Combined effects of night-time temperature and allelochemicals on performance of a generalist insect herbivore

To assess the pattern of temperature influencing the effect of allelochemicals on growth of insect herbivores and to examine the potential effect of warmer nights due to global warming, we examined the simultaneous effects of allelochemicals and warmer night-time temperatures on an insect herbivore (Spodoptera exigua; Lepidoptera: Noctuidae). Dietary chlorogenic acid, rutin and tomatine levels reflected those occurring naturally in the leaves of tomato, a hostplant of this herbivore. We compared the effects of four thermal regimes having a daytime temperature of 26 °C , with the night-time temperature increased from 14 to 26 °C by increments of 4 °C . The effect of a particular allelochemical on developmental rate was similar among the four thermal regimes. Chlorogenic acid and tomatine each reduced final larval weight, but there was no effect of night-time temperature. In contrast, rutin had no effect on final weight, whereas final weight declined with increasing night-time temperature. Night-time temperature did not influence amount eaten. Larvae ate less when chlorogenic acid or tomatine was in the diet. For each allelochemical, there were no allelochemical by thermal regime interactions. In addition, we compared the effects of allelochemicals and the thermal regime of 26:14 °C and constant 20 °C , which was the average temperature of the 26:14 °C regime. Developmental rate was lower at the constant 20 °C regime, chlorogenic acid and tomatine each depressed developmental rate, and there were no allelochemical by thermal regime interactions. Thus, regardless of the specific allelochemical or amount, the pattern of response at the fluctuating regime was similar to that at the constant temperature. In contrast, comparison of the thermal regime of 26:22 °C and constant 24 °C , which was the average temperature of the 26:22 °C regime, showed several allelochemical by thermal regime interactions. At the 26:22 °C regime, developmental rate was disproportionatly higher at the maximal rutin concentration compared to that at constant 24 °C . At the constant 24 °C , final larval mass was disproportionately lower at the moderate tomatine concentration compared to that at the 26:22 °C regime. Because these results differ from that of other studies examining another species, it appears that the response to incremental changes in night-time temperature will reflect the allelochemicals and insect species tested. The contrast between the constant 24 °C and 26:22 °C regimes indicates that even small fluctuations (±2 °C ) in temperature over 24 h can yield differences in the response to an allelochemical.     

Glycoprotein Biosynthesis in Peripheral Nervous System Myelin: Effect of Tunicamycin

Abstract: The effect of an inhibitor of N -glycosylation of glycoproteins, tunicamycin, on synthesis of PNS myelin proteins was investigated in vitro by using chopped sciatic nerves or spinal roots of 21-day-old Wistar rats. Tunicamycin when incubated with these nerves in the presence of ³H-labeled fucose, mannose, or glucosamine inhibited the uptake of radioactivity into myelin proteins including some high-molecular-weight proteins, P₀, 23K protein, and 19K protein by amounts ranging from 42 to 79%. Uptake of ¹⁴Camino acid mixture was inhibited much less by tunicamycin, but a new radioactive protein peak appeared when the protein mixtures had been separated by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. This protein ran directly in front of the P₀ peak, did not correspond to any bands stained by Fast green, and was not labeled by fucose. This peak appeared in increasing larger proportions with progressive time of incubation of nerves with ³H amino acids in the presence of tunicamycin. The new protein, which cross-reacts with P₀ antiserum, was tentatively identified as a nonglycosylated P₀ protein that appears to be almost as well incorporated as P₀ into the subcellular fraction containing myelin. At this time it is not possible to determine whether the unglycosylated P₀ is actually assembled into a site and configuration like that of P₀.     

Material Spiraling in Stream Corridors: A Telescoping Ecosystem Model

Stream ecosystems consist of several subsystems that are spatially distributed concentrically, analogous to the elements of a simple telescope. Subsystems include the central surface stream, vertically and laterally arrayed saturated sediments (hyporheic and parafluvial zones), and the most distal element, the riparian zone. These zones are hydrologically connected; thus water and its dissolved and suspended load move through all of these subsystems as it flows downstream. In any given subsystem, chemical transformations result in a change in the quantity of materials in transport. Processing length is the length of subsystem required to “process” an amount of substrate equal to advective input. Long processing lengths reflect low rates of material cycling. Processing length provides the length dimension of each cylindrical element of the telescope and is specific to subsystem (for example, the surface stream), substrate (for instance, nitrate), and process (denitrification, for example). Disturbance causes processing length to increase. Processing length decreases during succession following disturbance. The whole stream-corridor ecosystem consists of several nested cylindrical elements that extend and retract, much as would a telescope, in response to disturbance regime. This telescoping ecosystem model (TEM) can improve understanding of material retention in running water systems; that is, their “nutrient filtration” capacity. We hypothesize that disturbance by flooding alters this capacity in proportion to both intensity of disturbance and to the relative effect of disturbance on each subsystem. We would expect more distal subsystems (for example, the riparian zone) to show the highest resistance to floods. In contrast, we predict that postflood recovery of functions such as material processing (that is, resilience) will be highest in central elements and decrease laterally. Resistance and resilience of subsystems are thus both inversely correlated and spatially separated. We further hypothesize that cross-linkages between adjacent subsystems will enhance resilience of the system as a whole. Whole-ecosystem retention, transformation, and transport are thus viewed as a function of subsystem extent, lateral and vertical linkage, and disturbance regime. Received 15 April 1997; accepted 1 September 1997.     

Glyphosate-resistant goosegrass. Identification of a mutation in the target enzyme 5-enolpyruvylshikimate-3-phosphate synthase

The spontaneous occurrence of resistance to the herbicide glyphosate in weed species has been an extremely infrequent event, despite over 20 years of extensive use. Recently, a glyphosate-resistant biotype of goosegrass (Eleusine indica) was identified in Malaysia exhibiting an LD(50) value approximately 2- to 4-fold greater than the sensitive biotype collected from the same region. A comparison of the inhibition of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity by glyphosate in extracts prepared from the resistant (R) and sensitive (S) biotypes revealed an approximately 5-fold higher IC(50)(glyphosate) for the (R) biotype. Sequence comparisons of the predicted EPSPS mature protein coding regions from both biotypes revealed four single-nucleotide differences, two of which result in amino acid changes. One of these changes, a proline to serine substitution at position 106 in the (R) biotype, corresponds to a substitution previously identified in a glyphosate-insensitive EPSPS enzyme from Salmonella typhimurium. Kinetic data generated for the recombinant enzymes suggests that the second substitution identified in the (R) EPSPS does not contribute significantly to its reduced glyphosate sensitivity. Escherichia coli aroA- (EPSPS deficient) strains expressing the mature EPSPS enzyme from the (R) biotype exhibited an approximately 3-fold increase in glyphosate tolerance relative to strains expressing the mature EPSPS from the (S) biotype. These results provide the first evidence for an altered EPSPS enzyme as an underlying component of evolved glyphosate resistance in any plant species.     

Macroalgae and nutrients promote algal turf growth in the absence of herbivores

Coral Reefs - Closely cropped algal turfs are characteristic of healthy coral reefs, but unchecked growth can cause transitions into long sediment-laden turfs, which may be an alternative degraded...     

Heterogeneous genetic invasions of three insecticide resistance mutations in Indo‐Pacific populations of Aedes aegypti (L.)

Nations throughout the Indo‐Pacific region use pyrethroid insecticides to control Aedes aegypti, the mosquito vector of dengue, often without knowledge of pyrethroid resistance status of the pest or origin of resistance. Two mutations (V1016G + F1534C) in the sodium channel gene (Vssc) of Ae. aegypti modify ion channel function and cause target‐site resistance to pyrethroid insecticides, with a third mutation (S989P) having a potential additive effect. Of 27 possible genotypes involving these mutations, some allelic combinations are never seen whereas others predominate. Here, five allelic combinations common in Ae. aegypti from the Indo‐Pacific region are described and their geographical distributions investigated using genome‐wide SNP markers. We tested the hypothesis that resistance allele combinations evolved de novo in populations versus the alternative that dispersal of Ae. aegypti between populations facilitated genetic invasions of allele combinations. We used latent factor mixed‐models to detect SNPs throughout the genome that showed structuring in line with resistance allele combinations and compared variation at SNPs within the Vssc gene with genome‐wide variation. Mixed‐models detected an array of SNPs linked to resistance allele combinations, all located within or in close proximity to the Vssc gene. Variation at SNPs within the Vssc gene was structured by resistance profile, whereas genome‐wide SNPs were structured by population. These results demonstrate that alleles near to resistance mutations have been transferred between populations via linked selection. This indicates that genetic invasions have contributed to the widespread occurrence of Vssc allele combinations in Ae. aegypti in the Indo‐Pacific region, pointing to undocumented mosquito invasions between countries.     

Epstein-Barr Virus Latent Membrane Protein 2 Induces Autophagy To Promote Abnormal Acinus Formation

Epstein-Barr virus latent membrane protein 2A (LMP2A) induces many characteristics of carcinoma, including transformation, migration, invasion, and impaired differentiation. The MCF10A cell line differentiates to form hollow acini when grown in Matrigel, and expression of LMP2A inhibited differentiation and anoikis induced by loss of matrix attachment. LMP2A-infected cells formed large, lobular structures rather than hollow acini. Autophagy inhibitors impaired this abnormal growth and induced caspase 3 activation and acinus formation. LMP2A also increased autophagosome formation and expression of proteins in the autophagosome pathway. These findings suggest that LMP2A may inhibit anoikis and luminal clearance in acini through induction of autophagy.     

Nitrogen uptake in two frontal areas in the Greenland Sea

Summary During late spring, 1987, observations were made of nitrate and ammonium uptake in two regions of the Greenland Sea, the Arctic Front and the Polar Front. In the area of the Arctic Front, mixed layers were relatively deep (generally below 100m), and the 1% isolume averaged 35 m. Ambient nitrate concentrations were always greater than 6 M, whereas ammonium levels were always less than 0.6 M. Surface nitrate and ammonium specific uptake rates averages 4.4 and 2.3×10^–3 h^–1, respectively. The Polar Front generally coincided spatially with the location of the ice edge, and vertical mixed layers were shallow (pycnocline depth ranged from 8–14 m), and the 1 % isolume averaged 37 m. Nitrate concentrations were somewhat lower than in the Arctic Front, but remained above 3 M at all times. Ammonium levels reached 1.2 M. Nitrate and ammonium specific uptake rates at the surface averaged 4.8×10^–3 and 10×10^–3 h^–1, respectively. Integrated water column f-ratios for the Arctic and Polar Front regions averaged 0.63 and 0.31, and the ammonium relative preference indices at all depths within each study area were always greater than 8, indicating that ammonium remained the preferred nitrogen source for phytoplankton. New production in the two regions was approximately equal, but the Polar Front had a substantially greater amount of regenerated production, and hence total production as well. Irradiance (and not nutrient concentration) seems to be the most important environmental factor in controlling nitrogen uptake. The spatial variability observed within the Greenland Sea suggest that inclusion of this region in global carbon models will require increased spatial resolution of both the models and the data included.