TY - JOUR A1 - Otieno, Mark A1 - Karpati, Zsolt A1 - Peters, Marcell K. A1 - Duque, Laura A1 - Schmitt, Thomas A1 - Steffan-Dewenter, Ingolf T1 - Elevated ozone and carbon dioxide affects the composition of volatile organic compounds emitted by Vicia faba (L.) and visitation by European orchard bee (Osmia cornuta) JF - PLoS One N2 - Recent studies link increased ozone (O\(_3\)) and carbon dioxide (CO\(_2\)) levels to alteration of plant performance and plant-herbivore interactions, but their interactive effects on plant-pollinator interactions are little understood. Extra floral nectaries (EFNs) are essential organs used by some plants for stimulating defense against herbivory and for the attraction of insect pollinators, e.g., bees. The factors driving the interactions between bees and plants regarding the visitation of bees to EFNs are poorly understood, especially in the face of global change driven by greenhouse gases. Here, we experimentally tested whether elevated levels of O\(_3\) and CO\(_2\) individually and interactively alter the emission of Volatile Organic Compound (VOC) profiles in the field bean plant (Vicia faba, L., Fabaceae), EFN nectar production and EFN visitation by the European orchard bee (Osmia cornuta, Latreille, Megachilidae). Our results showed that O\(_3\) alone had significant negative effects on the blends of VOCs emitted while the treatment with elevated CO\(_2\) alone did not differ from the control. Furthermore, as with O\(_3\) alone, the mixture of O\(_3\) and CO\(_2\) also had a significant difference in the VOCs’ profile. O\(_3\) exposure was also linked to reduced nectar volume and had a negative impact on EFN visitation by bees. Increased CO\(_2\) level, on the other hand, had a positive impact on bee visits. Our results add to the knowledge of the interactive effects of O\(_3\) and CO\(_2\) on plant volatiles emitted by Vicia faba and bee responses. As greenhouse gas levels continue to rise globally, it is important to take these findings into consideration to better prepare for changes in plant-insect interactions. KW - Volatile Organic Compound (VOC) KW - Vicia faba (L.) KW - European orchard bee (Osmia cornuta) KW - carbon dioxide (CO2) KW - ozone (O3) KW - bees KW - flowering plants KW - plant-insect interactions KW - flowers KW - plant physiology KW - plant-herbivore interactions Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-350020 VL - 18 IS - 4 ER - TY - JOUR A1 - Stein, Katharina A1 - Coulibaly, Drissa A1 - Balima, Larba Hubert A1 - Goetze, Dethardt A1 - Linsenmair, Karl Eduard A1 - Porembski, Stefan A1 - Stenchly, Kathrin A1 - Theodorou, Panagiotis T1 - Plant-pollinator networks in savannas of Burkina Faso, West Africa JF - Diversity N2 - West African savannas are severely threatened with intensified land use and increasing degradation. Bees are important for terrestrial biodiversity as they provide native plant species with pollination services. However, little information is available regarding their mutualistic interactions with woody plant species. In the first network study from sub-Saharan West Africa, we investigated the effects of land-use intensity and climatic seasonality on plant–bee communities and their interaction networks. In total, we recorded 5686 interactions between 53 flowering woody plant species and 100 bee species. Bee-species richness and the number of interactions were higher in the low compared to medium and high land-use intensity sites. Bee- and plant-species richness and the number of interactions were higher in the dry compared to the rainy season. Plant–bee visitation networks were not strongly affected by land-use intensity; however, climatic seasonality had a strong effect on network architecture. Null-model corrected connectance and nestedness were higher in the dry compared to the rainy season. In addition, network specialization and null-model corrected modularity were lower in the dry compared to the rainy season. Our results suggest that in our study region, seasonal effects on mutualistic network architecture are more pronounced compared to land-use change effects. Nonetheless, the decrease in bee-species richness and the number of plant–bee interactions with an increase in land-use intensity highlights the importance of savanna conservation for maintaining bee diversity and the concomitant provision of ecosystem services. KW - bees KW - community composition KW - connectance KW - land-use intensity KW - modularity KW - mutualism KW - number of interactions KW - seasonality KW - woody plant richness Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-220157 SN - 1424-2818 VL - 13 IS - 1 ER - TY - THES A1 - Mayr, Antonia Veronika T1 - Following Bees and Wasps up Mt. Kilimanjaro: From Diversity and Traits to hidden Interactions of Species T1 - Auf den Spuren von Bienen und Wespen auf den Kilimandscharo: Eine Studie über die Diversität, Merkmale und verborgenen Wechselwirkungen zwischen Arten N2 - Chapter 1 – General Introduction One of the greatest challenges of ecological research is to predict the response of ecosystems to global change; that is to changes in climate and land use. A complex question in this context is how changing environmental conditions affect ecosystem processes at different levels of communities. To shed light on this issue, I investigate drivers of biodiversity on the level of species richness, functional traits and species interactions in cavity-nesting Hymenoptera. For this purpose, I take advantage of the steep elevational gradient of Mt. Kilimanjaro that shows strong environmental changes on a relatively small spatial scale and thus, provides a good environmental scenario for investigating drivers of diversity. In this thesis, I focus on 1) drivers of species richness at different trophic levels (Chapter 2); 2) seasonal patterns in nest-building activity, life-history traits and ecological rates in three different functional groups and at different elevations (Chapter 3) and 3) changes in cuticular hydrocarbons, pollen composition and microbiomes in Lasioglossum bees caused by climatic variables (Chapter 4). Chapter 2 – Climate and food resources shape species richness and trophic interactions of cavity-nesting Hymenoptera Drivers of species richness have been subject to research for centuries. Temperature, resource availability and top-down regulation as well as the impact of land use are considered to be important factors in determining insect diversity. Yet, the relative importance of each of these factors is unknown. Using trap nests along the elevational gradient of Mt. Kilimanjaro, we tried to disentangle drivers of species richness at different trophic levels. Temperature was the major driver of species richness across trophic levels, with increasing importance of food resources at higher trophic levels in natural antagonists. Parasitism rate was both related to temperature and trophic level, indicating that the relative importance of bottom-up and top-down forces might shift with climate change. Chapter 3 – Seasonal variation in the ecology of tropical cavity-nesting Hymenoptera Natural populations fluctuate with the availability of resources, presence of natural enemies and climatic variations. But tropical mountain seasonality is not yet well investigated. We investigated seasonal patterns in nest-building activity, functional traits and ecological rates in three different insect groups at lower and higher elevations separately. Insects were caught with trap nests which were checked monthly during a 17 months period that included three dry and three rainy seasons. Insects were grouped according to their functional guilds. All groups showed strong seasonality in nest-building activity which was higher and more synchronised among groups at lower elevations. Seasonality in nest building activity of caterpillar-hunting and spider-hunting wasps was linked to climate seasonality while in bees it was strongly linked to the availability of flowers, as well as for the survival rate and sex ratio of bees. Finding adaptations to environmental seasonality might imply that further changes in climatic seasonality by climate change could have an influence on life-history traits of tropical mountain species. Chapter 4 – Cryptic species and hidden ecological interactions of halictine bees along an elevational Gradient Strong environmental gradients such as those occurring along mountain slopes are challenging for species. In this context, hidden adaptations or interactions have rarely been considered. We used bees of the genus Lasioglossum as model organisms because Lasioglossum is the only bee genus occurring with a distribution across the entire elevational gradient at Mt. Kilimanjaro. We asked if and how (a) cuticular hydrocarbons (CHC), which act as a desiccation barrier, change in composition and chain length along with changes in temperature and humidity (b), Lasioglossum bees change their pollen diet with changing resource availability, (c) gut microbiota change with pollen diet and climatic conditions, and surface microbiota change with CHC and climatic conditions, respectively, and if changes are rather influenced by turnover in Lasioglossum species along the elevational gradient. We found physiological adaptations with climate in CHC as well as changes in communities with regard to pollen diet and microbiota, which also correlated with each other. These results suggest that complex interactions and feedbacks among abiotic and biotic conditions determine the species composition in a community. Chapter 5 – General Discussion Abiotic and biotic factors drove species diversity, traits and interactions and they worked differently depending on the functional group that has been studied, and whether spatial or temporal units were considered. It is therefore likely, that in the light of global change, different species, traits and interactions will be affected differently. Furthermore, increasing land use intensity could have additional or interacting effects with climate change on biodiversity, even though the potential land-use effects at Mt. Kilimanjaro are still low and not impairing cavity-nesting Hymenoptera so far. Further studies should address species networks which might reveal more sensitive changes. For that purpose, trap nests provide a good model system to investigate effects of global change on multiple trophic levels and may also reveal direct effects of climate change on entire life-history traits when established under different microclimatic conditions. The non-uniform effects of abiotic and biotic conditions on multiple aspects of biodiversity revealed with this study also highlight that evaluating different aspects of biodiversity can give a more comprehensive picture than single observations. N2 - Kapitel 1 – Allgemeine Einführung Eine der größten Herausforderungen der ökologischen Forschung ist es, die Reaktion der Ökosysteme auf den globalen Wandel, d.h. auf Veränderungen von Klima und Landnutzung, vorherzusagen. Eine komplexe Frage in diesem Zusammenhang ist, wie sich verändernde Umweltbedingungen auf die Ökosystemprozesse auf verschiedenen Ebenen von Gemeinschaften auswirken. Um dieses Thema näher zu beleuchten, untersuche ich die Triebkräfte der Biodiversität auf der Ebene des Artenreichtums, der funktionellen Eigenschaften und der Wechselwirkungen zwischen Arten bei Hautflüglern, die in Hohlräumen nisten. Zu diesem Zweck nutze ich den steilen Höhengradienten des Kilimandscharo, der starke Umweltveränderungen auf relativ kleinem Raum mit sich bringt und somit ein gutes System für die Untersuchung von Triebkräften der biologischen Vielfalt bietet. In dieser Arbeit konzentriere ich mich auf 1) Triebkräfte des Artenreichtums auf verschiedenen trophischen Ebenen (Kapitel 2); 2) saisonale Muster in der Nestbauaktivität, lebensgeschichtliche Merkmale und ökologische Raten in drei verschiedenen funktionellen Gruppen und in verschiedenen Höhenlagen (Kapitel 3) und 3) Veränderungen in kutikulären Kohlenwasserstoffen, Pollenzusammensetzung und Mikrobiomen bei Lasioglossum Bienen, die durch klimatische Faktoren verursacht werden (Kapitel 4). Kapitel 2 – Klima und Nahrungsressourcen prägen den Artenreichtum und die trophischen Wechselwirkungen von hohlraumnistenden Hautflüglern Die Triebkräfte des Artenreichtums werden seit Jahrhunderten erforscht. Temperatur, Ressourcenverfügbarkeit und Top-Down-Regulierung sowie die Auswirkungen der Landnutzung werden als wichtige Faktoren für die Bestimmung der Insektenvielfalt angesehen. Die relative Bedeutung jedes dieser Faktoren ist jedoch unbekannt. Mit Hilfe von Nisthilfen entlang des Höhengradienten des Kilimandscharo versuchten wir, die Triebkräfte des Artenreichtums auf verschiedenen trophischen Ebenen zu enträtseln. Die Temperatur war der Hauptfaktor für den Artenreichtum auf allen trophischen Ebenen, wobei die Bedeutung der Nahrungsressourcen auf den höheren trophischen Ebenen der natürlichen Antagonisten zunahm. Die Parasitierungsrate wurde sowohl durch die Temperatur als auch durch die trophische Ebene bestimmt, was darauf hindeutet, dass sich die relative Bedeutung der Bottom-up- und Top-down-Kräfte mit dem Klimawandel verschieben könnte. Kapitel 3 – Saisonale Schwankungen in der Ökologie von tropischen hohlraumnistenden Hautflüglern Natürliche Populationen schwanken mit der Verfügbarkeit von Ressourcen, dem Vorhandensein natürlicher Feinde und klimatischen Schwankungen. Die Saisonalität ist jedoch auf tropischen Bergen noch nicht gut untersucht. Wir untersuchten saisonale Muster in der Nestbauaktivität, funktionale Merkmale und ökologische Raten bei drei verschiedenen Insektengruppen in niedrigeren und höheren Höhenlagen. Insekten wurden mit Nisthilfen gefangen, die während eines Zeitraums von 17 Monaten, der drei Trocken- und drei Regenzeiten umfasste, monatlich überprüft wurden. Die Insekten wurden nach ihren funktionalen Gilden eingeteilt. Alle Gruppen zeigten eine starke Saisonalität im Nestbau, die in niedrigeren Lagen höher war und dort zwischen den Gruppen stärker synchronisiert war. Die Saisonalität im Nestbau von Raupen- und Spinnen- jagenden Wespen war mit saisonalen Klimaschwankungen verbunden, während sie bei Bienen stark von der Verfügbarkeit von Blüten abhing, genauso wie die Überlebensrate und das Geschlechterverhältnis der Bienen von der Blütenmenge abhing. Die Anpassung an die Saisonalität der Umwelt könnte bedeuten, dass weitere Veränderungen der saisonalen Klimaschwankungen durch den Klimawandel einen Einfluss auf die lebensgeschichtlichen Merkmale tropischer Bergarten haben könnten. Kapitel 4 – Kryptische Arten und versteckte ökologische Wechselwirkungen bei Schmalbienen entlang eines Höhengradienten Starke Umweltgradienten, wie sie an Berghängen auftreten, stellen für Arten eine Herausforderung dar. Versteckte Anpassungen oder Interaktionen wurden in diesem Zusammenhang selten berücksichtigt. Als Modellorganismen haben wir Bienen der Gattung Lasioglossum verwendet, da Lasioglossum die einzige Bienengattung ist, die über den gesamten Höhengradienten am Kilimandscharo weit verbreitet ist. Wir fragten, ob und wie (a) kutikuläre Kohlenwasserstoffe (CHC), die als Barriere gegen Austrocknung wirken, sich in ihrer Zusammensetzung und Kettenlänge entlang von Temperatur- und Feuchtigkeitsänderungen verändern; (b) Lasioglossum Bienen ihre Pollennahrung mit wechselnder Ressourcenverfügbarkeit ändern; (c) Änderungen von Darm-Mikrobiota mit Pollennahrung und Klimabedingungen und Änderungen von Oberflächen-Mikrobiota mit CHC und Klimabedingungen zusammen hängen, und ob die Veränderungen eher durch den Wechsel von Lasioglossum Arten entlang des Höhengradienten beeinflusst werden. Wir fanden physiologische Anpassungen an das Klima in CHC, sowie Veränderungen in der Zusammensetzung von Pollennahrung und Mikrobiota, die auch miteinander korrelierten. Diese Ergebnisse deuten darauf hin, dass komplexe Wechselwirkungen und Rückkopplungen zwischen abiotischen und biotischen Bedingungen die Artenzusammensetzung in einer Gemeinschaft bestimmen. Kapitel 5 – Allgemeine Diskussion Abiotische und biotische Faktoren förderten die Artenvielfalt, Eigenschaften und Wechselwirkungen von Arten und sie wirkten unterschiedlich, je nachdem, welche funktionelle Gruppe untersucht wurde und ob räumliche oder zeitliche Einheiten berücksichtigt worden sind. Es ist daher wahrscheinlich, dass im Lichte des globalen Wandels verschiedene Arten, Merkmale und Wechselwirkungen unterschiedlich betroffen sein werden. Darüber hinaus könnte eine zunehmende Landnutzungsintensität zusätzliche Auswirkungen oder Wechselwirkungen mit dem Klimawandel auf die Biodiversität haben, auch wenn die potenziellen Landnutzungseffekte am Kilimandscharo noch gering sind und bis jetzt die hohlraumnistenden Hautflüglern nicht beeinträchtigen. Weitere Studien sollten sich mit Nahrungsnetzwerken befassen, die empfindlichere Veränderungen aufzeigen könnten. Nisthilfen bieten dafür ein gutes Modellsystem, um die Auswirkungen des globalen Wandels auf mehreren trophischen Ebenen zu untersuchen, und können auch direkte Auswirkungen des Klimawandels auf ganze lebensgeschichtliche Merkmale aufzeigen, wenn sie unter verschiedenen mikroklimatischen Bedingungen etabliert werden. Die nicht einheitlichen Auswirkungen abiotischer und biotischer Bedingungen auf mehrere Aspekte der Biodiversität, die in dieser Studie gezeigt wurden, zeigen auch, dass die Untersuchung verschiedener Aspekte der Biodiversität ein umfassenderes Bild vermitteln kann als Einzelbetrachtungen. KW - land use KW - Landnutzung KW - climate change KW - bees KW - wasps KW - biodiversity KW - Klimawandel KW - Bienen KW - Wespen KW - Biodiversität Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-182922 ER - TY - JOUR A1 - Mayr, Antonia V. A1 - Peters, Marcell K. A1 - Eardley, Connal D. A1 - Renner, Marion E. A1 - Röder, Juliane A1 - Steffan-Dewenter, Ingolf T1 - Climate and food resources shape species richness and trophic interactions of cavity-nesting Hymenoptera JF - Journal of Biogeography N2 - Aim: Temperature, food resources and top‐down regulation by antagonists are considered as major drivers of insect diversity, but their relative importance is poorly understood. Here, we used cavity‐nesting communities of bees, wasps and their antagonists to reveal the role of temperature, food resources, parasitism rate and land use as drivers of species richness at different trophic levels along a broad elevational gradient. Location: Mt. Kilimanjaro, Tanzania. Taxon: Cavity‐nesting Hymenoptera (Hymenoptera: Apidae, Colletidae, Megachilidae, Crabronidae, Sphecidae, Pompilidae, Vespidae). Methods: We established trap nests on 25 study sites that were distributed over similar large distances in terms of elevation along an elevational gradient from 866 to 1788 m a.s.l., including both natural and disturbed habitats. We quantified species richness and abundance of bees, wasps and antagonists, parasitism rates and flower or arthropod food resources. Data were analysed with generalized linear models within a multi‐model inference framework. Results: Elevational species richness patterns changed with trophic level from monotonically declining richness of bees to increasingly humped‐shaped patterns for caterpillar‐hunting wasps, spider‐hunting wasps and antagonists. Parasitism rates generally declined with elevation but were higher for wasps than for bees. Temperature was the most important predictor of both bee and wasp host richness patterns. Antagonist richness patterns were also well predicted by temperature, but in contrast to host richness patterns, additionally by resource abundance and diversity. The conversion of natural habitats through anthropogenic land use, which included biomass removal, agricultural inputs, vegetation structure and percentage of surrounding agricultural habitats, had no significant effects on bee and wasp communities. Main conclusions: Our study underpins the importance of temperature as a main driver of diversity gradients in ectothermic organisms and reveals the increasingly important role of food resources at higher trophic levels. Higher parasitism rates at higher trophic levels and at higher temperatures indicated that the relative importance of bottom‐up and top‐down drivers of species richness change across trophic levels and may respond differently to future climate change. KW - land-use change KW - species richness KW - trophic levels KW - wasps KW - feeding guilds KW - antagonists KW - bees KW - bottom‐up and top‐down control KW - elevational gradients Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-208101 VL - 47 IS - 4 ER - TY - JOUR A1 - Stein, Katharina A1 - Coulibaly, Drissa A1 - Stenchly, Kathrin A1 - Goetze, Dethardt A1 - Porembski, Stefan A1 - Lindner, André A1 - Konaté, Souleymane A1 - Linsenmair, Eduard K. T1 - Bee pollination increases yield quantity and quality of cash crops in Burkina Faso, West Africa JF - Scientific Reports N2 - Mutualistic biotic interactions as among flowering plants and their animal pollinators are a key component of biodiversity. Pollination, especially by insects, is a key element in ecosystem functioning, and hence constitutes an ecosystem service of global importance. Not only sexual reproduction of plants is ensured, but also yields are stabilized and genetic variability of crops is maintained, counteracting inbreeding depression and facilitating system resilience. While experiencing rapid environmental change, there is an increased demand for food and income security, especially in sub-Saharan communities, which are highly dependent on small scale agriculture. By combining exclusion experiments, pollinator surveys and field manipulations, this study for the first time quantifies the contribution of bee pollinators to smallholders’ production of the major cash crops, cotton and sesame, in Burkina Faso. Pollination by honeybees and wild bees significantly increased yield quantity and quality on average up to 62%, while exclusion of pollinators caused an average yield gap of 37% in cotton and 59% in sesame. Self-pollination revealed inbreeding depression effects on fruit set and low germination rates in the F1-generation. Our results highlight potential negative consequences of any pollinator decline, provoking risks to agriculture and compromising crop yields in sub-Saharan West Africa. KW - bees KW - pollination KW - Burkina Faso KW - cash crops KW - cotton KW - sesame Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-169914 VL - 7 IS - 17691 ER - TY - JOUR A1 - Ruedenauer, Fabian A. A1 - Wöhrle, Christine A1 - Spaethe, Johannes A1 - Leonhardt, Sara D. T1 - Do honeybees (Apis mellifera) differentiate between different pollen types? JF - PLoS ONE N2 - Bees receive nectar and pollen as reward for pollinating plants. Pollen of different plant species varies widely in nutritional composition. In order to select pollen of appropriate nutritional quality, bees would benefit if they could distinguish different pollen types. Whether they rely on visual, olfactory and/or chemotactile cues to distinguish between different pollen types, has however been little studied. In this study, we examined whether and how Apis mellifera workers differentiate between almond and apple pollen. We used differential proboscis extension response conditioning with olfactory and chemotactile stimulation, in light and darkness, and in summer and winter bees. We found that honeybees were only able to differentiate between different pollen types, when they could use both chemotactile and olfactory cues. Visual cues further improved learning performance. Summer bees learned faster than winter bees. Our results thus highlight the importance of multisensory information for pollen discrimination. KW - pollen KW - bees KW - honey bees KW - conditioned response KW - behavioral conditioning KW - foraging KW - nutrients KW - sensory cues Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-177537 VL - 13 IS - 11 ER - TY - JOUR A1 - Sommerlandt, Frank M. J. A1 - Spaethe, Johannes A1 - Rössler, Wolfgang A1 - Dyer, Adrian G. T1 - Does Fine Color Discrimination Learning in Free-Flying Honeybees Change Mushroom-Body Calyx Neuroarchitecture? JF - PLoS One N2 - Honeybees learn color information of rewarding flowers and recall these memories in future decisions. For fine color discrimination, bees require differential conditioning with a concurrent presentation of target and distractor stimuli to form a long-term memory. Here we investigated whether the long-term storage of color information shapes the neural network of microglomeruli in the mushroom body calyces and if this depends on the type of conditioning. Free-flying honeybees were individually trained to a pair of perceptually similar colors in either absolute conditioning towards one of the colors or in differential conditioning with both colors. Subsequently, bees of either conditioning groups were tested in non-rewarded discrimination tests with the two colors. Only bees trained with differential conditioning preferred the previously learned color, whereas bees of the absolute conditioning group, and a stimuli-naïve group, chose randomly among color stimuli. All bees were then kept individually for three days in the dark to allow for complete long-term memory formation. Whole-mount immunostaining was subsequently used to quantify variation of microglomeruli number and density in the mushroom-body lip and collar. We found no significant differences among groups in neuropil volumes and total microglomeruli numbers, but learning performance was negatively correlated with microglomeruli density in the absolute conditioning group. Based on these findings we aim to promote future research approaches combining behaviorally relevant color learning tests in honeybees under free-flight conditions with neuroimaging analysis; we also discuss possible limitations of this approach.q KW - bees KW - behavioral conditioning KW - learning KW - color vision KW - vision KW - calyx KW - cognition KW - honey bees Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-147932 VL - 11 IS - 10 ER - TY - JOUR A1 - Stejskal, Kerstin A1 - Streinzer, Martin A1 - Dyer, Adrian A1 - Paulus, Hannes F. A1 - Spaethe, Johannes T1 - Functional Significance of Labellum Pattern Variation in a Sexually Deceptive Orchid (Ophrys heldreichii): Evidence of Individual Signature Learning Effects JF - PLoS One N2 - Mimicking female insects to attract male pollinators is an important strategy in sexually deceptive orchids of the genus Ophrys, and some species possess flowers with conspicuous labellum patterns. The function of the variation of the patterns remains unresolved, with suggestions that these enhance pollinator communication. We investigated the possible function of the labellum pattern in Ophrys heldreichii, an orchid species in which the conspicuous and complex labellum pattern contrasts with a dark background. The orchid is pollinated exclusively by males of the solitary bee, Eucera berlandi. Comparisons of labellum patterns revealed that patterns within inflorescences are more similar than those of other conspecific plants. Field observations showed that the males approach at a great speed and directly land on flowers, but after an unsuccessful copulation attempt, bees hover close and visually scan the labellum pattern for up to a minute. Learning experiments conducted with honeybees as an accessible model of bee vision demonstrated that labellum patterns of different plants can be reliably learnt; in contrast, patterns of flowers from the same inflorescence could not be discriminated. These results support the hypothesis that variable labellum patterns in O. heldreichii are involved in flower-pollinator communication which would likely help these plants to avoid geitonogamy. KW - nectar KW - color discrimination KW - bees KW - vision KW - evolution KW - pollination KW - guides KW - honeybee KW - apis mellifera KW - insects KW - signals KW - recognize images Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-137582 VL - 10 IS - 11 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 - Lichtenstein, Leonie A1 - Sommerlandt, Frank M. J. A1 - Spaethe, Johannes T1 - Dumb and Lazy? A Comparison of Color Learning and Memory Retrieval in Drones and Workers of the Buff-Tailed Bumblebee, Bombus terrestris, by Means of PER Conditioning JF - PLoS One N2 - More than 100 years ago, Karl von Frisch showed that honeybee workers learn and discriminate colors. Since then, many studies confirmed the color learning capabilities of females from various hymenopteran species. Yet, little is known about visual learning and memory in males despite the fact that in most bee species males must take care of their own needs and must find rewarding flowers to obtain food. Here we used the proboscis extension response (PER) paradigm to study the color learning capacities of workers and drones of the bumblebee, Bombus terrestris. Light stimuli were paired with sucrose reward delivered to the insects’ antennae and inducing a reflexive extension of the proboscis. We evaluated color learning (i.e. conditioned PER to color stimuli) in absolute and differential conditioning protocols and mid-term memory retention was measured two hours after conditioning. Different monochromatic light stimuli in combination with neutral density filters were used to ensure that the bumblebees could only use chromatic and not achromatic (e.g. brightness) information. Furthermore, we tested if bees were able to transfer the learned information from the PER conditioning to a novel discrimination task in a Y-maze. Both workers and drones were capable of learning and discriminating between monochromatic light stimuli and retrieved the learned stimulus after two hours. Drones performed as well as workers during conditioning and in the memory test, but failed in the transfer test in contrast to workers. Our data clearly show that bumblebees can learn to associate a color stimulus with a sugar reward in PER conditioning and that both workers and drones reach similar acquisition and mid-term retention performances. Additionally, we provide evidence that only workers transfer the learned information from a Pavlovian to an operant situation. KW - memory KW - bumblebees KW - behavioral conditioning KW - honey bees KW - flowers KW - sucrose KW - bees KW - learning Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-125832 VL - 10 IS - 7 ER - TY - JOUR A1 - Pamir, Evren A1 - Szyszka, Paul A1 - Scheiner, Ricarda A1 - Nawrot, Martin P. T1 - Rapid learning dynamics in individual honeybees during classical conditioning JF - Frontiers in Behavioral Neuroscience N2 - Associative learning in insects has been studied extensively by a multitude of classical conditioning protocols. However, so far little emphasis has been put on the dynamics of learning in individuals. The honeybee is a well-established animal model for learning and memory. We here studied associative learning as expressed in individual behavior based on a large collection of data on olfactory classical conditioning (25 datasets, 3298 animals). We show that the group-averaged learning curve and memory retention score confound three attributes of individual learning: the ability or inability to learn a given task, the generally fast acquisition of a conditioned response (CR) in learners, and the high stability of the CR during consecutive training and memory retention trials. We reassessed the prevailing view that more training results in better memory performance and found that 24 h memory retention can be indistinguishable after single-trial and multiple-trial conditioning in individuals. We explain how inter-individual differences in learning can be accommodated within the Rescorla Wagner theory of associative learning. In both data-analysis and modeling we demonstrate how the conflict between population-level and single-animal perspectives on learning and memory can be disentangled. KW - sucrose sensitivity KW - sucrose responsiveness KW - learning curve KW - bees KW - apis mellifera KW - single-trial learning KW - classical conditioning KW - Rescorla-Wagner model KW - proboscis extension response (PER) Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-115365 SN - 1662-5153 VL - 8 IS - 313 ER - TY - JOUR A1 - Hopfenmueller, Sebastian A1 - Steffan-Dewenter, Ingolf A1 - Holzschuh, Andrea T1 - Trait-Specific Responses of Wild Bee Communities to Landscape Composition, Configuration and Local Factors N2 - Land-use intensification and loss of semi-natural habitats have induced a severe decline of bee diversity in agricultural landscapes. Semi-natural habitats like calcareous grasslands are among the most important bee habitats in central Europe, but they are threatened by decreasing habitat area and quality, and by homogenization of the surrounding landscape affecting both landscape composition and configuration. In this study we tested the importance of habitat area, quality and connectivity as well as landscape composition and configuration on wild bees in calcareous grasslands. We made detailed trait-specific analyses as bees with different traits might differ in their response to the tested factors. Species richness and abundance of wild bees were surveyed on 23 calcareous grassland patches in Southern Germany with independent gradients in local and landscape factors. Total wild bee richness was positively affected by complex landscape configuration, large habitat area and high habitat quality (i.e. steep slopes). Cuckoo bee richness was positively affected by complex landscape configuration and large habitat area whereas habitat specialists were only affected by the local factors habitat area and habitat quality. Small social generalists were positively influenced by habitat area whereas large social generalists (bumblebees) were positively affected by landscape composition (high percentage of semi-natural habitats). Our results emphasize a strong dependence of habitat specialists on local habitat characteristics, whereas cuckoo bees and bumblebees are more likely affected by the surrounding landscape. We conclude that a combination of large high-quality patches and heterogeneous landscapes maintains high bee species richness and communities with diverse trait composition. Such diverse communities might stabilize pollination services provided to crops and wild plants on local and landscape scales. KW - habitats KW - bees KW - grasslands KW - species diversity KW - biodiversity KW - pollination KW - flowers KW - foraging Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-112872 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 - Keller, Alexander A1 - Grimmer, Gudrun A1 - Steffan-Dewenter, Ingolf T1 - Diverse Microbiota Identified in Whole Intact Nest Chambers of the Red Mason Bee Osmia bicornis (Linnaeus 1758) JF - PLoS One N2 - Microbial activity is known to have profound impact on bee ecology and physiology, both by beneficial and pathogenic effects. Most information about such associations is available for colony-building organisms, and especially the honey bee. There, active manipulations through worker bees result in a restricted diversity of microbes present within the colony environment. Microbial diversity in solitary bee nests remains unstudied, although their larvae face a very different situation compared with social bees by growing up in isolated compartments. Here, we assessed the microbiota present in nests and pre-adults of Osmia bicornis, the red mason bee, by culture-independent pyrosequencing. We found high bacterial diversity not comparable with honey bee colonies. We identified a variety of bacteria potentially with positive or negative interactions for bee larvae. However, most of the other diverse bacteria present in the nests seem to originate from environmental sources through incorporated nest building material and stored pollen. This diversity of microorganisms may cause severe larval mortality and require specific physiological or symbiotic adaptations against microbial threats. They may however also profit from such a diverse environment through gain of mutualistic partners. We conclude that further studies of microbiota interaction in solitary bees will improve the understanding of fitness components and populations dynamics. KW - bacteria KW - bacterial pathogens KW - bees KW - gut bacteria KW - honey bees KW - larvae KW - Pollen KW - Polymerase chain reaction Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-97305 ER - TY - JOUR A1 - Beier, Hildburg A1 - Gätschenberger, Heike A1 - Azzami, Klara A1 - Tautz, Jürgen T1 - Antibacterial Immune Competence of Honey Bees (Apis mellifera) Is Adapted to Different Life Stages and Environmental Risks JF - PLoS ONE N2 - The development of all honey bee castes proceeds through three different life stages all of which encounter microbial infections to a various extent. We have examined the immune strength of honey bees across all developmental stages with emphasis on the temporal expression of cellular and humoral immune responses upon artificial challenge with viable Escherichia coli bacteria. We employed a broad array of methods to investigate defence strategies of infected individuals: (a) fate of bacteria in the haemocoel; (b) nodule formation and (c) induction of antimicrobial peptides (AMPs). Newly emerged adult worker bees and drones were able to activate efficiently all examined immune reactions. The number of viable bacteria circulating in the haemocoel of infected bees declined rapidly by more than two orders of magnitude within the first 4–6 h post-injection (p.i.), coinciding with the occurrence of melanised nodules. Antimicrobial activity, on the other hand, became detectable only after the initial bacterial clearance. These two temporal patterns of defence reactions very likely represent the constitutive cellular and the induced humoral immune response. A unique feature of honey bees is that a fraction of worker bees survives the winter season in a cluster mostly engaged in thermoregulation. We show here that the overall immune strength of winter bees matches that of young summer bees although nodulation reactions are not initiated at all. As expected, high doses of injected viable E.coli bacteria caused no mortality in larvae or adults of each age. However, drone and worker pupae succumbed to challenge with E.coli even at low doses, accompanied by a premature darkening of the pupal body. In contrast to larvae and adults, we observed no fast clearance of viable bacteria and no induction of AMPs but a rapid proliferation of E.coli bacteria in the haemocoel of bee pupae ultimately leading to their death. KW - escherichia coli infections KW - honey bees KW - bees KW - antimicrobials KW - bacterial pathogens KW - larvae KW - pupae KW - winter Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-96895 ER - TY - THES A1 - Streinzer, Martin T1 - Sexual dimorphism of the sensory systems in bees (Hymenoptera, Apoidea) and the evolution of sex-specific adaptations in the context of mating behavior T1 - Sensorischer Geschlechtsdimorphismus bei Bienen (Hymenoptera, Apoidea) und die Evolution geschlechtsspezifischer Anpassungen im Kontext des Paarungsverhaltens N2 - Bees have had an intimate relationship with humans for millennia, as pollinators of fruit, vegetable and other crops and suppliers of honey, wax and other products. This relationship has led to an extensive understanding of their ecology and behavior. One of the most comprehensively understood species is the Western honeybee, Apis mellifera. Our understanding of sex-specific investment in other bees, however, has remained superficial. Signals and cues employed in bee foraging and mating behavior are reasonably well understood in only a handful of species and functional adaptations are described in some species. I explored the variety of sensory adaptations in three model systems within the bees. Females share a similar ecology and similar functional morphologies are to be expected. Males, engage mainly in mating behavior. A variety of male mating strategies has been described which differ in their spatiotemporal features and in the signals and cues involved, and thus selection pressures. As a consequence, males’ sensory systems are more diverse than those of females. In the first part I studied adaptations of the visual system in honeybees. I compared sex and caste-specific eye morphology among 5 species (Apis andreniformis, A. cerana, A. dorsata, A. florea, A. mellifera). I found a strong correlation between body size and eye size in both female castes. Queens have a relatively reduced visual system which is in line with the reduced role of visual perception in their life history. Workers differed in eye size and functional morphology, which corresponds to known foraging differences among species. In males, the eyes are conspicuously enlarged in all species, but a disproportionate enlargement was found in two species (A. dorsata, A. florea). I further demonstrate a correlation between male visual parameters and mating flight time, and propose that light intensities play an important role in the species-specific timing of mating flights. In the second study I investigated eye morphology differences among two phenotypes of drones in the Western honeybee. Besides normal-sized drones, smaller drones are reared in the colony, and suffer from reduced reproductive success. My results suggest that the smaller phenotype does not differ in spatial resolution of its visual system, but suffers from reduced light and contrast sensitivity which may exacerbate the reduction in reproductive success caused by other factors. In the third study I investigated the morphology of the visual system in bumblebees. I explored the association between male eye size and mating behavior and investigated the diversity of compound eye morphology among workers, queens and males in 11 species. I identified adaptations of workers that correlate with distinct foraging differences among species. Bumblebee queens must, in contrast to honeybees, fulfill similar tasks as workers in the first part of their life, and correspondingly visual parameters are similar among both female castes. Enlarged male eyes are found in several subgenera and have evolved several times independently within the genus, which I demonstrate using phylogenetic informed statistics. Males of these species engage in visually guided mating behavior. I find similarities in the functional eye morphology among large-eyed males in four subgenera, suggesting convergent evolution as adaptation to similar visual tasks. In the remaining species, males do not differ significantly from workers in their eye morphology. In the fourth study I investigated the sexual dimorphism of the visual system in a solitary bee species. Males of Eucera berlandi patrol nesting sites and compete for first access to virgin females. Males have enlarged eyes and better spatial resolution in their frontal eye region. In a behavioral study, I tested the effect of target size and speed on male mate catching success. 3-D reconstructions of the chasing flights revealed that angular target size is an important parameter in male chasing behavior. I discuss similarities to other insects that face similar problems in visual target detection. In the fifth study I examined the olfactory system of E. berlandi. Males have extremely long antennae. To investigate the anatomical grounds of this elongation I studied antennal morphology in detail in the periphery and follow the sexual dimorphism into the brain. Functional adaptations were found in males (e.g. longer antennae, a multiplication of olfactory sensilla and receptor neurons, hypertrophied macroglomeruli, a numerical reduction of glomeruli in males and sexually dimorphic investment in higher order processing regions in the brain), which were similar to those observed in honeybee drones. The similarities and differences are discussed in the context of solitary vs. eusocial lifestyle and the corresponding consequences for selection acting on males. N2 - Bienen und Menschen verbindet eine lange andauernde und enge Beziehung. Diese enge Beziehung hat zu einem ausgeprägten Wissen über die Ökologie und das Verhalten geführt. Die am besten untersuchte Bienenart ist die westliche Honigbiene, Apis mellifera. Der ausgeprägte Kasten- und Sexualdimorphismus hat das Studium der Geschlechterunterschiede vereinfacht und vorangetrieben. Unser Wissen über geschlechtsspezifische Investitionen bei Bienen ist jedoch in vielerlei Hinsicht lückenhaft geblieben. Die Signale und Achtungssignale die im Paarungsverhalten eine Rolle spielen sind nur bei einer Handvoll Arten hinreichend bekannt und funktionelle Anpassungen an diese sind in wenigen Arten beschrieben. In dieser Arbeit habe ich sensorische Anpassungen an geschlechtsspezifische Verhaltensweisen in drei Bienengruppen genauer untersucht. Weibchen und Arbeiterinnen haben generell eine ähnliche Lebensweise. Männchen beschäftigen sich fast ausschließlich mit der Partnersuche. Infolgedessen, zeigt die Sensorik der Männchen eine größere Vielfalt an morphologischen und funktionellen Anpassungen als die der Weibchen. Im ersten Abschnitt dieser Arbeit habe ich Anpassungen des visuellen Systems von 5 Honigbienenarten (Apis andreniformis, A. cerana, A. dorsata, A. florea, A. mellifera) untersucht. Ich finde eine deutliche Korrelation zwischen Körper- und Augengröße bei beiden weiblichen Kasten. Königinnen haben relativ kleinere Augen als Arbeiterinnen, was der verringerten Rolle visueller Wahrnehmung im Lebenszyklus dieser Kaste entspricht. Die Arbeiterinnen unterschieden sich sowohl in ihrer Augengröße als auch in der funktionellen Morphologie. Die Unterschiede passen jeweils zu der artspezifischen Ökologie. Drohnen aller Arten haben auffällig vergrößerte Augen, jedoch sind sie in zwei Arten (A. dorsata, A. florea) überproportional vergrößert. Zusätzlich zeige ich, dass bestimmte Augenparameter mit dem artspezifischen Paarungszeitpunkt korrelieren, und schlage vor, dass die Lichtintensität eine Rolle bei der Feststellung des richtigen Paarungszeitpunktes spielen könnte. In der zweiten Untersuchung habe ich die Augen von zwei Drohnenphänotypen von A. mellifera untersucht. Neben normalen Drohen werden in der Kolonie auch kleinere Drohnen aufgezogen, die unter einem geringeren Fortpflanzungserfolg leiden. Meine Ergebnisse zeigen, dass sich die Phänotypen vermutlich nicht in der räumlichen Auflösungsfähigkeit, jedoch in der Lichtempfindlichkeit der Augen von normalen Drohnen unterscheiden. In der dritten Untersuchung habe ich die Augenmorphologie bei 11 Hummelarten untersucht. Ich beschreibe in dieser Studie Anpassungen der Arbeiterinnen, die vermutlich mit der Habitatwahl im Zusammenhang stehen. Hummelköniginnen sind, im Gegensatz zu Königinnen der Honigbiene, in der ersten Zeit nach der Koloniegründung auf sich allein gestellt und müssen alle Aufgaben, die später von den Arbeiterinnen übernommen werden, selbst ausführen. Dementsprechend sind die Augen beider Weibchenkasten ähnlich in ihrer relativen Größe und funktionellen Morphologie. Vergrößerte Augen der Männchen können in Arten verschiedener Untergattungen gefunden werden und der Phänotyp ist im Laufe der Evolution mehrfach unabhängig entstanden, was ich mit phylogenetisch vergleichenden Methoden zeige. Die Augenmorphologie der vier untersuchten großäugigen Arten ist sehr ähnlich, was auf konvergente Evolution hinweist. Die Augenmorphologie der restlichen Arten unterscheidet sich hingegen nicht deutlich von jener der Weibchen. In der vierten Untersuchung habe ich mich dem Sexualdimorphismus der Solitärbienenart Eucera berlandi gewidmet. Männchen haben größere Augen und sowohl größere Facetten als auch eine höhere räumliche Auflösung im frontalen Gesichtsfeld als Weibchen. In einem Verhaltensversuch habe ich die Auswirkungen der Größe von Weibchendummies auf die Detektion getestet. In 3-D Rekonstruktionen der Weibchenverfolgung zeigte sich dass die Winkelgröße des Objektes, eine von der Distanz unabhängige Größe, eine wichtige Rolle spielt. Im Zusammenhang mit den gefundenen Daten diskutiere ich die Parallelen zu anderen Insektenarten. In der fünften Studie untersuche ich das olfaktorische System von E. berlandi. Männchen haben extreme lange Antennen. Um die anatomischen Grundlagen der geschlechtsspezifischen Antennenmorphologie zu untersuchen habe ich die Antennen beider Geschlechter im Detail studiert. Zusätzlich bin ich dem Dimorphismus entlang der olfaktorischen Bahn bis ins Gehirn gefolgt. Männchen zeige funktionelle Anpassungen (z.B. längere Antennen, eine höhere Anzahl an olfaktorischen Sensillen und Rezeptorneuronen, stark vergrößerte Glomeruli im Antennallobus, eine zahlenmäßige Reduktion der Glomeruli und geschlecherspezifische Investition in höhere Integrationszentren im Gehirn) an die Weibchendetektion. KW - Biene KW - Sinne KW - Verhalten KW - Neurobiologie KW - Geschlechtsunterschied KW - Biene KW - Hummel KW - Sinnesphysiologie KW - Evolution KW - bees KW - sensory ecology KW - evolution KW - visual system Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-78689 ER -