Variation of pyrrolizidine alkaloids in Ithomiinae: A comparative study between species feeding on Apocynaceae and Solanaceae

Summary The primitive, Apocynaceae-feeding Ithomiine,Tithorea harmonia, incorporates dehydropyrrolizidine alkaloids (PAs) from its larval foodplant (Prestonia acutifolia), rarely visiting PA sources pharmacophagously in the adult; females show higher concentrations of PAs than males, with similar variance. The close relativeAeria olena (feeding onP. coalita, without PAs) shows similar PA concentrations in both sexes and greater variation in males, like more advanced Solanaceae-feeding Ithomiine such asMechanitis polymnia, which likeA. olena obtain PAs by pharmacophagy in the adult (mainly males). This difference is due to the dynamics of PA incorporation in these species. Little variation in PA content was found among allopatric populations of the same species, but variation in available PA sources in different months was correlated with different average storage levels in the butterflies.     

Tropane and pyrrolizidine alkaloids in the ithomiinesPlacidula euryanassa andMiraleria cymothoe (Lepidoptera: Nymphalidae)

Summary Larvae of the ithomiine butterflyPlacidula euryanassa sequester tropane alkaloids (TAs) from the host plantBrugmansia suaveolens and pass them through the pupae to freshly emerged adults. Wild caught adults also show in their tissues, variable amounts of pyrrolidizine alkaloids (PAs), probably sequestered from variable plant sources and subject to dynamics of incorporation, accumulation and utilization of PAs by ithomiine butterflies. The ratio TAs/PAs is also variable between different populations.Miraleria cymothoe, another ithomiine that feeds onB. suaveolens as larvae, does not sequester TAs from the host-plant, but sequesters PAs from plant sources visited by the adult butterflies. The main alkaloid found in both butterflies is lycopsamine, which also is the principal PA found in all genera of Ithomiinae.     

Differential parasitism of least flycatchers and yellow warblers by the brown-headed cowbird

Summary Brown-headed cowbirds (Molothrus ater) parasitized yellow warblers (Dendroica petechia) six times more frequently than least flycatchers (Empidonax minimus) nesting in the same riparian habitat in southern Manitoba. This difference was surprising because least flycatchers were higher quality hosts; flycatchers always accepted cowbird eggs while warblers did so on only about half the occasions. Both hosts were equally good foster parents, at least until fledging; thus, once an egg was accepted there was probably no further advantage in parasitizing one species over the other. The probability that a nest was parasitized decreased with increasing nest height, perhaps as a consequence of the cowbird's habit of searching for nests close to the ground. Since least flycatchers nested higher in the canopy than yellow warblers, a greater proportion of flycatcher nests probably were not detected by cowbirds. Nevertheless, nest height alone could not account fully for the lower incidence of parasitism on flycatchers. Clutch initiation in flycatchers peaked 6 days after warbler clutch initiations and 5 days after that of cowbirds. Despite the later peak in initiations, flycatcher nests were always available as potential hosts over the entire cowbird laying season and it was not until new clutch initiations by warblers declined in late summer that flycatchers were actually used as hosts. Because least flycatchers responded more aggressively than yellow warblers to a model female cowbird at the nest, we concluded that greater nest defense by flycatchers may have also reduced the rate of brood parasitism in this host. Together, our results suggest the large difference in the frequency of parasitism between these two hosts was primarily a product of nest location but that differences in host nest-defense and breeding season asynchrony may have contributed to preferential host selection.Offprint requests to: J.V. Briskie     

Evidence of immunomodulation in nestling American kestrels (Falco sparverius) exposed to environmentally relevant PBDEs

We investigated whether exposure to environmentally relevant polybrominated diphenyl ethers (PBDEs) causes immunomodulation in captive nestling American kestrels (Falco sparverius). Eggs within each clutch, divided by laying sequence, were injected with safflower oil or penta-BDE congeners-47, -99, -100, and -153 dissolved in safflower oil (18.7 microg sigmaPBDEs/egg) approximating Great Lakes birds. For 29 days, nestlings consumed the same PBDE mixture (15.6+/-0.3 ng/g body weight per day), reaching sigmaPBDE body burden concentrations that were 120x higher in the treatment birds (86.1+/-29.1 ng/g ww) than controls (0.73+/-0.5 ng/g ww). PBDE-exposed birds had a greater PHA response (T-cell-mediated immunity), which was negatively associated with increasing BDE-47 concentrations, but a reduced antibody-mediated response that was positively associated with increasing BDE-183 concentrations. There were also structural changes in the spleen (fewer germinal centers), bursa (reduced apoptosis) and thymus (increased macrophages), and negative associations between the spleen somatic index and sigmaPBDEs, and the bursa somatic index and BDE-47. Immunomodulation from PBDE exposure may be exacerbated in wild birds experiencing greater environmental stresses.     

Detection of DNA adducts in declining hop plants grown on fields formerly treated with heptachlor, a persistent insecticide

Hop decline was observed in Alsace, eastern France, in reparcelled sugar beet fields formerly abundantly treated with an insecticide, heptachlor. Leaves were collected from 'declining hops' grown in an heptachlor-contaminated area and from 'healthy hops' grown in a soil not contaminated by heptachlor. These two samples came from hop vines treated with other usual pesticides. 'Control' hop leaves came from soil neither treated with pesticide nor contaminated with heptachlor. Hypermodified nucleotides (DNA adducts) were detected using the (32)P-postlabelling method. No detectable DNA adducts were found in the 'control' specimen, whereas eight adducts were detected in the 'healthy hops' specimen, probably due to the usual pesticide treatment. However, 16 adducts, nine of which were new adducts, could be detected in the 'declining hops' specimen. It may therefore be supposed that the presence of these hypermodified nucleotides perturbs gene expression and so contributes to the hop decline. In addition, to confirm the genotoxicity of heptachlor, it is shown that it induces DNA adducts in bean-cell suspension culture as well. Finally, it is proposed, in the case of alternate cultures scheduled in fields which were formerly treated with pesticides, adapted to other cultures, that particular attention should be given to the history of the soils.     

Emissions of NO and N2O from soils

Nitric oxide (NO) and nitrous oxide (N₂O) fluxes were measured from agricultural, forest and moorland environments, using chamber techniques. Maximum emissions of NO and N₂O were measured from the agricultural soils shortly after fertiliser application (7 ng NO-N m^–2 s^–1 and 91 ng N₂O-N m^–2 s^–1). For the non-agricultural soils the NO flux ranged from –0.3 to 0.5 ng NO-N m^–2 s^–1 and the N₂O flux ranged from 1 to 2.7 ng N₂O-N m^–2 s^–1. Emissions, however, were increased 2 to 7 fold when N deposition (uplands) and N fixation (alder plantations) contributed to the pool of soil available N. The best predictors of the NO emission were soil NO ₃ ^– and soil temperature, accounting for 60% of the variability observed. The prediction of N₂O was less successful. Only 30% of the variability could be explained by the soil NO ₃ ^– and the soil moisture content, soil temperature did not have a significant effect on the N₂O emission.     

Evaluation of diffusive samplers and photoionisation detectors for measuring very short peak exposures in the workplace

The extent to which very short peak widths, peak frequency, sampling time and post-sampling/pre-capping time impact upon occupational exposure measurements of toluene has been investigated using diffusive tubes. Additionally, the effect of the width of the peak on the estimation of peak maximum concentration and time-weighted average (TWA) concentration from real-time instruments (photoionisation detectors-PIDs) was also studied, and their responses modelled. No clear differences were perceived between diffusive and pumped tube results. Mean biases of -5 to +6% were recorded but no trend could be distinguished with respect to any of the variables examined; the main source of uncertainty was attributed to analytical uncertainty. The diffusive tubes can therefore be used to measure short term transient toluene concentrations (e.g. 5 s duration) over short (15 min) exposure periods. The two slower responding PIDs (t50 = 4 s) underestimated the maximum concentration of short term peaks having durations less than 10 s. The other three PIDs (t50 < or = 2 s) only significantly underestimated the maximum concentration of short term peaks having durations of 2 s and below. Pulse duration appeared to affect the PID's estimation of peak height more than peak area (TWA concentration).     

Intervention analysis in environmental engineering

Intervention analysis techniques are described for identifying and statistically modelling trends which may be present in water quality time series. At the exploratory data analysis stage, simple graphical and modelling methods can be employed for visually detecting and examining trends in a time series caused by one or more external interventions. For instance, a plot of a robust locally weighted regression smooth through a graph of the observations over time may reveal trends and other interesting statistical properties contained in the time series. In addition, statistical tests, such as different versions of the nonparametric Mann-Kendall test, can be used to detect the presence of trends caused by unknown or known external interventions. To characterize rigorously and estimate trends which may be known in advance or else detected using exploratory data analysis studies, different parametric methods can be utilized at the confirmatory data analysis stage. Specifically, the time series modelling approach to intervention analysis can be employed to estimate the magnitudes of the changes in the mean level of the series due to the interventions. Particular types of regression models can also be used for estimating trends, especially when there are many missing observations. To demonstrate how intervention analysis methods can be effectively used in environmental impact assessment, representative applications to water quality time series are presented.Invited Paper for Presentation at The Workshop on Statistical Methods for the Assessment of Point Source Pollution, The Canada Centre for Inland Waters, Burlington, Ontario, Canada, L7R 4A6, September 12–14, 1988.     

Iowa Statewide Stream Nitrate Load Calculated Using In Situ Sensor Network

Various techniques exist to estimate stream nitrate loads when measured concentration data are sparse. The inherent uncertainty associated with load estimation, however, makes tracking progress toward water quality goals more difficult. We used high‐frequency, in situ nitrate sensors strategically deployed across the agricultural state of Iowa to evaluate 2016 stream concentrations at 60 sites and loads at 35 sites. The generated data, collected at an average of 225 days per site, show daily average nitrate‐N yields ranging from 12 to 198 g/ha, with annual yields as high as 53 kg/ha from the intensely drained Des Moines Lobe. Thirteen of the sites that capture water from 82.5% of Iowa's area show statewide nitrate‐N loading in 2016 totaled 477 million kg, or 41% of the load delivered to the Mississippi–Atchafalaya River Basin (MARB). Considering the substantial private and public investment being made to reduce nitrate loading in many states within the MARB, networks of continuous, in situ measurement devices as described here can inform efforts to track year‐to‐year changes in nitrate load related to weather and conservation implementation. Nitrate and other data from the sensor network described in this study are made publicly available in real time through the Iowa Water Quality Information System.