Showing papers by "National University of Comahue published in 2003"

Null model analyses of specialization in plant–pollinator interactions

Abstract: Recent studies have suggested that plant–pollinator interactions may be less specialized than previously thought. We contrasted patterns of specialization observed in five plant–pollinator interaction webs with predictions based on null models. In the five data sets, the observed number of extreme specialists and extreme generalists was significantly higher than the null expectation. This pattern was mostly due to a positive correlation between species frequency of interaction (f) and their estimated degree of generalization (s). After accounting for this association, the expected frequency distribution of degree of specialization generated by the null model closely matched the observed frequency distribution in the five data sets. A second null model, which explicitly incorporated the correlation between f and s, also generated expected frequency distributions of specialization that closely resemble those observed in the data sets. To make progress in understanding the distribution of degree of specializ...

Molecular characterization of carotenogenic yeasts from aquatic environments in Patagonia, Argentina.

Abstract: Fifteen aquatic environments (lakes, lagoons and rivers) of glacial origin in the northern Andean Patagonia (Argentina) were surveyed for the occurrence of red yeasts. Subsurface water samples were filtered and used for colony counting and yeast isolation. A preliminary quantitative analysis indicated that total yeast counts ranged between 0 and 250 cells l−1. A polyphasic approach including physiological and molecular methods was used for the identification of 64 carotenogenic yeast strains. The molecular characterisation of the isolates was based on the mini/microsatellite-primed PCR technique (MSP-PCR) employing the (GTG)5 and the M13 primers. Comparison of representative fingerprints of each group with those of the type strains of pigmented yeasts allowed the expeditious identification of 87.5% isolates. The sequence analysis of the D1/D2 domains of the 26S rDNA was employed to confirm identifications and in the characterization of the unidentified MSP-PCR groups. Teleomorphic yeast species were detected by performing sexual compatibility assays. The isolates corresponded to 6 genera and 15 yeast species, including four new yeast species of the genera Cryptococcus (1), Rhodotorula (1) and Sporobolomyces (2). Rhodotorula mucilaginosa was found in the majority of the samples and represented ca. 50% of the total number of isolates. However, this yeast was not detected in aquatic environments with very low anthropic influence. Other frequent yeast isolates were teleomorphic yeast species of Rhodosporidium babjevae, R. kratochvilovae and Sporidiobolus salmonicolor. This study represents the first report on red yeast occurrence and biodiversity in northwestern Patagonia.

Biomarkers of effect in toads and frogs

Abstract: Amphibians are good bioindicators of environmental pollution due to their susceptibility to chemicals during their freshwater cycles. The effects of environmental pollution, together with changes in human activity and climate, have contributed to the reduction in the amphibian population over recent decades. However, toxicological research on amphibians has been rather scarce compared with that on other vertebrates. In this article we review the biochemical alterations underlying xenobiotic action and/or the detoxifying responses described for anuran species, with the aim of establishing possible biomarkers of effect. During the embryonic development of anurans, morphological and behavioural alterations are the effects most frequently cited in connection with chemical exposures. However, such biomarkers have a low sensitivity and are unspecific compared with biochemical alterations. Some primary pesticide targets, in particular cholinesterases for organophosphates and carbamates, have been evaluated. Esterases change seasonally and with the stage of development, and their sensitivity to anticholinesterase agents varies between species. Thus their use as biomarkers in anurans must be carefully analysed. Enzymes and endogenous compounds related to oxidative metabolism may also be used as biomarkers of effect. Glutathione pool, glutathione-S-transferases and metallothioneins respond in different ways to pesticides and heavy metals in anuran embryos and tadpoles. Mixed-function oxidases, in turn, are less developed in amphibians, and show a reduced induction in response to pesticide exposures. Endogenous polyamine levels are also proposed as good age-related biomarkers of damage. Finally, molecular biomarkers related to receptor binding, signal transduction and genetic response have gained increasing relevance, as they have been implicated in the fertilisation process and the earliest events in anuran development. The identification of transcription factors associated with the exposure of amphibians to xenobiotics as well as other alterations in hormone signalling appears highly promising. However, these techniques are likely to complement other methods. In conclusion, the use of several biomarkers with multiple endpoints is needed to link exposure to response and to provide better predictive tools for the environmental protection of endangered anuran species.

Influences of animal pollination and seed dispersal on winter flowering in a temperate mistletoe

Abstract: The evolution of flowering time can be influenced directly by pollinators and indirectly by seed dispersers. In temperate latitudes, interactions with climate, especially temperature, may affect both plants and their animal mutualists. Winter-flowering plants allow assessment of biotic influences on the evolution of flowering time because temperature is unlikely to select directly for this uncommon reproductive behavior. In northwestern Patagonia, the hemiparasitic mistletoe Tristerix corymbosusflowers from early fall, through the cool winter, to late spring. This species is pollinated by the hummingbird Sephanoides galeritus, and its seeds are dispersed by the marsupial Dromiciops australis. In two pop- ulations during two years, I analyzed seasonal variation in pollination, fruit production, and fruit removal. Hummingbird visitation was lowest in winter and late spring, and flowers opening during those periods showed reduced pollination and fruit set, partly due to pol- linator limitation, compared to flowers that opened during fall or early spring. Fruits that ripened during summer (January-March) had a higher chance of being removed than fruits ripening during either spring or fall, due to their overlap with the period of maximum disperser activity. Timing of flower opening was strongly associated with fruit maturation time and with fruit removal rates. Thus, even though flowers that opened during winter exhibited only moderate fruit production, their fruits benefited from high fruit removal and seed dispersal in mid to late summer. These results suggest that the activity period of this plant's disperser, in combination with a lack of strong pollination constraints, probably governed the evolution of flowering phenology in this mistletoe. However, the proximate influence of temperature on flower and fruit development may prevent a fine-tuned match between flowering phenology and the period of maximum mutualist activity.

Nutrient conservation strategies in native Andean-Patagonian forests

Abstract: Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life-span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C-, N-, P-, K- and lignin-concentrations in mature and senes- cent leaves of ten native woody species within the functional groups: broad-leaved deciduous species, broad-leaved ever- greens and conifers. We also examined mycorrhizal associa- tions in all species. Nutrient concentration in mature leaves and N- resorption were higher in broad-leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N-resorption and high lignin/N ratios in senescent leaves. P- and K-resorptions did not differ among functional groups. Broad-leaved evergreens ex- hibited a species-dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N- fertility. Despite the high P-retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad-leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad- leaved evergreen Lomatia hirsuta, would be possibly explain- ing why P is less limiting than N in these forests.

Field relevance of a synergistic effect observed in the laboratory between an EBI fungicide and a chloronicotinyl insecticide in the honeybee (Apis mellifera L, Hymenoptera)

Abstract: It had been found earlier that the chloronicotinyl insecticide thiacloprid (as the 480 g litre−1 SC Calypso®) poses a favourably low toxicity hazard to the honeybee, Apis mellifera L. As with pyrethroids, the metabolization of chloronicotinyl compounds involves monooxygenases, which are known to be inhibited by some ergosterol biosynthesis inhibitor (EBI) fungicides potentially co-applied with these insecticides. The potential synergistic enhancement of the toxicity of thiacloprid to honeybees when co-applied with such fungicides was therefore studied under laboratory and semi-field conditions. Fungicides of other chemical classes were also examined for synergistic potential to reveal other metabolic interactions. In the laboratory, only a slight synergistic effect was observed with the anilinopyrimidine fungicide examined, while a significant enhancement of thiacloprid toxicity to honeybees was found with EBI fungicides. In three tunnel tests conducted under different environmental conditions to simulate field exposure, no increased mortality was observed when honeybees were directly sprayed with thiacloprid (Calypso) alone or in combination with the EBI fungicide tebuconazole (250 g litre−1 EW, Folicur®). There was also no synergized reduction in the foraging intensity on the treated crop. In general, the foraging intensity decreased after thiacloprid treatment but was restored within 24–48 h. The hive vitality was not affected by either thiacloprid or its tank mix with tebuconazole. Our results suggest that, at the recommended use rates, thiacloprid poses a negligible lethal risk to honeybees when applied either alone or in tank mixes with fungicides of various chemical classes. © 2003 Society of Chemical Industry

Rinconsaurus caudamirus gen. et sp. nov., a new titanosaurid (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia, Argentina

Abstract: Rinconsaurus caudamirus gen et sp. nov. (Dinosauria, Saurpoda) es un nuevo y esbelto Titanosauridae proveniente de la Formacion Rio Neuquen, Cretacico Superior de Rincon de los Sauces, Provincia de Neuquen, Patagonia, Argentina. Sus restos estan integrados por 13 vertebras caudales articuladas y materiales craneales, cervicales, dorsales y apendiculares desarticulados, que pertenecen a tres individuos, dos adultos y un juvenil. Este nuevo taxon se caracteriza por la siguiente asociacion de autapomorfias: (1) vertebras dorsales medioanteriores con espinas neurales inclinadas posteriormente mas de 60 grados con respecto a la vertical, (2) vertebras caudales medias con procesos oseos que sostienen las carillas articulares de las poszigapofisis y (3) vertebras caudales procelicas con intercalaciones de series con centros anficelicos y bioconvexos, o con centros anficelicos, opistocelicos y biconvexos. Un analisis filogenetico cladista permite incluir a Rinconsaurus en la familia Titanosauridae. Dentro de Titanosauridae (Rinconsaurus +Aeolosaurus) es considerado un grupo hermano del clado (Opisthocoelicaudia + (Alamosaurus + (Neuquensaurus + Saltasaurus))). Rinconsaurus caudamirus presenta dos cortas secuencias caudales posteriores articuladas con centros anficelicos, opistocelicos y biconvexos. Esta inusual morfologia se registra por primera vez en dinosaurios sauropodos. Es importante desde el punto de vista sistematico, ya que Titanosauridae ha sido tradicionalmente definido, entre otros caracteres, por la presencia de fuerte procelia en sus vertebras caudales.

Soil N dynamics in relation to leaf litter quality and soil fertility in north‐western Patagonian forests

Abstract: Summary 1 We examined the relationships among soil N dynamics, soil chemistry and leaf litter quality in 28 forest stands dominated by conifers, woody broad-leaf deciduous species or broad-leaf evergreens Potential net N mineralization, net nitrification and microbial biomass N were used as indicators of soil N dynamics; pH, organic C, total N, exchangeable cations and extractable P as indicators of soil chemistry and N concentration, lignin concentration, C : N ratio and lignin : N ratio in senescent leaves as indicators of leaf litter quality N dynamics were assessed in two consecutive years with contrasting precipitation 2 Net N mineralization was lower in stands of the three conifers and one of three broadleaf evergreen species than in stands of the other six broad-leaf species (40‐77 vs 87‐ 250 mg N kg − 1 after 16-week incubations) and higher in the wetter year 3 The proportion of N nitrified was high beneath most species regardless of mineralization rates, soil N fertility and leaf litter quality, and was significantly higher for the wetter year Ammonium was the predominant form of N in three sites affected by seasonal waterlogging and in two sites the predominant form changed from ammonium in the drier year to nitrate during the wetter year, probably due to differences in soil texture affecting soil moisture 4 Net N mineralization was linearly related to microbial biomass N, implying that the microbial activity per biomass unit was quite similar beneath all species Constant microbial biomass during the wetter year suggested that as mineralization/nitrification increased, there was a higher potential risk of N losses 5 Although the litter lignin : N ratio allowed differentiation of soil N dynamics between broad-leaf species and conifers, its constant value (23‐28) in all broad-leaf species made it a poor predictor of the differences found within this group Across all sites and between broad-leaf species, soil N dynamics were best explained by a combination of leaf litter lignin and soil chemistry indicators, particularly soil total N for net N mineralization and net nitrification, and soil organic C for microbial biomass N

Comparison of wild edible plant diversity and foraging strategies in two aboriginal communities of northwestern Patagonia

Abstract: We have compared edible plant richness, diversity and differential patterns of use in two Mapuche communities of Argentina. The populations of Rams and Cayulef are located in a herbaceous steppe, far from the temperate forests of northwestern Patagonia where their ancestors lived in the past. Ecological concepts and methods, such as diversity indices, niche breadth and optimal foraging theory have been used in this comparative study. Our results indicate that the diversity of wild plants used in Rams and Cayulef is associated with the variety of gathering environments they visit. When comparing diversity indices among the three environments within each community, in Cayulef we found the highest diversity indices for steppe species and the lowest for forest plants. In contrast, in Rams the niche breadth is similar in all environments, indicating an ample exploration and use of edible wild plants. Cost and benefit trade-offs seem to be considered in both communities when edible plants are collected. Nevertheless, we found that the people from Rams not only utilize a greater richness of wild plants than the Cayulef people, but also use more nutritious resources, spend more time traveling to the gathering sites and a longer handling time in preparing these edible plants. This study has quantitatively shown that the restricted access to Pehuen forest (Araucaria araucana) is the main factor which seems to limit wild plant diversity used in these Mapuche communities.

Isozyme Polymorphisms Provide Evidence of Clinal Variation With Elevation in Nothofagus pumilio

Abstract: 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 FST. Clinal 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. Amongpopulation 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.

Introduced species and management of a Nothofagus/Austrocedrus forest.

Abstract: Isla Victoria (Nahuel Huapi National Park, Argentina), a large island dominated by native Nothofagus and Austrocedrus forest, has old plantations of many introduced tree species, some of which are famed invaders of native ecosystems elsewhere. There are also large populations of introduced deer and shrubs that may interact in a complex way with the introduced trees, as well as a recently arrived population of wild boar. Long-standing concern that the introduced trees will invade and transform native forest may be unwarranted, as there is little evidence of progressive invasion, even close to the plantations, despite over 50 years of opportunity. Introduced and native shrubs allow scattered introduced trees to achieve substantial size in abandoned pastures, but in almost all areas neither the trees nor the shrubs appear to be spreading beyond these sites. These shrub communities may be stable rather than successional, but the technology for restoring them to native forest is uncertain and probably currently impractical. Any attempt to remove the exotic tree seedlings and saplings from native forest would probably create the very conditions that would favor colonization by exotic plants rather than native trees, while simply clear-cutting the plantations would be unlikely to lead to regeneration of Nothofagus or Austrocedrus. The key to maintaining native forest is preventing catastrophic fire, as several introduced trees and shrubs would be favored over native dominant trees in recolonization. Deer undoubtedly interact with both native and introduced trees and shrubs, but their net effect on native forest is not yet clear, and specific management of deer beyond the current hunting by staff is unwarranted, at least if preventing tree invasion is the goal. The steep terrain and shallow soil make the recently arrived boar a grave threat to the native forest. Eradication is probably feasible and should be attempted quickly.

Relationship between plant nitrogen conservation strategies and the dynamics of soil nitrogen in the arid Patagonian Monte, Argentina

Abstract: During three consecutive years with contrasting precipitation, we analysed the relationship between strategies of N conservation in the dominant plant functional groups (perennial grasses and evergreen shrubs) of the Patagonian Monte and the main components of N cycling in soil. We hypothesised that the different patterns of N conservation in perennial grasses and evergreen shrubs would have direct consequences for soil-N, inorganic-N release and microbial-N flush in soil. In autumn and late spring of 1999, 2000, and 2001, we assessed N and C concentration in green and senesced leaves, N-resorption efficiency and C/N ratio in senesced leaves of three dominant species of each plant functional group. In the soil associated with species of each plant functional group, we determined N and C concentration, potential-N mineralisation, and the associated microbial-N flush. Slow-growing evergreen shrubs exhibited low N-concentration in green leaves, high N-concentration in senesced leaves and low N-resorption from senescing leaves. In contrast, fast-growing perennial grasses showed high N-concentration in green leaves, low N-concentration in senesced leaves, and high N-resorption from senescing leaves. In evergreen shrubs, the maintenance of long-lasting green leaves with low N-concentration was the most important mechanism of N conservation. In contrast, perennial grasses conserved N through high N-resorption from senescing leaves. Soil-N concentration, potential N-mineralisation, and microbial-N flush in the soil were higher underneath evergreen shrubs than beneath perennial grasses. Observed differences, however, were lower than expected considering the quality of the organic matter supplied by each plant fuctional group to the soil. A possible reason for this relatively weak trend may be the capacity of evergreen shrubs to slow down N cycling through low leaf turnover and the presence of secondary compounds in leaves. Alternatively or simultaneously, the weak relationship between plant and soil N could result from shrubs being able to colonise N-poor soils while grasses may preferably occupy fertile microsites previously influenced by the decomposition pathway of evergreen shrubs. Differences between evergreen shrubs and perennial grasses in the mechanisms of plant N-conservation and in components of N cycling in the underlying soil were consistent over the three years of the study with differing precipitation. Inter-annual differences in N concentration in green leaves and in the microbial-N flush in soil indicate that during the wettest year fast-growing perennial grasses would outcompete slow-growing evergreen shrubs and microorganisms for N uptake.

Down-facing flowers, hummingbirds and rain

Abstract: Flower orientation, the angle between a flower's main axis and the horizontal, is an important but understudied flower trait. I explore the relationship between flower orientation, hummingbird pollination, and rain, and review evidence for the adaptive significance of a down-facing orientation as a mechanism to avoid flower flooding. A screening of a tropical and a temperate flora showed that hummingbird flowers more commonly face down than insect flowers. In the temperate forests of southern South America, genera pollinated by hummingbirds and genera with down-facing flowers-irrespective of pollination mode-increase along a strong E-W precipitation gradient across the Andes. These patterns suggest that flowers with a down-facing orientation are associated with pollinators that, like hummingbirds, remain active during rain and that this type of flower orientation may constitute an adaptation against the deleterious effects of nectar dilution and pollen rainwash. Still scarce experimental evidence confirms that a down-facing morphology may prevent flower flooding. However, other morphological traits, like corolla closure and a narrow tubular shape, could also be effective in hindering nectar dilution and pollen rainwash.

An ontology approach to data integration

Abstract: The term Federated Databases refers to the data integration of distributed, autonomous and heterogeneous databases. However, a federation can also include information systems, not only databases. At integrating data, several issues must be addressed. Here, we focus on the problem of heterogeneity, more specifically on semantic heterogeneity that is, problems rela ted to semantically equivalent concepts or semantically related/unrelated concepts. In order to address this problem, we apply the idea of ontologies as a tool for data integration. In this paper, we explain this concept and we briefly describe a method for constructing an ontology by using a hybrid ontology approach.

Resource polymorphism in a Patagonian fish Percichthys trucha (Percichthyidae): phenotypic evidence for interlake pattern variation

Abstract: Within-species differentiation in phenotypic characters related to resource use (resource polymorphism) is frequently thought to result from divergent natural selection in a heterogeneous environment with ‘open niches’. In this study we found consistent resource-based polymorphism within three different populations of Percichthys trucha , a lake-dwelling fish native to the southern Andes. In each of three lakes we found two morphotypes that could be clearly distinguished by differences in gill raker length. However, the magnitude of the polymorphism, and the suite of phenotypic characteristics associated with the polymorphism, differed between lakes. Patterns of divergence were more similar between the two northern lakes which ultimately drain into a common river, than between these two lakes and a more southern, unconnected lake. The southern population, which had the largest divergence in gill raker length (32% vs. 16% and 19%), also showed substantial differences in diet. Evidence from the southern population suggests that polymorphism in P. trucha is present early during ontogeny. We conclude that while there are some strong parallels among lakes in the development of a trophic polymorphism, differences in environmental ­conditions and/or colonization history have led to substantial differences in the evolutionary history, resulting in ­different ecological roles of common morphotypes within different lakes. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society , 2003, 78, 497–515.

A comparative study of shiny cowbird parasitism of two large hosts, the chalk-browed mockingbird and the rufous-bellied thrush

Abstract: It is usually accepted that generalist brood parasites should avoid using hosts larger than themselves because host chicks may outcompete parasite chicks for food. We studied the interactions between the Shiny Cowbird (Molothrus bonariensis) and two common hosts larger than the parasite, the Chalk-browed Mockingbird (Mimus saturninus) and the Rufous-bellied Thrush (Turdus rufiventris). For each host we determined (1) frequency and intensity of parasitism during the breeding season, (2) nesting success, egg survival, hatching success, and chick survival in unparasitized and parasitized nests, and (3) antiparasitic defenses. We also determined Shiny Cowbird egg survival, hatching success, and chick survival in both hosts. Parasitism reached 50% in mockingbirds and 66% in thrushes. In both species the main cost of parasitism was egg destruction through punctures. Hatching success, survival of host chicks, and nest survival did not differ between unparasitized and parasitized nests. Both hosts reject...

The importance of location and visual cues during foraging in the German wasp (Vespula germanica F.) (Hymenoptera: Vespidae)

Abstract: The way in which foraging wasps use cues for prey location and choice appears to depend on both the context and on the type of prey. Vespula germanica is an opportunistic, generalist prey forager, and individual wasp foragers often return to hunt at sites of previous hunting success. In this paper, we studied which cues are used by this wasp when relocating a food source. Particularly we analysed the response to a displaced visual cue versus a foraging location at which either honey or cat food had been previously presented. We conclude that location is used over a displaced visual cue for directing wasp hovering, although the landing response is directed differently according to bait type. When wasps are exploiting cat food, location also elicits landing, but if they are exploiting honey, a displaced visual cue elicits landing more frequently than location.

Component population study of Acanthocephalus tumescens (Acanthocephala) in fishes from Lake Moreno, Argentina.

Abstract: Seasonal samples of all fish species from Lake Moreno were taken in order to determine the presence of paratenia, to evaluate the status of the hosts and to characterise the transmission of Acanthocephalus tumescens (von Linstow, 1896) at the component population level. Prevalence, mean abundance, mean intensity, numbers of gravid females, relative abundance of the different fish species, relative output of eggs and relative flow rates for each host species were computed. Acanthocephalus tumescens showed low host specificity, successfully parasitizing six out of eight fish species present in the lake. No paratenic infection was registered. If prevalence, mean abundance, and number of gravid females are considered, host species can be placed in a continuum from the most to least suitable as follows: Galaxias platei Steindachner, Diplomystes viedmensis (Mac Donagh), Oncorhynchus mykiss (Walbaum), Salvelinus fontinalis (Mitchill), Percichthys trucha (Cuvier et Valenciennes) and Galaxias maculatus (Jenyns). However, when parasite flow rates and egg output were calculated, including relative abundance of each fish species, the continuum was rearranged as follows: P. trucha, O. mykiss, G. platei / G. maculatus, S. fontinalis and D. viedmensis. The first four species would be the main contributors to the population of A. tumescens in this lake, P. trucha being the major one. Different regulatory and non-regulatory mechanisms are suggested.

Impact of different zooplankton structures on the microbial food web of a South Andean oligotrophic lake

Abstract: In oligotrophic Andean lakes, omnivorous calanoid copepods are the dominant zooplankters and, remarkably, phototrophic nanoflagellates and mixotrophic ciliates are the prevailing primary producers. In Lake Rivadavia (Patagonia, Argentina), the centropagids Boeckella michaelseni and Parabroteas sarsi coexist with the large cladoceran Daphnia middendorffiana . The particular feeding modes of these zooplanktonic species probably impact differentially on the microbial community. To determine the effect of predation on the pelagic microbial food web in this lake, we conducted a series of field experiments manipulating different zooplankton structures in 2 l enclosures. The results showed that the presence of B. michaelseni and rotifers depressed ciliates and nanoflagellates, but did not affect autotrophic picoplankton and total bacteria abundances. In contrast, the presence of Daphnia was decisive in decreasing autotrophic picoplankton abundances. P. sarsi was observed to prey on B. michaelseni copepodites and adults and a weak cascading effect on the microbial fraction could be detected.

Assessing sublethal effects of ultraviolet radiation in juvenile rainbow trout (Oncorhynchus mykiss)

Abstract: This paper presents a method for assessing sublethal effects of ultraviolet radiation in fish. The method is based on the assumption that UV-B exposure is stressful to fish. We measured oxygen consumption in UV-B-irradiated rainbow trout juveniles using a UV-transparent respirometer chamber. In addition, we simultaneously monitored fish behavior by videotaping. We found a direct relationship between UV-B irradiance and the percentage increase in oxygen consumption. Increased swimming activity and restless behavior were also noted under UV-B irradiation. The actual mechanisms by which fish perceive UV radiation and a behavioral reaction is triggered are unknown. Based on the present study, a response to UV-A irradiation cannot be ruled out.

Applicability of molecular markers in the context of protection of new varieties of cucumber

Abstract: The growing number of candidate varieties presented every year at each national Plant Variety Protection Office and their decreasing genetic variability forces strategies to be adopted that will reduce costs without losing rigour when deciding about the acceptance or rejection of a candidate variety. Molecular markers have been envisaged as a reliable tool to establish differences, but can molecular markers be used for assessing distinctness? A comparison between a molecular and a morphological characterization of 41 seed samples belonging to 36 cucumber varieties and including several external controls has been carried out to investigate the applicability of molecular markers in the context of distinctness, uniformity and stability (DUS) tests and the protection of new varieties. Both types of character indicate the same relationships among main groups, Dutch and Beth-Alpha types, and Gerking and Slice types, the correlation between distance matrices being only 0.6489. Varieties considered uniform for morphological traits proved not to be so for molecular markers. Therefore, molecular characterization is not offering the same estimates of uniformity and relatedness between varieties as does morphological characterization. External controls were used to establish distinction limits with morphological and molecular dendrograms to focus on those varieties, which were suspiciously similar. The results with cucumber show that molecular identity could be used to assess any lack of distinctness and so corroborate the morphological assessment of candidate varieties. The morphological trait ‘type’ provides distinct characterization of varieties and the molecular characterization of candidate varieties could be used to design better field experiments to assess distinction within each group of morphological cucumber type.

Conspecifics Enhance Attraction of Vespula germanica (Hymenoptera: Vespidae) Foragers to Food Baits

Abstract: Local enhancement has been shown to occur in the social wasp Vespula germanica (F.), a species that feeds on live insects as well as on dead animals. Some studies suggest local enhancement is based on sight, whereas others suggest that odors emanating from wasp bodies are more important in attracting conspecifc workers to a food source. We studied whether the attraction of V. germanica foragers to meat baits increases by the addition of live conspecific foragers and analyzed which cues (olfactory and visual) elicit this attraction. Our results show that the combination of meat and wasps strongly enhances the attraction of conspecific foragers. Presenting both visual and olfactory cues together leads to a wasp response that is much greater than if isolated visual or isolated olfactory cues were added, suggesting some synergistic action of both cues.

Owl Selection on Size and Sex Classes of Rodents: Activity and Microhabitat Use of Prey

Abstract: Our aim was to study selective owl predation on size and sex classes of rodents in northwestern Argentine Patagonia and to determine which behavioral traits may be involved in differential prey vulnerability. Diet of Magellanic horned owls (Bubo magellanicus) was studied for 2 years. Jaw and pelvic measurements were used to estimate size and sex of rodents eaten by owls. Livetrapping of rodents was conducted simultaneously with diet analysis to estimate proportion of size and sex classes of rodents available and to examine movement and microhabitat use. Owls generally selected individuals of smaller size and avoided heavier individuals. Sex classes of prey were consumed according to availability, except that the female silky desert mouse (Eligmodontia morgani) was selected. Smaller individuals of E. morgani, the long-haired mouse (Akodon longipilis), and the yellow-nosed mouse (A. xanthorhinus) tended to use open microhabitat where risk of predation was higher. Vulnerability to predation seemed t...

Influence of compatibility system and life form on plant reproductive success

Abstract: We studied the compatibility system and the autonomous selfing capacity of 32 native species from the Chaco Serrano forests (central Argentina), and compared fruit set, considering plant life form and compatibility status to evaluate: (i) the extent of the association between life form and compatibility system, (ii) the influence of the life form and/or of the compatibility system on natural fruit set, and (iii) the preemergent reproductive advantages provided by self-compatibility and autonomous self-pollination. Ca. 60 % of the species were self-compatible (SC). Natural fruit set of SC species triplicate those of self-incompatible (SI) species. Almost all SC species have autonomous selfing capacity. Nevertheless, on average, SC species produce more than twice as many fruits through natural pollination in comparison to autonomous selfing, and fruit set obtained after autonomous selfing was significantly lower than hand-selfed fruit set. Most SC species received insufficient pollen from themselves via autonomous selfing, and natural fruit set was mostly pollinator-mediated. Thus, the reproductive assurance provided by autonomous selfing is relatively low in comparison with that provided by pollinators. We supplemented our data with published results from different sites in South America, to assess how general are the associations between life form and compatibility system and between natural fruit production and the self compatibility index. There is a differential distribution of SC and SI species according to life form, with a skew towards incompatibility among woody plants and towards compatibility in herbs. On the other hand, regression analysis showed there is a general positive trend between natural fruit set and the self compatibility index of the species.

Formation of Al2O3 Scales on Single-Phase RuAl Produced by Reactive Sintering

Abstract: The oxidation behavior of single-phase RuAl produced by powder metallurgy combined with arc melting was investigated. Oxidation was conducted at 1000°C; oxide scale growth and phase formation were studied using scanning-electron microscopy (SEM) and x-ray diffraction (XRD). A dense protective scale with an Al–depleted sublayer was formed during oxidation. The oxide scale is the stable α-Al2O3. The oxide-scale morphology shows the presence of whiskers, with a needle-like form, which suggests that the growth of the oxide scale is produced by outward diffusion of Al. At the beginning, oxidation follows a parabolic law, but, after 100 hr of oxidation; the growth rate is slower than expected from a parabolic law.