Global change alters peatland carbon cycling through plant biomass allocation

Plant and Soil - Global change is shown to significantly affect the C storage function of peatlands; however, a majority of previous research is focused on a single environmental stressor such as...     

Interactions between different predator–prey states: a method for the derivation of the functional and numerical response

Journal of Mathematical Biology - In this paper we introduce a formal method for the derivation of a predator’s functional response from a system of fast state transitions of the prey or...     

The crystal structure of the mycobacterial trehalose monomycolate transport factor A,TtfA, reveals an atypical fold

Trehalose monomycolate (TMM) represents an essential element of the mycobacterial envelope. While synthesized in the cytoplasm, TMM is transported across the inner membrane by MmpL3 but, little is known regarding the MmpL3 partners involved in this process. Recently, the TMM transport factor A (TtfA) was found to form a complex with MmpL3 and to participate in TMM transport, although its biological role remains to be established. Herein, we report the crystal structure of the Mycobacterium smegmatis TtfA core domain. The phylogenetic distribution of TtfA homologues in non-mycolate containing bacteria suggests that TtfA may exert additional functions.     

The importance of seasonal environmental factors in the foraging habitat selection of Alpine Ring Ouzels Turdus torquatus alpestris

Species inhabiting mountain ecosystems are expected to be particularly vulnerable to environmental change, yet information on their basic ecology is often lacking. Knowledge from field-based empirical studies remains essential to refine our understanding of the impact of current habitat alterations and for the consequential development of meaningful conservation management strategies. This study focuses on a poorly investigated and vulnerable mountain bird species in Europe, the Ring Ouzel Turdus torquatus. Our aim was to identify the species’ key ecological requirements during the crucial period of nestling provisioning in the context of environmental change. We radiotracked and observed Alpine Ring Ouzels in a high-density population, investigating their pattern of foraging habitat selection in 2015 and 2017, and evaluated the transferability of these results over a wider geographical range across the SW Swiss Alps. Foraging birds selected, consistently in space and time, short grass swards (< 10 cm) with interspersed patches of accessible and penetrable soils, at intermediate moisture levels (around 40–65% volumetric water content). In Alpine ecosystems, this microhabitat configuration is typically widespread during the spring snowmelt, but extremely seasonal, with a rapid decrease in its availability over the course of the breeding season. This underlines the high vulnerability of the Ring Ouzel to environmental change: an earlier snowmelt could generate a temporal mismatch between the peak of the breeding effort and optimal foraging conditions; however, abandoning grazing activities on semi-wooded Alpine pastures may further decrease foraging habitat suitability through taller and denser grass swards, and subsequent woody vegetation encroachment. This study provides a mechanistic appraisal of the challenges Ring Ouzels will face in the future, as well as initial guidelines for targeted habitat management within timberline ecotones.     

Effect of zinc and calcium ions on the rat kidney membrane-bound form of dipeptidyl peptidase IV

Dipeptidyl peptidase IV (DPP-IV) is an ectopeptidase with many roles, and a target of therapies for different pathologies. Zinc and calcium produce mixed inhibition of porcine DPP-IV activity. To investigate whether these results may be generalized to mammalian DPP-IV orthologues, we purified the intact membrane-bound form from rat kidney. Rat DPP-IV hydrolysed Gly-Pro-p-nitroanilide with an average V_max of 0.86±0.01 μmol min^–1mL^–1 and K_M of 76±6 μM. The enzyme was inhibited by the DPP-IV family inhibitor l-threo-Ile-thiazolidide (K_i=64.0±0.53 nM), competitively inhibited by bacitracin (K_i=0.16±0.01 mM) and bestatin (K_i=0.23±0.02 mM), and irreversibly inhibited by TLCK (IC₅₀ value of 1.20±0.11 mM). The enzyme was also inhibited by divalent ions like Zn²⁺ and Ca²⁺, for which a mixed inhibition mechanism was observed (K_i values of the competitive component: 0.15±0.01 mM and 50.0±1.05 mM, respectively). According to bioinformatic tools, Ca²⁺ ions preferentially bound to the β-propeller domain of the rat and human enzymes, while Zn²⁺ ions to the α-β hydrolase domain; the binding sites were essentially the same that were previously reported for the porcine DPP-IV. These data suggest that the cationic susceptibility of mammalian DPP-IV orthologues involves conserved mechanisms.     

Pioneer marine biofilms on artificial surfaces including antifouling coatings immersed in two contrasting French Mediterranean coast sites

Marine biofilm communities that developed on artificial substrata were investigated using molecular and microscopic approaches. Polystyrene, Teflon® and four antifouling (AF) paints were immersed for 2 weeks at two contrasting sites near Toulon on the French Mediterranean coast (Toulon military harbour and the natural protected area of Porquerolles Island). Biofilms comprising bacteria and diatoms were detected on all the coatings. The population structure as well as the densities of the microorganisms differed in terms of both sites and coatings. Lower fouling densities were observed at Porquerolles Island compared to Toulon harbour. All bacterial communities (analysed by PCR-DGGE) showed related structure, controlled both by the sites and the type of substrata. Pioneer microalgal communities were dominated by the same two diatom species, viz. Licmophora gracilis and Cylindrotheca closterium, at both sites, irrespective of the substrata involved. However, the density of diatoms followed the same trend at both sites with a significant effect of all the AF coatings compared to Teflon and polystyrene.     

Conformations Consistent with Charge Migration Observed in DNA and RNA X-ray Structures

Abstract

Electron holes are known to migrate along the DNA or RNA duplexes and to localize preferentially on successive guanines. The stationary point conformations of Gua pairs that can trap or let pass these holes have been characterized by quantum chemistry calculations. Here we show their recurrent occurrence in DNA and RNA X-ray structures, often in quadruplex conformations or in interaction with proteins, ligands or metal ions. These findings give support to the biological, possibly regulatory, roles of charge migration in cell functioning.     

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.     

Possible relationship between H-Y antigen and female gonadogenesis in the Colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Summary

The Daudi cell line, a male human line from Burkitt's lymphoma, possesses the peculiarity of releasing H-Y antigen into its culture medium. Daudi-conditioned medium was injected into Colorado potato beetles either during the blastoderm stage, when individualization of the pole cells occurs, or later, during gonadal differentiation. Ovarian and testicular sections examined at hatching showed that only ovarian differentiation was affected by the Daudi conditioned medium, which, irrespective of the day of injection, reduced the number of the terminal filaments of the future lateral ovarioles. Furthermore, in some cases sexual differentiation was blocked altogether. When H-Y antigen was precipitated from the conditioned medium with specific H-Y antisera, the effectiveness of Daudi-conditioned medium was partially destroyed. These results suggest that mammalian H-Y antigen inhibits morphogenetic events leading to ovarian differentiation in the Colorado potato beetle.