Species Sensitivity Distributions for Ecotoxicological Risk Assessment: elaboration of a shiny app to facilitate data analysis

Living organisms have different sensitivities to toxicants. This variability can be represented by constructing a species sensitivity distribution (SSD) curve, whereby the toxicity of a substance to a group of species is described by a statistical distribution. Building the SSD curve allows calculating the HC5, that is, the concentration at which 5% of the considered species are affected. The HC5 is widely used as an environmental quality criterion and a tool for ecological risk assessment. The objectives of the present work were (1) to develop a user interface using the shiny package, (2) generate a graphic as visualization to evaluate for which pesticides there is enough data for the calculation of the SSD curve, (3) allow the user to apply quality criteria to the database, (4) to estimate the HC5 for a number of pesticides from a user provided toxicological database. We present the completed work here. The first tab allows the user to upload or complete their own database that can consist of several toxicological endpoints for different pesticides. The second tab of the user interface is used for visualization of the number of species for which toxicological data is available for each pesticide in the dataset. The number of data points available at every case is important as there is a minimum sample size for building a valid SSD curve. After selecting the pesticide and animal groups, the user can filter and select subsets of data from the whole database by applying different quality criteria, (e.g., if the studies reported a chemical confirmation of the concentrations of pesticide tested). The final SSD curve is fitted to different distributions using the package fitdistrplus. The HC5 is estimated by the distribution presenting the best goodness of fit. By facilitating and streamlining species toxicity data analysis and the creation of SSD curves, the user interface proposed here should be useful for environmental managers and regulators conducting ecological risk assessments.Sociedad Argentina de Informática e Investigación Operativ

Species Sensitivity Distributions for Ecotoxicological Risk Assessment: elaboration of a shiny app to facilitate data analysis

Living organisms have different sensitivities to toxicants. This variability can be represented by constructing a species sensitivity distribution (SSD) curve, whereby the toxicity of a substance to a group of species is described by a statistical distribution. Building the SSD curve allows calculating the HC5, that is, the concentration at which 5% of the considered species are affected. The HC5 is widely used as an environmental quality criterion and a tool for ecological risk assessment. The objectives of the present work were (1) to develop a user interface using the shiny package, (2) generate a graphic as visualization to evaluate for which pesticides there is enough data for the calculation of the SSD curve, (3) allow the user to apply quality criteria to the database, (4) to estimate the HC5 for a number of pesticides from a user provided toxicological database. We present the completed work here. The first tab allows the user to upload or complete their own database that can consist of several toxicological endpoints for different pesticides. The second tab of the user interface is used for visualization of the number of species for which toxicological data is available for each pesticide in the dataset. The number of data points available at every case is important as there is a minimum sample size for building a valid SSD curve. After selecting the pesticide and animal groups, the user can filter and select subsets of data from the whole database by applying different quality criteria, (e.g., if the studies reported a chemical confirmation of the concentrations of pesticide tested). The final SSD curve is fitted to different distributions using the package fitdistrplus. The HC5 is estimated by the distribution presenting the best goodness of fit. By facilitating and streamlining species toxicity data analysis and the creation of SSD curves, the user interface proposed here should be useful for environmental managers and regulators conducting ecological risk assessments.Sociedad Argentina de Informática e Investigación Operativ

shinyssd v1.0: Species Sensitivity Distributions for Ecotoxicological Risk Assessment

Living organisms have different sensitivities to toxicants. This variability can be represented by constructing a species sensitivity distribution (SSD) curve, whereby the toxicityof a substance to a group of species is described by a statistical distribution. Buildingthe SSD curve allows calculating the Hazard Concentration 5% (HC5), that is, the concentration at which 5% of the considered species are affected. The HC5 is widely used asan environmental quality criterion and a tool for ecological risk assessment (Posthuma,Suter II, & Traas, 2001).The shinyssd web application is a versatile and easy to use tool that serves to simultaneously model the SSD curve of a user-defined toxicity dataset based on four differentstatistical distribution models (log-normal, log-logistic, Weibull, Pareto). shinyssd directly calculates three estimators HC1, HC5 and HC10 associated to the four distributionmodels together with its confidence intervals, allowing the user to select the statisticaldistribution and associated HC values that best adjust the dataset.The level of confidence of the results obtained from a SSD curve will depend on the numberof species used to produce the SSD. In this sense, the first tab of the user interface is usedfor visualizing the number of species for which toxicological data are available for eachtoxicant, species group, and endpoint combination in the uploaded dataset. A minimumof species is necessary to build a SSD curve varies according to the literature (Belangeret al., 2016; Newman et al., 2000; Plant Protection Products & Residues, 2013; Wheeler,Grist, Leung, Morritt, & Crane, 2002).After selecting the toxicant and species groups, the user can filter and select subsets ofdata from the whole database by applying different quality criteria (e.g., if the studiesreported a chemical confirmation of the concentrations of the toxicant tested). The valuesentered in each column of the database serve as categories to filter the database in relationto characteristics of the bioassays. The final SSD curve is fitted to different distributionsusing the package fitdistrplus and actuar. The HC is estimated for all the distributions.By facilitating and streamlining toxicity data analysis and the creation of SSD curves, theuser interface proposed here should be useful for environmental managers and regulatorsconducting ecological risk assessments and scientific research.Fil: D'andrea, María Florencia. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Brodeur, Celine Marie Julie. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Species Sensitivity Distributions for Ecotoxicological Risk Assessment: elaboration of a shiny app to facilitate data analysis

Living organisms have different sensitivities to toxicants. This variability can be represented by constructing a species sensitivity distribution (SSD) curve, whereby the toxicity of a substance to a group of species is described by a statistical distribution. Building the SSD curve allows calculating the HC5, that is, the concentration at which 5% of the considered species are affected. The HC5 is widely used as an environmental quality criterion and a tool for ecological risk assessment. The objectives of the present work were (1) to develop a user interface using the shiny package, (2) generate a graphic as visualization to evaluate for which pesticides there is enough data for the calculation of the SSD curve, (3) allow the user to apply quality criteria to the database, (4) to estimate the HC5 for a number of pesticides from a user provided toxicological database. We present the completed work here. The first tab allows the user to upload or complete their own database that can consist of several toxicological endpoints for different pesticides. The second tab of the user interface is used for visualization of the number of species for which toxicological data is available for each pesticide in the dataset. The number of data points available at every case is important as there is a minimum sample size for building a valid SSD curve. After selecting the pesticide and animal groups, the user can filter and select subsets of data from the whole database by applying different quality criteria, (e.g., if the studies reported a chemical confirmation of the concentrations of pesticide tested). The final SSD curve is fitted to different distributions using the package fitdistrplus. The HC5 is estimated by the distribution presenting the best goodness of fit. By facilitating and streamlining species toxicity data analysis and the creation of SSD curves, the user interface proposed here should be useful for environmental managers and regulators conducting ecological risk assessments.Sociedad Argentina de Informática e Investigación Operativ

Body condition of Pseudis minuta Günther, 1858 (Anura: Hylidae) inhabiting an agroecosystem from south Santa Fe Province, Argentina

We present the first data on the body condition of P. minuta adults in a pond associated with an agroecosystem of the south Santa Fe Province, Argentina. Fieldwork was conducted from November 2012 to December 2013. Females and males did not differ in body condition, weight, nor length. However, males from December 2013 were in better condition than males from November 2012. Similarly, females from January 2013 were in better condition than those registered in November 2012. Our report provides for the first time an observation of the species in a landscape dominated by intensive agriculture in southern Santa Fe Province, corresponding to the Pampean region. Further studies should investigate habitat conditions and resources that allow the growth and development of this population of P. minuta in order to ensure its long-term permanence in the region.Fil: Vera Candioti, Josefina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria Oliveros. Agencia de Extension Rural Venado Tuerto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: D'andrea, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; ArgentinaFil: Brodeur, Celine Marie Julie. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Acute and Subchronic Toxicity of Arsenite and Zinc to Tadpoles of Rhinella arenarum Both Alone and in Combination

The current study evaluated acute and subchronic toxicity of arsenite (As3+) and zinc (Zn2+) to stage 25 tadpoles of Rhinella arenarum in both single and joint laboratory exposures. LC50 values obtained for As3+ were elevated and remained within the range of 46 to 50 mg/L of As3+ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+) and zinc (Zn2+) to stage 25 tadpoles of Rhinella arenarum in both single and joint laboratory exposures. LC50 values obtained for As3+ were elevated and remained within the range of 46 to 50 mg/L of As3+ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.in both single and joint laboratory exposures. LC50 values obtained for As3+ were elevated and remained within the range of 46 to 50 mg/L of As3+ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+ were elevated and remained within the range of 46 to 50 mg/L of As3+ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1?2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.2+ serves to antagonize growth effects in this range of concentrations.Fil: Brodeur, Celine Marie Julie. Fundación Pro Salud y Medio Ambiente. Instituto de Ciencias Ambientales y Salud; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Asorey, Cynthia Melina. Fundación Pro Salud y Medio Ambiente. Instituto de Ciencias Ambientales y Salud; ArgentinaFil: Sztrum, Abelardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Pro Salud y Medio Ambiente. Instituto de Ciencias Ambientales y Salud; ArgentinaFil: Herkovits, Jorge. Fundación Pro Salud y Medio Ambiente. Instituto de Ciencias Ambientales y Salud; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

South American Cowbirds as Avian Models for Environmental Toxicity Testing

In environmental toxicity testing, the use of native species is normally recommended as it provides greater environmental realism and insures a more conservative end point for protecting ecosystems. Although pesticide products are vastly used in South American agriculture, no test protocols or guidelines exist for testing effects on native or indigenous bird species.  Instead, recommended testspecies and guidelines are essentially the ones developed for Europe and North America.  At the same time, avian pesticide regulatory assessment in South America does not require testing on passerine species although Passeriformes are normally more sensitive than other groups of birds and represent approximately 60% of all living species of bird.  The aim of this chapter is to propose South American cowbirds as candidate passerine avian models for environmental toxicity testing in South American countries.  Three species of cowbirds are widely distributed in South America and can be considered potential avian model for environmental toxicity testing: the shiny cowbird (Molothrus Bonariensis), the screaming cowbird (Molothrus rufoaxillaris) and the bay winged cowbird (Ageloides badius).  This chapters briefly reviews and compares avian environmental toxicity testing in South America and the rest of the world, and describes requirements for maintaining cowbirds in captivity and using them in toxicity testing.Fil: Brodeur, Celine Marie Julie. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Poliserpi, Maria Belen. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentin

Toxicity and effects on anuran tadpole metamorphosis of the anthranilic diamide insecticides chlorantraniliprole and cyantraniliprole

The present study examined the acute and chronic toxicity attributed to commercial formulations of the anthranilic diamide insecticides chlorantraniliprole (CHLO) and cyantraniliprole (CYAN) on the neotropical amphibian species Rhinella arenarum, Rhinella fernandezae and Scinax granulatus. The median lethal concentrations obtained after 96 hr exposure (96 hr-LC50) were generally greater than 100 mg/L, except for stage 25 S. Granulatus, which were the most sensitive animals tested with a 96 hr-LC50 value of 46.78 mg/L. In subchronic exposures of R. arenarum, the 21day-LC50 were 151.4 mg/L for CHLO and >160 mg/L for CYAN, the weight gain of the tadpoles during this period not being markedly affected in both cases. Finally, when tadpoles of R. arenarum were exposed to CHLO throughout the metamorphic process, an inverted U-shaped non-monotonic dose-response relationship was observed between exposure concentrations and both % of individuals transiting between stage 39 and 42 and the time required to accomplish this. Data obtained raise the hypothesis of an effect of CHLO on the hypothalamic-pituitary-thyroid (HPT) axis, either directly or through an interaction with the stress-hormone system, as metamorphic progression from stage 39 to S42 occurs under the strict control of thyroid hormones. These observations are important as the anthranilic diamide insecticides are not currently known as endocrine disruptors. Further investigations are needed to clarify the pathways leading to these effects and examine whether environmentally-relevant aquatic concentrations of anthranilic diamides might be impacting amphibian populations in the wild.Fil: Fonseca Peña, Shirley Vivian Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales; ArgentinaFil: Brodeur, Celine Marie Julie. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales; Argentin

Effects of the neonicotinoid insecticides thiamethoxam and imidacloprid on metamorphosis of the toad Rhinella arenarum at environmentally-relevant concentrations

The goal of the present study was to examine the effects of environmentally relevant concentrations of the neonicotinoid insecticides thiamethoxam and imidacloprid on the metamorphosis of the toad Rhinella arenarum. Tadpoles were exposed from stage 27 until completion of metamorphosis to concentrations of thiamethoxam ranging between 1.05 and 1050 µg/L and concentrations of imidacloprid varying between 3.4 and 3400 µg/L. The two neonicotinoids were found to act differently at the range of concentrations tested. Thiamethoxam did not markedly alter the final % tadpoles completing metamorphosis but extended by 6–20 days the time needed for tadpoles to complete metamorphosis. The extra number of days required to reach metamorphosis was concentration-dependent between 1.05 and 100.5 µg/L, and then stable at 20 days between 100.5 and 1005 µg/L. In contrast, imidacloprid did not significantly interfere with the overall time needed to complete metamorphosis but decreased success of metamorphosis at 3400 µg/L, the highest concentration tested. Both neonicotinoid concentrations did not markedly alter body size and weight of the newly metamorphosed toads. With a lowest observed effect concentration (LOEC) of 1.05 µg/L, thiamethoxam may be more likely to impact tadpole development in the wild compared to imidacloprid, which was without any apparent effect at concentrations up to 340 µg/L (no-observed effect concentration or NOEC). As the influence of thiamethoxam was triggered after tadpoles had reached Stage 39, when metamorphosis is strictly dependent upon thyroid hormones, this observed effect is attributed to result from actions of this neonicotinoid insecticide on the hypothalamic-pituitary-thyroid axis.Fil: Brodeur, Celine Marie Julie. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; ArgentinaFil: Fonseca Peña, Shirley Vivian Daniela. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Proliferation of myogenic progenitor cells following feeding in the sub-Antarctic notothenioid fish <i>Harpagifer bispinis</i>

Feeding metabolism and the activation of myogenic progenitor cells were investigated in the fast myotomal muscle of the sub-Antarctic fish Hapagifer bispinis acclimatized to either simulated summer (10degreesC; 18h:6h light:dark) or simulated winter (5degreesC; 6h:18h light:dark) conditions. Ingestion of a single meal equivalent to 10% and 15% of body mass in simulated winter and summer groups, respectively, resulted in an average 2.6-fold and 3.6-fold increase in oxygen consumption, declining to 75% of peak values after 63 h and 46 h. In fasted individuals, the number of myogenic progenitor cells, identified by the expression of c-met, was not significantly different between simulated summer and winter fish, representing 6.6% and 5.8% of total myonuclei, respectively. However, the number of cells expressing myogenin was higher whereas the expression of MyoD was lower in winter than in summer groups. The ingestion of a single meal under winter and summer treatment regimes resulted in a significant increase in the number of cells expressing MyoD (51% and 111%) and PCNA (88% and 140%, respectively). This was followed by an increase in the abundance of c-met (74 and 85%) and myogenin (42 and 97%, respectively) positive cells, indicating the production of new myogenic progenitor cells and the commitment to differentiation of a number of them. These results show that the proliferation of myogenic progenitor cells can be induced by feeding in teleost fishes and that temperature and photoperiod influence the expression of myogenic regulatory factors.</p