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.     

Methane Fluxes from a Wetland using the Flux-Gradient Technique The Measurement of Methane Flux from a Natural Wetland Pond and Adjacent Vegetated Wetlands using a TDL-Based Flux-Gradient Technique

Methane emissions were measured from a bog andlake in the Experimental Lakes Area in Northern Ontario in 1992and 1993, prior to and following flooding. Bog fluxes were smallin 1992 (0.27 mg m^-2 d^-1) but increased 5-fold in 1993 afterflooding. Over the bog, there was a diel cycle of nighttimeemission and daytime uptake in 1992 in contrast to constantemission in 1993. Lake emissions decreased after flooding butwere much greater than bog emissions in both years (average = 7.3 mg m^-2 d^-1). Seasonally, the bog flux was correlated withground temperatures after flooding. In 1992, lake fluxes werecorrelated with air temperature on a daily basis. In contrast,seasonal lake fluxes were correlated with water and sedimenttemperatures in 1992, but only with sediment temperatures in1993. These results are explained with respect to the effects offlooding on lake and bog dynamics.     

Predicting regional spread of non-native species using oceanographic models: validation and identification of gaps

Predicting spread is a central goal of invasion ecology. Within marine systems, researchers have increasingly made use of oceanographic circulation models to estimate currents and track species dispersal. However, the accuracy of these models for predicting biological patterns, particularly for non-native species, has generally not been validated. Particularly, we wished to examine the ability of models to predict physical and biological processes, which jointly determine the spread of marine larval organisms. We conducted two empirical studies—a recruitment study and a drift card study—along the coast of New England, USA, focusing on two invaders of concern—the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus), to explicitly evaluate the ability of oceanographic models to predict patterns of spread. We used data from the large-scale drift card study to validate our ability to capture dispersal patterns driven purely by physical processes. Next, we conducted a recruitment study to evaluate our ability to reproduce patterns of biological dispersal. We were generally capable of reproducing drift cards patterns—suggesting that the physical mechanics in the model were predictive. However, predicted biological patterns were inconsistent—we were able to predict dispersal patterns for H. sanguineus but not for C. maenas. Our results highlight the importance of validating models and suggest that more work is necessary before we can reliably use oceanographic models to predict biological spread of intertidal organisms.     

Climate vs. soil factors in local adaptation of two common plant species

Evolutionary theory suggests that divergent natural selection in heterogeneous environments can result in locally adapted plant genotypes. To understand local adaptation it is important to study the ecological factors responsible for divergent selection. At a continental scale, variation in climate can be important while at a local scale soil properties could also play a role. We designed an experiment aimed to disentangle the role of climate and (abiotic and biotic) soil properties in local adaptation of two common plant species. A grass (Holcus lanatus) and a legume (Lotus corniculatus), as well as their local soils, were reciprocally transplanted between three sites across an Atlantic-Continental gradient in Europe and grown in common gardens in either their home soil or foreign soils. Growth and reproductive traits were measured over two growing seasons. In both species, we found significant environmental and genetic effects on most of the growth and reproductive traits and a significant interaction between the two environmental effects of soil and climate. The grass species showed significant home site advantage in most of the fitness components, which indicated adaptation to climate. We found no indication that the grass was adapted to local soil conditions. The legume showed a significant home soil advantage for number of fruits only and thus a weak indication of adaptation to soil and no adaptation to climate. Our results show that the importance of climate and soil factors as drivers of local adaptation is species-dependent. This could be related to differences in interactions between plant species and soil biota.     

ERI evaluation of injectates used at a dry‐cleaning site

A former dry‐cleaning site in Jackson, Tennessee, has undergone remediation to treat dense nonaqueous‐phase liquid (trichloroethene [TCE] and tetrachloroethene [PCE]) contamination in the subsurface. The dry cleaning operation closed in 1977. In 2002, a series of injections were made at the site consisting of corn syrup, vegetable oils, and Simple Green®. In 2004, approximately 200 cubic yards of contaminated soil were excavated, and the bottom of the excavation was covered with sodium lactate. In 2009, the site was characterized using proprietary electrical resistivity imaging (ERI; commercially available as Aestus GeoTrax Surveys^TM). Follow‐up confirmation soil borings targeted anomalies detected via the geophysical work. The results indicate an extremely electrically conductive (less than 1 ohm‐m) vadose zone downgradient from the injection wells, and extremely electrically resistive areas (greater than 10,000 ohm‐m) in the phreatic zone near the injection area. The sample data indicate that the electrically resistive anomalous zones contain moderate to high concentrations of undegraded dry‐cleaning compounds. Electrically conductive anomalous zones are interpreted to be areas of biological activity generated by the amendments injected into the subsurface based on the extreme conductivity values detected, the chemical composition (i.e., PCE degradates are present), and the dominant vadose‐zone location of the conductive zones. © 2012 Wiley Periodicals, Inc.     

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.