Nuchal glands: a novel defensive system in snakes

Of the various chemical defensive adaptations of vertebrates, nuchal glands are among the most unusual. First described in a Japanese natricine snake, Rhabdophis tigrinus, in 1935, these organs are embedded under the skin of the neck region as a series of paired glands that have neither lumina nor ducts. The major chemical components of the glandular fluid are bufadienolides, which are cardiotonic steroids also found in the skin secretion of toads. Here we review early studies of nuchal glands and briefly introduce our recent findings on the sequestration of bufadienolides from consumed toads and the maternal provisioning of those sequestered compounds. We summarize behavioral studies associated with the antipredator function of the nuchal glands, which have been conducted during our more than decade-long collaboration. Results of preliminary analyses on the possible costs of toad-eating and on the ultrastructure of the nuchal glands are also presented. Finally, we discuss the evolutionary origin of the nuchal glands and suggest future directions designed to understand the biological importance of these novel vertebrate organs, which have evolved in a limited number of snake species.     

Historical processes constrain patterns in global diatom diversity

There is a long-standing belief that microbial organisms have unlimited dispersal capabilities, are therefore ubiquitous, and show weak or absent latitudinal diversity gradients. In contrast, using a global freshwater diatom data set, we show that latitudinal gradients in local and regional genus richness are present and highly asymmetric between both hemispheres. Patterns in regional richness are explained by the degree of isolation of lake districts, while the number of locally coexisting diatom genera is highly constrained by the size of the regional diatom pool, habitat availability, and the connectivity between habitats within lake districts. At regional to global scales, historical factors explain significantly more of the observed geographic patterns in genus richness than do contemporary environmental conditions. Together, these results stress the importance of dispersal and migration in structuring diatom communities at regional to global scales. Our results are consistent with predictions from the theory of island biogeography and metacommunity concepts and likely underlie the strong provinciality and endemism observed in the relatively isolated diatom floras in the Southern Hemisphere.     

Comparing petroleum fiscal regimes under oil price uncertainty

This study investigates and compares five upstream petroleum fiscal systems under crude oil price uncertainty. The fiscal systems analyzed are: the Alberta Canada tax and royalty system, the Papua New Guinea (PNG) (pre-2003) traditional Rate of Return (ROR) system, the Sao Tome and Principe/Nigerian Joint Development Zone (SNJDZ) Production Sharing Contract (PSC), the Tanzanian PSC/ROR hybrid system and the Trinidad and Tobago PSC. Contingent claims analysis is used to value the governments’ tax claims under uncertainty using a numerical approach, viz., Monte Carlo simulation. Each system is tested to obtain the after-tax value accruing to firms as well as the distortionary effects introduced by the fiscal systems. The results are then ranked. The Alberta Canada and PNG fiscal systems provide companies with the highest after-tax values while also being the least distortionary. The Tanzanian system is the lowest in both rankings, providing relatively low after-tax values and introducing strong distortionary effects. The SNJDZ PSC imposed a relatively high tax burden on companies with median distortionary effects. The Trinidadian PSC generated a median tax burden on companies but has strong distortionary effects.     

Conducting and delivering integrated research to influence land-use policy: salinity policy in Australia

Researchers can find the process of engaging with policy to be both rewarding and frustrating. In the context of land-use policy, we discuss various aspects of the research-policy nexus, including the various influences of research and policy on land use, the adoption of research results by policy makers, differences between policy and research, and the roles that researchers can play in policy. We present a case study from Australia in which a range of research into land use was integrated to develop an investment framework for policy makers and natural resource managers. We conclude that, to enhance their influence on land-use policy, researchers should strive to: understand the policy maker's perspective, practice excellent communication, be solution oriented, find a champion, avoid appearances of vested interest, and be simple, patient, persistent, resilient, responsive and timely.     

The limitations of environmental management systems in Australian agriculture

The efficacy of government-supported programs to encourage improved management of land and water systems associated with agricultural land in Australia has been mixed. The broad approach of Australian governments is reviewed briefly. Evidence is presented from case assessments of a program to promote adoption of environmental management systems (EMSs) to improve environmental outcomes from agricultural practices. EMSs are systems implemented to manage the environmental impacts and ameliorate environmental risk associated with business activity. Data are presented on reported EMS activity and experience of four selected groups of farmers in Victoria, south-eastern Australia, representing broad-acre cropping, beef and dairy farming. The pro-environmental behaviours of farmers were mediated through voluntary adoption of government and industry sponsored EMSs, often with financial incentives and other support. Findings from the study were that adoption of EMS practices with sufficient public benefits is unlikely to occur at sufficient scale for significant environmental impact. Farmers more readily adopted practices which were financially beneficial than those which had a positive environmental impact. Although the focus on voluntary market-based instrument (MBI) type programs is popular in western countries, enforcing regulation is an important, but usually politically unpopular, component of land use policy. The comparative advantage of EMSs differed for the industries studied, but overall there were insufficient market drivers for widespread EMS adoption in Australia. Environmental outcomes could be more effectively achieved by directly funding land management practices which have highest public net benefits. Having a clear and unambiguous management objective for a particular land management policy is more likely to achieve outcomes than having multiple objectives as occurs in a number of international programs currently.     

Examining the coupling of carbon and nitrogen cycles in Appalachian streams: the role of dissolved organic nitrogen

Although regional and global models of nitrogen (N) cycling typically focus on nitrate, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds and thus the dominant form of dissolved N in many streams. Our understanding of the processes controlling DON export from temperate forests is poor. In pristine systems, where biological N limitation is common, N contained in recalcitrant organic matter (OM) can dominate watershed N losses. This recalcitrant OM often has moderately constrained carbon:nitrogen (C:N) molar ratios (approximately 25-55) and therefore, greater DON losses should be observed in sites where there is greater total dissolved organic carbon (DOC) loss. In regions where anthropogenic N pollution is high, it has been suggested that increased inorganic N availability can reduce biological demand for organic N and therefore increase watershed DON losses. This would result in a positive correlation between inorganic and organic N concentrations across sites with varying N availability. In four repeated synoptic surveys of stream water chemistry from forested watersheds along an N loading gradient in the southern Appalachians, we found surprisingly little correlation between DON and DOC concentrations. Further, we found that DON concentrations were always significantly correlated with watershed N loading and stream water [NO3-] but that the direction of this relationship was negative in three of the four surveys. The C:N molar ratio of dissolved organic matter (DOM) in streams draining watersheds with high N deposition was very high relative to other freshwaters. This finding, together with results from bioavailability assays in which we directly manipulated C and N availabilities, suggests that heterotrophic demand for labile C can increase as a result of dissolved inorganic N (DIN) loading, and that heterotrophs can preferentially remove N-rich molecules from DOM. These results are inconsistent with the two prevailing hypotheses that dominate interpretations of watershed DON loss. Therefore, we propose a new hypothesis, the indirect carbon control hypothesis, which recognizes that heterotrophic demand for N-rich DOM can keep stream water DON concentrations low when N is not limiting and heterotrophic demand for labile C is high.     

Effect of visual background complexity and light level on the detection of visual signals of male <Emphasis Type="Italic">Schizocosa ocreata</Emphasis> wolf spiders by female conspecifics

For visual signaling to be effective, animal signals must be detected and discriminated by receivers, often against complex visual backgrounds with varying light levels. Accordingly, in many species, conspicuous visual displays and ornaments have evolved as a means to enhance background contrast and thereby increase the detection and discrimination of male courtship signals by females. Using video playbacks, we tested the hypothesis that visual courtship displays and leg decorations of male Schizocosa ocreata wolf spiders are more conspicuous against complex leaf-litter backgrounds. Video exemplars of courting males with manipulated leg tufts were superimposed on different backgrounds (complex leaf litter in sun or shade, featureless gray background) and presented to female spiders. Females were more likely to orient to males presented against lighter backgrounds (litter in sun, gray) than the darker ones (litter—shade). Males with larger tufts were also more likely to be detected, as latency to orient was shortest for enlarged and longest for removed tufts. Latency of females to approach was shorter against lighter backgrounds, and approach latency was longest for males without tufts. Female receptivity scores were significantly greater for males against lighter backgrounds, and males with larger tufts had higher scores. These results suggest that both complexity and light level of display backgrounds affect the detection of male visual courtship signals by females and that aspects of the male phenotype may increase chances of detection (and receptivity) against visually complex backgrounds.     

Processes influencing secondary aerosol formation in the San Joaquin Valley during winter

Air quality data collected in the California Regional PM10/ PM(2.5) Air Quality Study (CRPAQS) are analyzed to qualitatively assess the processes affecting secondary aerosol formation in the San Joaquin Valley (SJV). This region experiences some of the highest fine particulate matter (PM(2.5)) mass concentrations in California (< or = 188 microg/m3 24-hr average), and secondary aerosol components (as a group) frequently constitute over half of the fine aerosol mass in winter. The analyses are based on 15 days of high-frequency filter and canister measurements and several months of wintertime continuous gas and aerosol measurements. The phase-partitioning of nitrogen oxide (NO(x))-related nitrogen species and carbonaceous species shows that concentrations of gaseous precursor species are far more abundant than measured secondary aerosol nitrate or estimated secondary organic aerosols. Comparisons of ammonia and nitric acid concentrations indicate that ammonium nitrate formation is limited by the availability of nitric acid rather than ammonia. Time-resolved aerosol nitrate data collected at the surface and on a 90-m tower suggest that both the daytime and nighttime nitric acid formation pathways are active, and entrainment of aerosol nitrate formed aloft at night may explain the spatial homogeneity of nitrate in the SJV. NO(x) and volatile organic compound (VOC) emissions plus background O3 levels are expected to determine NO(x) oxidation and nitric acid production rates, which currently control the ammonium nitrate levels in the SJV. Secondary organic aerosol formation is significant in winter, especially in the Fresno urban area. Formation of secondary organic aerosol is more likely limited by the rate of VOC oxidation than the availability of VOC precursors in winter.     

Wintertime vertical variations in particulate matter (PM) and precursor concentrations in the San Joaquin Valley during the California Regional Coarse PM/Fine PM Air Quality Study

Air quality monitoring was conducted at a rural site with a tower in the middle of California's San Joaquin Valley (SJV) and at elevated sites in the foothills and mountains surrounding the SJV for the California Regional PM10/ PM2.5 Air Quality Study. Measurements at the surface and n a tower at 90 m were collected in Angiola, CA, from December 2000 through February 2001 and included hourly black carbon (BC), particle counts from optical particle counters, nitric oxide, ozone, temperature, relative humidity, wind speed, and direction. Boundary site measurements were made primarily using 24-hr integrated particulate matter (PM) samples. These measurements were used to understand the vertical variations of PM and PM precursors, the effect of stratification in the winter on concentrations and chemistry aloft and at the surface, and the impact of aloft-versus-surface transport on PM concentrations. Vertical variations of concentrations differed among individual species. The stratification may be important to atmospheric chemistry processes, particularly nighttime nitrate formation aloft, because NO2 appeared to be oxidized by ozone in the stratified aloft layer. Additionally, increases in accumulation-mode particle concentrations in the aloft layer during a fine PM (PM2.5) episode corresponded with increases in aloft nitrate, demonstrating the likelihood of an aloft nighttime nitrate formation mechanism. Evidence of local transport at the surface and regional transport aloft was found; transport processes also varied among the species. The distribution of BC appeared to be regional, and BC was often uniformly mixed vertically. Overall, the combination of time-resolved tower and surface measurements provided important insight into PM stratification, formation, and transport.     

The effect of silica on the degradation of organohalides in granular iron columns

Dissolved silica species are naturally occurring, ubiquitous groundwater constituents with corrosion-inhibiting properties. Their influence on the performance and longevity of iron-based permeable reactive barriers for treatment of organohalides was investigated through long-term column studies using Connelly iron as the reactive medium. Addition of dissolved silica (0.5 mM) to the column feed solution led to a reduction in iron reactivity of 65% for trichloroethylene (TCE), 74% for 1,1,2-trichloroethane (1,1,2-TCA), and 93% for 1,1,1-trichloroethane (1,1,1-TCA), compared to columns operated under silica-free conditions. Even though silica adsorption was a gradual process, the inhibitory effect was evident within the first week, with subsequent decreases in reactivity over 288 days being relatively minor. Lower concentrations of dissolved silica species (0.2 mM) led to a lesser decrease (70%) in iron reactivity toward 1,1,1-TCA. The presence of dissolved silica species produced a shift in TCE product distribution toward the more highly chlorinated product cis-dichloroethylene (cis-DCE), although it did not appear to alter products originating from the trichloroethanes. The major corrosion products identified were magnetite (Fe3O4) or maghemite (gamma-Fe2O3) and carbonate green rust ([Fe4(2+)Fe(2)3+(OH)12][CO(3).2H2O]). Iron carbonate hydroxide (Fe(II)1.8Fe(III)0.2(OH)2.2CO3) was only found in the silica-free column, indicating that silica may hinder its formation. A comparison with columns operated under the same conditions, but using Master Builder iron as the reactive matrix, showed that Connelly iron is initially less reactive, but performs better than Master Builder iron over 288 days.