Thermal niche variation among individuals of the poison frog,Oophaga pumilio,in forest and converted habitats

The conversion of natural habitats to human land uses often increases local temperatures, creating novel thermal environments for species. The variable responses of ectotherms to habitat conversion, where some species decline while others persist, can partly be explained by variation among species in their thermal niches. However, few studies have examined thermal niche variation within species and across forest‐land use ecotones, information that could provide clues about the capacity of species to adapt to changing temperatures. Here, we quantify individual‐level variation in thermal traits of the tropical poison frog, Oophaga pumilio, in thermally contrasting habitats. Specifically, we examined local environmental temperatures, field body temperatures (T_b), preferred body temperatures (T_pref), critical thermal maxima (CT_max), and thermal safety margins (TSM) of individuals from warm, converted habitats and cool forests. We found that frogs from converted habitats exhibited greater mean T_b and T_pref than those from forests. In contrast, CT_max and TSM did not differ significantly between habitats. However, CT_max did increase moderately with increasing T_b, suggesting that changes in CT_max may be driven by microscale temperature exposure within habitats rather than by mean habitat conditions. Although O. pumilio exhibited moderate divergence in T_pref, CT_max appears to be less labile between habitats, possibly due to the ability of frogs in converted habitats to maintain their T_b below air temperatures that reach or exceed CT_max. Selective pressures on thermal tolerances may increase, however, with the loss of buffering microhabitats and increased frequency of extreme temperatures expected under future habitat degradation and climate warming. Abstract in Spanish is available with online material.     

Effects of temperature and water availability on light energy utilization in photosynthetic processes of Deschampsia antarctica

Regional climate change in Antarctica would favor the carbon assimilation of Antarctic vascular plants, since rising temperatures are approaching their photosynthetic optimum (10–19°C). This could be detrimental for photoprotection mechanisms, mainly those associated with thermal dissipation, making plants more susceptible to eventual drought predicted by climate change models. With the purpose to study the effect of temperature and water availability on light energy utilization and putative adjustments in photoprotective mechanisms of Deschampsia antarctica Desv., plants were collected from two Antarctic provenances: King George Island and Lagotellerie Island. Plants were cultivated at 5, 10 and 16°C under well‐watered (WW) and water‐deficit (WD, at 35% of the field capacity) conditions. Chlorophyll fluorescence, pigment content and de‐epoxidation state were evaluated. Regardless of provenances, D. antarctica showed similar morphological, biochemical and functional responses to growth temperature. Higher temperature triggered an increase in photochemical activity (i.e. electron transport rate and photochemical quenching), and a decrease in thermal dissipation capacity (i.e. lower xanthophyll pool, Chl a/b and β carotene/neoxanthin ratios). Leaf mass per unit area was reduced at higher temperature, and was only affected in plants exposed to WD at 16°C and exhibiting lower electron transport rate and amount of chlorophylls. D. antarctica is adapted to frequent freezing events, which may induce a form of physiological water stress. Photoprotective responses observed under WD contribute to maintain a stable photochemical activity. Thus, it is possible that short‐term temperature increases could favor the photochemical activity of this species. However, long‐term effects will depend on the magnitude of changes and the plant's ability to adjust to new growth temperature.     

Measurements of lipopolysaccharide (endotoxin) in meningococcal protein and polysaccharide preparations for vaccine usage

Lipopolysaccharide (LPS, i.e. endotoxin) present in meningococcal outer-membrane protein and polysaccharide preparations made for vaccine use was quantitated by a silver-stain method following SDS-PAGE. The reactivities of LPS in the preparations were also measured by rabbit pyrogenicity and Limulus amoebocyte lysate (LAL) assay. Although rabbit pyrogenicity and LAL assay are more sensitive than the silver stain method, the latter provided an actual amount of LPS present in the protein or in the polysaccharide. For a meningococcal protein preparation, rabbit pyrogenicity showed about one-tenth, and even less by LAL assay, of the actual amount of LPS. This is because protein-bound LPS in meningococcal protein preparations is about 10-fold less active in causing fever in rabbits, and 20- to 40-fold less active in the gelation of LAL than the same amount of a purified free LPS which is generally used as a reference in quantitating LPS in these two assays. As for the small amount of LPS present in a meningococcal polysaccharide preparation, similar LPS content was obtained when measured by the three methods suggesting that the LPS is not bound to the polysaccharide in contrast to that in the proteins mentioned above. The purified meningococcal LPS was pyrogenic in rabbits at 1 ng/kg.     

IgE receptor type I-dependent regulation of a Rab3D-associated kinase: a possible link in the calcium-dependent assembly of SNARE complexes

Following activation through high affinity IgE receptors (FcepsilonRI), mast cells release, within a few minutes, their granule content of inflammatory and allergic mediators. FcepsilonRI-induced degranulation is a SNARE (soluble N-ethylmaleimide attachment protein receptors)-dependent fusion process. It is regulated by Rab3D, a subfamily member of Rab GTPases. Evidence exists showing that Rab3 action is calcium-regulated although the molecular mechanisms remain unclear. To obtain an understanding of Rab3D function we have searched for Rab3D-associated effectors that respond to allergic triggering through FcepsilonRI. Using the RBL-2H3 mast cell line we detected a Ser/Thr kinase activity, termed here Rak3D (from Rab3D-associated kinase), because it was specifically co-immunoprecipitated with anti-Rab3D antibody. Rak3D activity, as measured by its auto- or transphosphorylation, was maximal in resting cells and decreased upon stimulation. The down-regulation of the observed activity was blocked with EGTA, but not with other degranulation inhibitors, suggesting that its activity functions downstream of calcium influx. We found that Rak3D phosphorylates the NH(2)-terminal regulatory domain of the t-SNARE syntaxin 4, but not syntaxin 2 or 3. The phosphorylation of syntaxin 4 decreased its binding to its partner SNAP23. Thus, we propose a novel phosphorylation-dependent mechanism by which Rab3D controls SNARE assembly in a calcium-dependent manner.     

Regulation of skeletal muscle tension redevelopment by troponin C constructs with different Ca2+ affinities

In maximally activated skinned fibers, the rate of tension redevelopment (ktr) following a rapid release and restretch is determined by the maximal rate of cross-bridge cycling. During submaximal Ca2+ activations, however, ktr regulation varies with thin filament dynamics. Thus, decreasing the rate of Ca2+ dissociation from TnC produces a higher ktr value at a given tension level (P), especially in the [Ca2+] range that yields less than 50% of maximal tension (Po). In this study, native rabbit TnC was replaced with chicken recombinant TnC, either wild-type (rTnC) or mutant (NHdel), with decreased Ca2+ affinity and an increased Ca2+ dissociation rate (koff). Despite marked differences in Ca2+ sensitivity (>0.5 DeltapCa50), fibers reconstituted with either of the recombinant proteins exhibited similar ktr versus tension profiles, with ktr low (1-2 s-1) and constant up to approximately 50% Po, then rising sharply to a maximum (16 +/- 0.8 s-1) in fully activated fibers. This behavior is predicted by a four-state model based on coupling between cross-bridge cycling and thin filament regulation, where Ca2+ directly affects only individual thin filament regulatory units. These data and model simulations confirm that the range of ktr values obtained with varying Ca2+ can be regulated by a rate-limiting thin filament process.     

The MMP/TIMP system in the nervous system

The matrix metalloproteinases (MMP) belong to a growing family of secreted or membrane-bound (MT-MMP) enzymes that cleave protein components of the extracellular matrix and bioactive factors involved in intercellular signaling. MMP activity is counterbalanced by their four physiological inhibitors, the tissue inhibitors of MMP (TIMPs). Together, MMP and TIMP control cell-cell and cell-matrix interactions associated with physiological processes. However, the breakdown of the protease-inhibitor balance may lead to the loss of tissue homeostasis and the development of degenerative and tumorigenic processes in various tissues. The emerging idea is that the MMP/TIMP system also plays a major role in the pathology and physiology of the nervous system and that mastering MMP activity will set the basis for new and more efficient therapeutic strategies against nervous system disorders.     

Ascorbate distribution during hibernation is independent of ascorbate redox state

Distribution of ascorbate into tissues is an essential process in ascorbate antioxidant defense. Hibernating animals are studied as a model of tolerance to ischemia-reperfusion because of their tolerance to fluctuations in blood flow associated with prolonged torpor and periodic arousal episodes. Throughout hibernation, plasma ascorbate concentration ([Asc](p)) repetitively increases during torpor, then falls during periodic arousal bouts. We previously proposed that high [Asc](p) provides a ready source of antioxidant protection for distribution to the central nervous system and peripheral tissues during arousal. Here we tested whether deliberate oxidation of plasma ascorbate by intravenous administration of ascorbate oxidase (AO), prior to arousal, compromised tissue levels of ascorbate or the other water-soluble antioxidants, glutathione (GSH) and urate. Although AO decreased [Asc](p) to below the level of detection during torpor and after arousal, ascorbate oxidation did not decrease post-arousal tissue levels of reduced ascorbate, glutathione, or urate in any tissue examined, except liver. The data imply that ascorbate is taken up equally well into brain and other tissues as either ascorbate or its oxidized product dehydroascorbate, with subsequent intracellular reduction of dehydroascorbate. Lack of effect of ascorbate oxidation on tissue levels of GSH or urate indicates that dehydroascorbate uptake and reduction do not compromise tissue concentrations of these other water-soluble antioxidants. Thus, we show equal availability of reduced and oxidized plasma ascorbate during metabolically demanding thermogenesis and reperfusion associated with arousal from hibernation.     

Black flower coloration in wild Lisianthius nigrescens: its chemistry and ecological consequences

The major pigments responsible for the flower color within the black flowered Gentianaceae, Lisianthius nigrescens, were characterized by HPLC and chemical analyses HPLC analysis showed one major and one minor anthocyanin and 3 major and 3 minor flavone glycosides. The anthocyanins [delphinidin-3-O-rhamnol(1-6)galactoside and its 5-O-glucoside] comprised an extraordinary 24% of the dry weight of wild collected L. nigrescens corallas, and were accompanied in a 1:1 ratio by a range of apigenin and luteolin 8-C-glucosides and their 7-O-methyl ethers. The high levels of anthocyanins and flavones (and their co-pigmentation) is thought to account for the almost complete absorption of both UV and visible wavebands observed by reflectance photography.