Males vs workers: testing the assumptions of the haploid susceptibility hypothesis in bumblebees

The haploid state of males in eusocial Hymenoptera—the ants, bees, and wasps—has been proposed as a driving force in the evolution of social behavior under the assumption that haploidy results in higher susceptibility to pathogens. In this study, we present the first test of the assumptions of the “haploid male susceptibility hypothesis”. We challenged males and workers of the bumblebee Bombus terrestris with its parasite Crithidia bombi but found no differences in either initial susceptibility or the intensity of infection between haploid males and diploid females. We reviewed observational studies on parasitism in haplodiploid insects and found that in 15 out of 26 cases, haploid males had lower parasite prevalence. However, the majority of available data related to nontransmissible parasites and thus any general statements about haploid susceptibility remain unclear. Using a simulation model, we studied how diverse genetic mechanisms could affect the values for resistance; results suggest that only a phenomenon that renders workers effectively haploid, e.g., imprinting, could explain our experimental results. A more likely explanation is that, in eusocial Hymenoptera with predominantly female populations, parasites may simply become more adapted to the more common female hosts and, thus, male haploid susceptibility may be hidden due to parasite adaptation. Our results do not support the idea that the haploid susceptibility hypothesis explains the origin or maintenance of social systems in the eusocial Hymenoptera.     

Nutrient bioassimilation capacity of aquacultured oysters: quantification of an ecosystem service

Like many coastal zones and estuaries, the Chesapeake Bay has been severely degraded by cultural eutrophication. Rising implementation costs and difficulty achieving nutrient reduction goals associated with point and nonpoint sources suggests that approaches supplemental to source reductions may prove useful in the future. Enhanced oyster aquaculture has been suggested as one potential policy initiative to help rid the Bay waters of excess nutrients via harvest of bioassimilated nutrients. To assess this potential, total nitrogen (TN), total phosphorous (TP), and total carbon (TC) content were measured in oyster tissue and shell at two floating-raft cultivation sites in the Chesapeake Bay. Models were developed based on the common market measurement of total length (TL) for aquacultured oysters, which was strongly correlated to the TN (R2 = 0.76), TP (R2 = 0.78), and TC (R2 = 0.76) content per oyster tissue and shell. These models provide resource managers with a tool to quantify net nutrient removal. Based on model estimates, 10(6) harvest-sized oysters (76 mm TL) remove 132 kg TN, 19 kg TP, and 3823 kg TC. In terms of nutrients removed per unit area, oyster harvest is an effective means of nutrient removal compared with other nonpoint source reduction strategies. At a density of 286 oysters m(-2), assuming no mortality, harvest size nutrient removal rates can be as high as 378 kg TN ha(-1), 54 kg TP ha(-1), and 10,934 kg TC ha(-1) for 76-mm oysters. Removing 1 t N from the Bay would require harvesting 7.7 million 76-mm TL cultivated oysters.     

Evaluation of vacuum filter sock surface sample collection method for Bacillus spores from porous and non-porous surfaces

Vacuum filter socks were evaluated for recovery efficiency of powdered Bacillus atrophaeus spores from two non-porous surfaces, stainless steel and painted wallboard and two porous surfaces, carpet and bare concrete. Two surface coupons were positioned side-by-side and seeded with aerosolized Bacillus atrophaeus spores. One of the surfaces, a stainless steel reference coupon, was sized to fit into a sample vial for direct spore removal, while the other surface, a sample surface coupon, was sized for a vacuum collection application. Deposited spore material was directly removed from the reference coupon surface and cultured for enumeration of colony forming units (CFU), while deposited spore material was collected from the sample coupon using the vacuum filter sock method, extracted by sonication and cultured for enumeration. Recovery efficiency, which is a measure of overall transfer effectiveness from the surface to culture, was calculated as the number of CFU enumerated from the filter sock sample per unit area relative to the number of CFU enumerated from the co-located reference coupon per unit area. The observed mean filter sock recovery efficiency from stainless steel was 0.29 (SD = 0.14, n = 36), from painted wallboard was 0.25 (SD = 0.15, n = 36), from carpet was 0.28 (SD = 0.13, n = 40) and from bare concrete was 0.19 (SD = 0.14, n = 44). Vacuum filter sock recovery quantitative limits of detection were estimated at 105 CFU m(-2) from stainless steel and carpet, 120 CFU m(-2) from painted wallboard and 160 CFU m(-2) from bare concrete. The method recovery efficiency and limits of detection established in this work provide useful guidance for the planning of incident response environmental sampling for biological agents such as Bacillus anthracis.     

Using Information on Spatial Variability of Small Estuaries in Designing Large-Scale Estuarine Monitoring Programs

In the early 1990s, EPA's Environmental Monitoring and Assessment Program (EMAP) documented the ecological condition of the overall population of small estuaries along the mid-Atlantic coast of the United States. However, the Program did not provide detailed information on the condition of individual estuaries less than 260 km² in surface area, a group of estuaries of concern to environmental managers. To address the needs of environmental managers, when EMAP returned to the region in summer 1997, it included a study of the spatial variability of ecological indicators within individual small estuaries. At 127 probability-based sites in 10 estuaries, EMAP measured a variety of parameters of water quality and sediments, including dissolved oxygen (DO), nutrients, grain size of sediments, contaminants in sediments, and community structures of benthic macroinvertebrates. From this information the ecological condition (e.g., percent area with DO concentrations below 5mg L^–1) for each estuary, along with 90% confidence interval, was determined. The width of the confidence interval was then recalculated for sample sizes ranging from two stations to the total number of stations sampled in that estuary. Confidence interval widths were then plotted against sample size. These plots can be useful in designing future regional monitoring programs with a goal of describing conditions in individual systems as well as broad geographic regions. Results illustrate that beyond five stations per estuary, the reduction in the width of the confidence interval with increasing sampling intensity is relatively small; however, individual program managers need to determine "how small is small enough."     

Condition of the Mid-Atlantic Estuaries: Production of a State of the Environment Report

The U.S. Environmental Protection Agency has released a report entitled Condition of the Mid-Atlantic Estuaries. That report summarizes the findings of several studies conducted by federal and state agencies and academic institutions in Chesapeake Bay, Delaware Estuary, and the coastal bays of Delaware, Maryland, and Virginia, and simultaneously addresses two distinct audiences: environmental managers and the general public. This paper documents the process of preparing the Estuaries Report, emphasizing the lessons learned in merging information from a wide-variety of sources and in reporting the results to multiple audiences. The major difficulties in preparing the report included: 1) choosing a format and topics that adequately addressed both environmental managers and the public, 2) resolving spatial and temporal disparities in the assembled data sets, and 3) establishing threshold values that distinguished between acceptable and unacceptable conditions in indicators. Our solutions to these challenges and alternatives are discussed. We conclude that a small team of knowledgeable scientists can effectively merge the information of diverse sources into a document that is useful to both environmental managers and the interested public. However, considerable interaction between the team and other scientists was necessary to resolve ambiguities and assure relevancy and accuracy. These findings support the proposition that the vast sources of existing environmental information can be easily and effectively used to assess the ecological condition across large regions.     

Influence of reagent purity on the ion chromatographic determination of bromate in water using 3,3'-dimethoxybenzidine as a prochromophore for photometric detection

Variable availability of the purified dihydrochloride salt of 3,3'-dimethoxybenzidine (DMB; ortho-dianisidine) led us to investigate the effects of reagent purity on the analytical results obtained when this reagent is used in the photometric determination of the disinfection byproduct bromate. After analyte ions are separated by ion chromatography, a solution of DMB (post-column reagent) is added to the eluate and the DMB is oxidized, thereby producing a chromophore detected by its absorbance. Although some commercial products of undefined grade performed well, others did not. Variability was also observed between lots of purified material. Sensitivity at low concentrations (< 5 micrograms L-1 BrO3-) varied by a factor of up to 10. In some cases, the lower limit of detection for photometric detection was greater than that obtained using conductivity detection, as high as 5-7 micrograms L-1 BrO3-. An impurity or several impurities are suspected to be responsible for deviations from linearity at low analyte concentrations. This investigation underscores the need for ensuring reagent purity in environmental analyses. Ideally, chemical manufacturers will meet the needs of analytical chemists who test potable water and begin producing a high grade material in sufficient quantities to meet monitoring requirements. The establishment of third-party standards for a spectrophotometric grade of DMB.2HCl would be helpful in ensuring that a variety of manufacturers could supply products of uniformly high quality that would be suitable for the measurement of bromate in public drinking water supplies.     

A CFD-based wind solver for an urban fast response transport and dispersion model

In many cities, ambient air quality is deteriorating leading to concerns about the health of city inhabitants. In urban areas with narrow streets surrounded by clusters of tall buildings, called street canyons, air pollution from traffic emissions and other sources may accumulate resulting in high pollutant concentrations. For various situations, including the evacuation of populated areas in the event of an accidental or deliberate release of chemical, biological and radiological agents, it is important that models should be developed that produce urban flow fields quickly. Various computational techniques have been used to calculate these flow fields, but these techniques are often computationally intensive. Most fast response models currently in use are at a disadvantage in these cases as they are unable to correlate highly heterogeneous urban structures with the diagnostic parameterizations on which they are based. In this paper, a novel variant of the popular projection method for solving the Navier–Stokes equations has been developed and applied to produce fast and reasonably accurate parallel computational fluid dynamics (CFD) solutions for flow in complex urban areas. This model, called QUIC-CFD represents an intermediate balance between fast (on the order of minutes for a several block problem) and reasonably accurate solutions. This paper details the solution procedure and validates this model for various simple and complex urban geometries.     

An energetic perspective on the relationship between disturbance and ecosystem productivity

Previous ecological models for disturbance from energetic perspectives have focused on destructive pulses by which storages in a system are quickly drained during disturbance events and recovered thereafter. However, considering the wide range of disturbance intensities, frequencies, and durations in nature, disturbance effects on ecosystem energetics would be better understood by diversifying the disturbance effects on specific system configurations or energy pathways. Based on two hypotheses, we built simulation models of the variable disturbance-productivity relationships observed in a freshwater aquatic microcosm study. First, we hypothesized that disturbances will differentially alter the intrinsic rates of energy pathways in a system. Second, we hypothesized that there is a disturbance threshold where response of the intrinsic rates changes abruptly. Simulation results showed variable patterns of gross primary productivity (GPP) during the disturbance and post-disturbance periods under the diverse scenarios of disturbance effects on the intrinsic rates. Simulation results confirmed that the second hypothesis (i.e., disturbance threshold) was essential to achieve a U-shaped or peaked disturbance-productivity relationship. We evaluated the models by comparing them with the results of the microcosm tests, and suggested possible mechanisms of the variable disturbance-productivity relationships by varying parameters related to the disturbance effects on the intrinsic rates and the disturbance thresholds.     

The ecological impact of invasive cane toads on tropical snakes: field data do not support laboratory-based predictions

Predicting which species will be affected by an invasive taxon is critical to developing conservation priorities, but this is a difficult task. A previous study on the impact of invasive cane toads (Bufo marinus) on Australian snakes attempted to predict vulnerability a priori based on the assumptions that any snake species that eats frogs, and is vulnerable to toad toxins, may be at risk from the toad invasion. We used time-series analyses to evaluate the accuracy of that prediction, based on >3600 standardized nocturnal surveys over a 138-month period on 12 species of snakes and lizards on a floodplain in the Australian wet-dry tropics, bracketing the arrival of cane toads at this site. Contrary to prediction, encounter rates with most species were unaffected by toad arrival, and some taxa predicted to be vulnerable to toads increased rather than declined (e.g., death adder Acanthophis praelongus; Children's python Antaresia childreni). Indirect positive effects of toad invasion (perhaps mediated by toad-induced mortality of predatory varanid lizards) and stochastic weather events outweighed effects of toad invasion for most snake species. Our study casts doubt on the ability of a priori desktop studies, or short-term field surveys, to predict or document the ecological impact of invasive species.     

Allocation of nuptial gifts in tree crickets changes with both male and female diet

Male tree crickets, Oecanthus nigricornis, offer a nuptial gift to females during mating in the form of a secretion from a dorsal metanotal gland. I examined the effects of male and female nutrient limitation on allocation of the gift. Males were fed ¹⁴C radiolabeled amino acids, placed onto high- or low-quality diets and then mated with females also maintained on high- or low-quality diets. Female acquisition of radiolabel increased, and residual radiolabel within the metanotal gland decreased, over time verifying that gift size correlates with duration of courtship feeding. High-diet females produced greater egg numbers and allocated proportionally more of the male-derived amino acids to their ovaries. As predicted, duration of courtship feeding was greater for males on high-quality diets and females on low-quality diets. Amino acid transfer, measured as the proportion of total radiolabel transferred to the female, showed a significant interaction between male and female diet. High-diet females acquired available radiolabel more rapidly from high-diet males, but low-diet females acquired available radiolabel more rapidly from low-diet males. The causes of these differences between feeding duration and nutrient allocation are discussed.