Unmittelbare, dauerhafte sowie evolutionäre Anpassung an Fremdstoffexpositionen

Eine der Hauptursachen für unerwünschte oder reduzierte Wirkungen von Medikamenten ist die Induktion von Enzymen und Transportern des Medikamentenstoffwechsels. Diese Induktion stellt ursprünglich eine physiologische Reaktion auf die Aufnahme von potentiell schädlichen Fremdstoffen aus der Umwelt dar und sichert so die Gesundheit und Fortpflanzungsfähigkeit von Lebewesen. Beim Menschen sowie anderen Säugetieren werden Fremdstoffe hauptsächlich von den nukleären Rezeptoren PXR und CAR in der Leber und im Dünndarm detektiert. Zu den Medikamenten, welche über PXR und CAR wirken, gehören unter anderem Antikonvulsiva, Statine, antiretrovirale Medikamente, Glucocorticoide sowie Antimykotika. Die durch Fremdstoffe aktivierten Transkriptionsfaktoren PXR und CAR steigern die Menge der Enzyme und Transporter des Fremdstoffmetabolismus. Hierzu zählen vor allem die Cytochrom P450-Enzyme (Cyp-Enzyme) mit breitem Substratspektrum oder der Transporter MDR1, welcher eine Vielzahl von Substraten über Membranen transportiert. Durch die Biotransformation werden die induzierenden, lipophilen Substanzen so modifiziert, dass sie leichter über den Urin oder die Galle ausgeschieden werden können. \r\nDie Dauer der Induktion sollte auf die Zeit der Fremdstoffexposition beschränkt sein, um Störungen des endogenen Stoffwechsels zu vermindern. In dieser Arbeit werden jedoch Hinweise auf dauerhafte und sogar generationsübergreifende Effekte von Medikamenten in Mäusen geliefert. Nachkommen von Müttern, welche bereits vor ihrer Verpaarung einmalig mit TCPOBOP, einem Liganden des murinen CAR, injiziert wurden, hatten eine ungefähr 100-fach gesteigerte Genexpression von Cyp2b10. Auch gab es Expressionsänderungen von Genen, deren Produkte eine Rolle im Lipidstoffwechsel sowie bei Immunkrankheiten spielen. Eine Hochdurchsatz-RNA-Sequenzierung der injizierten Elterngeneration ergab außerdem dauerhafte Expressionsveränderungen anderer Gene des Medikamentenstoffwechsels sowie von Genen mit Verbindung zum Energiemetabolismus. \r\nBerücksichtigt man die enge evolutionäre Verwandtschaft der nukleären Rezeptoren CAR und PXR, sind Langzeitveränderungen auch für PXR möglich und wurden im Verlauf dieser Arbeit ebenfalls untersucht. Eine Hochdurchsatz-Sequenzierung ergab für Mäuse, welche mit dem PXR-Aktivator PCN induziert wurden, dass selbst noch drei Monate nach der Exposition Gene verändert exprimiert waren, welche im Zusammenhang mit Lebernekrosen stehen. Bei Nachkommen von PCN-injizierten Müttern wurden Gene unterschiedlich exprimiert, welche eine Rolle bei der Energiehomöostase sowie im Glukosestoffwechsel spielen. Im Erwachsenenalter sind bei diesen Nachkommen darüber hinaus noch Gene unterschiedlich exprimiert, deren Produkte eine Funktion in der Immunantwort haben. \r\nDa Erwachsene aufgrund ihrer Lebensdauer sowie der absoluten Krankheitshäufigkeit wesentlich öfter Kontakt mit Fremdstoffen haben, war medizinisch von besonderem Interesse, ob anhaltende Genexpressionsänderungen auch bei Erwachsenen zu beobachten sind. So konnte im Rahmen dieser Arbeit gezeigt werden, dass auch einmalig exponierte Adulttiere Gene dauerhaft verändert exprimieren und die Veränderungen im Medikamentenstoffwechsel an die nächste Generation übertrugen. \r\n\r\nBisher sind klinische Studien zur Risikobewertung von Medikamenten (Pharmakovigilanz) nicht generationsübergreifend angelegt. Diese Arbeit gibt Anstöße dafür, dass dies in Zukunft für viel mehr Medikamente notwendig werden könnte. Neben Veränderungen im Medikamentenstoffwechsel ergeben sich Nebenwirkungen von PXR- und CAR-Liganden vor allem aus ihrer Beteiligung an endogenen Stoffwechselwegen. Nach Aktivierung von CAR, welcher viele metabolische Stoffwechselwege steuert, treten beispielsweise Störungen des Energiestoffwechsels auf. Ein tieferes Verständnis der Rezeptoraktivität von CAR samt einer gezielten Modulierung seiner Aktivität würde wichtige Beiträge zum Verständnis der Regulation des Fremdstoffmetabolismus sowie der Entstehung von Nebenwirkungen durch eine Behandlung mit CAR-Liganden leisten. Dauerhafte Veränderungen endogener Stoffwechselwege könnten dann möglicherweise über eine pharmakologische Modulierung der CAR-Aktivität reduziert werden. \r\nZu diesem Zweck wurden im Verlauf dieser Arbeit die CAR-Rezeptoren der Amphibien (Xenopus tropicalis, Xenopus laevis) und Reptilien (Anolis carolinensis) erstmals kloniert, als Proteine exprimiert und charakterisiert. Vergleiche zwischen Tierarten ermöglichen ein besseres Verständnis von humanen Proteinen. Funktionelle Analysen ergaben Ähnlichkeiten des Xenopus laevis-CAR mit dem PXR der Säugetiere: eine niedrige basale Aktivität sowie eine starke Induzierbarkeit durch Liganden. In weiteren funktionellen Analysen wurden die Determinanten der basalen Aktivität des Xenopus laevis-CAR untersucht. Die basale Aktivität war nicht abhängig von der subzellulären Lokalisation, sondern ergab sich aus der Proteinstruktur, welche nur beim CAR der Landvertebraten in einer aktiven Konformation fixiert ist. Ähnlich dem PXR der Säugetiere besitzt CAR der Amphibien eine Aktivierungsdomäne, welche erst durch Ligandenbindung in eine aktive Konformation gebracht wird. Mutationen einzelner Aminosäuren zum jeweils humanen Homolog erhöhten die basale Aktivität des Xenopus laevis-CAR auf die des humanen Rezeptors. Diese Mutanten mit erhöhter basalen Aktivität zeigten eine verstärkte Interaktion mit dem Kofaktor PGC-1a, einem Regulator des Energiestoffwechsels bei Säugetieren. Die hepatischen Zielgene des CAR der Amphibien überlappen zum Teil mit den humanen Zielgenen und spielen ebenfalls eine Rolle im Energiestoffwechsel.

Variation in body size and sexual dimorphism across geographical and environmental space in the frogs Limnodynastes tasmaniensis and L. peronii

This study aimed to identify potential factors responsible for geographically structured morphological variation within the widespread Australian frogs Limnodynastes tasmaniensis Gunther and L. peronii Dumeril & Bibron. There was support for James's rule, and both latitude and present climate explained large amounts of the variation in body size and shape (particularly in L. peronii). There was also some support for the influence of several biogeographical barriers. Finally, both species were sexually dimorphic for body size and the degree of sexual size dimorphism (SSD) varied geographically. Climate was an important explanation for SSD variation in L. peronii, while latitude was most important for L. tasmaniensis. Geographical variations in sexual selection via male-male physical competition and climate-related resources are suggested as potential explanations for SSD variation in L. peronii. (C) 2004 The Linnean Society of London.

Experience overrides colour in lizard contests

We examined the role of conspicuous coloration in male-male contests for two species of Australian dragon lizards, Ctenophortis decresii and C. vadnappa, in which conspicuous coloration has a demonstrated predation cost. We conducted contests in which the overall conspicuousness of male coloration was manipulated using paints that matched the spectral reflectance of the lizards, as well as natural (control) contests. There was little evidence for an influence of colour on contest outcome or aggression levels for either species when all experiments were considered. However, we found a significant effect of trial order and experience on contest outcome and aggression levels (the same pair of males was used for both types of contest), despite a 2-3 week interval between contests. When we examined only the first trial between unfamiliar males, we found that male C. vadnappa that had been painted to appear more conspicuous consistently won. Comparison with the natural trials suggests that the aspect of colour manipulation that was responsible for this result was the 'hue' of the throat: males with yellower throats consistently beat males with bluer throats in both natural and painted trials. The difference in coloration of flank markings also predicted the difference in aggression scores between contestants in the natural trials. These results suggest that although colour is important in opponent assessment and in determining contest outcome in C vadnappa, previous agonistic experience can override the effects of colour and have a long-lasting influence on aggressive behaviour.

Ecology of frontier populations of the invasive grey squirrel (Sciurus carolinensis) in Ireland

The rise in invasive species, together with habitat destruction, is associated with worldwide declines in biodiversity and ecosystem functioning. Management of invasive species, as well as amelioration of invasion impacts, provide challenges to species and ecosystem ecologists and conservation managers. Although any species can become invasive if it is transported to, establishes in and spreads in a new environment outside of its native range, rodents are a particularly frequent invader. Rodent introductions are often inadvertent but are also commonly intentional as these animals are traded and transported as pets and may escape from captivity. Tree squirrel species are attractive to humans and are able to establish populations with only a few founding individuals, making them a group well suited to performing the role of biological invaders. The eastern grey squirrel (Sciurus carolinensis) is the most commonly introduced squirrel species worldwide. This research addressed the grey squirrel invasion and frontier population biology. Novel results were generated through diverse research techniques. Public sighting surveys and hairtube surveys were used to locate the southern frontier of grey squirrel range expansion in Ireland. A 22-month intensive live trapping study of two frontier populations facilitated the collection of personality and demographic data from squirrels in increasing populations. A systematic literature search on grey squirrel demography provided context for the studied populations, among frontier and established introduced populations, as well as those in the native range. Advanced spatially explicit population modeling techniques predicted future range expansion and objectively compared the outcomes of 12 grey squirrel management strategies. The methods and results are discussed in both a basic scientific and applied invasion management context. An improved understanding of the behaviour, population dynamics, and future scenarios at the frontier of species invasions is crucial for managers worldwide and this is provided here for the grey squirrel in Ireland.

Habitat associations of the red squirrel Sciurus vulgaris and grey squirrel S-carolinensis in Northern Ireland

A survey of red and grey squirrel habitat associations in Northern Ireland was conducted between September 1994 and August 1995. Two hundred and sixty-one sites were visited and a list of habitat characteristics for each site was noted. Multiple discriminant function analysis of the habitat type was employed to group squirrel occurrence, while contingency analysis examined independence of habitat type and squirrel species presence. Habitat associations differed between the two species. One-way ANOVAs of habitat data suggested that sites occupied by red squirrels only were predominantly coniferous, at higher altitude and latitude and much larger in area than sites occupied by grey squirrels only, which were mostly deciduous. When both species were sympatric, sites were more likely to be coniferous and larger in area than sites occupied by either species. Grey squirrels were less frequent than expected in upland plantations and more frequent than expected in parkland and gardens; the opposite was true for red squirrels. The mean distance between sites with only red squirrels and the nearest site with grey squirrels was greater than the mean distance between sites with only grey squirrels and the nearest site with red squirrels. An approach to conserving the red squirrel in view of the continued expansion in the grey squirrel's distribution in Ireland is discussed.

Distribution and status of the Red Squirrel (Sciurus vulgaris) and Grey Squirrel (Sciurus carolinensis) in Ireland

The distributions of the Red and Grey Squirrel were surveyed in Northern Ireland and the Republic of Ireland between 1994 and 1996. Survey methods differed between the two studies. In the former, all suitable habitat, of at least 15 ha, was inspected for species presence or absence. In the Republic, data were gathered through questionnaires to governmental and independent wildlife bodies. The combined results indicate that the Red Squirrel remains widespread and locally abundant, and is present in all but two counties. The Grey Squirrel is now more widespread than ever before, and can be found in 22 of the 32 counties. Its range expansion has varied from 0 km/yr to an estimated 13.4 km/yr, as various geographical features, principally rivers, have hindered its progress in certain directions.

Effects of Parasitism and Morphology on Squirrelpox Virus Seroprevalence in Grey Squirrels (Sciurus carolinensis)

Invasive species have been cited as major causes of population extinctions in several animal and plant classes worldwide. The North American grey squirrel (Sciurus carolinensis) has a major detrimental effect on native red squirrel (Sciurus vulgaris) populations across Britain and Ireland, in part because it can be a reservoir host for the deadly squirrelpox virus (SQPV). Whilst various researchers have investigated the epizootiology of SQPV disease in grey squirrels and have modelled the consequent effects on red squirrel populations, less work has examined morphological and physiological characteristics that might make individual grey squirrels more susceptible to contracting SQPV. The current study investigated the putative relationships between morphology, parasitism, and SQPV exposure in grey squirrels. We found geographical, sex, and morphological differences in SQPV seroprevalence. In particular, larger animals, those with wide zygomatic arch widths (ZAW), males with large testes, and individuals with concurrent nematode and/or coccidial infections had an increased seroprevalence of SQPV. In addition, males with larger spleens, particularly those with narrow ZAW, were more likely to be exposed to SQPV. Overall these results show that there is variation in SQPV seroprevalence in grey squirrels and that, consequently, certain individual, or populations of, grey squirrels might be more responsible for transmitting SQPV to native red squirrel populations.

Hepatozoon griseisciuri in grey squirrels (Sciurus carolinensis): changes of blood leucocyte numbers resulting from infection

Numbers of leucocytes in squirrels with gametocytes of Hepatozoon in their blood (infected) were compared with animals without gametocytes (uninfected). Typical values for leucocytes/mm(3) blood in uninfected squirrels were: leucocytes 5-7 x 10(3), granulocytes 3-4 x 10(3), lymphocytes 2-0 x 10(3) and monocytes 0-3 x 10(3) cells. Infection caused an increase in monocytes, lymphocytes and granulocytes, and there was a significant positive association between parasitaemia level and numbers of both total leucocytes and monocytes. Infected animals had more uninfected monocytes/mm(3) blood than did uninfected animals. The proportions of monocytes were more variable over time in infected animals, but no shift between infected and uninfected status was detected. Transfer of serum from infected squirrels to mice resulted in elevated counts of total blood leucocytes, monocytes and granulocytes, but not of lymphocytes, as compared with controls. Serum from squirrels with high parasitaemias had a more marked effect than serum from squirrels with low parasitaemias. Results indicate an infection - related monocytosis, possibly controlled by cytokines, that increases the number of cells available for invasion by gametocytes, thus enhancing the chances of parasite transmission.

Effects of Alcohol and Training on Exercise Performance and Muscle Recovery Biochemistry in the Brown Anole (Anolis sagrei)

Contrary to previous research, training may improve exercise performance in a lizard, the brown anole. A brief, two-week training period resulted in increased performance speed and distance before exhaustion in trained lizards. Trained lizards were also able to more effectively use leg glycogen stores, however each of these improvements were not found in lizards treated with alcohol. Liver glycogen concentrations were also lower in alcohol-treated lizards, and patterns of liver glycogen concentrations during recovery indicate some hepatic lactate gluconeogenesis.

Pulmonary infection in two sympatric lizards, Mabuya arajara (Scincidae) and Anolis brasiliensis (Polychrotidae) from a cloud forest in Chapada do Araripe, Ceará, Northeastern Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Filogenia molecular e taxonomia do grupo Anolis chrysolepis Duméril & Bibron, 1837 (Squamata, Polychrotidae)

A Amazônia é considerada a maior floresta tropical contínua do mundo e diversos mecanismos têm sido propostos para tentar explicar a sua alta diversidade biológica. Um dos mecanismos mais discutidos desde sua proposição é a hipótese dos Refúgios, que se baseia na retração da floresta em períodos mais secos, isolando a fauna de florestas em refúgios imersos em uma matriz de vegetação aberta. Essas retrações e subseqüentes expansões em períodos mais mésicos provocariam a interrupção do fluxo gênico entre as populações isoladas e poderiam gerar especiação. Contudo, estudos moleculares recentes indicam que a diversificação de espécies de vertebrados de florestas tropicais provavelmente precede o período pleistocênico, originalmente indicado na hipótese dos Refúgios como o período em que esses eventos teriam ocorrido. A espécie politípica Anolis chrysolepis, juntamente com Anolis bombiceps, foi previamente estudada como um típico exemplo de diversificação gerada pelas flutuações climáticas do Pleistoceno, embora estudos posteriores tenham domonstrado a presença de grande divergência molecular entre parte das subespécies, indicando uma separação mais antiga desses táxons e levantando o questionamento sobre seu status taxonômico. Utilizamos o gene mitocondrial ND2 para investigar as relações filogenéticas entre as subespécies de Anolis chrysolepis e os táxons determinados em estudos anteriores como mais próximos a elas. Além disso, a sua morfologia e o seu status taxonômico foram revisados, a fim de verificar a congruência entre os dados morfológicos e moleculares, determinando se os táxons previamente reconhecidos morfologicamente são espécies válidas. Com base nos dois conjuntos de dados, nós elevamos as cinco subespécies do grupo Anolis chrysolepis ao status de espécies, diagnosticamos cada uma delas com comentários sobre as principais diferenças morfológicas entre as espécies irmãs e fornecemos novos dados de distribuição.

Análise evolutiva da morfologia e ecologia em espécies continentais de lagartos do gênero Anolis daudin 1804 (Squamata : Polychrotidae)

A tese compreende 3 capítulos. No primeiro capítulo apresento os resultados sobre a associação entre similaridade morfológica entre as espécies e suas relações filogenéticas, para 35 espécies que se distribuem nas áreas continentais e 59 no Caribe. Determino quais espécies continentais agrupam com as classes de ecomorfos propostos para as espécies caribenhas, investigo os casos de similaridade morfológica entre as espécies continentais, e verifico se existem agrupamentos entre as espécies morfologicamente similares. No capítulo dois, analiso evolutivamente a relação entre morfologia e ecologia para 19 espécies continentais de Anolis. No capítulo três, um estudo de caso, caracterizo as estruturas do habitat e outros atributos ecológicos de três espécies que ocorrem na Amazônia brasileira e busco associar as diferenças morfológicas entre elas com as diferenças de habitat, à luz dos resultados encontrados nos capítulos anteriores e em outros estudos ecomorfológicos.

Der Rotkohl-Anolis im Terrarium

Von Otto Tofohr