Showing papers by "National University of Comahue published in 2000"

Effects of climatic variability on facilitation of tree establishment in northern patagonia

Abstract: Facilitation of tree establishment by nurse shrubs, which ameliorate otherwise unfavorable microenvironmental conditions, is a widely studied phenomenon. However, relatively little is known about how facilitative influences change in relation to interannual climatic variability. In northern Patagonia, Argentina, we examined influences of potential nurse shrubs on the establishment of the conifer Austrocedrus chilensis and assessed the significance of those influences to establishment during years of contrasting climate. We also experimentally investigated the effects of nurse shrubs and different water availability on tree seedling emergence and survival. A strong spatial association of Austrocedrus juveniles with shrubs, both beneath shrub canopies and near shrub canopies, indicates that shrubs favorably influence tree regeneration and that in some habitats and time periods nurse plants appear to be required for successful tree seedling establishment. Protection from direct sunlight was the main factor c...

A new species of Araripesuchus (Crocodylomorpha, Mesoeucrocodylia) from the lower Cretaceous of Patagonia (Argentina)

Abstract: A new species of the genus Araripesuchus from the Albian-Cenomanian locality of the El Chocon (Neuquen Province, Argentina) is described. The diagnosis of the genus is reviewed and its phylogenetic placement within Crocodylomorpha discussed. Araripesuchus is proposed here as being the sister taxon of Neosuchia, corroborating previous phylogenetic analysis. The new species, Araripesuchus patagonicus, differs from the type species, A. gomesii in the relationships of the prefronto-nasal and lachrymo-nasal sutures, the dermal placement of the postorbital bar on the medial side of the jugal, and the greater extension of the squamosals in the skull dorsum. The African species, “Araripesuchus” wegeneri, does not share the diagnostic traits of the genus, and its reassignment to a new genus needs to be considered. The phylogenetic context of Araripesuchus and “A.” wegeneri permits a reanalysis of the role played by their amphiatlantic distribution in the Aptian-Albian. “Araripesuchus” wegeneri and the Sou...

Mistletoe seed dispersal by a marsupial

Abstract: The temperate forest that extends from 35° S to 55° S along the Pacific rim of southern South America is home to an endemic and threatened flora and fauna1. Many species belong to lineages that can be traced back to ancient Gondwanaland2,3, and there are some unusual interactions between plants and animals. Here we describe an exclusive association that involves the dispersal of the sticky seeds of a mistletoe by a marsupial, Dromiciops australis, endemic to this region — a task previously thought to be carried out exclusively by birds.

Isozyme variation and recent biogeographical history of the long-lived conifer Fitzroya cupressoides

Abstract: Aim Palaeoenvironmental records of Pleistocene glaciation and associated vegetation changes in Patagonia have led to the hypothesis that during the last glacial maximum (LGM) tree species survived locally in favourable habitats. If present populations originated from spread from only one refugium, such as an ice-free area of coastal Chile (Single Refugium hypothesis), we would expect that eastern populations would be genetically depauperate and highly similar to western populations. In contrast, if the ice cap was not complete and tree species persisted in forest patches on both slopes of the Andes (Multiple Refugia hypothesis), we would expect a greater degree of genetic divergence between populations either on opposite sides of the Cordillera (Cordillera Effect scenario) or towards its present-day southern distributional limit where the ice sheet reached its maximum coverage (Extent-of-the-Ice scenario). Location We tested this refugia hypothesis using patterns of isozyme variation in populations sampled over the entire modern range of the endemic conifer Fitzroya cupressoides (Mol.) Johnst. (Cupressaceae) in temperate South America. Methods Fresh foliage was collected from twenty-four populations and analysed by horizontal electrophoresis on starch gels. Results Twenty-one putative loci were reliably scored and 52% were polymorphic in at least one population. Populations from the eastern slope of the Andes were genetically more variable than those from the western slope; the former had a greater mean number of alleles per locus, a larger total number of alleles and rare alleles, and higher polymorphism. Genetic identities within western populations were greater than within eastern populations. Discriminant analyses using allelic frequencies of different grouping schedules of populations were non significant when testing for the Single Refugium hypothesis whereas significant results were obtained for the Multiple Refugia hypothesis. Main conclusions Our results indicate that present Fitzroya populations are the result of spreading from at least two, but possibly more, glacial refugia located in Coastal Chile and on the southern flanks of the Andes in Argentina.

Un nuevo saltasaurino (Sauropoda, Titanosauridae) de la provincia de Río Negro (Formación Allen, Cretácico superior), Patagonia, Argentina

Abstract: "A new saltasaurine taxon based on a femur, pelvic bones and dorsal and caudal vertebrae is described. The closest relationships of the new taxon are with Saitasaurus loricatus Bonaparte and Powell from northwestem Argentina. These species share caudal vertebrae bearing a ventral depression divided by a longitudinal septum. The record of Saltasaurinae is thus limited to the Upper Cretaceous of Argentina, with three distinct taxa: Saliasaurus loricatus, Neuquensaurus ausiralis Lyddeker and Rocasaurus muniozi n. gen., n. sp."

Friulimicins: Novel Lipopeptide Antibiotics with Peptidoglycan Synthesis Inhibiting Activity from Actinoplanes friuliensis sp. nov. : I. Taxonomic Studies of the Producing Microorganism and Fermentation

Abstract: A strain that produces new lipopeptide antibiotics is a new species of the genus Actinoplanes for which we propose the name Actinoplanes friuliensis (type strain: HAG 010964). The strain is an actinoplanete actinomycete having cell wall II composition and forming sporangia. Comparisons with Actinoplanes spp. which have similarities with our isolate, including fatty acid analysis, showed that the isolate belongs to a new species. Taxonomic studies and fermentation are presented.

Edible Wild Plant Use in a Mapuche Community of Northwestern Patagonia

Abstract: Mapuche Indians have a long tradition of using edible wild resources. The people of Rams (Neuquen, Argentina) consider themselves descendants of the Pehuenches, an Indian group that once inhabited the Pehuen forest region. They now live in the steppe, far away from the forest. Our primary interests are how this community uses edible resources and in analyzing which plants are still utilized. We conducted an ethnobotanical study, which consisted in interviewing several Mapuche families and collecting plants with their help. Ecological variables of plant use, such as search cost, handling time, and nutritional content, were analyzed from the perspective of Optimal Foraging Theory. Our results indicate that the Rams inhabitants have a thorough understanding of their environment, expressed in a selective gathering of wild resources. Cost and benefit trade-offs seem to be considered when edible plants are collected.

Local enhancement in the wasp Vespula germanica Are visual cues all that matter

Abstract: Local enhancement, a simple process of social transmission, occurs in the wasp Vespula germanica. Past studies have focused on the role played by visual rather than odour cues in attracting conspecific foragers to a food source. However, odour is known to be important in insect communication in general and it has been suggested to influence naive forager wasp choice. In this study, we experimentally studied local enhancement in Vespula germanica, discriminating between odour and visual cues. We show that conspecific odour attracts Vespula germanica foraging workers and that this attraction is comparable to that of an attractive bait. We thus conclude that odour may be playing a central role in local enhancement by this social wasp.

Toughness and microstructure of 13Cr4NiMo high-strength steel welds

Abstract: The microstructures and tensile, Charpy, and crack tip opening displacement (CTOD) properties of 13Cr4NiMo soft martensitic stainless steel flux cored are welding process (FCAW) weld metals have been studied through different applied postweld heat treatments (PWHT). Phases and microstructural characteristics have been analyzed by scanning electron microscopy (SEM) and x-ray diffraction. The effect of the tempering and double tempering, with and without previous solution annealing, on the impact and fracture toughness has been studied. The role of the retained austenite resulting from tempering has been recognized, and it is suggested that the austenite particles improve the toughness of the welds through their transformation by the transformation-induced plasticity (TRIP) mechanism.

The Importance of Where to Dump the Refuse: Seed Banks and Fine Roots in Nests of the Leaf-Cutting Ants Atta cephalotes and A. colombica1

Abstract: The location of the nutrient-rich organic refuse produced by a leaf-cutting ant colony varies among ant species. Atta cephalotes locate their organic refuse in subterranean chambers, whereas A. colombica place their organic refuse on the soil surface near the nest. We studied the effect of the absence or presence of external organic refuse on the abundance of fine roots and seed bank composition in the superficial horizons of ant nests. We sampled soils from ant nests or dumps and adjacent areas of 15 adult nests of A. cephalotes at La Selva (LS), Costa Rica, and of 15 of A. colombica nests on Barro Colorado Island (BCI), Panama. Soils from A. cephalotes nests did not differ from adjacent soils in abundance of fine-root and seed diversity. In contrast, organic refuse from A. colombica nests was less diverse in seed composition (due to the great abundance of Miconia argentea) and had a greater abundance of fine roots than adjacent areas. Thus the external location of the ant-nest organic refuse is potentially important in determining the different types of plant recolonization in abandoned or dead ant nests. The relative abundance of these Atta species may influence the structure and/or composition of tropical forests.

The earliest known pipoid frog from South America: a new genus from the middle Cretaceous of Argentina

Abstract: Vertebrate remains from the Late Albian–Early Cenomanian Candeleros Formation of northwestern Patagonia include those of a pipoid frog, which is described herein. The fossils consist of partially articulated and disarticulated elements, some of them badly broken, that are mostly exposed in ventral aspect. The description is based on one incomplete skeleton that presumably belongs to a single individual; this specimen possesses a combination of character states not present in other known non-palaeobatrachid pipimorph taxa and is identified here as a new genus and species, Avitabatrachus uliana. The species is moderately small (estimated snout-vent length ca. 35 mm) and shares with Pipidae conch-like squamosals, deeply excavated prootics to form channels for the Eustachian tubes, articulations for the lower jaws at the anterolateral corners of otic capsules, and fused sacrum and urostyle. Avitabatrachus possesses at least eight presacral vertebrae, the first two of which are fused, with flat, opist...

Summer classification of Southern Hemisphere temperate lakes (Patagonia, Argentina)

Abstract: The purpose of this paper was to synthesize observations of 21 cold temperate lakes from Patagonia, Argentina To do this, objective limnological variables and the phytoplankton summer structure were analysed using multivariate statistical tools The results suggest that the most important variables defined a trophic gradient based on nutrients, conductivity and phytoplanktonic attributes Cluster analysis pointed to three groups of lakes Steppe lakes (group III) were distinguished from mountain-Andean lakes (groups I and II) through their higher conductivity and ammonia concentration values, higher net phytoplankton density and lower species diversity The two groups of Andean lakes differed with regard to the biomass of Bacillariophyceae and Prymnesiophyceae, water temperature and dissolved inorganic nitrogen concentration The influence of the biomass (as biovolume) of each taxonomic group in lakes of different trophic status was examined Although all Andean lakes appear to be similar, as shown by their similar salt and nutrient concentration values, the phytoplankton biomass split into different taxa and clearly distinguished subgroups The work presents original information about the phytoplanktonic community structure from all the lakes and the first limnological data on 10 of them, from a region that is poorly known

Effects of ultraviolet radiation on the eggs of landlocked Galaxias maculatus (Galaxiidae, Pisces) in northwestern Patagonia

Abstract: Summary 1 Ultraviolet radiation (UVR) damages early life stages of several fish species. Galaxias maculatus is a small catadromous fish, with landlocked forms occurring in many lakes within the Nahuel Huapi National Park (Patagonia, Argentina). In this work, the vulnerability of G. maculatus eggs exposed to both natural and artificial UVR was investigated in relation to water transparency. 2 Field experiments were performed in two lakes differing in UVR attenuation. Galaxias maculatus eggs were exposed to in situ levels of UVR in quartz tubes incubated at various depths. For laboratory experiments, the eggs were exposed to five levels of artificial UVB radiation. 3 Exposure to natural UVR causes various degrees of egg mortality depending on water transparency and incubation depth. In the less transparent lake (Kd320 = 3.08 m-1), almost complete mortality was observed near the surface. At a depth of 43 cm the observed mortality was only 22%, but was still significantly different from the dark control. In the most transparent lake (Kd320 = 0.438 m-1), almost total mortality was observed in tubes incubated at 2.56 m or shallower. A gradual decline in mortality was recorded from that depth to 3.78 m where the values approached those in the dark control treatments. 4 A monotonic relationship between mortality and UV exposure could be observed both in field and laboratory experiments. Using the results from field incubations, a LD50 of 2.5 J cm-2 nm-1 was estimated. In a few mountain lakes, this value would be exceeded even if the eggs were laid at the maximum depth of the lake. Thus UVR seems a sufficient cause to explain the absence of G. maculatus populations in some mountain lakes. For most lakes, however, UVR is probably one of several important environmental factors, which together determine the habitat suitability.

Biological weighting function for the mortality of Boeckella gracilipes (Copepoda, Crustacea) derived from experiments with natural solar radiation.

Abstract: We performed in situ experiments during the austral summer of 1998 to quantify the mortality of the freshwater copepod Boeckella gracilipes as a function of the UV dose. The copepods were exposed to solar radiation at the water-surface for ∼24–34 h. Long-pass cut-off filters (Schott) were used in the exposure experiments. UV radiation and PAR were measured with an IL-1700 (International Light Inc.) and a PUV-500 radiometer (Biospherical Instruments Inc.). A biological weighting function for UV-induced mortality was calculated by fitting a model based on a logistic curve. Our results show that UV damage in this species is strongly wavelength- and dose-dependent. B. gracilipes was highly vulnerable to both UV-B (290–320 nm) and UV-A radiation (< 360 nm). The shape of the BWF obtained for B. gracilipes resembles more closely the action spectra (AS)† for UV-induced erythema, than the AS for naked DNA.

Cuando ciento setenta y uno se escribe 10071 : niños de 5 a 8 años produciendo numerales

Abstract: ResumenSe solicito a ninos de cinco a ocho anos (n =162) que anotasen numeros, presentados como colecciones de fichas o bien en su forma oral. Las categorias notacionales mas importantes fueron: a) notaciones multiples, que involucran una correspondencia uno a uno entre las unidades y las formas graficas (como 1-1-1 para 3); b) notaciones unitarias pero idiosincrasicas (como una forma para 7) o que registran caracteristicas particulares de los numeros representados a traves de indices diversos (como la cantidad de cifras o la inclusion de ceros); c) notaciones con errors sintacticos (como 100701 o 10071 para 171); d) notaciones convencionales Muchos sujetos produjeron varias de estas clases durante la sesion. Se realizaron analisis Factoriales de Correspondenciasy de Clasificacion, que mostraron varias asociaciones entre item, edad y clase de respuesta y, en menor medida, entorno sociocultural. Las notaciones convencionales aumentan con la edad, pero aun a los 8 anos no todas las notaciones son correctas....

Conservation genetics of the endangered conifer Fitzroya cupressoides in Chile and Argentina

Abstract: Intraspecific patterns of genetic variation can often be used toidentify biogeographic divisions which can be especially useful in thedesign of conservation strategies. Although abundant empirical evidenceexist on the genetic characteristics of plant species from the NorthernHemisphere as well as tropical endangered taxa, this information isparticularly limited on threatened species from endemism-rich areas inthe southern Andes of Argentina and Chile. The objective of the currentstudy was to analyze the levels and distribution of the isozymevariation in Fitzroya cupressoides (Mol.) Johnst.(Cupressaceae), a rare conifer restricted to temperate rainforests ofnorthern Patagonia, and to evaluate the role of current conservationareas protecting the gene pool of this valuable long-lived conifer.Sampling schedules consisted of fresh foliage collected from 30 randomlyselected trees at each of 24 different populations located along thegeographic range of the species. Extraction of enzymes followed standardprocedures and homogenates were loaded in 12% starch gels whichwere analyzed by horizontal electrophoresis. Eleven enzyme systems wereresolved using a combination of four different buffer solutions whichyielded information on 21 putative loci, 52% of them werepolymorphic in at least one population. Relatively low levels ofwithin-population genetic variability were scored in Fitzroyapopulations which were approximately half of the typical levelspublished for gymnosperms (percent of polymorphic loci, P = 23 vs.53% and expected heterozygosity, HE = 0.077 vs. 0.155for Fitzroya and other conifers respectively). Substantialbetween-population variation was detected, and certain individualpopulations stand out as much more genetically variable than nearbypopulations, which in turn are located outside protected areas. Ourfindings suggest that if the objective is to protect key species likeFitzroya, spatially explicit genetic information can be auseful tool to attain this goal.

Phosphorus release rates from freshwater sediments affected by fish farming

Abstract: The main wastes from fish production are fish faeces and uneaten feed, rich in nitrogen and phosphorus (P), which have the potential to alter the trophic state of the water body. It has been estimated that about 66% of P in fish feed accumulates on the bottom sediments. The P associated with these sediments can be released to the water column. The objectives of this work were to: (a) assess the release of phosphorus from sediments affected by intensive production of salmonids in two lakes in Patagonia, Argentina: Lago Moreno (PMOR) and Alicura Reservoir (PALI); (b) evaluate the efficiency of anionic exchange membranes (AEMs) for the determination of P release rates from sediments and compare this technique with the traditional chemical method; and (c) assess the usefulness of AEMs in estimating the labile fraction of phosphorus from sediments affected by fish farms. For all the conditions assayed, the release rates estimated with AEMs were higher than those estimated by syringe (n = 23, P= 0.001). The AEMs appear to have higher sensitivity than chemical methods, particularly at low concentrations. The AEMs are more reliable for the estimation of labile P, particularly in sediments low in labile P concentration. The difference between the release rates estimated by the AEMs and the syringe are indicative of the amount of labile P that will be available in the water over the short term. The release rates were higher under anaerobic conditions than under aerobic conditions for the two types of sediments affected by fish farms. The calcium and organic matter content of sediments, rather than the iron concentration, appears to control the availability of P.

Threatened fishes of the world : Gymnocharacinus bergi Steindachner, 1903 (Characidae)

Abstract: Common names: Mojarra desnuda, mojarra bronceada (spanish), naked characin (E). Conservation status: ‘Endangered’, Red Data Book (IUCN 1996). Identification: Robust and small characin (up to 100 mm TL) that belongs to a monotypic subfamily Gymnocharacininae. The fin rays are D 12, A 19, the caudal fin (P14-M1-R17(9/8)M1-P12) is forked with rounded lobes and lacks the adipose fin. The mouth is terminal with a slight superior prognatism. In adults, the lips do not cover the external series of pentacuspidal teeth. Each premaxillae and dentaries bear two rows of teeth. The maxillae bear two pentacuspidal teeth. The continuous lateral line is straight. Juveniles between 33–36.3 mm TL begin to reabsorb the scales and adults greater than 50 mm TL only show scales on the lateral line and posterior to the opercula. The colour is dark brown, greenish, the belly is creamish and present a band copper-coloured on the flanks, beneath the lateral line. The opercular zone shows golden reflections (Ringuelet et al. 1967, Miquelarena & Aramburu 1983, Ortubay 1998). Drawing by Ortubay (1998). Distribution: Endemic to the Somuncura Plateau at the NE of Argentinean Patagonia, restricted to the thermal headwaters of the two branches, ‘Frio’ and ‘Caliente’, of the Valcheta Stream (500–900 m altitude), an endorheic system of 100 km which disappears in the patagonian esteppe (Luling 1978). Abundance: Fish are scarce at the Frio branch and abundant at the Caliente branch (Ortubay 1998). Habitat and ecology: water temperature has a range of 21.5–26◦C. Ortubay (1998) summarises water chemistry and habitat description. Gymnocharacinus bergi has gregarian habits. Larvae feed on ostracods, chironomid larvae and acari. Juveniles and adults, with a grinding feeding apparatus, feed on periphitic algae. Reproduction: Maturity is reached at 37 mm TL in males and 38 mm TL in females, the breeding season occurs during later winter and early spring (August–October). Females present up to 200 oocytes (1.4-mm diameter) rich in yolk. Threats: In 1941, Oncorhynchus mykiss and Salvelinus fontinalis were introduced in the stream; in the colder Frio branch headwater, O. mykiss preys upon G. bergi and in winter months trout ascend the Caliente branch (Ortubay 1998). Nevertheless, the thermal barrier protects G. bergi at the warmer headwaters of Valcheta Stream. There, the mayor problems are the goat and cattle, pollution and catches for illegal sale of this species to collectors. The Frio branch is easily accessible by road. A single catastrophic event could eliminate the entire subfamily. Conservation actions: The Somuncura Plateau, of 15 000 km, was declared a Reserve Area in 1986 because of the presence of numerous endemics. Up to date, the limits are not established and there is no effective protection. In 1994, G. bergi was declared Natural Monument and catalogued as ‘Endangered’ (IUCN 1996). Conservation recommendations: Resettle two humans from the Caliente branch, educate the local people from the Frio branch, control the use of waters for cultivation and bathing, eradicate the salmonids from the headwaters, and construct a definitive barrier at the confluence of the two branches where the temperatures are extreme and out of the thermal tolerance for G. bergi (Ortubay et al. 1997, Ortubay 1998).

On speed and rotor position estimation in permanent-magnet AC drives

Abstract: This letter deals with rotor position and speed estimation of permanent magnet AC drives. Two reduced-order observers, a linear (AO) and a nonlinear one (NLO), are compared, an adaptive speed estimation scheme is also considered, analysis and simulations show that the NLO has better performance and demands less computational load than the AO plus the adaptive scheme.

Remarks on the biogeography of land invasions

Abstract: Se analiza el porcentaje de especies de plantas exoticas (PES) a escala macrogeografica en forma de mapas politicos (Texas y America del Norte) y mapas de isolineas (Gran Bretana). En estos ultimos se observa mayor concentracion del PES en puertos y areas urbanas e industriales mas que en areas agricolas. En consecuencia, es predecible que la razon entre ruderales y arvenses siga aumentando en el futuro. Sobre la base de un censo de 200 floras del mundo se hace un analisis de regresion multiple para determinar la importancia de factores que contribuyen a la variacion en el PES (disturbios 55 %, riqueza de especies 14%, insularidad 9% y latitud 2%). Precipitacion y temperatura media anual no contribuyen significativamente en la varianza. La predominancia de Europa como principal distribuidora mundial de malezas ha sido atribuida a su geopolitica imperialista y construccion de la primera flota marina internacional. A ello, sin embargo, debio contribuir tambien el tamano de Eurasia. Ya que varios autores hallaron una debil correlacion positiva entre la tasa de dispersion y el exito invasor en plantas, se hizo una comparacion entre taxones mediante 153 datos colectados. Las tasas lineales de dispersion, en km/ano, fueron 64,2 en microorganismos, 48,5 en invertebrados, 17,2 en vertebrados, 6,9 en plantas y 0,19 en registros palinologicos. Otra manera de comparar la capacidad invasora, especialmente, en plagas agricolas, es a traves del indice de cosmopolitismo (C*), que resulto ser 0,642 para fitopatogenos, 0,439 para insectos y 0,259 para malezas. Las malezas son 15, los insectos agricolas 26 veces y los fitopatogenos 37 veces mas cosmopolitas que los mamiferos, tomados como ejemplo comparativo. Finalmente, aunque los animales (invertebrados y vertebrados) muestran mayor tasa media de dispersion que las plantas, y son mejores colonizadores de comunidades pristinas o poco disturbadas, las plantas son mas exitosas en ambientes antropicos

Biased diffusion in anisotropic disordered systems

Abstract: We investigate a diffusion process into an anisotropic disordered medium in the presence of a bias. The medium is modeled by a two-dimensional square lattice in which the anisotropic disorder is represented by a bond percolation model with different occupation probabilities on each direction. The biased diffusion process is mapped by a random walk with unequal transition probabilities along and against the field ~in the @1,1# direction! by performing Monte Carlo simulations. We observe a transition from pure to drift diffusion when the bias reaches a threshold Bc . In order to estimate this Bc ,a neffective exponent is used to characterize the diffusion process. This Bc is also compared with another estimation for the critical field.

A Java Framework for Multi-agent Systems

Abstract: The complexity of distributed systems (multi-agent systems in particular) involves the design and coordination of many entities (called agents). This activity is not trivial and there is not a standard way to do this. So, it is desirable to have tools for reusing previous designed components and relations between them. Frameworks allow design and code to be reused. Intelligent agents cover a big amount of application domains but we can detect an important set of common characteristics that can be abstracted for reusing. This paper presents a framework for multi-agent systems (FraMaS) composed by these common characteristics. FraMaS is used to design agents that have capabilities for perceiving environment, communicating, and deliberating about what to do next.

Annual shoot-growth in Nothofagus antarctica (G. Forster) Oersted (Nothofagaceae) from northern Patagonia

Abstract: The growth dynamics of annual shoots of Nothofagus antarctica shrubs from northern Patagonia was studied. The pattern of extension of the shoots derived from the three most distal buds of 100 parent shoots was registered. Weekly measurements and observations of extending shoots were carried out during the 1996–1997 growth season. The date of shoot extension initiation was less variable than the date of shoot extension cessation. Extension curves had an asymmetrically sigmoid outline. Most extension took place uninterruptedly between mid-September 1996 and the end of January 1997. Extension rate reached its highest value in the second half of the extension period. Leaf unfolding rate had a peak early in the extension period and fluctuated irregularly later on. The apical meristem of all shoots died by the end of shoot extension. In general terms, shoot length, diameter, leaf number and extension duration decreased from the first to the third position from the parent shoot’s apex, although exceptions to this pattern were found. Shoot extension rate was affected by maximum and minimum daily temperatures but not by the amount of precipitation during the extension period. The size of a bud was not related to the size of the shoot derived from it. The size of shoots in the third position from the apex was related to parent shoot size; this was not the case for more distal shoots.

Fright reaction in Gymnocharacinus bergi (Pisces, Characidae), a relic fish from Patagonia

Abstract: Fright reaction, mediated by pheromones, is an antipredatory mechanism in the scale-less ‘mojarra’ Gymnocharacinus bergi (Pisces, Characidae). The aim of this study was to characterise and quantify the fright reaction of this species and to analyse the alarm response to different doses of alarm substance. The alarm response consisted in a general decrease in the swimming speed and a tendency to remain at the bottom of the test aquarium. A threshold effect was induced by a very low dose of alarm substance, and the intensity of the fright reaction was positively correlated to the dose concentration. The main characteristics of the alarm response appear to be consistent with G. bergi's environmental conditions such as: a higher predation risk in the upper stratum, the abundant pond-weeds of the stream and the great flow and fast speed of the clear waters.

Excess molar volumes and excess viscosities of the ternary system diethylamine(1) + ethyl acetate(2) + n-heptane(3) at 25°C

Abstract: Densities and viscosities were experimentally determined in the whole range ofcomposition at 25°C for the ternary system diethylamine(1) + ethyl acetate(2)+ n-heptane(3) and for the three corresponding binary systems. Excess molarvolumes and excess viscosities were calculated for the binaries and the ternarysystems. Results were fitted and predicted with expressions from the literatureand are analyzed to gain insight about liquid mixture interactions.