Black‐capped chickadees Poecile atricapillus sing at higher pitches with elevated anthropogenic noise,but not with decreasing canopy cover

Several songbird species sing at higher frequencies (i.e. higher pitch) when anthropogenic noise levels are elevated. Such frequency shifting is thought to be an adaptation to prevent masking of bird song by anthropogenic noise. However, no study of this phenomenon has examined how vegetative differences between noisy and quiet sites influence frequency shifting. Variation in vegetative structure is important because the acoustic adaptation hypothesis predicts that birds in more open areas should also sing at higher frequencies. Thus, vegetative structure may partially explain the observation of higher frequency songs in areas with high levels of anthropogenic noise. To distinguish between frequency shifting due to noise or vegetative structure we recorded the songs of black‐capped chickadees Poecile atricapillus vocalizing in high and low noise sites with open and closed canopy forests. Consistent with the noise‐dependent frequency hypothesis, black‐capped chickadees sang at higher frequencies in high noise sites than in low noise sites. In contrast, birds did not sing at higher frequencies in sites with more open canopies. These results suggest that frequency shifting in chickadees is more strongly related to ambient noise levels than to vegetative structure. A second frequency measure, inter‐note ratio, was reduced at higher levels of canopy cover. We speculate that this may be due to a non‐random distribution of dominant males. In sum, our results support the hypothesis that some birds sing at higher frequencies to avoid overlap with anthropogenic noise, but suggest that vegetative structure may play a role in the modification of other song traits.     

Amazon forest carbon dynamics predicted by profiles of canopy leaf area and light environment

Tropical forest structural variation across heterogeneous landscapes may control above‐ground carbon dynamics. We tested the hypothesis that canopy structure (leaf area and light availability) – remotely estimated from LiDAR – control variation in above‐ground coarse wood production (biomass growth). Using a statistical model, these factors predicted biomass growth across tree size classes in forest near Manaus, Brazil. The same statistical model, with no parameterisation change but driven by different observed canopy structure, predicted the higher productivity of a site 500 km east. Gap fraction and a metric of vegetation vertical extent and evenness also predicted biomass gains and losses for one‐hectare plots. Despite significant site differences in canopy structure and carbon dynamics, the relation between biomass growth and light fell on a unifying curve. This supported our hypothesis, suggesting that knowledge of canopy structure can explain variation in biomass growth over tropical landscapes and improve understanding of ecosystem function.     

Replacement of non-heme Fe(II) with Cu(II) in the alpha-ketoglutarate dependent DNA repair enzyme AlkB: spectroscopic characterization of the active site

The bacterial DNA repair enzyme AlkB is an alpha-ketoglutarate (alphaKG) dependent non-heme Fe(II) containing dioxygenase. Here we describe, for the first time, the preparation of a Cu(II)-reconstituted form of AlkB in various complexes. Spectroscopic characterization showed correct AlkB folding upon incorporation of Cu(II) in the active site. The Cu site was classified as a type 2 site by EPR spectroscopy. The accessibility of the active site metal was studied using imidazole as a probe. Although addition of imidazole did not change the EPR spectrum of the AlkB-Cu-alphaKG complex, the spectrum of the AlkB-Cu-succinate complex clearly changed, indicating binding of imidazole at the Cu site. Binding of substrate (methylated DNA) to the AlkB-Cu-alphaKG complex did not induce changes in the EPR spectrum, demonstrating that the substrate does not bind in the immediate vicinity of the metal centre. This work provides a basis for advanced EPR approaches aimed at studying the interactions and dynamics of AlkB complexes in solution.     

An extracellular Leptospira interrogans leucine‐rich repeat protein binds human E‐ and VE‐cadherins

Pathogenic Leptospira bacteria are the causative agents of leptospirosis, a zoonotic disease affecting animals and humans worldwide. These pathogenic species have the ability to rapidly cross host tissue barriers by a yet unknown mechanism. A comparative analysis of pathogens and saprophytes revealed a higher abundance of genes encoding proteins with leucine‐rich repeat (LRR) domains in the genomes of pathogens. In other bacterial pathogens, proteins with LRR domains have been shown to be involved in mediating host cell attachment and invasion. One protein from the pathogenic species Leptospira interrogans, LIC10831, has been previously analysed via X‐ray crystallography, with findings suggesting it may be an important bacterial adhesin. Herein we show that LIC10831 elicits an antibody response in infected animals, is actively secreted by the bacterium, and binds human E‐ and VE‐cadherins. These results provide biochemical and cellular evidences of LRR protein‐mediated host–pathogen interactions and identify a new multireceptor binding protein from this infectious Leptospira species.     

Mechanism of reduction of chromium(VI) ion by 2-mercaptosuccinic acid in aqueous solution

The kinetics of the reduction of the chromium(VI) ion by 2-mercaptosuccinic acid (thiomalic acid) were studied by rapid scanning stopped flow spectrophotometry. The conditions used were [Cr(VI)]_T=0.20 mM, [MSA]_T=5-90 mM, 3.0≤pH≤5.6 in citric acid-phosphate buffer, or 3.3≤pH≤5.4 in 0.40 M acetic acid-acetate buffer, 20.0≤T≤35.0 °C at I=0.50 M (NaClO₄). Spectrophotometric titration at 350 nm indicates the stoichiometry of the reaction to be 1:3. The kinetics of both formation and decay of the intermediate chromium(VI) thioester were followed at λ_max=425 nm and rate expressions, specific rate constants and corresponding activation parameters were derived from the proposed mechanism. The acetic acid-acetate buffer was found to catalyze the formation but not the decay rate of the intermediate. The citric acid-phosphate buffer and dissolved oxygen did not have any significant effect on the reaction rates. The justification of the mechanism was discussed in terms of standard biological conditions.     

Benthic invertebrate assemblage change following dam removal in a Wisconsin stream

Small dams (height <10 m) have transformed stream networks across the United States. Shopiere Dam was removed from Turtle Creek, a fourth order stream in Southeastern Wisconsin in the fall of 1999. We sampled three sites (upstream of the impoundment, immediately below the dam, and farther downstream) before and after dam removal to identify changes in the invertebrate assemblage following removal. Prior to removal, upstream and downstream sites had similar taxonomic composition. In contrast the dam site had more taxonomic variation. The upstream, dam and downstream sites responded differently to dam removal in analyses of diversity, functional feeding groups, and invertebrate composition. Upstream at the reference site, changes in functional feeding group composition appeared to be associated with a decrease in silt coverage. At the dam site, taxonomic composition changed following dam removal, however diversity and functional feeding groups remained similar. At the downstream site, the invertebrate assemblage remained similar in all analyses. Our observations indicate that the effects of dam removal were not uniform through the stream, rather each site responded in a different way.     

Effect of minor water depth treatments on competitive effect and response of eight wetland plants

Two facets of plant competition, competitive effect (CE) and competitive response (CR), can be used to explain plant community composition but our understanding of abiotic factors that may differentially affect species’ competitive ability is incomplete. We tested whether water-depth affected CE (ability to suppress neighbour) and CR (avoid suppression from neighbour), and if so whether there was consistence in the rank order of both measures of competition under different water depth treatments. CE and CR were measured and compared for eight wetland plant species (Carex lurida, Carex tribuloides, Elymus virginicus, Juncus tenuis, Lythrum salicaria, Phalaris arundinacea, Rumex orbiculatus and Verbesina alternifolia) at five different water-depth treatments (+2, 0, −2, −4 and −6 cm relative to the substrate). Overall, we found that mean CE was at its lowest value at +2 cm water depth, while mean CR was highest at +2 and −6 cm compared to the other water treatments. There was a significant variation of CE between species, with a defined hierarchical order. Pairwise CE rank order correlations between water depth treatments were significant but CR correlations were generally not. There was no significant correlation between CE and CR. CE was significantly correlated with biomass of species grown alone but CR was not. These findings indicate that CE may be used as a general measure to predict wetland species performance, and thus community assemblage, across a range of water depths. CR does not seem to demonstrate predicable patterns between species and water depth treatments. Our results suggest that competition intensity may be reduced in a non-resource-stressed flooded environment by a reduction in CE, but the corresponding increase in CR could dampen this effect on overall competitive ability.