The effects of adaptation on the perception of similar and dissimilar odors

The Pubishers wish to apologise for the inadvertent mis-spellingof Charles J. Wysocki and other errors in the above article,which should be corrected as follows. On Page 471, Table I, the first Number in the second columnshould read 2:6. On page 477, Table II, the results under d-limonene should readas below. On page 481, the NIH grant number to CJW is DC00298.     

Escherichia coli dGTP triphosphohydrolase is inhibited by gene 1.2 protein of bacteriophage T7

Escherichia coli has a unique enzyme, deoxyguanosine triphosphate triphosphohydrolase (dGTPase) that cleaves dGTP into deoxyguanosine and tripolyphosphate. An E. coli mutant, optA1, has a 50-fold increased level of the dGTPase (Beauchamp, B.B., and Richardson, C.C. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 2563-2567). Successful infection of E. coli optA1 by bacteriophage T7 is dependent on a 10-kDa protein encoded by gene 1.2 of the phage. In this report we show that the gene 1.2 protein is a specific inhibitor of the E. coli dGTPase. Gene 1.2 protein inhibits dGTPase activity by forming a complex with the dGTPase with an apparent stoichiometry of two monomers of gene 1.2 protein/tetramer of dGTPase. The interaction is reversible with a half-life of the complex of 30 min and an apparent binding constant Ki of 35 nM. The binding of inhibitor of dGTPase is cooperative, indicating allosteric interactions between dGTPase subunits with a Hill coefficient of 1.7. The interaction is modulated differentially by DNA, RNA, and deoxyguanosine mono-, di-, and triphosphate. Both the binding of the substrate dGTP and of the inhibitor gene 1.2 protein induce conformational changes in dGTPase. The conformation of the enzyme in the presence of saturating concentrations of dGTP virtually prevents the association with, and the dissociation from, gene 1.2 protein.     

Group-foraging is not associated with longevity in North American birds

Group-foraging is common in many animal taxa and is thought to offer protection against predators and greater foraging efficiency. Such benefits may have driven evolutionary transitions from solitary to group-foraging. Greater protection against predators and greater access to resources should reduce extrinsic sources of mortality and thus select for higher longevity according to life-history theory. I assessed the association between group-foraging and longevity in a sample of 421 North American birds. Taking into account known correlates of longevity, such as age at first reproduction and body mass, foraging group size was not correlated with maximum longevity, with and without phylogenetic correction. However, longevity increased with body mass in non-passerine birds. The results suggest that the hypothesized changes in predation risk with group size may not correlate with mortality rate in foraging birds.     

Frequency-dependent conspecific attraction to food patches

In many ecological situations, resources are difficult to find but become more apparent to nearby searchers after one of their numbers discovers and begins to exploit them. If the discoverer cannot monopolize the resources, then others may benefit from joining the discoverer and sharing their discovery. Existing theories for this type of conspecific attraction have often used very simple rules for how the decision to join a discovered resource patch should be influenced by the number of individuals already exploiting that patch. We use a mechanistic, spatially explicit model to demonstrate that individuals should not necessarily simply join patches more often as the number of individuals exploiting the patch increases, because those patches are likely to be exhausted soon or joining them will intensify future local competition. Furthermore, we show that this decision should be sensitive to the nature of the resource patches, with individuals being more responsive to discoveries in general and more tolerant of larger numbers of existing exploiters on a patch when patches are resource-rich and challenging to locate alone. As such, we argue that this greater focus on underlying joining mechanisms suggests that conspecific attraction is a more sophisticated and flexible tactic than currently appreciated.     

Glutaredoxin-2 Is Required to Control Proton Leak through Uncoupling Protein-3

Glutathionylation has emerged as a key modification required for controlling protein function in response to changes in cell redox status. Recently, we showed that the glutathionylation state of uncoupling protein-3 (UCP3) modulates the leak of protons back into the mitochondrial matrix, thus controlling reactive oxygen species production. However, whether or not UCP3 glutathionylation is mediated enzymatically has remained unknown because previous work relied on the use of pharmacological agents, such as diamide, to alter the UCP3 glutathionylation state. Here, we demonstrate that glutaredoxin-2 (Grx2), a matrix oxidoreductase, is required to glutathionylate and inhibit UCP3. Analysis of bioenergetics in skeletal muscle mitochondria revealed that knock-out of Grx2 (Grx2^−/−) increased proton leak in a UCP3-dependent manner. These effects were reversed using diamide, a glutathionylation catalyst. Importantly, the increased leak did not compromise coupled respiration. Knockdown of Grx2 augmented proton leak-dependent respiration in primary myotubes from wild type mice, an effect that was absent in UCP3^−/− cells. These results confirm that Grx2 deactivates UCP3 by glutathionylation. To our knowledge, this is the first enzyme identified to regulate UCP3 by glutathionylation and is the first study on the role of Grx2 in the regulation of energy metabolism.     

The cell cycle of cultured iris epithelial cells: Its possible role in cell-type conversion

Cell cycle parameters were estimated in primary cultures of iris epithelial cells, obtained from explanted dorsal and ventral irises of adult newts (Notophthalmus viridescens). No significant difference was found between parameters of dorsal and ventral iris epithelial cell cultures. Compared with the total cell cycle time of iris epithelial cells in situ in the pathway of conversion, that of cultured iris epithelial cells is longer by a factor of 1.88. The results support the working hypothesis that the basic requirement for conversion of iris epithelial cells into lens cells is the passage of a definite number of cell cycles instead of the inductive influence of neural retina.     

Relationship between Distance to Cover,Vigilance and Group Size in Staging Flocks of Semipalmated Sandpipers

Cover can be either a source of protection or a source of danger for foragers. Distance to cover creates a gradient in predation risk that allows examining adjustments in anti‐predator behaviour such as group size and vigilance. As distance to obstructive cover increases, both group size and vigilance are expected to decrease given that individuals have more time to react to a more distant source of danger. I provide an empirical test of these predictions in staging semipalmated sandpipers (Calidris pusilla) in a system controlling for many confounding factors that have marred earlier research. Controlling for food density, forager density and phenotypic attributes often correlated with distance to cover, I found that as distance to obstructive cover increased, sandpipers foraged in sparser groups, were less flighty and to some extent less vigilant. Such controlled studies are needed to re‐assess the relationship between distance to cover and anti‐predator behaviour.     

Interactions between Tamarix ramosissima (Saltcedar), Populus fremontii (Cottonwood), and Mycorrhizal Fungi: Effects on Seedling Growth and Plant Species Coexistence

Little is known about the composition and function of the mycorrhizal fungal community in riparian areas, or its importance in competitive interactions between Populus fremontii, a dominant tree in southwestern United States riparian forests which forms arbuscular and ectomycorrhizas, and Tamarix ramosissima, an introduced tree species that has spread into riparian areas. The objectives of this study were to determine the mycorrhizal status of Tamarixand to evaluate the effect of mycorrhizal fungal inoculation on Tamarix growth and on the coexistence between Tamarix and Populus.Arbuscular mycorrhizal fungal colonization of Tamarix was very low in both field and greenhouse grown roots, but levels of colonization by dark septate endophytes were high. Fungal inoculation had little effect on Tamarix seedling growth in monoculture. When Populus and Tamarix were grown together in a greenhouse pot experiment, fungal inoculation reduced the height and biomass of Tamarix but had no effect on Populus. Fungal inoculation shifted coexistence ratios. When Tamarix and Populuswere grown together, Tamarixplants averaged 20 of pot biomass in the uninoculated control but only 5 of pot biomass in the inoculated treatment. These results indicate that Tamarix is non-mycotrophic and that in this greenhouse experiment inoculation altered patterns of coexistence between Populus and Tamarix.