TY - JOUR A1 - Meuche, Ivonne A1 - Brusa, Oscar A1 - Linsenmair, K. Eduard A1 - Keller, Alexander A1 - Pröhl, Heike T1 - Only distance matters - non-choosy females in a poison frog population JF - Frontiers in Zoology N2 - Background: Females have often been shown to exhibit preferences for certain male traits. However, little is known about behavioural rules females use when searching for mates in their natural habitat. We investigated mate sampling tactics and related costs in the territorial strawberry poison frog (Oophaga pumilio) possessing a lek-like mating system, where both sequential and simultaneous sampling might occur. We continuously monitored the sampling pattern and behaviour of females during the complete period between two successive matings. Results: We found no evidence that females compared males by visiting them. Instead females mated with the closest calling male irrespective of his acoustic and physical traits, and territory size. Playback experiments in the natural home ranges of receptive females revealed that tested females preferred the nearest speaker and did not discriminate between low and high call rates or dominant frequencies. Conclusions: Our results suggest that females of O. pumilio prefer the closest calling male in the studied population. We hypothesize that the sampling tactic in this population is affected by 1) a strongly female biased sex ratio and 2) a low variance in traits of available males due to strong male-male competition, preventing low quality males from defending a territory and mating. KW - operational sex ratio KW - sequential mate choice KW - gray tree frogs KW - treefrogs hyla-gratiosa KW - male mating success KW - Bocas-del-Toro KW - dendrobates pumilio KW - oophaga pumilio KW - pied flycatchers KW - sampling behavior Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-122617 SN - 1742-9994 VL - 10 IS - 29 ER - TY - JOUR A1 - Menzel, Florian A1 - Blüthgen, Nico A1 - Tolasch, Till A1 - Conrad, Jürgen A1 - Beifuss, Uwe A1 - Beuerle, Till A1 - Schmitt, Thomas T1 - Crematoenones - a novel substance class exhibited by ants functions as appeasement signal JF - Frontiers in Zoology N2 - Background: Parasitic, commensalistic, and mutualistic guests in social insect colonies often circumvent their hosts' nestmate recognition system to be accepted. These tolerance strategies include chemical mimicry and chemical insignificance. While tolerance strategies have been studied intensively in social parasites, little is known about these mechanisms in non-parasitic interactions. Here, we describe a strategy used in a parabiotic association, i.e. two mutualistic ant species that regularly share a common nest although they have overlapping food niches. One of them, Crematogaster modiglianii, produces an array of cuticular compounds which represent a substance class undescribed in nature so far. They occur in high abundances, which suggests an important function in the ant's association with its partner Camponotus rufifemur. Results: We elucidated the structure of one of the main compounds from cuticular extracts using gas chromatography, mass spectrometry, chemical derivatizations and nuclear magnetic resonance spectroscopy (NMR). The compound consists of two fused six-membered rings with two alkyl groups, one of which carries a keto functionality. To our knowledge, this is the first report on the identification of this substance class in nature. We suggest naming the compound crematoenone. In behavioural assays, crematoenones reduced interspecific aggression. Camponotus showed less aggression to allospecific cuticular hydrocarbons when combined with crematoenones. Thus, they function as appeasement substances. However, although the crematoenone composition was highly colony-specific, interspecific recognition was mediated by cuticular hydrocarbons, and not by crematoenones. Conclusions: Crematenones enable Crematogaster to evade Camponotus aggression, and thus reduce potential costs from competition with Camponotus. Hence, they seem to be a key factor in the parabiosis, and help Crematogaster to gain a net benefit from the association and thus maintain a mutualistic association over evolutionary time. To our knowledge, putative appeasement substances have been reported only once so far, and never between non-parasitic species. Since most organisms associated with social insects need to overcome their nestmate recognition system, we hypothesize that appeasement substances might play an important role in the evolution and maintenance of other mutualistic associations as well, by allowing organisms to reduce costs from antagonistic behaviour of other species. KW - cuticular hydrocarbons KW - appeasement substance KW - bees KW - ecology KW - parasitism KW - alkyloctahydronaphthalene KW - usurpation KW - venom KW - pheromone KW - crematogaster KW - parabiotic ants KW - Dufours gland KW - polyergus rufescens KW - formicidae KW - interspecific aggression KW - nestmate recognition cues KW - parabiotic association Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-122595 SN - 1742-9994 VL - 10 IS - 32 ER - TY - JOUR A1 - Ngwa, Che Julius A1 - Scheuermayer, Matthias A1 - Mair, Gunnar Rudolf A1 - Kern, Selina A1 - Brügl, Thomas A1 - Wirth, Christine Clara A1 - Aminake, Makoah Nigel A1 - Wiesner, Jochen A1 - Fischer, Rainer A1 - Vilcinskas, Andreas A1 - Pradel, Gabriele T1 - Changes in the transcriptome of the malaria parasite Plasmodium falciparum during the initial phase of transmission from the human to the mosquito JF - BMC Genomics N2 - Background: The transmission of the malaria parasite Plasmodium falciparum from the human to the mosquito is mediated by dormant sexual precursor cells, the gametocytes, which become activated in the mosquito midgut. Because gametocytes are the only parasite stages able to establish an infection in the mosquito, they play a crucial role in spreading the tropical disease. The human-to-mosquito transmission triggers important molecular changes in the gametocytes, which initiate gametogenesis and prepare the parasite for life-cycle progression in the insect vector. Results: To better understand gene regulations during the initial phase of malaria parasite transmission, we focused on the transcriptome changes that occur within the first half hour of parasite development in the mosquito. Comparison of mRNA levels of P. falciparum gametocytes before and 30 min following activation using suppression subtractive hybridization (SSH) identified 126 genes, which changed in expression during gametogenesis. Among these, 17.5% had putative functions in signaling, 14.3% were assigned to cell cycle and gene expression, 8.7% were linked to the cytoskeleton or inner membrane complex, 7.9% were involved in proteostasis and 6.4% in metabolism, 12.7% were cell surface-associated proteins, 11.9% were assigned to other functions, and 20.6% represented genes of unknown function. For 40% of the identified genes there has as yet not been any protein evidence. For a subset of 27 genes, transcript changes during gametogenesis were studied in detail by real-time RT-PCR. Of these, 22 genes were expressed in gametocytes, and for 15 genes transcript expression in gametocytes was increased compared to asexual blood stage parasites. Transcript levels of seven genes were particularly high in activated gametocytes, pointing at functions downstream of gametocyte transmission to the mosquito. For selected genes, a regulated expression during gametogenesis was confirmed on the protein level, using quantitative confocal microscopy. Conclusions: The obtained transcriptome data demonstrate the regulations of gene expression immediately following malaria parasite transmission to the mosquito. Our findings support the identification of proteins important for sexual reproduction and further development of the mosquito midgut stages and provide insights into the genetic basis of the rapid adaption of Plasmodium to the insect vector. KW - parasitophorous vacuole KW - sexual development KW - gametocyte KW - transcriptome KW - signal peptide peptidase KW - host cell interface KW - alpha-tubulin-II KW - life-cycle KW - protein kinases KW - in-vitro KW - erythroyte invation KW - blocking antibodies KW - malaria KW - plasmodium falciparum KW - gametogenesis KW - mosquito KW - transmission Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121905 SN - 1471-2164 VL - 14 IS - 256 ER - TY - JOUR A1 - Kang, Ji Hyoun A1 - Schartl, Manfred A1 - Walter, Ronald B. A1 - Meyer, Axel T1 - Comprehensive phylogenetic analysis of all species of swordtails and platies (Pisces: Genus Xiphophorus) uncovers a hybrid origin of a swordtail fish, Xiphophorus monticolus, and demonstrates that the sexually selected sword originated in the ancestral lineage of the genus, but was lost again secondarily JF - BMC Evolutionary Biology N2 - Background: Males in some species of the genus Xiphophorus, small freshwater fishes from Meso-America, have an extended caudal fin, or sword - hence their common name "swordtails". Longer swords are preferred by females from both sworded and - surprisingly also, non-sworded (platyfish) species that belong to the same genus. Swordtails have been studied widely as models in research on sexual selection. Specifically, the pre-existing bias hypothesis was interpreted to best explain the observed bias of females in presumed ancestral lineages of swordless species that show a preference for assumed derived males with swords over their conspecific swordless males. However, many of the phylogenetic relationships within this genus still remained unresolved. Here we construct a comprehensive molecular phylogeny of all 26 known Xiphophorus species, including the four recently described species (X. kallmani, X. mayae, X. mixei and X. monticolus). We use two mitochondrial and six new nuclear markers in an effort to increase the understanding of the evolutionary relationships among the species in this genus. Based on the phylogeny, the evolutionary history and character state evolution of the sword was reconstructed and found to have originated in the common ancestral lineage of the genus Xiphophorus and that it was lost again secondarily. Results: We estimated the evolutionary relationships among all known species of the genus Xiphophorus based on the largest set of DNA markers so far. The phylogeny indicates that one of the newly described swordtail species, Xiphophorus monticolus, is likely to have arisen through hybridization since it is placed with the southern platyfish in the mitochondrial phylogeny, but with the southern swordtails in the nuclear phylogeny. Such discordance between these two types of markers is a strong indication for a hybrid origin. Additionally, by using a maximum likelihood approach the possession of the sexually selected sword trait is shown to be the most likely ancestral state for the genus Xiphophorus. Further, we provide a well supported estimation of the phylogenetic relationships between the previously unresolved northern swordtail groups. Conclusions: This comprehensive molecular phylogeny of the entire genus Xiphophorus provides evidence that a second swordtail species, X. monticolus, arose through hybridization. Previously, we demonstrated that X. clemenciae, another southern swordtail species, arose via hybridization. These findings highlight the potential key role of hybridization in the evolution of this genus and suggest the need for further investigations into how hybridization contributes to speciation more generally. KW - parten-offspring conflict KW - introgressive hybridization KW - mitochondrial DNA KW - molecular phylogeny KW - likelihood approach KW - tree selection KW - preexisting bias KW - adaptive radiation KW - evolution KW - poeciliidae Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121853 SN - 1471-2148 VL - 13 IS - 25 ER - TY - JOUR A1 - Rybalka, Nataliya A1 - Wolf, Matthias A1 - Andersen, Robert A1 - Friedl, Thomas T1 - Congruence of chloroplast- and nuclear-encoded DNA sequence variations used to assess species boundaries in the soil microalga Heterococcus (Stramenopiles, Xanthophyceae) JF - BMC Evolutionary Biology N2 - Background: Heterococcus is a microalgal genus of Xanthophyceae (Stramenopiles) that is common and widespread in soils, especially from cold regions. Species are characterized by extensively branched filaments produced when grown on agarized culture medium. Despite the large number of species described exclusively using light microscopic morphology, the assessment of species diversity is hampered by extensive morphological plasticity. Results: Two independent types of molecular data, the chloroplast-encoded psbA/rbcL spacer complemented by rbcL gene and the internal transcribed spacer 2 of the nuclear rDNA cistron (ITS2), congruently recovered a robust phylogenetic structure. With ITS2 considerable sequence and secondary structure divergence existed among the eight species, but a combined sequence and secondary structure phylogenetic analysis confined to helix II of ITS2 corroborated relationships as inferred from the rbcL gene phylogeny. Intra-genomic divergence of ITS2 sequences was revealed in many strains. The 'monophyletic species concept', appropriate for microalgae without known sexual reproduction, revealed eight different species. Species boundaries established using the molecular-based monophyletic species concept were more conservative than the traditional morphological species concept. Within a species, almost identical chloroplast marker sequences (genotypes) were repeatedly recovered from strains of different origins. At least two species had widespread geographical distributions; however, within a given species, genotypes recovered from Antarctic strains were distinct from those in temperate habitats. Furthermore, the sequence diversity may correspond to adaptation to different types of habitats or climates. Conclusions: We established a method and a reference data base for the unambiguous identification of species of the common soil microalgal genus Heterococcus which uses DNA sequence variation in markers from plastid and nuclear genomes. The molecular data were more reliable and more conservative than morphological data. KW - xanthophyceae KW - psbA/rbcL spacer KW - ITS2 KW - tool KW - RBCL KW - alignment KW - evolution KW - chlorophyta KW - RNA secondary structure KW - terrestrial habitats KW - phylogenetic trees KW - mixed models KW - green algae KW - heterococcus KW - systematics KW - molecular phylogeny KW - species concept Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121848 SN - 1471-2148 VL - 13 IS - 39 ER - TY - JOUR A1 - Dietz, Mariana S. A1 - Hasse, Daniel A1 - Ferraris, Davide M. A1 - Göhler, Antonia A1 - Niemann, Hartmut H. A1 - Heilemann, Mike T1 - Single-molecule photobleaching reveals increased MET receptor dimerization upon ligand binding in intact cells JF - BMC Biophysics N2 - Background: The human receptor tyrosine kinase MET and its ligand hepatocyte growth factor/scatter factor are essential during embryonic development and play an important role during cancer metastasis and tissue regeneration. In addition, it was found that MET is also relevant for infectious diseases and is the target of different bacteria, amongst them Listeria monocytogenes that induces bacterial uptake through the surface protein internalin B. Binding of ligand to the MET receptor is proposed to lead to receptor dimerization. However, it is also discussed whether preformed MET dimers exist on the cell membrane. Results: To address these issues we used single-molecule fluorescence microscopy techniques. Our photobleaching experiments show that MET exists in dimers on the membrane of cells in the absence of ligand and that the proportion of MET dimers increases significantly upon ligand binding. Conclusions: Our results indicate that partially preformed MET dimers may play a role in ligand binding or MET signaling. The addition of the bacterial ligand internalin B leads to an increase of MET dimers which is in agreement with the model of ligand-induced dimerization of receptor tyrosine kinases. KW - single-molecule photobleaching KW - fluorescence correlation spectroscopy KW - fluorescence KW - EGF receptor KW - rat hepatocytes KW - structural insights KW - Scatter factor KW - SEMA domain KW - hepatocyte-growth-factor KW - invasion protein-INLB KW - listeria-monocytogenes KW - tyrosine kinase KW - living cells KW - dimerization KW - MET receptor KW - Signal transduction Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121835 SN - 2046-1682 VL - 6 IS - 6 ER - TY - JOUR A1 - Bogdan, Sven A1 - Schultz, Jörg A1 - Grosshans, Jörg T1 - Formin’ cellular structures: Physiological roles of Diaphanous (Dia) in actin dynamics JF - Communicative & Integrative Biology N2 - Members of the Diaphanous (Dia) protein family are key regulators of fundamental actin driven cellular processes, which are conserved from yeast to humans. Researchers have uncovered diverse physiological roles in cell morphology, cell motility, cell polarity, and cell division, which are involved in shaping cells into tissues and organs. The identification of numerous binding partners led to substantial progress in our understanding of the differential functions of Dia proteins. Genetic approaches and new microscopy techniques allow important new insights into their localization, activity, and molecular principles of regulation. KW - Drosophila KW - cytoskeleton KW - actin KW - nucleator KW - development KW - formin Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121305 VL - 6 IS - e27634 ER - TY - THES A1 - Zovko, Josip T1 - Die E3-Ubiquitinligase HectD1 reguliert die Stabilität des antiapoptotischen Bcl-2-Familienmitglieds A1 T1 - The E3-Ubiquitinligase HectD1 regulates the stabiliy of the anti-apoptotic Bcl-2-protein A1 N2 - Die Bcl-2-Familienmitglieder A1 und sein humanes Homolog Bfl-1 gewährleisten das Überleben der Zelle. Gleichzeitig trägt eine Dysregulation der Expression von A1/ Bfl-1 zur Krebsentstehung bei. Die Stabilität von A1/ Bfl-1 wird durch deren Ubiquitinylierung sowie die anschließende proteosomale Degradation gesteuert. Mit Hilfe eines Yeast-Two-Hybrid-Screens wurde die E3-Ubiquitinligase HectD1 als potentieller Interaktionspartner von A1/ Bfl-1 identifiziert. Die Interaktion von A1 und HectD1 des Yeast-Two-Hybrid-Screens konnte in Säugerzellen bestätigt werden. Desweiteren konnte gezeigt werden, dass lediglich 87 Aminosäuren für eine Interaktion von HectD1 und A1 nötig sind. Da membrangebundenes HectD1 zu einer Translokation von zytosolischem A1 an die Zellmembran führt, kann man davon ausgehen, dass beide Proteine auch in vivo miteinander interagieren. Eine dominant negative HectD1-Mutante schließlich beeinflusst die Ubiqutinylierung von A1 und führt somit zu dessen Stabilisierung. Diese Daten legen nahe, dass HectD1 ein wichtiger negativer Regulator von A1/ Bfl-1 ist und dass HectD1 für die Regulierung der A1/ Bfl-1-Proteinmenge in (Krebs)zellen sehr wichtig ist. N2 - The Bcl-2 family members A1 and its human orthologue Bfl-1 support survival of cells. Dysregulation of their expression contributes to cancer. Stability of A1/ Bfl-1 is controlled by ubiquitination followed by degradation via the proteasome. Using a yeast two-hybrid screen we identified the E3 ubiquitin-ligase HectD1 as potential A1/ Bfl-1-interacting partner. We confirmed interaction of these two proteins in mammalian cells. Only 87 amino acids of HectD1 are necessary for the interaction of the protein with A1. Membrane-bound HectD1 recruits A1 to the membranes further supporting the notion that the two proteins interact in vivo. Importantly, dominant negative versions of HectD1 interfered with ubiquitination of A1 stabilizing the protein. These findings indicate that HectD1 maybe an important negative regulator of the A1/ Bfl-1 anti-apoptotic protein, providing an important target for interfering with dysregulation of A1/ Bfl-1 in cancer. KW - Zelltod KW - Ubiquitinierung KW - Bcl-2 Familie KW - Bcl-2 family KW - Regeneration KW - Bcl-2-Proteinfamilie KW - Ubiquitination Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-87922 ER - TY - THES A1 - Hoiß, Bernhard T1 - Effects of climate change, extreme events and management on plants, pollinators and mutualistic interaction networks T1 - Auswirkungen von Klimawandel, Extremereignissen und Management auf Pflanzen, Bestäuber und mutualistische Netzwerke N2 - I. Climate change comprises average temperatures rise, changes in the distribution of precipitation and an increased amount and intensity of extreme climatic events in the last decades. Considering these serious changes in the abiotic environment it seems obvious that ecosystems also change. Flora and fauna have to adapt to the fast changing conditions, migrate or go extinct. This might result in shifts in biodiversity, species composition, species interactions and in ecosystem functioning and services. Mountains play an important role in the research of these climate impacts. They are hotspots of biodiversity and can be used as powerful natural experiments as they provide, within short distances, the opportunity to research changes in the ecosystem induced by different climatic contexts. In this dissertation two approaches were pursued: i) surveys of biodiversity, trait dominance and assembly rules in communities depending on the climatic context and different management regimes were conducted (chapters II and III) and ii) the effects of experimental climate treatments on essential ecosystem features along the altitudinal gradient were assessed (chapters IV, V and VI). II. We studied the relative importance of management, an altitudinal climatic gradient and their interactions for plant species richness and the dominance of pollination types in 34 alpine grasslands. Species richness peaked at intermediate temperatures and was higher in grazed grasslands compared to non-managed grasslands. We found the climatic context and also management to influence the distribution and dominance structures of wind- and insect-pollinated plants. Our results indicate that extensive grazing maintains high plant diversity over the full subalpine gradient. Rising temperatures may cause an upward shift of the diversity peak of plants and may also result in changed species composition and adaptive potential of pollination types. III. On the same alpine grasslands we studied the impact of the climatic context along an altitudinal gradient on species richness and community assembly in bee communities. Species richness and abundance declined linearly with increasing altitude. Bee species were more closely related at high altitudes than at low altitudes. The proportion of social and ground-nesting species, as well as mean body size and altitudinal range of bees, increased with increasing altitude, whereas the mean geographic distribution decreased. Our results suggest that community assembly at high altitudes is dominated by environmental filtering effects, while the relative importance of competition increases at low altitudes. We conclude that ongoing climate change poses a threat for alpine specialists with adaptations to cool environments but low competitive capacities. IV. We determined the impacts of short-term climate events on flower phenology and assessed whether those impacts differed between lower and higher altitudes. For that we simulated advanced and delayed snowmelt as well as drought events in a multi site experiment along an altitudinal gradient. Flower phenology was strongly affected by altitude, however, this effect declined through the season. The manipulative treatments caused only few changes in flowering phenology. The effects of advanced snowmelt were significantly greater at higher than at lower sites, but altitude did not influence the effect of the other treatments. The length of flowering duration was not significantly influenced by treatments. Our data indicate a rather low risk of drought events on flowering phenology in the Bavarian Alps. V. Changes in the structure of plant-pollinator networks were assessed along an altitudinal gradient combined with the experimental simulation of potential consequences of climate change: extreme drought events, advanced and delayed snowmelt. We found a trend of decreasing specialisation and therefore increasing complexity in networks with increasing altitude. After advanced snowmelt or drought networks were more specialised especially at higher altitudes compared to control plots. Our results show that changes in the network structures after climate manipulations depend on the climatic context and reveal an increasing susceptibility of plant-pollinator networks with increasing altitude. VI. The aim of this study was to determine the combined effects of extreme climatic events and altitude on leaf CN (carbon to nitrogen) ratios and herbivory rates in different plant guilds. We found no overall effect of climate manipulations (extreme drought events, advanced and delayed snowmelt) on leaf CN ratios and herbivory rates. However, plant guilds differed in CN ratios and herbivory rates and responded differently to altitude. CN ratios of forbs (legume and non-legume) decreased with altitude, whereas CN ratios of grasses increased with altitude. Further, CN ratios and herbivory rates increased during the growing season, indicating a decrease of food plant quality during the growing season. Insect herbivory rates were driven by food plant quality. Contrasting altitudinal responses of forbs versus grasses give reason to expect changed dominance structures among plant guilds with ongoing climate change. VII. This dissertation contributes to the understanding of factors that determine the composition and biotic interactions of communities in different climates. The results presented indicate that warmer climates will not only change species richness but also the assembly-rules for plant and bee communities depending on the species' functional traits. Our investigations provide insights in the resilience of different ecosystem features and processes towards climate change and how this resilience depends on the environmental context. It seems that mutualistic interactions are more susceptible to short-term climate events than flowering phenology and antagonistic interactions such as herbivory. However, to draw more general conclusions more empirical data is needed. N2 - I. Das Klima ändert sich: die Durchschnittstemperaturen steigen, die Niederschlagsverteilung ändert sich und sowohl die Anzahl als auch die Intensität von klimatischen Extremereignissen hat in den letzten Jahrzehnten zugenommen. In Anbetracht dieser beträchtlichen Veränderungen in der abiotischen Umwelt scheint es offensichtlich, dass sich auch die Ökosysteme verändern. Flora und Fauna müssen sich an die sich schnell verändernden Bedingungen anpassen, wandern oder sie sterben aus. Dies kann zu Veränderungen in der Biodiversität, der Artzusammensetzung, den Ökosystemfunktionen sowie von Ökosystemdienstleistungen führen. Gebirge spielen eine wichtige Rolle in der Erforschung dieser Klimafolgen. Sie sind Biodiversitäts-Hotspots und können als großräumige natürliche Experimente genutzt werden, da sie die Möglichkeit bieten, innerhalb kurzer Distanzen Veränderungen im Ökosystem unter verschiedenen klimatischen Bedingungen zu untersuchen. In dieser Dissertation wurden zwei Ansätze verfolgt: i) Es wurden Untersuchungen zur Abhängigkeit von Biodiversität, der Dominanz von funktionalen Merkmalen sowie den Gesetzmäßigkeiten in der Zusammensetzung von Artengemeinschaften vom klimatischen Kontext sowie verschiedenen Management Regimen durchgeführt. ii) Die Effekte von Klimaexperimenten auf essentielle Ökosystemeigenschaften, biotische Interaktionen und Nahrungsnetze entlang eines Höhengradienten wurden untersucht. II. Die relative Bedeutung von Höhenlage, Bewirtschaftungsform sowie ihre Interaktionen für den Artenreichtum von Pflanzen und die Dominanz von Bestäubungstypen wurden in 34 alpinen Wiesen untersucht. Der Artenreichtum erreichte bei mittleren Temperaturen ein Maximum und war auf beweideten Flächen höher als auf nicht bewirtschafteten Wiesen. Wir stellten außerdem fest, dass sowohl der klimatische Kontext als auch die Bewirtschaftungsform die Verteilung und Dominanzstrukturen von wind- und insektenbestäubten Pflanzen beeinflusste. Unsere Ergebnisse zeigen, dass extensive Beweidung eine hohe Artenvielfalt über den gesamten subalpinen Gradienten erhält. Steigende Temperaturen könnten eine Verschiebung des Bereiches mit maximaler Artenvielfalt nach oben sowie veränderte Zusammensetzungen von Artengemeinschaften und Veränderungen in der Bedeutung von Bestäubungstypen als Anpassung verursachen. III. Auf den selben alpinen Wiesen untersuchten wir den Einfluss der klimatischen Gegebenheiten entlang des Höhengradienten auf die Artenzahl und die Gesetzmäßigkeiten in der Zusammensetzung von Wildbienen Artengemeinschaften. Die Artenzahl und Abundanz nahm mit zunehmender Höhe linear ab. Die Bienenarten in höheren Lagen waren näher miteinander verwandt als in niedrigen Lagen. Der Anteil sozialer, im Boden nistender Arten sowie die mittlere Körpergröße und Höhenverbreitung der Bienen nahm mit zunehmender Höhe zu, wohingegen die mittlere geographische Verbreitung der Arten abnahm. Unsere Ergebnisse legen nahe, dass die Zusammensetzung von Artengemeinschaften in höheren Lagen primär vom Filtereffekt der Umwelt bestimmt wird, wohingegen der Einfluss von Konkurrenz in niedrigen Lagen an Bedeutung gewinnt. Wir folgern, dass der fortschreitende Klimawandel eine Gefährdung für alpine Spezialisten darstellt, die zwar Anpassungen an kühle Bedingungen aber oft eine nur geringe Konkurrenzfähigkeit aufweisen. IV. Wir untersuchten die Auswirkung von kurzzeitigen klimatischen Ereignissen auf die Blütenphänologie und analysierten, ob sich diese Auswirkungen zwischen hohen und tiefen Lagen unterscheiden. Dazu simulierten wir verfrühte und verspätete Schneeschmelze sowie Dürreereignisse in Experimenten auf multiplen Standorten entlang eines Höhengradienten. Die Blütenphänologie wurde von der Höhenlage stark beeinflusst, dieser Effekt nahm im Laufe der Saison allerdings ab. Die Manipulationen zeitigten nur wenige Effekte auf die Blühphänologie. Die Auswirkungen von verfrühter Schneeschmelze waren auf hohen Flächen signifikant höher als in niedrigen Lagen, es wurden jedoch keine Unterschiede für die anderen Behandlungen zwischen den Höhenstufen gefunden. Die Blühdauer wurde durch die Behandlungen nicht beeinflusst. Unsere Daten zeigen ein relativ geringes Risiko für die Blütenphänologie durch Dürreereignisse in den bayerischen Alpen auf. V. Veränderungen in der Struktur von Pflanzen-Bestäuber Netzwerken wurden entlang eines Höhengradienten in Kombination mit der experimentellen Simulation von potentiellen Konsequenzen des Klimawandels (extreme Dürre, verfrühte und verspätete Schneeschmelze) untersucht. Wir fanden einen Trend hin zu einem abnehmenden Spezialisierungsgrad und daher einer Zunahme der Komplexität in Netzwerken mit zunehmender Höhe. Die Netzwerke nach verfrühter Schneeschmelze und nach Dürre waren, insbesondere in höheren Lagen, stärker spezialisiert als in den Kontrollflächen. Unsere Ergebnisse zeigen, dass Veränderungen in den Netzwerkstrukturen nach Klimamanipulationen vom klimatischen Zusammenhang abhängen und zeigen auf, dass die Anfälligkeit von Pflanzen-Bestäuber Netzwerken mit der Höhe zunimmt. VI. Das Ziel dieser Studie war es die kombinierten Auswirkungen von kurzzeitigen klimatischen Ereignissen und Meereshöhe auf das CN (Kohlenstoff zu Stickstoff) Verhältnis in Blättern und den Blattfraß in verschiedenen Pflanzengruppen zu untersuchen. Wir fanden keinen Gesamteffekt der Klimamanipulationen (extremes Dürreereignis, verfrühte und verspätete Schneeschmelze) auf das CN Verhältnis und die Herbivorieraten. Die Pflanzengruppen unterschieden sich jedoch in ihrer Reaktion auf die Meereshöhe hinsichtlich ihres CN Verhältnisses und des Blattfraßes. Das CN Verhältnis in Gräsern nahm mit der Höhe zu, wohingegen das CN Verhältnis in den restlichen krautigen Pflanzen mit zunehmender Höhe abnahm. Außerdem nahmen CN Verhältnis und die Herbivorierate im Laufe der Saison zu, was auf eine Abnahme der Futterqualität im Saisonverlauf hindeutet. Die Herbivorieraten wurden von der Futterqualität der Pflanzen bestimmt. Die gegensätzlichen Muster von Gräsern und anderen krautigen Pflanzen über die Höhe lassen veränderte Dominanzstrukturen zwischen Pflanzengruppen mit fortschreitendem Klimawandel zu erwarten. VII. Diese Dissertation leistet einen Beitrag zur Identifikation von Gesetzmäßigkeiten in der Zusammensetzung von Artengemeinschaften unter unterschiedlichen klimatischen Bedingungen. Die präsentierten Ergebnisse weisen darauf hin, dass ein wärmeres Klima nicht nur den Artenreichtum, sondern auch diese Gesetzmäßigkeiten für Pflanzen- und Bienenvergesellschaftungen in Abhängigkeit von den funktionellen Merkmalen der Arten verändern wird. Unsere Untersuchungen liefern Erkenntnisse über die Stabilität verschiedener Ökosystemaspekte und -prozesse gegenüber dem Klimawandel und wie diese Stabilität vom Umweltkontext abhängt. Es scheint, dass mutualistische Interaktionen anfälliger sind für kurzfristige Klimaereignisse als die Phänologie von Blüten oder antagonistische Interaktionen wie die Herbivorie. Um allgemeinere Rückschlüsse ziehen zu können bedarf es jedoch dringend weiterer empirischer Daten. KW - Klimaänderung KW - Alpen KW - Biodiversität KW - Bestäubungsökologie KW - Mutualismus KW - climate change KW - land use KW - altitudinal gradient KW - elevation KW - life history traits KW - bees KW - vascular plants KW - alpine ecosystems KW - environmental filtering KW - Klimawandel KW - Extremereignisse KW - Management KW - Gefäßpflanzen KW - mutualistische Netzwerke KW - Pflanzen-Bestäuber-Interaktionen KW - Höhengradient Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-87919 ER - TY - JOUR A1 - Gross, Hans J. A1 - Samhita, Laasya T1 - The “Clever Hans Phenomenon” revisited N2 - In the first decade of the 20th century, a horse named Hans drew worldwide attention in Berlin as the first and most famous “speaking” and thinking animal. Hans solved calculations by tapping numbers or letters with his hoof in order to answer questions. Later on, it turned out that the horse was able to give the correct answer by reading the microscopic signals in the face of the questioning person. This observation caused a revolution and as a consequence, experimenters avoided strictly any face-to-face contact in studies about cognitive abilities of animals—a fundamental lesson that is still not applied rigorously. KW - Clever Hans Phenomenon Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-112626 ER -