Trophic strategies of a non-native and a native amphibian species in shared ponds.

One of the critical factors for understanding the establishment, success and potential impact on native species of an introduced species is a thorough knowledge of how these species manage trophic resources. Two main trophic strategies for resource acquisition have been described: competition and opportunism. In the present study our objective was to identify the main trophic strategies of the non-native amphibian Discoglossus pictus and its potential trophic impact on the native amphibian Bufo calamita.We determine whether D. pictus exploits similar trophic resources to those exploited by the native B. calamita (competition hypothesis) or alternative resources (opportunistic hypothesis). To this end, we analyzed the stable isotope values of nitrogen and carbon in larvae of both species, in natural ponds and in controlled laboratory conditions. The similarity of the δ15N and δ13C values in the two species coupled with isotopic signal variation according to pond conditions and niche partitioning when they co-occurred indicated dietary competition. Additionally, the non-native species was located at higher levels of trophic niches than the native species and B. calamita suffered an increase in its standard ellipse area when it shared ponds with D. pictus. These results suggest niche displacement of B. calamita to non-preferred resources and greater competitive capacity of D. pictus in field conditions. Moreover, D. pictus showed a broader niche than the native species in all conditions, indicating increased capacity to exploit the diversity of resources; this may indirectly favor its invasiveness. Despite the limitations of this study (derived from potential variability in pond isotopic signals), the results support previous experimental studies. All the studies indicate that D. pictus competes with B. calamita for trophic resources with potential negative effects on the fitness of the latter

Evaluando los factores que afectan a la tasa de mortalidad en la carretera: el caso de Sapo Común Bufo bufo, cerca de un área de reproducción

The Common Toad Bufo bufo is the amphibian with the highest rates of road mortality in many European countries. This elevated incidence of road kills has frequently been associated with migration to breeding sites. In this study, we analysed the mortality of the Common Toad in the road network in Catalonia (NE Spain), and investigated the related causative factors on four roads near a breeding site in the Pyrenees. Results suggest that the high mortality rate is due to a combination of factors: toad abundance, traffic density and quality of water bodies for breeding. On the road with the highest incidence of road kills we investigated whether deaths occurred at specific spots or in a random manner. The road was divided into 500 m sections and each section was classified according to biotic (type of vegetation) and abiotic (presence of streams, roadside topography) variables. Multiple correspondence analysis showed that sections with streams crossing under the road had the highest mortality rate, suggesting that such water bodies flowing into the breeding pond are the toads’ main migratory pathways for hibernation and breeding. As toads use the same migratory routes each year, it is critical to identify areas with a high potential mortality so that efficient measures can be designed to increase wildlife permeability, and thereby reduce habitat fragmentation. This methodology could be applied in other areas with high amphibian mortality. Key words: Amphibian, Common Toad, Bufo bufo, Landscape fragmentation, Migration, Mortality, Road permeability, Pyrenees.El Sapo Común Bufo bufo, es el anfibio con mayor tasa de mortalidad en la carretera en numerosos países de Europa. Esta elevada mortalidad se debe principalmente a las migraciones que realiza hacia las zonas de reproducción. En este estudio se analiza la mortalidad del Sapo Común en la red de carreteras de Cataluña (NE España) y más específicamente qué factores influyen sobre dicha mortalidad en cuatro carreteras cercanas a un punto de reproducción en los Pirineos. Los resultados sugieren que la alta tasa de mortalidad se debe a la combinación de tres factores: abundancia de sapos, densidad de tráfico y calidad de los puntos de agua para la reproducción. En la carretera con mayor índice de atropellos, se analizó si existía agregación en los animales atropellados o estos se distribuían al azar. Para ello, la carretera se dividió en tramos de 500 m, cada uno de los cuales se caracterizó por el tipo de vegetación circundante, así como otros factores que pudieran influir sobre la migración de los sapos (p.e. inclinación del margen de la carretera, presencia de riachuelos, etc.). El análisis de correspondencias múltiple demostró que los tramos con torrentes cruzando bajo la carretera presentaban mayor mortalidad. Esto sugiere que dichos torrentes son las vías principales usadas por los sapos para acudir a los puntos de reproducción. Dado que los sapos utilizan cada año las mismas vías migratorias, es fundamental identificar dichos puntos para predecir cuáles presentan mayor mortalidad potencial y así diseñar más eficazmente los mecanismos de permeabilidad para la fauna en las vías de comunicación. Esta metodología puede ser aplicada a otras zonas con elevada mortalidad de anfibios en la red de carreteras. Palabras clave: Anfibio, Sapo Común, Bufo bufo, Fragmentación del paisaje, Migración, Mortalidad, Permeabilidad de la carretera, Pirineos

Variation in developmental rates is not linked to environmental unpredictability in annual killifishes

Comparative evidence suggests that adaptive plasticity may evolve as a response to predictable environmental variation. However, less attention has been placed on unpredictable environmental variation, which is considered to affect evolutionary trajectories by increasing phenotypic variation (or bet hedging). Here, we examine the occurrence of bet hedging in egg developmental rates in seven species of annual killifish that originate from a gradient of variation in precipitation rates, under three treatment incubation temperatures (21, 23, and 25 degrees C). In the wild, these species survive regular and seasonal habitat desiccation, as dormant eggs buried in the soil. At the onset of the rainy season, embryos must be sufficiently developed in order to hatch and complete their life cycle. We found substantial differences among species in both the mean and variation of egg development rates, as well as species-specific plastic responses to incubation temperature. Yet, there was no clear relationship between variation in egg development time and variation in precipitation rate (environmental predictability). The exact cause of these differences therefore remains enigmatic, possibly depending on differences in other natural environmental conditions in addition to precipitation predictability. Hence, if species-specific variances are adaptive, the relationship between development and variation in precipitation is complex and does not diverge in accordance with simple linear relationships

Differential trophic traits between invasive and native anuran tadpoles

How trophic resources are managed is a key factor in our understanding of the success of invasive species. In amphibians that usually occupy ephemeral ponds, the capacity to acquire resources and food selection are especially important because as a pond dries, the larval density increases and food resources are limited. Abundant and high-quality food can increase the final size and reduce the duration of development of amphibians. The aim of this work was to assess the trophic traits of tadpoles of the invasive (originally North African) anuran Discoglossus pictus compared to those of native European Epidalea calamita tadpoles under laboratory conditions. Food of two different levels of quality was supplied, and the feeding activity and food preference of the two species were analysed alone and in co-occurrence. D. pictus was capable of modifying its behaviour and food preferences; while E. calamita displayed much milder differences between treatments. Both alone and in co-occurrence with the native species, the invasive tadpoles obtained higher feeding activity values and showed a stronger preference for high-quality food. Additionally, when high densities of the two species shared food resources, the feeding activity results indicated potential displacement of the native tadpoles to lowquality resources. D. pictus thus presents trophic traits that are favourable for invasion and could limit the fitness of E. calamita when resources are limited or there is a risk of pond desiccation

Evaluating factors affecting amphibian mortality on roads: the case of the Common Toad Bufo bufo near a breeding place.

The Common Toad Bufo bufo is the amphibian with the highest rates of road mortality in many European countries. This elevated incidence of road kills has frequently been associated with migration to breeding sites. In this study, we analysed the mortality of the Common Toad in the road network in Catalonia (NE Spain), and investigated the related causative factors on four roads near a breeding site in the Pyrenees. Results suggest that the high mortality rate is due to a combination of factors: toad abundance, traffic density and quality of water bodies for breeding. On the road with the highest incidence of road kills we investigated whether deaths occurred at specific spots or in a random manner. The road was divided into 500 m sections and each section was classified according to biotic (type of vegetation) and abiotic (presence of streams, roadside topography) variables. Multiple correspondence analysis showed that sections with streams crossing under the road had the highest mortality rate, suggesting that such water bodies flowing into the breeding pond are the toads' main migratory pathways for hibernation and breeding. As toads use the same migratory routes each year, it is critical to identify areas with a high potential mortality so that efficient measures can be designed to increase wildlife permeability, and thereby reduce habitat fragmentation. This methodology could be applied in other areas with high amphibian mortality

El estudio de las tolerancias térmicas para el examen de hipótesis biogeográficas y de la vulnerabilidad de los organismos ante el calentamiento global: ejemplos en anfíbios

La temperatura afecta de manera decisiva a las reacciones químicas que condicionan todos los procesos fisiológicos (Hochachka & Somero, 2002), determinando los patrones de distribución y abundancia de los organismos, así como numerosas interacciones ecológicas (Andrewartha & Birch, 1954; Dunson & Travis, 1991). Podemos, por tanto, afirmar que la temperatura, como componente abiótico fundamental, representa un factor selectivo de primer orden al influir en la supervivencia, crecimiento y dispersión de los organismos (Angiletta, 2009). El estudio de los rangos de tolerancia fisiológicos, especialmente los rangos térmicos, resulta imprescindible para comprender numerosos aspectos de la biología de los organismos, ya que representan las condiciones que limitan su nicho fundamental y, por tanto, su presencia y evolución en un determinado hábitat y área geográfica (Hutchinson, 1981; Kearney & Porter, 2009; Soberón & Nakamura, 2009; Townsend et al., 2011; Seebacher & Franklin, 2012). Se espera que las condiciones térmicas locales dirijan la evolución de los límites de tolerancia térmica, de su potencial plástico de aclimatación y en definitiva deriven en adaptaciones térmicas (Angiletta, 2009; Bozinovic et al., 2011). El interés por el estudio de la evolución y funcionalidad de estos límites térmicos es fuente de numerosas hipótesis biogeográficas y representa un elemento crucial en la determinación de la vulnerabilidad de las especies a los impactos del cambio climático.Fil: Tejedo, Miguel. Consejo Superior de Investigaciones Científicas; EspañaFil: Duarte, Helder. Consejo Superior de Investigaciones Científicas; EspañaFil: Guiérrez Pesquera, Luis M.. Consejo Superior de Investigaciones Científicas; EspañaFil: Beltran, Juan Francisco. Universidad de Sevilla; EspañaFil: Katzenberger, Marcos. Consejo Superior de Investigaciones Científicas; EspañaFil: Marangoni, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Misiones; ArgentinaFil: Navas, Carlos Arturo. Universidade de Sao Paulo; BrasilFil: Nicieza, Alfredo G.. Universidad de Oviedo; EspañaFil: Relyea, Rick A.. University of Pittsburgh; Estados UnidosFil: Rezende, Enrico L.. Universitat Autònoma de Barcelona; EspañaFil: Richter Boix, Alex. University Uppsala; SueciaFil: Santos, Mauro. Universitat Autònoma de Barcelona; EspañaFil: Simon, Monique. Universidade de Sao Paulo; BrasilFil: Solé, Mirco. Universidade Estadual de Santa Cruz; Brasi

Rapid Growth Reduces Cold Resistance: Evidence from Latitudinal Variation in Growth Rate, Cold Resistance and Stress Proteins

Background: Physiological costs of rapid growth may contribute to the observation that organisms typically grow at submaximal rates. Although, it has been hypothesized that faster growing individuals would do worse in dealing with suboptimal temperatures, this type of cost has never been explored empirically. Furthermore, the mechanistic basis of the physiological costs of rapid growth is largely unexplored. Methodology/Principal Finding: Larvae of the damselfly Ischnura elegans from two univoltine northern and two multivoltine southern populations were reared at three temperatures and after emergence given a cold shock. Cold resistance, measured by chill coma recovery times in the adult stage, was lower in the southern populations. The faster larval growth rates in the southern populations contributed to this latitudinal pattern in cold resistance. In accordance with their assumed role in cold resistance, Hsp70 levels were lower in the southern populations, and faster growing larvae had lower Hsp70 levels. Yet, individual variation in Hsp70 levels did not explain variation in cold resistance. Conclusions/Significance: We provide evidence for a novel cost of rapid growth: reduced cold resistance. Our results indicate that the reduced cold resistance in southern populations of animals that change voltinism along the latitudinal gradient may not entirely be explained by thermal selection per se but also by the costs of time constraint-induced higher growth rates. This also illustrates that stressors imposed in the larval stage may carry over and shape fitness in the adul

Different Prey Resources Suggest Little Competition Between Non-Native Frogs and Insectivorous Birds Despite Isotopic Niche Overlap

Non-native amphibians often compete with native amphibians in their introduced range, but their competitive effects on other vertebrates are less well known. The Puerto Rican coqui frog (Eleutherodactylus coqui) has colonized the island of Hawaii, and has been hypothesized to compete with insectivorous birds and bats. To address if the coqui could compete with these vertebrates, we used stable isotope analyses to compare the trophic position and isotopic niche overlap between the coqui, three insectivorous bird species, and the Hawaiian hoary bat. Coquis shared similar trophic position to Hawaii amakihi, Japanese white-eye, and red-billed leiothrix. Coquis were about 3 ‰ less enriched in δ15N than the Hawaiian hoary bat, suggesting the bats feed at a higher trophic level than coquis. Analyses of potential diet sources between coquis and each of the three bird species indicate that there was more dietary overlap between bird species than any of the birds and the coqui. Results suggest that Acari, Amphipoda, and Blattodea made up \u3e90% of coqui diet, while Araneae made up only 2% of coqui diet, but approximately 25% of amakihi and white-eye diet. The three bird species shared similar proportions of Lepidoptera larvae, which were ~25% of their diet. Results suggest that coquis share few food resources with insectivorous birds, but occupy a similar trophic position, which could indicate weak competition. However, resource competition may not be the only way coquis impact insectivorous birds, and future research should examine whether coqui invasions are associated with changes in bird abundance

Measurement of the W mass by direct reconstruction in e+e−e^+ e^- collisions at 172 GeV

The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 10.65~pb$^{-1}$ collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 \GEV. The invariant mass distribution of simulated events are fitted to the experimental distributions and the following W masses are obtained: $WW \to q\overline{q}q\overline{q } m_W = 81.30 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to l\nu q\overline{q}(l=e,\mu) m_W = 80.54 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to \tau\nu q\overline{q} m_W = 79.56 +- 1.08(stat.) +- 0.23(syst.) GeV/C62$. The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data. The combination of these measurements gives: $m_W = 80.80 +- 0.11(syst.) +- 0.03(LEP energy) GeV/^2$