Dendroecological analysis of defoliator outbreaks on Nothofagus pumilio and their relation to climate variability in the Patagonian Andes

In the temperate forests of the southern Andes, Nothofagus pumilio, the dominant species of the most extensive forest type, experiences severe defoliation caused by caterpillars of the Ormiscodes genus (Lepidoptera: Saturniidae). This study uses tree rings to reconstruct the history of Ormiscodes outbreaks for the 1850–2005 period and examines relationships between outbreaks and climate variability. We used local climate records to compare outbreak–climate relationships in the northern Patagonian Andes (c. 41°S) and the cooler southern Patagonian Andes (c. 49°S). We also examined relationships between outbreak events and regional climate variability driven by variability in the Southern Annular Mode (SAM) and the El Niño‐Southern Oscillation. Although relationships between Ormiscodes outbreaks and climate proved to be complex, in northern Patagonia defoliation events are associated with drier and warmer than average growing seasons. Warming and drying trends in Patagonia during the latter part of the 20th century have been linked to a positive trend in SAM. During the post‐1976 period of accelerated warming in Patagonia, widespread defoliation outbreaks have occurred in both northern and southern Patagonia but the increase in frequency of events has been greater in the south. In southern Patagonia the increases in frequency of outbreaks in the late 20th century appear to be unprecedented over the c. 150 year tree‐ring record of reconstructed outbreaks. These results are consistent with the greater magnitude of recent warming in southern Patagonia, and suggest that under predicted warmer and drier climates in the 21st century, defoliator outbreaks may continue to increase in frequency. This study is the first systematic reconstruction of past insect outbreaks in South America and provides a preliminary understanding of how climate variability affects defoliator outbreaks in Patagonian Nothofagus forests.     

NUMB does not impair growth and differentiation status of experimental gliomas

The cell fate determinant NUMB orchestrates asymmetric cell division in flies and mammals and has lately been suggested to have a tumor suppressor function in breast and lung cancer. Here, we studied NUMB in the context of malignant gliomas. We used ectopic expression of NUMB in order to inhibit proliferation and induce differentiation in glioma cells by alteration of Notch, Hedgehog and p53 signaling. We found that NUMB is consistently expressed in glioma biopsies with predominance of NUMB2/4 isoforms as determined by isoform-specific real-time PCR and Western blotting. Upon lentiviral overexpression, in vitro proliferation rate and the grade of differentiation as assessed by morphology and expression of neural and glial markers remained unchanged. Orthotopic xenografts of NUMB-transduced human U87 glioma cells could be established in nude rats without impairing engraftment or causing significant changes in morphology based on magnetic resonance imaging (MRI). The previously reported alteration of Hedgehog and p53 signaling by NUMB could not be recapitulated in glioma cells. We thus show that in experimental gliomas, NUMB overexpression most likely does not exert a tumor suppressor function such as seen in epithelial cancers.     

Differential hypogeous sporocarp production from Nothofagus dombeyi and N. pumilio forests in southern Argentina

Mycorrhizal fungi that form hypogeous sporocarps are an important component of the temperate forest soil community. In many regions, such as the Nothofagus forest in the Patagonian Andes, this group of fungi has been poorly studied. Here we examined the spring and autumn community composition of "sequestrate fungi", based on sporocarp production in pure forests of Nothofagus dombeyi (evergreen) and N. pumilio (deciduous). We investigated the possible relationships between these communities and environmental factors over 2 y. The rarefaction curves and the minimal richness estimates converged at nearly the same level for each forest type, and the asymptotes suggested that the sampling effort was sufficient to capture most of the hypogeous sporocarp richness in these forest stands. In total 27 species were recovered. Basidiomycota, Ascomycota and Glomeromycota respectively accounted for nine, two and one genera. Species richness of hypogeous sporocarps varied in relation to forest type but not to season (fall and spring), whereas sporocarp biomass varied according to an interaction between season and forest type. Species richness and sporocarp biomass were positively correlated with rainfall and negatively correlated with altitude. In addition sporocarp species richness was positively related to number of trees per transect. We found that two different forest stands, each dominated by different species of Nothofagus, exhibited different hypogeous sporocarp communities.     

Interannual variations in primary and secondary growth of Nothofagus pumilio and their relationships with climate

Key message

The aim of this study is to evaluate the relationships between primary and secondary growth as well as the influences of climate variations on both types of growth.

Abstract

The relationships between apical (or primary) and radial (or secondary) growth, and climatic influences on both types of growth, were evaluated for Nothofagus pumilio (Nothofagaceae), the dominant subalpine tree in Patagonia. We measured the spacing and number of nodes of annual shoots developed in the period 2001–2010 in 40 N. pumilio trees growing near the upper treeline in the northern Patagonian Andes (41°S). Variations in ring width at the base of each trunk were also recorded. Interannual variations in primary and secondary growth were significantly related to each other, and to several climate variables. Mean temperatures in winter and early spring (June–October) prior to the period of shoot extension were positively associated with both primary and secondary growth. In addition, total summer precipitation (December–March) was positively related to shoot extension, whereas mean summer temperature during the previous growth season (January–March) was directly related to radial growth. These climatic influences on N. pumilio growth may play a major role in regulating the expressions of preformation and neoformation.     

A long‐term record of Nothofagus dominance in the southern Andes,Chile

Abstract The general model of regeneration dynamics in Nothofagus forests of southern South America could have value in community ecology if predictive relationships between disturbance history, functional traits and site attributes could be identified. Examined here is the proposal that on favourable sites shade‐intolerant Nothofagus are likely not to survive in competition with shade‐tolerant, broad‐leaved evergreen taxa of temperate rain forests, and persistence, thus, is dependent on periodic coarse‐scale disturbance. Comparison of stand dynamics of three old‐growth Nothofagus forests at different elevations in the southern Andes, Chile where deciduous Nothofagus alpina dominates the upper canopy, and examination of the life history trade‐offs of this variation were made. Stem density of all stems ≥5.0 cm d.b.h. was 233–303 stems per hectare, and basal area was 123.9–171.0 m²ha^?1. Maximum lifespan of N. alpina was found to be greater than ca 640 years, exceeding all previously reported ages for this species in the region. Forests had a stable canopy composition for this long‐term, but some appeared to lack effective regeneration of N. alpina in recent years. Regeneration of N. alpina was generally greater in disturbed stands and higher elevation than in undisturbed stands and at lower elevation. Recruitment emerged to be strongly affected by competitive over‐ and understorey associates. There was a gradient of increasing dependence of N. alpina on disturbance towards the more productive end of the environment gradients, and hence less dependence of N. alpina on disturbance for its regeneration towards higher elevation. The study confirms that changes in forest composition may be explained by processes occurring in accordance with the predictions of the existing model of Nothofagus regeneration dynamics, providing stronger evidence specifically directed at mid‐tolerant N. alpina, and by factoring out regeneration dynamics on favourable sites. Thus, for N. alpina, trait differences probably contribute to the competitive advantage over its associates in productive habitats, and may be linked to small‐to‐intermediate‐sized disturbances which inevitably occur as older trees die, enabling N. alpina to persist in forests and therefore maintain species coexistence for the long‐term.     

Intraspecific trait variation and covariation in a widespread tree species (Nothofagus pumilio) in southern Chile

? The focus of the trait-based approach to study community ecology has mostly been on trait comparisons at the interspecific level. Here we quantified intraspecific variation and covariation of leaf mass per area (LMA) and wood density (WD) in monospecific forests of the widespread tree species Nothofagus pumilio to determine its magnitude and whether it is related to environmental conditions and ontogeny. We also discuss probable mechanisms controlling the trait variation found. ? We collected leaf and stem woody tissues from 30-50 trees of different ages (ontogeny) from each of four populations at differing elevations (i.e. temperatures) and placed at each of three locations differing in soil moisture. ? The total variation in LMA (coefficient of variation (CV) = 21.14%) was twice that of WD (CV = 10.52%). The total variation in traits was never less than 23% when compared with interspecific studies. Differences in elevation (temperature) for the most part explained variation in LMA, while differences in soil moisture and ontogeny explained the variation in WD. Traits covaried similarly in the altitudinal gradient only. ? Functional traits of N. pumilio exhibited nonnegligible variation; LMA varied for the most part with temperature, while WD mostly varied with moisture and ontogeny. We demonstrate that environmental variation can cause important trait variation without species turnover.     

Climate adaptation is not enough: warming does not facilitate success of southern tundra plant populations in the high Arctic

Rapidly rising temperatures are expected to cause latitudinal and elevational range shifts as species track their optimal climate north and upward. However, a lack of adaptation to environmental conditions other than climate – for example photoperiod, biotic interactions, or edaphic conditions – might limit the success of immigrants in a new location despite hospitable climatic conditions. Here, we present one of the first direct experimental tests of the hypothesis that warmer temperatures at northern latitudes will confer a fitness advantage to southern immigrants relative to native populations. As rates of warming in the Arctic are more than double the global average, understanding the impacts of warming in Arctic ecosystems is especially urgent. We established experimentally warmed and nonwarmed common garden plots at Alexandra Fiord, Ellesmere Island in the Canadian High Arctic with seeds of two forb species (Oxyria digyna and Papaver radicatum) originating from three to five populations at different latitudes across the Arctic. We found that plants from the local populations generally had higher survival and obtained a greater maximum size than foreign individuals, regardless of warming treatment. Phenological traits varied with latitude of the source population, such that southern populations demonstrated substantially delayed leaf‐out and senescence relative to northern populations. Our results suggest that environmental conditions other than temperature may influence the ability of foreign populations and species to establish at more northerly latitudes as the climate warms, potentially leading to lags in northward range shifts for some species.     

CS-US delay does not impair appetitive conditioning in Chasmagnathus

Habituation and appetitive conditioning have been already described in the crab Chasmagnathus. The purpose of this work is to study whether associative learning can be obtained despite a long conditioned stimulus-unconditioned stimulus interval. Results of the first experiment show that the weakening of temporal contiguity does not prevent appetitive conditioning to occur while after a long 4-h delay, conditioning wanes completely. A second experiment was conducted, after one and three days of training respectively, confirming the above results. Though initially neutral the context trace may be still available immediately after training and for the period of two but not after 4:00 h, demonstrating a forward limit for the conditioning window. After 3 days of training, a further decrease in the exploratory activity suggested that a longer training could increase the relative weight of habituation. Conditioning and habituation seem to work as opponent processes in the crab CHASMAGNATHUS GRANULATUS: if habituation training in the box is followed by the administration of reinforcement after a short period of time, appetitive conditioning will take place. However, as this interval is increased, habituation prevails. A persistent effect of the exposure to a given environment that may underlie trace conditioning in this crab is discussed in adaptive terms.     

Isozyme polymorphisms provide evidence of clinal variation with elevation in Nothofagus pumilio

Variable physical conditions along elevational gradients strongly influence patterns of genetic differentiation in tree species. Here, the hypothesis is tested that different growth forms of Nothofagus pumilio, which characterizes the subalpine forests in the southern Andes, will display continuous genetic variation with elevation. At each of four elevational strips in three different mountain ranges, fresh leaf tissue was sampled from 30 randomly selected individuals to be analyzed by protein electrophoresis. Allelic frequencies were used to test for heterogeneity across populations and to classify populations into different elevational strips by discriminant analysis. The degree of population divergence was estimated by F(ST). Clinical variation on within-population genetic characteristics was analyzed by linear regressions against elevation. Seven enzyme systems coded for 14 putative isozyme loci, 57% of which were polymorphic in at least one population. Allele frequencies significantly varied with elevation and discriminant analysis separated populations at different elevational strips. Among-population divergence within any mountain range was small, but greater than among different mountain ranges. Overall, low-elevation populations were more variable than high-elevation populations, and regression analyses suggested continuous variation in populations of N. pumilio 100 m apart. Marked stepwise phenological differences on mountain slopes are most probably responsible for the isolation of nearby populations.     

Facilitative interactions do not wane with warming at high elevations in the Andes

Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interactions is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases in temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis, we selected individuals of the native grass species Hordeum comosum growing within the nurse cushion species Azorella madreporica at 3,600 m.a.s.l. in Los Andes (Chile), and performed nurse removal and seedling survival experiments under natural and warmer conditions. For warmer conditions, we used open-top chambers, which increased the temperature by 4 °C. After two growing seasons, we compared the effect of nurse removal on the survival, biomass, and photochemical efficiency of H. comosum individuals under warmer and natural conditions. Nurse removal significantly decreased the survival, biomass, and photochemical efficiency of H. comosum, demonstrating the facilitative effects of nurse cushions. Seedling survival was also enhanced by cushions, even under warmer conditions. However, warmer conditions only partially mitigated the negative effects of nurse removal, suggesting that facilitative effects of cushions do not wane under warmer conditions. Thus, facilitative interactions are vital to the performance and survival of alpine species, and these positive interactions will continue to be important in the warmer conditions of the future in high-alpine habitats.     

Peroxynitrite does not impair pulmonary and systemic vascular responses.

The effects of peroxynitrite (ONOO-) on vascular responses were investigated in the systemic and hindquarters vascular bed and in the isolated perfused rat lung. Intravenous injections of ONOO- decreased systemic arterial pressure, and injections of ONOO- into the hindquarters decreased perfusion pressure in a dose-related manner. Injections of ONOO- into the lung perfusion circuit increased pulmonary arterial perfusion pressure. Responses to ONOO- were rapid in onset, short in duration, and repeatable without exhibiting tachyphylaxis. Repeated injections of ONOO- did not alter systemic, hindquarters, or pulmonary responses to endothelium-dependent vasodilators or other vasoactive agonists and did not alter the hypoxic pulmonary vasoconstrictor response. Injections of sodium nitrate or nitrite or decomposed ONOO- had little effect on vascular pressures. Pulmonary and hindquarters responses to ONOO- were not altered by a cyclooxygenase inhibitor in a dose that attenuated responses to arachidonic acid. These results demonstrate that ONOO- has significant pulmonary vasoconstrictor, systemic vasodepressor, and vasodilator activity; that short-term repeated exposure does impair vascular responsiveness; and that responses to ONOO- are not dependent on cyclooxygenase product release.     

Spatial and temporal variation in Nothofagus pumilio growth at tree line along its latitudinal range (35°40'–55° S) in the Chilean Andes

Aim To identify the dominant spatial and temporal patterns of Nothofagus pumilio radial growth over its entire latitudinal range in Chile, and to find how these patterns relate to temperature and precipitation variation from instrumental records. Location This study comprises 48 tree line or high elevation N. pumilio sites in the Chilean Andes between 35° 36′ and 55° S. Nothofagus pumilio is a deciduous tree species that dominates the upper tree line of the Chilean and Argentinean Andes in this latitudinal range. Methods At each of the sampled sites, two cores from 15 to 40 living trees were collected using increment borers. Cores were processed, tree rings were measured and cross‐dated, using standard dendrochronological procedures. Radii from nearby sites were grouped into 13 study regions. A composite tree‐ring width chronology was developed for each region in order to capture and integrate the common growth patterns. For the identification of the dominant patterns of growth, as well as temperature and precipitation variation, we used principal components (PCs) analysis. Correlation analysis was used for the study of the relationship of N. pumilio tree‐ring growth with temperature and precipitation records. Results Nothofagus pumilio tree line elevation is 1600 m in the northernmost region and gradually decreases to 400 m in the southernmost region. Despite local differences along the transect, the decrease in tree line elevation is fairly constant, averaging c. 60 m per degree of latitude (111 km). Tree growth at the northernmost regions shows a positive correlation with annual precipitation (PC1‐prec) and negative correlation with mean annual temperature (PC2‐temp), under a Mediterranean‐type climate where water availability is a major limiting factor. Conversely, tree growth is positively correlated with mean annual temperature (PC1‐temp) in the southern portion of the gradient, under a relatively cooler climate with little seasonality in precipitation. Main conclusions Our findings indicate that temperature has a spatially larger control of N. pumilio growth than precipitation, as indicated by a significant (P < 0.05) either positive or negative correlation of tree growth and PC1‐temp and/or PC2‐temp for nine of the 13 regional chronologies (69.2% of the total), whereas precipitation is significantly correlated with only two chronologies (15.4% of the total). Temporal patterns of N. pumilio tree growth reflected in PC1‐growth for the period between 1778 and 1996 indicate an increasing trend with above the mean values after 1963, showing high loadings in the southern part of the gradient. This trend may be explained by a well‐documented increase in temperature in southern Patagonia. Ongoing and future research on N. pumilio growth patterns and their relationship to climate covering the Chilean and Argentinean Andes will improve the understanding of long‐term climate fluctuations of the last three to four centuries, and their relationship to global change at a wide range of spatial and temporal scales.     

Insulin resistance does not impair contractile responses of cerebral arteries

Insulin resistance (IR) impairs endothelium-mediated vasodilation in cerebral arteries as well as K+ channel function in vascular smooth muscle. Peripheral arteries also show an impaired endothelium-dependent vasodilation in IR and concomitantly show an enhanced contractile response to endothelin-1 (ET-1). However, the contractile responses of the cerebral arteries in IR have not been examined systematically. This study examined the contractile responses of pressurized isolated middle cerebral arteries (MCAs) in fructose-fed IR and control rats. IR MCAs showed no difference in pressure-mediated (80 mmHg) vasoconstriction compared to controls, either in time to develop spontaneous tone (control: 61+/-3 min, n=30; IR: 63+/-2 min, n=26) or in the degree of that tone (control: 60 min: 33+/-2%, n=22 vs. IR 60 min: 34+/-3%, n=17). MCAs treated with ET-1 (10(-8.5) M) constrict similarly in control (53+/-3%, n=14) and IR (53+/-3%, n=14) arteries. Constrictor responses to U46619 (10(-6) M) are also similar in control (48+/-9%, n=8) and IR (42+/-5%, n=6) MCAs as are responses to extraluminal uridine 5'-triphosphate (UTP; 10(-4.5) M) (control: 35+/-7%, n=11 vs. IR: 38+/-3%, n=10). These findings demonstrate that constrictor responses remain intact in IR despite a selective impairment of dilator responses and endothelial and vascular smooth muscle K+ channel function in cerebral arteries. Thus, it appears that the increased susceptibility to cerebrovascular abnormalities associated with IR and diabetes (including cerebral ischemia, stroke, vertebrobasilar transient ischemic attacks) is not due to an enhanced vasoreactivity to constrictor agents.     

Single millimeter wave treatment does not impair gastrointestinal transit in mice

Millimeter wave treatment (MWT) is based on those biological effects that develop following skin exposure to low power electromagnetic waves. This method of treatment is in wide clinical use in several Eastern European countries for treatment of a variety of conditions, including pain syndromes. However, most treatment modes of MWT were developed empirically, and certain indications and contraindications for the use of MWT remain to be established. In our previous blind experiments we have shown that the hypoalgesic effect of MWT may be quantitatively evaluated, and most probably mediated by the neural system in general, and the system of endogenous opioids in particular. Taking in consideration a well-known ability of opioids to cause gastrointestinal disturbances, which could limit clinical application of MWT, the main aim of the present study was to investigate whether a single MWT, that can produce opioid-related hypoalgesia, may also retard gut transit and colorectal passage in mice. The charcoal meal test was used to quantitatively evaluate upper gastrointestinal transit, and the glass bead test was employed to examine colonic propulsion in mice. MWT was applied to the nose area of mice. The MWT characteristics were: frequency = 61.22 GHz; incident power density = 15 mW/cm(2); and duration = 15 min. The results obtained have shown that MWT does not significantly change small intestinal or colonic transit in mice, and thus suppression of gastrointestinal motility should not be a setback in the clinical use of MWT.