The functional morphology of xenarthrous vertebrae in the armadillo Dasypus novemcinctus (Mammalia, Xenarthra).

In order to assess the mechanical properties of xenarthrous vertebrae, and to evaluate the role of xenarthrae as fossorial adaptations, in vitro bending tests were performed on posterior thoracic and lumbar vertebral segments excised from specimens of the armadillo Dasypus novemcinctus and the opossum Didelphis virginiana, the latter being used to represent the primitive mammalian condition. The columns of the two species were subjected to dorsal, ventral, and lateral bending, as well as torsion, in order to determine their stiffness in each of these directions. During these tests, bone strains in the centra of selected vertebrae were determined using rosette strain gages. Overall stiffness of the armadillo backbone at physiologically relevant displacement levels was significantly higher than that of the opossum for both dorsal and lateral bending. The two species also exhibited significant differences in angular displacement of individual vertebrae and in vertebral strain magnitudes and orientations in these two directions. No significant differences were observed when the columns of the two species were subjected to torsion or to ventral bending. Our results suggest that some, but not all, of the mechanical differences between the two species are due to the presence of xenarthrae. For example, removal of the xenarthrae from selected vertebrae (L2-L4) changes strain orientation and shear, but not strain magnitudes. Comparisons with functional data from other digging mammals indicate that the modified mechanical properties of the Dasypus column are consistent with an interpretation of xenarthrae as digging adaptations and lend support to the idea that the order Xenarthra represents an early offshoot of placental mammals specialized for fossoriality.     

Head of the Class: John R. Wible’s Transformative Insights Into Mammalian Craniodental Anatomy

Journal of Mammalian Evolution -     

The complete history of salmonid introductions in the Kerguelen Islands, Southern Ocean

Since the early 1950s, several species of salmonids have been introduced more or less successfully in the Kerguelen Islands, a 7,215 km² archipelago located in the Southern Ocean (49°S, 70°E) and previously devoid of any freshwater fish. The aim of this work was to establish a documented chronicle of these events from available archives, to better understand the causes of the colonization failure or success for the different species. The history that emerged from the analysis of the archives appeared much more complex than previously published. Stocks of various origins were used, and numerous attempts were made at different sites involving variable numbers of fish released at different life stages. Between 1951 and 1991, 22 importation attempts took place, involving about 2 million individuals. Of the 8 species introduced (Salmo trutta, S. salar, Oncorhynchus mykiss, O. tshawytscha, O. kisutch, Salvelinus namaycush, S. fontinalis and S. alpinus), only 3 failed to establish local populations (O. mykiss, O. tshawytscha and S. namaycush). Overall, 23 watersheds were stocked. At present, 45 watersheds are colonized by one or several species. S. trutta, S. fontinalis, S. alpinus and O. kisutch were capable of migrating toward new habitats. The brown trout (S. trutta) was the only species to colonize a large number of watersheds (32 in about 10 generations). Its success can be explained by the diversity of origins, the number and importance of introduction and transfer attempts, the diversity of release sites and the peculiarities of its life cycle.     

Chelate-assisted phytoextraction of lead using Fagopyrum esculentum: laboratory vs. field experiments

Abstract

The development of more sustainable remediation techniques has been receiving greater attention, as an alternative to soil excavation plan in urban gardens. An in situ phytoextraction experiment with buckwheat (Fagopyrum esculentum) was performed with a 5?mmol kg^?1 citric acid (CA) application. Joint experiments under laboratory conditions were conducted using various cultivars of F. esculentum in two soils with a Pb contamination of either geogenic or anthropogenic origin and various chelate concentrations. Results show that a minimum dose of 50?mmol kg^?1 of CA is required to lower soil pH and raise the concentration of mobile Pb–CaCl₂ for both soils. Consequently, Pb shoot uptake is increased from 6.3 to 8.9 times depending on soil type. Phytoextraction efficiency is found to be 1.3 to 2.0 times higher in the anthropogenic contaminated soil than in the soil with geogenic Pb. A scale effect has also been identified since Pb root accumulation under laboratory conditions was 2.4 times higher than in the field experiment. Despite an increase in the Pb extraction rate with CA, buckwheat appears to lack the efficiency needed to remove Pb in moderately contaminated soils. The calculated remediation period would last 166?years to remove the mobile Pb fraction.     

Growth of an anaerobic sulfate-reducing bacterium sustained by oxygen respiratory energy conservation after O2-driven experimental evolution

Desulfovibrio species are representatives of microorganisms at the boundary between anaerobic and aerobic lifestyles, since they contain the enzymatic systems required for both sulfate and oxygen reduction. However, the latter has been shown to be solely a protective mechanism. By implementing the oxygen-driven experimental evolution of Desulfovibrio vulgaris Hildenborough, we have obtained strains that have evolved to grow with energy derived from oxidative phosphorylation linked to oxygen reduction. We show that a few mutations are sufficient for the emergence of this phenotype and reveal two routes of evolution primarily involving either inactivation or overexpression of the gene encoding heterodisulfide reductase. We propose that the oxygen respiration for energy conservation that sustains the growth of the O₂-evolved strains is associated with a rearrangement of metabolite fluxes, especially NAD⁺/NADH, leading to an optimized O₂ reduction. These evolved strains are the first sulfate-reducing bacteria that exhibit a demonstrated oxygen respiratory process that enables growth.     

The activation by Ca of the ATPase of extracted muscle fibrils with variation of ionic strength, pH and concentration of MgATP

1. The alteration of the Ca²⁺ requirements of the ATPase activity of fibrils from rabbits and crabs at varying ionic strength, pH and concentration of MgATP (i.e. MgATP²⁻ + MgHATP⁻) was investigated.

2. Under physiological conditions, it was found that the ATPase activity of rabbit and crab fibrils after an initial increase decreased steeply when the Ca²⁺ concentration is raised above 1×10⁻⁴ M. This is a primary effect of the over-optimal Ca²⁺ concentration and not a secondary one caused by the influence of accompanying ions.

3. The Ca²⁺ requirements for ATP splitting by rabbit fibrils remain constant at an ionic strength from 0.1 to 0.2 and for a MgATP concentration in the range from 0.5 to 10 mM. At I = 0.05 it is about 5 times smaller than at 0.1. When the pH is decreased from 8 to 7, the Ca²⁺ requirements are increased some 10 times but only 3 times when the pH is varied between 7 and 6.

4. In crab fibrils, there is no alteration of the Ca²⁺ requirements when the ionic strength is varied between 0.05 and 0.2, but a reduction of the pH from 8.0 to 6.0 raises the Ca²⁺ requirements for half activation and for threshold by a factor of 10. Changing the MgATP concentration increases the Ca²⁺ requirements only in the range from 1 to 5 mM, while the concentration required in 0.5 mM is identical with that at 1 mM, and 10 mM corresponds to 5 mM.

5. It can be deduced from the experimental results that at a pH above 6.0 maximal activation is always obtained if the Ca²⁺ concentration is 5×10⁻⁵ M. By contrast, relaxation is only achieved when the Ca²⁺ concentration is below 1×10⁻⁷ M for pH 7.0 and I > 0.1 or below 1×10⁻⁸ for pH > 7.0 or I < 0.1.

6. To achieve complete relaxation, an ethyleneglycoldiaminotetraacetate (EGTA) concentration of 1 mM is sufficient, even when there is a large degree of contamination by Ca²⁺ as long as the pH stays above 6.5.     

Polyamine derivatives as selective RNaseA mimics

Site-selective scission of ribonucleic acids (RNAs) has attracted considerable interest, since RNA is an intermediate in gene expression and the genetic material of many pathogenic viruses. Polyamine-imidazole conjugates for site-selective RNA scission, without free imidazole, were synthesized and tested on yeast phenylalanine transfer RNA. These molecules catalyze RNA hydrolysis non-randomly. Within the polyamine chain, the location of the imidazole residue, the numbers of nitrogen atoms and their relative distances have notable influence on cleavage selectivity. A norspermine derivative reduces the cleavage sites to a unique location, in the anticodon loop of the tRNA, in the absence of complementary sequence. Experimental results are consistent with a cooperative participation of an ammonium group of the polyamine moiety, in addition to it’s binding to the negatively charged ribose-phosphate backbone, as proton source, and the imidazole moiety as a base. There is correlation between the location of the magnesium binding sites and the RNA cleavage sites, suggesting that the protonated nitrogens of the polycationic chain compete with some of the magnesium ions for RNA binding. Therefore, the cleavage pattern is specific of the RNA structure. These compounds cleave at physiological pH, representing novel reactive groups for antisense oligonucleotide derivatives or to enhance ribozyme activity.