Experiencias en germinación y reproducción vegetativa aplicadas a la reforestación con Polylepis australis (Rosaceae) en las Sierras Grandes de Córdoba, Argentina

Se realizaron experiencias de propagación con Polylepis australis BITT, en invernáculo y en las Sierras Grandes de Córdoba, con el fin de facilitar la recuperación de sus bosques mediante una reforestación. El porcentaje de germinación fue muy variable entre semillas provenientes de distintos individuos, y estuvo correlacionado positivamente con el grado de cobertura de P. australis del sitio dondese colectaron las semillas. No se encontraron diferencias en la germinación entre los substratos: arena, hojarasca, y tierra con arena, ni con la esterilización de éstos. El tratamiento de las semillas con frío húmedo fue perjudicial. La propagación mediante estacas es factible; la mejor época es la primavera y el uso de enraizante no es recomendable. La supervivencia de los plantines transplantados a su habitat natural fue alta tanto para los producidos mediante semillas como para los de estaca, aunque el crecimiento de los plantines de semillas fue mayor al de los plantines de estaca

Glacial-Interglacial changes in moisture balance and the impact on vegetation in the southern hemisphere tropical Andes (Bolivia/Peru)

A palynological investigation of the last glacial-interglacial cycle in the southern hemisphere tropical Andes reveals changes in the moisture balance as the main driver in vegetation change. Thirty accelerated mass spectrometry radiocarbon dates, biostratigraphy and tephra correlation reveal that a 119 metre sediment core recovered from the Huiñaimarca sub-basin of Lake Titicaca (16.0° to 17.5° S, 68.5° to 70° W; 3810 masl) contains sediments covering >151,000 years. Correlation of aridity indicators with precessional variations in insolation is used to fine tune the structure of the age-depth curve within this period. Variations in Isoëtes concentration (above/below 10,000 grains/cm3) identify the extent of shallow water environments. Examination of other palaeolimnological indicators (Pediastrum) and consideration of the bathymetry of the Huiñaimarca sub-basin allow the reconstruction of lake level fluctuations. These data indicate five wet/dry cycles between c. 151,000 and 14,200 cal yr BP. High stands are suggested during the transition into (c. 134,000 cal yr BP), and out of (c. 114,000, 92,000 cal yr BP), the last interglacial,and during full glacial conditions (c. 70,000 and 45,000 cal yr BP). These cycles are superimposed on a general trend of deepening lake levels through the glacial period. This interpretation is supported by correlation with sediments from Salar de Uyuni (20oS, 68oW; 3653 masl). The youngest wet episode is concurrent with palaeolake Minchin (c. 45,000 cal yr BP), with further evidence for an additional wet period commencing c. 28,000 cal yr BP, concomitant with palaeolake Tauca. The timing of lake level fluctuations is also supported by palaeoshoreline reconstructions from the Uyuni-Poopó region. However, our data do not suggest a major peak in lake level in Huiñaimarca during the Ouki lake cycle (c. 120,000-98,000 cal yr BP) as inferred from U-Th ages obtained from palaeoshorelines around Lago Poopó. The most extreme dry event occurs during the last interglacial period and resulted in a sedimentary hiatus tentatively dated to c. 121,000-129,000 cal yr BP. The observed wet/dry cycles are shown to have a marked and rapid impact on the vegetation. The aridity of the last interglacial promoted a community dominated by Chenopodiaceae/Amaranthacae, with no modern Andean analogue. Polylepis/Acaena pollen is also shown to fluctuate markedly (0-20%), particularly during the transitions into, and out of, the last interglacial. It is probable that this pollen taxon is primarily representative of the high altitude arboreal genus Polylepis, which is a key component of highly biodiverse Andean woodlands today. Rapid fluctuations indicate the sensitivity of this ecosystem to natural environmental pressure and potential vulnerability to future human impact and climate change. The 100,000 year (eccentricity) solar cycle is shown to be the major controlling factor in moisture balance and vegetation over the last glacial-interglacial cycle. However, significant fluctuations in moisture balance are also evident on timescales considerably shorter than the full glacial-interglacial cycle. We have linked these to precessional (21,000 year) forcing. Nevertheless, precise independent dating during the full glacial cycle is required to confirm the importance of this forcing mechanism

Arbuscular mycorrhizal fungal diversity in rhizosphere spores versus roots of an endangered endemic tree from Argentina: is fungal diversity similar among forest disturbance types?

The aim of this study was to compare the arbuscular mycorrhizal fungal (AMF) community of the rhizosphere and inside the roots of the perennial Polylepis australis tree. Three forest types differing in their structural complexity due to anthropogenic disturbances were chosen at three different sites at the high mountains of central Argentina. Rhizosphere spores and P. australis roots of four randomly selected trees were isolated from 36 soil samples, DNA was extracted and the 18S rDNA fragments were amplified by nested-PCR. The products were analyzed by DGGE and the bands were excised for sequencing. In total, 36 OTUs were defined from 56 DGGE bands successfully sequenced. Forest disturbance types showed similar communities of AMF, as rhizosphere spores and within the roots of P. australis. However, DGGE clustering showed mainly differences between rhizosphere spores and root-colonizing AMF. Members of Glomeraceae, Pacisporaceae, Acaulosporaceae and Gigasporaceae were shown in rhizosphere spore samples. Root samples showed only members of Acaulosporaceae and Gigasporaceae, which might be complementary in terms of soil resources exploration. The prevalence of the root system with their community of symbionts might explain the resilience of AMF soil communities to forests structural changes. This study presents evidence of a possible preference in the AMF?P. australis interactio

<i>Polylepis</i> woodland dynamics during the last 20,000 years

AimTo determine the palaeoecological influences of climate change and human land use on the spatial distribution patterns of Polylepis woodlands in the Andes.LocationTropical Andes above 2,900 m between 2°S and 18°S of latitude.MethodsPollen and charcoal data were gathered from 13 Andean lake sediment records and were rescaled by the maximum value in each site. The rescaled pollen data were used to estimate a mean abundance and coefficient of variation to show woodland expansions/contractions and woodland fragmentation over the last 20,000 years. The rescaled charcoal was displayed as a 200‐year moving median using 500‐year bins to infer the influence of fire on woodland dynamics at landscape scale. Pollen and charcoal were compared with speleothem, clastic flux and archaeological data to assess the influence of moisture balance, glacial activity and human impact on the spatial distribution of Polylepis woodlands.ResultsWoodland expansion and fire were correlated with precipitation changes and glacier dynamics from c. 20 to 6 kcal BP (thousands of calibrated years before present). Charcoal abundances between 20 and 12 kcal BP were less common than from 12 kcal BP to modern. However, human‐induced fires were unlikely to be the main cause of a woodland decline centred at 11 kcal BP, as woodlands recovered from 10.5 to 9.5 kcal BP (about twofold increase). Charcoal peaks analogous to those that induced the woodland decline at 11 kcal BP were commonplace post‐9.5 kcal BP but did not trigger an equivalent woodland contraction. An increase in the coefficient of variation after c. 5.5 kcal BP suggests enhanced fragmentation and coincided with the shift from logistic to exponential growth of human populations. Over the last 1,000 years, Polylepis became hyper‐fragmented with over half of sites losing Polylepis from the record and with coefficients of variation paralleling those of glacial times.Main conclusionsPolylepis woodlands formed naturally patchy woodlands, rather than a continuous vegetation belt, prior to human occupation in the Andes. The main factors controlling pre‐human woodland dynamics were precipitation and landscape heterogeneity. Human activity led to hyper‐fragmentation during the last c. 1,000 years

Integrating personality research and animal contest theory: aggressiveness in the green swordtail <i>Xiphophorus helleri</i>

&lt;p&gt;Aggression occurs when individuals compete over limiting resources. While theoretical studies have long placed a strong emphasis on context-specificity of aggression, there is increasing recognition that consistent behavioural differences exist among individuals, and that aggressiveness may be an important component of individual personality. Though empirical studies tend to focus on one aspect or the other, we suggest there is merit in modelling both within-and among-individual variation in agonistic behaviour simultaneously. Here, we demonstrate how this can be achieved using multivariate linear mixed effect models. Using data from repeated mirror trials and dyadic interactions of male green swordtails, &lt;i&gt;Xiphophorus helleri&lt;/i&gt;, we show repeatable components of (co)variation in a suite of agonistic behaviour that is broadly consistent with a major axis of variation in aggressiveness. We also show that observed focal behaviour is dependent on opponent effects, which can themselves be repeatable but were more generally found to be context specific. In particular, our models show that within-individual variation in agonistic behaviour is explained, at least in part, by the relative size of a live opponent as predicted by contest theory. Finally, we suggest several additional applications of the multivariate models demonstrated here. These include testing the recently queried functional equivalence of alternative experimental approaches, (e. g., mirror trials, dyadic interaction tests) for assaying individual aggressiveness.&lt;/p&gt

A single-blinded trial of methotrexate versus azathioprine as steroid-sparing agents in generalized myasthenia gravis

<p>Abstract</p> <p>Background</p> <p>Long-term immunosuppression is often required in myasthenia gravis (MG). There are no published trials using methotrexate (MTX) in MG. The steroid-sparing efficacy of azathioprine (AZA) has been demonstrated after 18-months of starting therapy. However, AZA is considered expensive in Africa. We evaluated the steroid-sparing efficacy of MTX (17.5 mg weekly) compared with AZA (2.5 mg/kg daily) in subjects recently diagnosed with generalized MG by assessing their average monthly prednisone requirements.</p> <p>Methods</p> <p>The primary outcome was the average daily prednisone requirement by month between the two groups. Prednisone was given at the lowest dose to manage MG symptoms and adjusted as required according to protocol. Single-blinded assessments were performed 3-monthly for 2-years to determine the quantitative MG score and the MG activities of daily living score in order to determine those with minimal manifestations of MG.</p> <p>Results</p> <p>Thirty-one subjects (AZA n = 15; MTX n = 16) satisfied the inclusion criteria but only 24 were randomized. Baseline characteristics were similar. There was no difference between the AZA- and MTX-groups in respect of prednisone dosing (apart from months 10 and 12), in quantitative MG Score improvement, proportions in sustained remission, frequencies of MG relapses, or adverse reactions and/or withdrawals. The MTX-group received lower prednisone doses between month 10 (p = 0.047) and month 12 (p = 0.039). At month 12 the prednisone dose per kilogram bodyweight in the MTX-group (0.15 mg/kg) was half that of the AZA-group (0.31 mg/kg)(p = 0.019).</p> <p>Conclusions</p> <p>This study provides evidence that in patients with generalized MG methotrexate is an effective steroid-sparing agent 10 months after treatment initiation. Our data suggests that in generalized MG methotrexate has similar efficacy and tolerability to azathioprine and may be the drug of choice in financially constrained health systems.</p> <p>Trial registration</p> <p>SANCTR:DOH-27-0411-2436</p

The Cost of Male Aggression and Polygyny in California Sea Lions (Zalophus californianus)

In polygynous mating systems, males often increase their fecundity via aggressive defense of mates and/or resources necessary for successful mating. Here we show that both male and female reproductive behavior during the breeding season (June–August) affect female fecundity, a vital rate that is an important determinant of population growth rate and viability. By using 4 years of data on behavior and demography of California sea lions (Zalophus californianus), we found that male behavior and spatial dynamics—aggression and territory size—are significantly related to female fecundity. Higher rates of male aggression and larger territory sizes were associated with lower estimates of female fecundity within the same year. Female aggression was significantly and positively related to fecundity both within the same year as the behavior was measured and in the following year. These results indicate that while male aggression and defense of territories may increase male fecundity, such interactions may cause a reduction in the overall population growth rate by lowering female fecundity. Females may attempt to offset male-related reductions in female fecundity by increasing their own aggression—perhaps to defend pups from incidental injury or mortality. Thus in polygynous mating systems, male aggression may increase male fitness at the cost of female fitness and overall population viability