Reversible inhibition of CO2 fixation by ribulose 1,5‐bisphosphate carboxylase/oxygenase through the synergic effect of arsenite and a monothiol

The activity of the photosynthetic carbon‐fixing enzyme, ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco), is partially inhibited by arsenite in the millimolar concentration range. However, micromolar arsenite can fully inhibit Rubisco in the presence of a potentiating monothiol such as cysteine, cysteamine, 2‐mercaptoethanol or N‐acetylcysteine, but not glutathione. Arsenite reacts specifically with the vicinal Cys172‐Cys192 from the large subunit of Rubisco and with the monothiol to establish a ternary complex, which is suggested to be a trithioarsenical. The stability of the complex is strongly dependent on the nature of the monothiol. Enzyme activity is fully recovered through the disassembly of the complex after eliminating arsenite and/or the thiol from the medium. The synergic combination of arsenite and a monothiol acts also in vivo stopping carbon dioxide fixation in illuminated cultures of Chlamydomonas reinhardtii. Again, this effect may be reverted by washing the cells. However, in vivo inhibition does not result from the blocking of Rubisco since mutant strains carrying Rubiscos with Cys172 and/or Cys192 substitutions (which are insensitive to arsenite in vitro) are also arrested. This suggests the existence of a specific sensor controlling carbon fixation that is even more sensitive than Rubisco to the arsenite–thiol synergism.     

Hoarding patterns of sigmodontine rodent species in the Central Monte Desert (Argentina)

Hoarding food is an important strategy of rodents in desert environments characterized by unpredictable and poor food resource availability. In the Monte Desert, Prosopis produces abundant food, unevenly in time and space, in the form of pods and seeds. Sigmodontine rodents (Graomys griseoflavus, Akodon molinae, Eligmodontia typus and Calomys musculinus) use Prosopis propagules extensively, and they could be predators or dispersers depending on how they handle and where they leave the propagules. The objectives of this study were: (1) to know what rodent species transported propagules; (2) to evaluate what hoarding pattern was used by species that transport propagules (larder and scatterhoarding); and (3) to analyse in which condition were propagules left by the rodent species, both at the food source and in caches. Our results showed that all four species transported propagules, with G. griseoflavus and E. typus being the species that carried more seeds. Our study supported the evidence that food caching is common among species and that many species both larderhoard and scatterhoard food. Graomys griseoflavus and A. molinae, the largest species, larderhoarded more than did the smaller E. typus. These results uphold the hypothesis that larger species will show greater propensity to larderhoard than smaller species. Considering the interaction between seed‐hoarding patterns and plants, E. typus was the species that could most improve germination because it scatterhoarded propagules and left seeds out of pods. In contrast, G. griseoflavus could have a negative impact on plant populations because this was the species that predated more seeds and larderhoarded a high percentage of them. The smallest C. musculinus was the species that transported propagules least, and left them as seeds inside pods or pod segments mainly at the food source, which makes seeds more vulnerable to predation.     

Terrestrial Activity in Pitheciins (Cacajao,Chiropotes, and Pithecia)

Neotropical monkeys of the genera Cacajao, Chiropotes, and Pithecia (Pitheciidae) are considered to be highly arboreal, spending most of their time feeding and traveling in the upper canopy. Until now, the use of terrestrial substrates has not been analyzed in detail in this group. Here, we review the frequency of terrestrial use among pitheciin taxa to determine the ecological and social conditions that might lead to such behavior. We collated published and unpublished data from 14 taxa in the three genera. Data were gleaned from 53 published studies (including five on multiple pitheciin genera) and personal communications of unpublished data distributed across 31 localities. Terrestrial activity was reported in 61% of Pithecia field studies (11 of 18), in 34% of Chiropotes studies (10 of 29), and 36% of Cacajao studies (4 of 11). Within Pithecia, terrestrial behavior was more frequently reported in smaller species (e.g. P. pithecia) that are vertical clingers and leapers and make extensive use of the understory than in in the larger bodied canopy dwellers of the western Amazon (e.g. P. irrorata). Terrestrial behavior in Pithecia also occurred more frequently and lasted longer than in Cacajao or Chiropotes. An apparent association was found between flooded habitats and terrestrial activity and there is evidence of the development of a “local pattern” of terrestrial use in some populations. Seasonal fruit availability also may stimulate terrestrial behavior. Individuals also descended to the ground when visiting mineral licks, escaping predators, and responding to accidents such as a dropped infant. Overall, the results of this review emphasize that terrestrial use is rare among the pitheciins in general and is usually associated with the exploitation of specific resources or habitat types. Am. J. Primatol. 74:1106‐1127, 2012. © 2012 Wiley Periodicals, Inc.     

Ecological assessment of an intermittent Mediterranean river using community structure and function: evaluating the role of different organism groups

1. Reliable lotic ecological monitoring requires knowledge of river typology, environmental factors, the effect of stressors known here as ‘pressures’ and appropriate indicators of anthropogenically induced change. We sampled benthic macroinvertebrate, fish, bird and macrophyte communities along an intermittent Mediterranean river and analysed community structure (relative abundance) and function (metrics) relative to environmental and pressure gradients in order to identify suitable indicator group(s) for future monitoring and mitigation programmes. 2. Principal components analysis revealed that scale‐dependent longitudinal differences in valley form separated narrower higher lying sites and tributaries with good quality habitats from more open degraded sites lower down the river continuum on a small floodplain and large scale pressures describing changes in land use related to agriculture with associated physical bankside and channel impacts. 3. Forward selection of variables in redundancy analysis (RDA) showed that reach scale environmental variables were selected more frequently than pressure variables for each organism group. Altitude and pH were highly redundant within and between groups, indicating essentially longitudinal structural and functional distribution patterns. Redundancy was far lower between selected pressure variables, but single or no pressure variables were retained for some organism groups indicating poor association of functional data, in particular, with the identified pressures. All RDA results indicated a longitudinal pH gradient, highlighting the combined effect of multiple environmental and pressure based mechanisms on organism groups. 4. Large, mobile organisms such as fish and birds provided a reliable link between organism structure and function, environmental factors and physical disturbance of the channel, bankside and wider river corridor. Benthic macroinvertebrate and macrophyte structural data revealed distribution patterns in relation to water velocity, a key parameter for developing appropriate compensation measures. 5. Results clearly show the importance of assessing patterns of both functional and structural change across multiple organism groups in order to identify typologically appropriate links with complex environmental and pressure gradients and develop and implement appropriate monitoring systems.     

Biochemical Changes in Cultures of Nectria galligena during the Autolytic Phase of Growth

Some biochemical changes occurring in cultures of Nectria galligenaduring its autolytic phase of growth have been investigated.In nitrate-grown and autolysed cultures of this fungus the degreeof autolysis amounted to 57 per cent. The amount of myceliallipids decreased continuously with the age of the culture. Totalmycelial nitrogen did not substantially change within the first50 days of autolysis. The constancy in the amount of bound aminoacids released from mycelium of Nectria galligena strongly suggeststhat mycelial protein are not affected by autolysis.     

Impact of grazing on species composition: Adding complexity to a generalized model

The impact of grazing widely differs among plant communities. A generalized model published in 1988 proposed that this variation could be accounted for by the interaction between primary productivity and the evolutionary history of grazing. As productivity increased, the model predicted larger changes of species composition. Evolutionary history of grazing interacted with productivity: the changes in low‐production systems were smaller if evolutionary history was long, whereas the changes in high‐production systems were independent of evolutionary history. In this paper, we focus on: (i) the difficulties of determining the evolutionary history of grazing of a community, and (ii) additional mechanisms, which, as a sequence of filters in the process of community assembly, could be operating across the gradient of primary production. Assigning a given evolutionary history of grazing to a site has been difficult due to the lack of information on the historical population and distribution of herbivores with an adequate spatial and temporal resolution, and the lack of agreement on the size of the relevant evolutionary time window. Regarding the variation through a gradient of primary production, we propose three additional mechanisms coherent with the prediction of the model. First, the regional pool of available species increases with primary production. Second, grazing intensity (consumption as a proportion of above‐ground production) also increases with primary production. Third, the strength of interspecific positive biotic interactions that protect plants from herbivores decreases with primary production. We highlight an additional potential mechanism, seed dispersal, whose variation across the gradient of productivity is not yet sufficiently understood. By connecting the logic of environmental filters to explain community assemblage with the original proposition of the generalized model, we suggest a series of research lines that can lead to a better understanding of why different communities respond differently to grazing.