Tolerating castration by hiding flowers in plain sight

A key challenge in the study of inter-specific cooperation, or mutualisms, is to understand the mechanisms that prevent cheating. However, many mutualisms are still invaded by parasites, and we propose that plant ‘tolerance strategies’, which allow an individual to re-grow and/or reproduce after damage, might have evolved to recover some of the fitness lost to parasitism. We focus on the ant plant Cordia nodosa and its protecting ant symbionts Allomerus octoarticulatus and Azteca spp. Allomerus is a castration parasite, destroying host flowers. However, some flowers are produced on new branch shoots, where they escape castration. Here, we ask whether C. nodosa tolerates castration by directing floral growth to new shoots. We find that C. nodosa produces four times more floral buds on the new shoots of Allomerus-inhabited plants, compared to Azteca-inhabited plants. Additionally, on Allomerus-inhabited plants, the production of floral buds is three times greater on new than on mature shoots, and more floral buds are grown on plants with new shoots than on those without. We conclude therefore that C. nodosa tolerates castration by re-allocating floral resources to new shoots. We also test whether tolerance exploits behavioural differences between the brood-tending ‘nurse’ ant worker caste, which is active on mature shoots, and the new shoot-protecting ‘patroller’ caste. Behavioural assay experiments reveal that nurse ants are strongly attracted to extracts of flowers, whereas patrollers are not, suggesting that nurses are the primary castrating caste. Thus, producing flowers on new shoots avoids the castrating caste. We finish by proposing that tolerance strategies can promote the evolution and maintenance of mutualism.     

Grid search: an innovative method for the estimation of the rates of lead exchange between body compartments

This paper describes a new metabolic model for lead in humans and a numerical method to solve the differential equations governing the transfer of lead between body compartments. The model includes 3 compartments-cortical bone, trabecular bone and blood-and accounts for absorption from external sources and release through excreta. Estimation of the lead kinetics parameters was performed using the grid search method. Grid search is a simple procedure that allows the fit of an arbitrary function to data. When applied to data from occupationally exposed populations, the method demonstrated the exposure dependence of the rate of lead uptake and release by the compartments in the model. The results confirm and refine previous observations of the significant decrease of the transfer rate of lead from cortical bone to blood with increasing exposure, as expressed by half-lives of (in years): 6.5 +/- 0.7, 13.6 +/- 1.0 and 47.5 +/- 2.3, in subgroups of low, intermediate and high long-term lead exposure. A similar trend was observed for the transfer rate from trabecular bone, which could be statistically supported for the first time. Reduction by a factor of 7 to 10 in the default values assigned to the fractional removal of lead from cortical bone to plasma in existing metabolic models was also predicted. These results can be used in the review of current metabolic models for lead, which are still based on the assumption of a constant rate of lead removal from bone, independently of the level of exposure.     

The first monoclonal antibody-based,matrix-resistant immunoassay for the carbamate herbicide asulam,in water

To date, no ligand binding assay has been described for the carbamate herbicide asulam, although a variety of physical methods, dependent on pre-concentration of water samples, have been documented for its assessment. However, asulam is increasingly used in sensitive agricultural areas, and statutory regulations concerning its monitoring will undoubtedly become more stringent. Antibodies are optimal partners in ligand binding assays, but it is commonly understood by immunological researchers that where no antibody reactive with a particular antigen has yet been described, the immunogenicity of the antigen may be particularly restricted. By the expedient of employing a specialised approach to final immunisation with an asulam-protein conjugate, prior to the immortalisation of a specific anti-asulam antibody-producing cell, we have succeeded in generating a monoclonal antibody reactive specifically with asulam that can be configured in a convenient immunoassay. This antibody may be used flexibly in a number of ways: small sample volumes of 10 microl can be assessed to sensitivities of 4.35 x 10(-7) M (10 microg L(-1)) while avoiding discrepancies contributed by the assay matrix; this antibody-based assay can also be formatted to deliver sensitivities at levels stipulated by regulatory authorities (e.g., 4.35 x 10(-9) M or 0.1 microg L(-1)) directly from a water sample, without prior pre-concentration.     

Observation and collection of deep-reef fishes off the coasts of Jamaica and British Honduras (Belize)

Over 60 species of reef fishes were observed from submersibles between 50 and 305 m depth, and 25 species were collected from the same depth range using fish traps and submersibles. Short transects gave relative abundance of some species with depth. Many shallow-water coral-reef fishes reach depths far below the lower growth limits of reef-building corals. A true “deep-reef” fauna exists, but the juveniles of some of these species are found at depths of less than 50 m.     

Characterization and growth response of bacteria in soil following application of carbofuran.

Enhanced biodegradation of carbofuran (2, 3-dihydro-2, 2 dimethyl-7-benzofuranyl methyl carbamate) is an economically significant, but poorly understood, microbial phenomenon in soil. A series of experiments was conducted to examine short term changes in soil bacterial populations stimulated by carbofuran application at field rates. In the field experiment, commercially formulated carbofuran and butylate (S-ethyl diisobutyl carbamothioate) were applied at 5.6 kg ai ha-1 and 8.4 kg ai ha-1, respectively, on a soil (Putnam silt loam) exhibiting enhanced degradation of carbofuran. In laboratory studies, technical grade carbofuran (20 mg kg-1 soil) was applied to samples of the field soil. Bacterial populations were estimated using non-selective (tryptic soy agar) and selective media containing carbofuran or butylate. Largest population increases in pesticide-treated soil were observed between 7 and 15 days after treatment (DAT) compared to populations in non-treated soil. Significant increases (P less than 0.05) in total bacterial populations and presumed carbofuran-degraders due to carbofuran application were associated with increased populations of Pseudomonas spp. and Flavobacterium spp. Application of carbofuran appeared to provide a competitive advantage to these species over actinomycetes persisting beyond 20 DAT. Growth responses of bacteria to carbofuran in the Putnam soil were compared to those in a native prairie soil (Mexico silt loam), which exhibited a much slower rate of carbofuran degradation. Bacterial population response to carbofuran was measurable, but small and short-lived. Perpetuation of the enhanced degradation phenomenon may lie in a persistent pesticide-induced competitive advantage given to a very small segment of the microbial population. This advantage may not be detectable after 20 days using conventional plating techniques.     

Determinants of nitrous oxide emission from agricultural drainage waters

Emissions of the powerful greenhouse gas nitrous oxide (N₂O) from agricultural drainage waters are poorly quantified and its determinants are not fully understood. Nitrous oxide formation in agricultural soils is known to increase in response to N fertiliser application, but the response of N₂O in field drainage waters is unknown. This investigation combined an intensive study of the direct flux of N₂O from the surface of a fertilised barley field with measurement of dissolved N₂O and nitrate (NO₃) concentrations in the same fields drainage waters. Dissolved N₂O in drainage waters showed a clear response to field N fertilisation, following an identical pattern to direct N₂O flux from the field surface. The range in N₂O concentrations between individual field drains sampled on the same day was large, indicating considerable spatial variability exists at the farm scale. A consistent pattern of very rapid outgassing of the dissolved N₂O in open drainage ditches was accentuated at a weir, where increased turbulence led to a clear drop in dissolved N₂O concentration. This study underlines the need for carefully planned sampling campaigns wherever whole farm or catchment N₂O emission budgets are attempted. It adds weight to the argument for the downward revision of the IPCC emission factor (EF₅-g) for NO₃ in drainage waters.     

Airborne measurements of peroxy radicals using the PERCA technique

The Peroxy Radical Chemical Amplifier (PERCA) technique is a proven method for measurement of ambient levels of peroxy radicals at ground level, but there are no published instances of the technique being used on an aerial platform. Here we describe deployment of a PERCA on the former UK Meteorological Office C-130 Hercules research aircraft. The instrument uses the established method of chemical amplification and conversion of peroxy radicals to nitrogen dioxide (NO2) by doping the sample air-flow matrix with CO and NO, subsequently measuring the NO2 yield with an improved 'Luminox' LMA-3 NO2 detector. NO2 from the amplification chemistry is distinguished from other sources of NO2 reaching the detector by periodically injecting CO approximately 1 s downstream of the NO injection point (termination mode). Chain lengths (CL's) for the amplification chemistry were typically approximately 260 (ground level) to approximately 200 (7,000 m). This variation with altitude is less than the variation associated with the 'age' of the PFA inlet material where the amplification chemistry occurs; CL's of approximately 200 with old tubing to approximately 300 with new clean tubing were typical (ground level values). The CL determinations were made in-flight using an onboard calibration unit based on the 254 nm photolysis of 7.5 to 10 parts per billion (by volume, ppbv) of CH3I in air, producing CH3O2 in a quantitative manner. The noise-equivalent detection limit for peroxy radicals (HO2 + RO2) is 2 parts per trillion (by volume, pptv) at 3,650 m when the background ambient ozone levels are stable, based on a 5 min average of five 30 s amplification cycles and five 30 s termination cycles. This detection limit is a function of several factors but is most seriously degraded when there is large variability in the ambient ozone concentration. This paper describes the instrument design, considers its performance and proposes design improvements. It concludes that the performance of an airborne PERCA in the free troposphere can be superior to that of ground-based instruments when similar sampling frequencies are compared.     

A Survey of Strategies Adopted by UK Wildlife Trusts in the Promotion of Gardening for Wildlife

With the decline of wildlife due to, among other things, agricultural intensification, gardening for wildlife has an increasingly recognized role in the conservation of biodiversity and habitats. The United Kingdom (UK) Wildlife Trusts have a key role in the promotion of awareness and best practice of wildlife gardening. In spring 2001, a survey of all 46 United Kingdom County Wildlife Trusts was carried out, focussing on their level of awareness of the issue, whether they actively promoted it, and what literature they employ, and whether they form partnerships in implementing this project.The survey achieved an 83 percent reply rate. The Trusts carried out a wide variety of promotional activities, although its importance as an issue varied from Trust to Trust. Some Trusts have developed excellent promotional literature and strategies, but there could be a greater degree of sharing of ideas and cross fertilization to avoid reinventing the wheel. Few Trusts had developed partnerships, although local government was the most frequent partner.     

The Impact of Conifer Harvesting on Stream Water Quality: A Case Study in Mid-Wales

A 12-year record of water quality data for runoff from a spruce forested hillslope with podzolic soils shows the impacts of conifer harvesting and replanting in relation to nitrate generation and its influence on surface water acidification. With felling, nitrate increases from a background of 18 Eq/l to about 50 Eq/l after 1 to 2 years and then declines to background levels over the next 1 to 2 years and to lower concentrations thereafter. This change is mirrored by an acidification process as manifest by a change in Gran alkalinity, acid neutralization capacity (ANC) and aluminium concentrations as well as pH. For example, Gran alkalinity and ANC, which start at negative concentrations prior to felling (about –20 and –50 Eq/l, respectively), become more negative (–30 and –100 Eq/l, respectively) at high nitrate concentrations. Correspondingly, pH decreases from about 4.7 to 4.5 and aluminium concentrations increase from about 14 to 16 M. Subsequently, the acidification is reversed as nitrate concentrations decline and after five years post-felling the system has higher pH, Gran alkalinity and ANC together with lower aluminium concentrations than even before the felling took place (the post-felling values are about 4.9, -15 Eq/l, –20 Eq/l and 7 M/l, respectively).Other determinands show clear changes over time. For example, there is a marked increase in sodium and chloride prior to and around the time of felling (200 to 300 and 230 to 400 Eq/l, respectively), with a subsequent decline in concentration to pre-felling and to lower values of around 160 and 170 Eq/l, respectively, thereafter. This change is probably associated with abnormally high inputs of sea-salts from the atmosphere during the first quarter of the year of felling, and dilution thereafter, rather than a direct consequence of the felling activity itself: this change in sea salt loading has had an impact on stream acidity. Dissolved organic carbon and iron also change with concentrations increasing over time (60 to 200 and 1.0 to 1.5 M/l, respectively) and this mirrors a general pattern observed across the Plynlimon catchments irrespective of whether or not there has been felling activity.The implications of the findings are discussed in relations to environmental management and hydrochemical processes.