L’écotoxicité de nanoparticules de dioxyde de cérium (CeO2 NP) en milieu dulçaquicole a été évaluée à l’aide (i) d’essais monospécifiques standardisés et (ii) de chaînes trophiques expérimentales exposées en microcosme. Aucune toxicité n’a été observée chez Nitzschia palea et Chironomus riparius en conditions monopsécifiques. Une inhibition de croissance a été observée chez les amphibiens Xenopus laevis et Pleurodeles waltl., ainsi qu’une toxicité aiguë chez le xénope et une génotoxicité dose-dépendante chez le pleurodèle. Les expositions en microcosme ont mis en évidence une toxicité aiguë chez le pleurodèle, des modifications des communautés bactériennes, une diminution de la décomposition de la litière, ainsi que des effets tératogènes chez le chironome. Les effets observés varient suivant la nature des CeO2 NP étudiées. L’utilisation d’un système biologique complexe permet l’étude des mécanismes de toxicité dans des conditions plus représentatives des conditions environnementales. / The ecotoxicity of cerium dioxide nanoparticles (CeO2 NPs) was studied on freshwater organisms (i) in standardized monospecific conditions and (ii) on experimental trophic chains exposed in microcosms. No toxicity was observed on Nitzschia palea and Chironomus riparius in monospecific conditions. Growth inhibition was observed on the amphibian species Xenopus laevis and Pleurodeles waltl., as well as acute toxicity and dose-dependent genotoxicity observed on Xenopus and Pleurodeles, respectively. Microcosm experiments revealed acute effects on Pleurodeles, changes in bacterial communities, a decrease in leaf litter decomposition and teratogenicity on chironomids. The observed effects vary depending on the type of CeO2 NPs. The use of complex biological system enables the study of toxicity mechanisms in environmentally relevant conditions.

The anuran Xenopus tropicalis tadpole is an attractive model animal in toxicological evaluation of suspected thyroid disrupting xenobiotics. Due to its reliance of a functioning hypothalamic-pituitary-thyroid (HPT) axis for normal metamorphosis, effects on the HPT axis produces apical endpoints, which are easy to measure. More sensitive endpoints of mRNA expression and histological evaluation of the thyroid gland itself provide strong indications of in vivo thyroid endocrine disruption. X. tropicalis is traditionally exposed in groups of 20 animals in four replicates for each treatment group. However, exposing tadpoles individually can provide stronger statistics and a reduction of total animal sacrifice. In this study we have developed and optimized an individual exposure system by a method development study. This method was then applied in an exposure experiment of a suspected thyroid endocrine disruptor, propylparaben (PrP). Prometamorphotic (NF stage 51) X. tropicalis tadpoles were distributed in three treatment groups (0.05, 0.5 and 5.0 mg PrP/L water) and maintained semi-statically for 14 days. Afterwards, apical measurements (body weight (BW), total body length (BL), snout to vent length (SVL) and hind limb length (HLL)) and reached developmental stage were assessed. In addition, mRNA expression of HPT axis relevant genes encoding deiodinase 2 (D2, hepatic tissue), deiodinase 3 (D3, hepatic and tail tissue) and transthyretin (Ttr, hepatic tissue) were measured by quantitative reverse transcription PCR (qRT-PCR). The PrP exposure did not affect general growth and development, but it did cause a downregulation of dio3 and ttr. The downregulation of dio3 could possibly be associated with a reduced serum content of thyroid hormone, while ttr might be connected to a previously described xenoestrogenic effect of PrP in vitro and in fish.

<p>Threats from man-made radionuclides include waste issues, increasing number of power plants, underground bomb testing, nuclear weapons, and “dirty bombs”. Until recently the ionizing radiation protection system focused on protecting humans with an implied protection of biota. However, goals of sustainable development and precautionary principles for human activity are leading to an inclusion of plant and animal populations in the protection system.</p><p>From this perspective, the present thesis examines wetlands that function as sinks for the radionuclide 137Cs, and describes calculated and measured radiation doses to residing biota. Also, multi-level effects from exposure to low-dose rate ionizing radiation were studied. Accumulation of 137Cs after the Chernobyl accident fallout was studied in a riparian wetland with a mean activity concentration of 1 200 kBq m-2 in Sweden (paper I). A mass balance budget of 137Cs showed that the sedimentation of new material was balanced by the decay process of 137Cs in parts of the wetland (paper I).</p><p>Frogs were identified as organisms of concern in this wetland. Internal radiation doses, based on whole body measurements of frogs, were estimated to be lower than external doses based on soil samples (paper II). Current dose models for biota resulted in a wide range of doses depending on different levels of conservatism in the models. Therefore, in situ measurements with frog-phantoms were found to provide valuable dose information (paper III). Measured doses using frog-phantoms were lower than calculated doses using several dose models. Although a dose conversion factor by FASSET was found to be useful for comparison with measurements in the field. A higher dose was measured to the phantom surface in comparison to inner parts, i.e. the sensitive skin of frogs receives the highest dose. Estimated and measured radiation doses to frogs were below suggested dose rate limits.</p><p>Low-dose rate 137Cs exposure of eggs and tadpoles from three amphibian species, Scaphiopus holbrookii, Bufo terrestris, and Rana catesbeiana, showed no increased levels of strand breaks in red blood cells, and no effects on development, survival or growth up to metamorphosis (paper IV). The ecological factor larval density had a stronger effect on metamorphic traits than low-dose rate radiation. Higher levels of strand breaks were detected after an acute dose in R. catesbeiana than after a chronic dose supporting a dose rate limit for protection of amphibians rather than a dose limit (paper IV).</p><p>Based on current knowledge, frogs in the contaminated wetland are probably not exposed to radiation doses from 137Cs that are harmful for the population. However, variations in sensitivity between populations and species, and adaptive responses have been shown for amphibians exposed to other stressors. This supports further research on effects of chronic low-dose rates of ionizing radiation on amphibians.</p>

Amphibian populations are declining on a global scale and although disease outbreaks are a commonly accepted hypothesis they are not the only one. My aims for my thesis were to study the home range of Leiopelma hamiltoni, to determine whether a photographic database could be used to individual identified them and monitor the health status of the population. Habitat loss is a possible cause. For this reason monitoring an animals' home range is a possible method to detect early impacts the population is facing. By tracking 12 L. hamiltoni within a 12 m x 6 m grid on Maud Island, it was shown that the home range size can vary from 0.5 m2 to 25 m2 based on the minimum convex polygon method. However, to track multiple individuals it is important to be able to distinguish among frogs. The commonly used methods of identification, such as toe clipping, pose potentially detrimental effects. Therefore, non-invasive methods based on natural markings need to be established. Through the use of the dark pigmented patterns found on the skin of L. hamiltoni individuals can be identified on recapture with a mean accuracy of 93%. By developing a database to maintain the photographs used for individual identification, the database can also be used to monitor the status of the population. During 2003 numerous L. hamiltoni were observed with denuded patches predominantly on the facial region. By monitoring five individuals within the captive facility at the University of Canterbury it was discovered that frogs appear to be able to cure themselves. Through researching the home range requirements and developing a photographic database to monitor the population status of L. hamiltoni, it will aid in the management of ensuring the long-term survival of this archaic species of frog.

Humans are modifying the global landscape at an unprecedented scale and pace. As a result, species are declining and going extinct at an alarming rate. Here, I investigate two main aspects of species’ declines: what factors are contributing to their declines and how effective our conservation efforts have been. I assessed one of the main mechanisms for protecting species by looking at the Endangered Species Act (ESA) in the United States. I examined three separate indicators of species declines for different groups of species: range contractions in Canadian imperilled species, declines in abundance in global amphibian populations and increases in temporal variability in abundance in North American breeding birds. I found that change in recovery status of ESA listed species was only very weakly related to the number of years listed, number of years with a recovery plan, and funding. These tools combined explained very little of the variation in recovery status among species. Either these tools are not very effective in promoting species’ recovery, or species recovery data are so poor that it is impossible to tell whether the tools are effective or not. I examined patterns of species’ declines in three different groups in relation to a number of anthropogenic variables. I found high losses of Canadian imperiled bird, mammal, amphibian and reptile species in regions with high proportions of agricultural land cover. However, losses of imperiled species are significantly more strongly related to the proportion of the region treated with agricultural pesticides. This is consistent with the hypothesis that agricultural pesticide use, or something strongly collinear with it (perhaps intensive agriculture more generally), has contributed significantly to the decline of imperiled species in Canada. Global increases in UV radiation do not appear to be a major cause of amphibian population declines. At individual sites, temporal changes in amphibian abundance are not predictably related to changes in UV intensity. Variability in species’ abundance of North American breeding birds, after accounting for mean abundance, is not systematically higher in areas of high human-dominated land cover or climate change. Rather, it appears that areas with a high proportion of human-dominated cover come to have a higher proportion of highly abundant, and thus more variable, species.

Doctor of Philosophy / Division of Biology / Walter K. Dodds / Tallgrass prairie evolved with fire-grazer interactions. Fire and grazing are vital processes for maintaining grasslands and cattle production, and therefore will be continued as land management schemes. The effects of fire and grazers on prairie streams are understudied, but may significantly influence stream ecology. This dissertation examined how prescribed burning, bison grazing, and patch-burn grazing (by cattle) influence water quality, stream biota, and riparian amphibians and reptiles at Konza Prairie, Kansas, or Osage Prairie, Missouri. Using Global Positioning System, we monitored bison and cattle distribution throughout watersheds. The immediate effects of prescribed burning were examined at both Konza and Osage Prairies. The impacts of bison on water quality were determined by using a long-term dataset from Konza Prairie and compared watersheds with and without bison. Amphibian and reptile assemblages were monitored for two years at Osage, and assemblage data were analyzed using redundancy analysis, permuted analysis of variance, and occupancy modeling. A patch-burn grazing experiment occurred for 5 years at Osage (2 years pretreatment data and 3 years of treatments) and was analyzed using a before-after, control-impact design. Prescribed burning had minimal effects on water chemistry. At Konza Prairie, bison did not alter water quality likely because they spent negligible time (<5%) in streams. Contrarily, cattle at Osage Prairie significantly increased stream concentrations of total suspended solids, nutrients, Escherichia coli bacteria, algal biomass, and primary production. Unlike bison, cattle spent significant time (~21%) in streams if allowed access to riparian zones. In watersheds with cattle excluded from streams by riparian fencing, water quality contaminant concentrations increased significantly, but not to the magnitude of unfenced streams. Amphibian abundance and richness were not different among patch types; instead, they were restricted to specific basins. However, reptiles displayed preference for certain patch-types, and had the highest abundance and richness in watersheds with fire and grazing. These results have implications for natural resource management. Riparian fencing of cattle may be a useful practice in areas where water resource protection is the priority. However, overland flow may alter water quality in watersheds with grazers despite fencing. Land managers will need to define management objectives and accept trade-offs in water quality, amphibian and reptile habitat, and cattle production.

The pyrrolidine and piperidine ring systems are present in a variety of different classes of amphibian alkaloids. We have found the iridium catalyzed N-heterocylization reaction of diols with amines to be very useful for the construction of novel pyrrolidine, piperidine and piperazine derivatives. The scope and utility of the iridium catalyzed N-heterocyclization reaction for the construction of novel anuran scaffolds using amino diols and triols are presented. Studies directed towards the total synthesis of 4,6-disubstituted quinolizidine and (±)-epiquinamide are discussed. The second study is focused on the selective conversion of terminal dienes to primary diols. This conversion has always had problems with regioselectivity and low yields due to polymer formation with carbon chains having more than 7 carbon atoms. An improvement in the yield and regioselectivity was observed with disiamylborane prepared in situ using 2-methyl-2-butene and BH3•DMS. The scope of this method with 7, 8 and 9 carbon chains and different alcohol protecting groups for synthesis of triols is presented.

A exibição do comportamento vocal em muitas espécies de anfíbios anuros é relacionada aos níveis de hormônios esteroides gonadais e interrenais. Esses hormônios poderiam mediar a relação entre intensidade de sinais e imunidade, pois estão envolvidos no desenvolvimento das características sexuais secundárias, comportamento de corte e mobilização de reservas energéticas durante a atividade reprodutiva, enquanto apresentam também efeitos imunomoduladores. Nesse sentido, o objetivo deste trabalho foi explorar as relações entre comportamento reprodutivo, imunidade e níveis plasmáticos de testosterona e corticosterona em machos do sapo do semiárido brasileiro, Rhinella granulosa, em atividade reprodutiva e após manipulação hormonal. A precipitação foi o principal determinante ambiental para o aumento dos níveis de testosterona e corticosterona circulantes em machos de R. granulosa, estimulando o comportamento de vocalização. As relações fisiológicas encontradas indicam que os altos níveis plasmáticos de testosterona nos primeiros dias após a chuva devem promover o início do turno vocal, porém a corticosterona deve modular o esforço de vocalização. De forma geral, a exacerbação do comportamento vocal de R. granulosa tem efeitos negativos sobre a imunocompetência, porém alguns indivíduos que apresentam maiores concentrações plasmáticas de corticosterona apresentam concomitantemente alto esforço vocal e alta imunidade. De acordo, a aplicação transdérmica de corticosterona promoveu elevação aguda dos níveis plasmáticos deste glicocorticoide, bem como um aumento da função imune. Assim, apesar de a atenção principal ser comumente colocada no papel da testosterona na mediação de sinais honestos, nossos resultados corroboram a importância da corticosterona na mediação da expressão do comportamento de corte e imunocompetência em machos R. granulosa / In most anuran species, vocal behavior is usually related to plasmatic levels of gonadal and interrenal steroid hormones. These hormones could mediate the relationship between signal intensity and immunocompetence, since they are involved in the development of sexual traits, courtship behavior and energetic mobilization during reproductive activity and also exert immunomodulatory effects. The aim of this study was to explore relations among vocal behavior, immunity and plasmatic levels of testosterone and corticosterone in males of a toad species from Brazilian semi-arid, Rhinella granulosa, during reproductive activity and after hormonal manipulation. Precipitation was the main environmental determinant to increase circulating levels of testosterone and corticosterone in R. granulosa males, stimulating vocal behavior. Physiological relations indicate that high circulating testosterone levels in the days right after rain may promote the initiation of vocal behavior, while corticosterone may modulate vocal effort. In general, exacerbation of vocal behavior in R. granulosa has negative effects on immunocompetence, however, some individuals with higher plasmatic levels of corticosterone can present both high vocal effort and good immunocompetence. Corroborating this interpretation, acute increase in glucocorticoid plasmatic levels after hormonal manipulation was accompanied by raised immune function. Despite the emphasis on androgens influence on sexual selected male traits, our results corroborate greater influence of corticosterone in the mediation of expression of courtship behavior and immunocompetence in R. granulosa

Diversos aspectos metabólicos e comportamentais possuem uma estreita relação com as condições do ambiente, havendo um compromisso entre as condições naturais e a dinâmica de modificações sobre os organismos. Devido ao grande índice de degradação ambiental proveniente da atividade humana nos últimos tempos, populações de anfíbios têm sido particularmente mais afetadas devido a sua alta sensibilidade a alterações ambientais. Em uma paisagem fragmentada, a manutenção de metapopulações viáveis é um importante fator a persistência das populações. Dentro deste contexto, este estudo propõe investigar as relações entre a fragmentação florestal e habilidade das algumas espécies de anuros para se deslocar entre os fragmentos, ou entre estes e corpos d\'água. Assim, realizamos comparações, fisiológicas e comportamentais intra e interespecífica de espécies de anuros residentes em paisagens contínuas e fragmentadas em duas localidades da Floresta Atlântica, com base em suas características morfológicas. De acordo com nossos resultados, as diferenças ambientais entre as paisagens estão relacionadas com as diferenças morfofisiológicas entre as espécies. / In the last few decades, human activity has changed environmental condition, resulting in amphibian populations decline all around the world. In this study we analyze the relationships between forest fragmentation and the ability of some frog species to move between forest fragments or between fragments and breeding sites. Our study focus relies on anuran locomotor performance and supporting physiology, and the relationship between these traits and resistance to forest fragmentation. We compare morphological, physiological and behavioral traits between populations of anurans species living in different landscapes (continuous or fragmented) of two sites in the Atlantic Forest. According to our data, differences in environmental conditions of landscape are related to morpho-physiological traits. This relationship, however, depends on the site of the Atlantic Forest and also varies between species.

De acordo com o modelo de seleção intersexual mediado por parasitas, variações nas condições de ornamentos ou taxa de displays sexuais refletem diferentes graus de resistência ao parasitismo. Em coros naturais de anfíbios, vocalizações mais altas, longas e complexas e/ou emitidas a maiores taxas são, provavelmente, mais facilmente detectadas e atraem mais fêmeas. Entretanto, o esforço vocal está positivamente relacionado aos níveis plasmáticos de esteróides potencialmente imunossupressores, tais como testosterona e corticosterona. O objetivo deste trabalho foi avaliar as relações entre taxa de vocalização, imunocompetência e níveis plasmáticos de corticosterona em Hypsiboas albopunctatus, um anuro de médio porte que ocorre na América do Sul. Tais relações foram estudadas a partir de observação focal do comportamento vocal em coro natural, seguido de coleta de sangue para dosagem de corticosterona e avaliação de alguns parâmetros imunitários. O presente estudo demonstrou uma relação positiva entre a taxa de vocalização com níveis plasmáticos de corticosterona e negativa entre estes dois parâmetros com a imunocompetência mediada por células. Estes resultados apontam para a corticosterona como possível hormônio mediador do compromisso entre esforço vocal e imunidade mediada por células em anuros. / According to the model of intersexual selection mediated by parasites, changes in conditions of sexual ornaments or display rates reflect different degrees of resistance to parasitism. In natural choruses of amphibians, calls that are higher, longer, more complex and / or issued at higher rates are probably more easily detected and attract more females. However, the vocal effort is positively related to plasma levels of potentially immunosuppressive steroids, such as testosterone and corticosterone. The aim of this study was to evaluate the relationship between calling rates, immunocompetence and plasma levels of corticosterone in Hypsiboas albopunctatus, a midsize anuran occurring in South America. Such relationships were studied from focal observations of calling behavior, followed by blood collection for measurements of corticosterone plasma levels and evaluation of some immune parameters. The present study showed a positive relationship between the calling rate with plasma levels of corticosterone, and a negative correlation between these two parameters with cell-mediated immunocompetence. These results highlight the importance of the hormone corticosterone as a possible mediator of trade-off between vocal effort and cell-mediated immunity in anurans.