparse—with phage predator loads being low for most bacterial strains, and phages being host-strain-specific. Paradoxically, we also find that although overlap in killing is generally rare between tailed phages, recombination is common. Together, these results suggest that recombination during cryptic co-infections is an important mode of phage evolution in microbial communities. In the development of phages for bioengineering and therapeutics it is important to consider that nucleic acids of introduced phages may spread into local phage populations through recombination, and that the likelihood of transfer is not predictable based on lytic host range.

59 BASIC BIOLOGICAL SCIENCES↗