Assessing the importance of disturbance, site conditions, and the biotic barrier for dandelion invasion in an Alpine habitat

Several factors have been identified as relevant in determining the abundance of non-native invasive species. Nevertheless, the relative importance of these factors will vary depending on the invaded habitat and the characteristics of the invasive species. Due to their harsh environmental conditions and remoteness, high-alpine habitats are often considered to be at low risk of plant invasion. However, an increasing number of reports have shown the presence and spread of non-native plant species in alpine habitats; thus, it is important to study which factors control the invasion process in these harsh habitats. In this study, we assessed the role of disturbance, soil characteristics, biotic resistance and seed rain in the establishment and abundance of the non-native invasive species Taraxacum officinale (dandelion) in the Andes of central Chile. By focusing on human-disturbed patches, naturally disturbed patches, and undisturbed patches, we did not find that disturbance per se, or its origin, affected the establishment and abundance of T. officinale. The abundance of this non-native invasive species was not negatively related to the diversity of native species at local scales, indicating no biotic resistance to invasion; instead, some positive relationships were found. Our results indicate that propagule pressure (assessed by the seed rain) and the abiotic soil characteristics are the main factors related to the abundance of this non-native invasive species. Hence, in contrast to what has been found for more benign habitats, disturbance and biotic resistance have little influence on the invasibility of T. officinale in this high-alpine habitat.     

MicroRNAs in metamorphic and non-metamorphic transitions in hemimetabolan insect metamorphosis

ABSTRACT: BACKGROUND: Previous work showed that miRNAs play key roles in the regulation of metamorphosis in the hemimetabolan species Blattella germanica. To gain insight about which miRNAs might be important, we have constructed two miRNA libraries, one of the penultimate, pre-metamorphic nymphal instar (N5) and the other of the last, metamorphic nymphal instar (N6). RESULTS: High throughput sequencing gave 61 canonical miRNAs present in the N5 and N6 libraries, although at different proportions in each. Comparison of both libraries led to identify three and 37 miRNAs significantly more expressed in N5 and N6 respectively. Twelve of these 40 miRNAs were then investigated further by qRT-PCR and results indicated that miR-252-3p was well expressed in N5 but not in N6, whereas let-7-5p, miR-100-5p and miR-125-5p showed the reverse pattern. 20-Hydroxyecdysone (20E) tended to stimulate miRNA expression, whereas juvenile hormone (JH) inhibited the 20E stimulatory effect. Expression of let-7, miR-100 and miR-125 was increased by 20E, which has also been observed in D. melanogaster. The only miRNA that was inhibited by 20E was miR-252-3p. The involvement of let-7, miR-100 and miR-125 in metamorphosis has been demonstrated in other insects. Depletion of miR-252-3p caused growth and developmental delays, which suggests that this miRNA is involved in regulating these processes prior to metamorphosis. CONCLUSIONS: The comparative analysis of miRNA libraries from pre-metamorphic (N5) and metamorphic stages (N6) of B. germanica proved to be a useful tool to identify miRNAs with roles in hemimetabolan metamorphosis. Three miRNAs emerged as important factors in the metamorphic stage (N6): let-7-5p, miR-100-5p and miR-125-5p, whereas miR-252-3p appears to be important in the pre-metamorphic stage (N5).     

Oxidative stress in Ca2+‐induced membrane permeability transition in brain mitochondria

Mitochondrial permeability transition (PT) is a non-selective inner membrane permeabilization, typically promoted by the accumulation of excessive quantities of Ca(2+) ions in the mitochondrial matrix. This phenomenon may contribute to neuronal cell death under some circumstances, such as following brain trauma and hypoglycemia. In this report, we show that Ca(2+)-induced brain mitochondrial PT was stimulated by Na(+) (10 mM) and totally prevented by the combination of ADP and cyclosporin A. Removal of Ca(2+) from the mitochondrial suspension by EGTA or inhibition of Ca(2+) uptake by ruthenium red partially reverted the dissipation of the membrane potential associated with PT. Ca(2+)-induced brain mitochondrial PT was significantly inhibited by the antioxidant catalase, indicating the participation of reactive oxygen species in this process. An increased detection of reactive oxygen species, measured through dichlorodihydrofluorescein oxidation, was observed after mitochondrial Ca(2+) uptake. Ca(2+)-induced dichlorodihydrofluorescein oxidation was enhanced by Na(+) and prevented by ADP and cyclosporin A, indicating that PT enhances mitochondrial oxidative stress. This could be at least in part a consequence of the extensive depletion in NAD(P)H that accompanied this Ca(2+)-induced mitochondrial PT. NADPH is known to maintain the antioxidant function of the glutathione reductase/peroxidase and thioredoxin reductase/peroxidase systems. In addition, the occurrence of mitochondrial PT was associated with membrane lipid peroxidation. We conclude that PT further increases Ca(2+)-induced oxidative stress in brain mitochondria leading to secondary damage such as lipid peroxidation.     

Insulin secretion and GLUT-2 expression in undernourished neonate rats

In previous studies, we verified increased insulin sensitivity in adult male offspring of lactating rats readjusting to lack of insulin secretion reduction brought about by protein restriction during lactation. The present study aims to evaluate the effects of maternal protein undernutrition during lactation on glucose-induced insulin secretion and GLUT-2 expression in beta-cells of neonate male and female rats. Lactating Wistar rats were given a protein-free diet during the first 10 days and a normal diet (22% of protein) until weaning. The neonates were separated at birth by sex and diet and studied at 4, 8 and 21 days of lactation. Glucose-induced insulin secretion by pancreatic islets was analyzed by radioimmunoassay and GLUT-2 expression in beta-cells by Western blot. Glucose-induced insulin secretion of the undernourished groups was higher than in the control groups except among females. When comparing the male and female groups and the control and undernourished groups, female neonates showed significantly greater insulin secretion than the male group. Also it was noted that undernutrition induced greater GLUT-2 expression. For instance, comparing the undernourished male and female neonates there was an increase in female GLUT-2 expression on day 4. On the other hand, in undernourished male neonates a GLUT-2 expression increased later in lactation. In conclusion, during a short term, maternal undernutrition induces an increase of the glucose-induced insulin secretion only in male neonates and is associated with an increase in GLUT-2 expression in the beta-cell.     

Ca2+-induced oxidative stress in brain mitochondria treated with the respiratory chain inhibitor rotenone

In this study we show that micromolar Ca(2+) concentrations (>10 microM) strongly stimulate the release of reactive oxygen species (ROS) in rotenone-treated isolated rat forebrain mitochondria. Ca(2+)-stimulated mitochondrial ROS release was associated with membrane lipid peroxidation and was directly correlated with the degree of complex I inhibition by rotenone. On the other hand, Ca(2+) did not increase mitochondrial ROS release in the presence of the complex I inhibitor 1-methyl-4-phenylpyridinium. Cyclosporin A had no effect on Ca(2+)-stimulated mitochondrial ROS release in the presence of rotenone, indicating that mitochondrial permeability transition is not involved in this process. We hypothesized that Ca(2+)-induced mitochondrial oxidative stress associated with partial inhibition of complex I may be an important factor in neuronal cell death observed in the neurodegenerative disorder Parkinson's disease.     

Hypertriglyceridemia Increases Mitochondrial Resting Respiration and Susceptibility to Permeability Transition

High plasma level of triglycerides (TGs) is a common feature in atherosclerosis, obesity, diabetes, alcoholism, stress, and infection. Since mitochondria have been implicated in cell death under a variety of metabolic disorders, we examined liver mitochondrial functions in hypertriglyceridemic transgenic mice. Hypertriglyceridemia increased resting respiration and predisposed to mitochondrial permeability transition (MPT). Ciprofibrate therapy reduced plasma TG levels, normalized respiration, and prevented MPT. The higher resting respiration in transgenic mitochondria remained in the presence of the adenine nucleotide carrier inhibitor, carboxyatractyloside, bovine serum albumin, and the uncoupling proteins (UCPs) inhibitor, GDP. UCP2 content was similar in both control and transgenic mitochondria. We propose that faster resting respiration represents a regulated adaptation to oxidize excess free fatty acid in the transgenic mice.     

Pine invasions in treeless environments: dispersal overruns microsite heterogeneity

Understanding biological invasions patterns and mechanisms is highly needed for forecasting and managing these processes and their negative impacts. At small scales, ecological processes driving plant invasions are expected to produce a spatially explicit pattern driven by propagule pressure and local ground heterogeneity. Our aim was to determine the interplay between the intensity of seed rain, using distance to a mature plantation as a proxy, and microsite heterogeneity in the spreading of Pinus contorta in the treeless Patagonian steppe. Three one‐hectare plots were located under different degrees of P. contorta invasion (Coyhaique Alto, 45° 30′S and 71° 42′W). We fitted three types of inhomogeneous Poisson models to each pine plot in an attempt for describing the observed pattern as accurately as possible: the “dispersal” models, “local ground heterogeneity” models, and “combined” models, using both types of covariates. To include the temporal axis in the invasion process, we analyzed both the pattern of young and old recruits and also of all recruits together. As hypothesized, the spatial patterns of recruited pines showed coarse scale heterogeneity. Early pine invasion spatial patterns in our Patagonian steppe site is not different from expectations of inhomogeneous Poisson processes taking into consideration a linear and negative dependency of pine recruit intensity on the distance to afforestations. Models including ground‐cover predictors were able to describe the point pattern process only in a couple of cases but never better than dispersal models. This finding concurs with the idea that early invasions depend more on seed pressure than on the biotic and abiotic relationships seed and seedlings establish at the microsite scale. Our results show that without a timely and active management, P. contorta will invade the Patagonian steppe independently of the local ground‐cover conditions.     

Processes at multiple scales affect richness and similarity of non‐native plant species in mountains around the world

Aim To investigate how species richness and similarity of non‐native plants varies along gradients of elevation and human disturbance. Location Eight mountain regions on four continents and two oceanic islands. Methods We compared the distribution of non‐native plant species along roads in eight mountainous regions. Within each region, abundance of plant species was recorded at 41–84 sites along elevational gradients using 100‐m² plots located 0, 25 and 75 m from roadsides. We used mixed‐effects models to examine how local variation in species richness and similarity were affected by processes at three scales: among regions (global), along elevational gradients (regional) and with distance from the road (local). We used model selection and information criteria to choose best‐fit models of species richness along elevational gradients. We performed a hierarchical clustering of similarity to investigate human‐related factors and environmental filtering as potential drivers at the global scale. Results Species richness and similarity of non‐native plant species along elevational gradients were strongly influenced by factors operating at scales ranging from 100 m to 1000s of km. Non‐native species richness was highest in the New World regions, reflecting the effects of colonization from Europe. Similarity among regions was low and due mainly to certain Eurasian species, mostly native to temperate Europe, occurring in all New World regions. Elevation and distance from the road explained little of the variation in similarity. The elevational distribution of non‐native species richness varied, but was always greatest in the lower third of the range. In all regions, non‐native species richness declined away from roadsides. In three regions, this decline was steeper at higher elevations, and there was an interaction between distance and elevation. Main conclusions Because non‐native plant species are affected by processes operating at global, regional and local scales, a multi‐scale perspective is needed to understand their patterns of distribution. The processes involved include global dispersal, filtering along elevational gradients and differential establishment with distance from roadsides.     

Norbixin ingestion did not induce any detectable DNA breakage in liver and kidney but caused a considerable impairment in plasma glucose levels of rats and mice

From the seeds of Bixa orellana are extracted the carotenoids bixin and norbixin that have been widely used for coloring food. In this study, the toxicity of norbixin, purified or not (annatto extract containing 50% norbixin), was investigated in mice and rats after 21 days of ingestion through drinking water. Mice were exposed to doses of 56 and 351 mg/kg (annatto extract) and 0.8, 7.6, 66 and 274 mg/kg (norbixin). Rats were exposed to doses of 0.8, 7.5 and 68 mg/kg (annatto extract) and 0.8, 8.5 and 74 mg/kg (norbixin). In rats, no toxicity was detected by plasma chemistry. In mice, norbixin induced an increase in plasma alanine aminotransferase activity (ALT) while both norbixin and annatto extract induced a decrease in plasma total protein and globulins (P < 0.05). However, no signs of toxicity were detected in liver by histopathological analysis. No enhancement in DNA breakage was detected in liver or kidney from mice treated with annatto pigments, as evaluated by the comet assay. Nevertheless, there was a remarkable effect of norbixin on the glycemia of both rodent species. In rats, norbixin induced hyperglycemia that ranged from 26.9% (8.5 mg/kg norbixin, to 52.6% (74 mg/kg norbixin, P < 0.01) above control levels. In mice, norbixin induced hypoglycemia that ranged from 14.4% (0.8 mg/kg norbixin, P < 0.05) to 21.5% (66 mg/kg norbixin, P < 0.001) below control levels. Rats and mice treated with annatto pigments showed hyperinsulinemia and hypoinsulinemia, respectively indicating that pancreatic beta-cells were functional. More studies should be performed to fully understand of how species-related differences influences the biological fate of norbixin.