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ERK1/2 are known key players in the pathophysiology of heart failure, but the members of the ERK cascade, in particular Raf1, can also protect the heart from cell death and ischemic injury. An additional autophosphorylation (ERK1 at Thr208, ERK2 at Thr188) empowers ERK1/2 translocation to the nucleus and phosphorylation of nuclear targets which take part in the development of cardiac hypertrophy. Thereby, targeting this additional phosphorylation is a promising pharmacological approach.
In this thesis, an in silico model of ERK cascade in the cardiomyocyte is introduced. The model is a semi-quantitive model and its behavior was tested with different softwares (SQUAD and CellNetAnalyzer). Different phosphorylation states of ERK1/2 as well as different stimuli can be reproduced. The different types of stimuli include hypertrophic as well as non-hypertrophic stimuli. With the introduced in-silico model time courses and synergistic as well as antagonistic receptor stimuli combinations can be predicted. The simulated time courses were experimentally validated. SQUAD was mainly used to make predictions about time courses and thresholds, whereas CNA was used to analyze steady states and feedback loops.
Furthermore, new targets of ERK1/2 which partially contribute, also in the formation of cardiac hypertrophy, were identified and the most promising of them were illuminated. Important further targets are Caspase 8, GAB2, Mxi-2, SMAD2, FHL2 and SPIN90.
Cardiomyocyte gene expression data sets were analyzed to verify involved components and to find further significantly altered genes after induced hypertrophy with TAC (transverse aortic constriction). Changes in the ultrastructure of the cardiomyocyte are the final result of induced hypertrophy.
How diversity of life is generated, maintained, and distributed across space and time is the central question of community ecology. Communities are shaped by three assembly processes: (I) dispersal, (II) environ-mental, and (III) interaction filtering. Heterogeneity in environmental conditions can alter these filtering processes, as it increases the available niche space, spatially partitions the resources, but also reduces the effective area available for individual species. Ultimately, heterogeneity thus shapes diversity. However, it is still unclear under which conditions heterogeneity has positive effects on diversity and under which condi-tions it has negative or no effects at all. In my thesis, I investigate how environmental heterogeneity affects the assembly and diversity of diverse species groups and whether these effects are mediated by species traits.
In Chapter II, I first examine how much functional traits might inform about environmental filtering pro-cesses. Specifically, I examine to which extent body size and colour lightness, both of which are thought to reflect the species thermal preference, shape the distribution and abundance of two moth families along elevation. The results show, that assemblages of noctuid moths are more strongly driven by abiotic filters (elevation) and thus form distinct patterns in colour lightness and body size, while geometrid moths are driven by biotic filters (habitat availability), and show no decline in body size nor colour lightness along elevation. Thus, one and the same functional trait can have quite different effects on community assembly even between closely related taxonomic groups.
In Chapter III, I elucidate how traits shift the relative importance of dispersal and environmental filtering in determining beta diversity between forests. Environmental filtering via forest heterogeneity had on aver-age higher independent effects than dispersal filtering within and among regions, suggesting that forest heterogeneity determines species turnover even at country-wide extents. However, the relative importance of dispersal filtering increased with decreasing dispersal ability of the species group. From the aspects of forest heterogeneity covered, variations in herb or tree species composition had overall stronger influence on the turnover of species than forest physiognomy. Again, this ratio was influenced by species traits, namely trophic position, and body size, which highlights the importance of ecological properties of a taxo-nomic group in community assembly.
In Chapter IV, I assess whether such ecological properties ultimately determine the level of heterogeneity which maximizes species richness. Here, I considered several facets of heterogeneity in forests. Though the single facets of heterogeneity affected diverse species groups both in positive and negative ways, we could not identify any generalizable mechanism based on dispersal nor the trophic position of the species group which would dissolve these complex relationships.
In Chapter V, I examine the effect of environmental heterogeneity of the diversity of traits itself to evalu-ate, whether the effects of environmental heterogeneity on species richness are truly based on increases in the number of niches. The results revealed that positive effects of heterogeneity on species richness are not necessarily based on an increased number of niches alone, but proposedly also on a spatially partition of resources or sheltering effects. While ecological diversity increased overall, there were also negative trends which indicate filtering effects via heterogeneity.
In Chapter VI, I present novel methods in measuring plot-wise heterogeneity of forests across continental scales via Satellites. The study compares the performance of Sentinel-1 and LiDar-derived measurements in depicting forest structures and heterogeneity and to their predictive power in modelling diversity. Senti-nel-1 could match the performance of Lidar and shows high potential to assess free yet detailed infor-mation about forest structures in temporal resolutions for modelling the diversity of species.
Overall, my thesis supports the notion that heterogeneity in environmental conditions is an important driv-er of beta-diversity, species richness, and ecological diversity. However, I could not identify any general-izable mechanism which direction and form this effect will have.
The Chimpanzees of the Comoé National Park, Ivory Coast. Status, distribution, ecology and behavior
(2021)
Although wild chimpanzees (Pan troglodytes) have been studied intensely for more than 50 years, there are still many aspects of their ecology and behavior that are not well understood. Every time that a new population of chimpanzees has been studied, new behaviors and unknown aspects of their ecology have been discovered. All this accumulated knowledge is helping us to piece together a model of how could last human and chimpanzee common ancestors have lived and behaved between seven and five million years ago. Comoé chimpanzees had never been studied in depth, until we started our research in October 2014, only a few censuses had been realized. The last surveys prior our work, stated that the population was so decimated that was probably functionally extinct. When we started this research, we had to begin with a new intensive survey, using new methods, to ascertain the real status and distribution of the chimpanzees living in Comoé National Park (CNP). During the last five years, we have realized a deep study aiming to know more about their ecology and behavior. We combined transects and reconnaissance marches (recces) with the use of camera traps, for the first time in CNP, obtaining a wealth of data that is not fully comprised in this dissertation. With this research, we determined that there is a sustainable continuous population of Western chimpanzees (Pan troglodytes verus) in CNP and the adjacent area of Mont Tingui, to the West, with a minimum of 127 weaned chimpanzees living in our main 900 km2 study area, SW of CNP. We found that this population is formed by a minimum of eight different chimpanzee communities, of which we studied seven, four of them more in detail. These chimpanzees spent much more time in the forest than in the savanna habitats.
We also found that Comoé chimpanzees consumed at least 58 different food items in their dit, which they obtained both from forest and savanna habitats. Another finding was that insectivory had an important role in their diet, with at least four species of ants, three of termites and some beetle larvae. These chimpanzees also hunted at least three species of monkeys and maybe rodents and duikers and occasionally consumed the big land snails of genus Achatina. We found that, during the fruit scarcity period in the late rainy season, they intensely consumed the cambium of Ceiba pentandra, as fallback food, much more than the bark or cambium of any other tree species. Another interesting finding was that all the chimpanzees in the studied area realized this particular bark-peeling behavior and had been repeatedly peeling the trees of this species for years. This did not increase tree mortality and the damage caused to the trees was healed in two years, not reducing the growth, thus being a sustainable use of the trees. We found that Comoé chimpanzees produced and used a great variety of tools, mainly from wooden materials, but also from stone and herbaceous vegetation.
Their tool repertory included stick tools to dip for Dorylus burmeisteri ants, to fish for Camponotus and Crematogaster ants, to dip for honey, mainly from Meliponini stingless bees, but sometimes from honey bees (Apis mellifera). It also included the use of stick tools to fish termites of Macrotermes subhyalinus and Odontotermes majus (TFTs), to dip for water from tree holes and investigatory probes for multiple purposes. Additionally, these chimpanzees used leaf-sponges to drink from tree holes and to collect clayish water from salt-licks. They also used stones to hit the buttresses of trees during displays, the so called accumulative stone throwing behavior and probably used stones as hammers, to crack open hard-shelled Strichnos spinosa and Afraegle paniculata fruits and Achatina snails. The chimpanzees also used objects that are not generally accepted as animal tools, for being attached to the substrate, with different purposes: they drummed buttresses of trees with hands and/or feet to produce sound during male displays and they pounded open hard-shelled fruits, Achatina snails and Cubitermes termite mounds on stone or root anvils. We finally measured the stick tools and found significant differences between them suggesting that they were specialized tools made specifically for every purpose. We studied more in detail the differences between apparently similar tools, the honey dipping tools and the water dipping tools, often with brushes made at their tips to collect the fluids. These last tools were exclusive from Comoé and have not been described at any other site. We found that total length, diameter and brush length were significantly different, suggesting that they were specialized tools. We concluded that Comoé chimpanzees had a particular culture, different from those of other populations of Western chimpanzees across Africa. Efficient protection, further research and permanent presence of research teams are required to avoid that this unique population and its culture disappears by the poaching pressure and maybe by the collateral effects of climate change.
Temporal development of communities with a focus on insects, in time series of one to four decades
(2021)
Changes and development are fundamental principles in biocenoses and can affect a multitude of ecological processes. In insect communities phenological and density changes, changes in species richness and community composition, as well as interactions between those changes, are the most important macro processes. However, climate change and other factors like habitat degradation and loss alter these processes leading to shifts and general biodiversity declines. Even though knowledge about insect decline in central Europe increased during the last decades, there are significant knowledge gaps about the development of insect communities in certain habitats and taxa. For example, insect communities in small lentic as well as in forested habitats are under-sampled and reported to be less endangered than communities in other habitats. Furthermore, the changes within habitats and taxa are additionally influenced by certain traits, like host or feeding specialization. To disentangle these influences and to increase the knowledge about the general long-term development of insect communities, comprehensive long-term monitoring studies are needed. In addition, long-term effects of conservation strategies should also be evaluated on large time scales in order to be able to decide on a scientific base which strategies are effective in promoting possibly declining taxa. Hence, this thesis also tackles the effects of an integrative conservation strategy on wood dependent beetle and fungi, beside the development of water beetle and macro moth communities over multiple decades. In Chapter 2 I present a study on the development of water beetle communities (Dytiscidae, Haliplidae, Noteridae) in 33 water bodies in Southern Germany from 1991 to 2018. Time-standardized capture per waterbody was used during three periods: between 1991 and 1995, 2007 and 2008, and 2017 and 2018. Results showed annual declines in both species number (ca. -1%) and abundance (ca. -2%). In addition, community composition shifted over time in part due to changing pH values. Hence, the recorded changes during the 28-year study period partly reflect natural succession processes. However, since also moor-related beetle species decreased significantly, it is likely that water beetles in southern Germany are also threatened by non-successional factors, including desiccation, increased nitrogen input and/or mineralization, as well as the loss of specific habitats. The results suggest, that in small to midsize lentic waterbodies, current development should aim for constant creation of new water bodies and protection of moor waterbodies in order to protect water beetle communities on a landscape scale. In Chapter 3 I present an analysis of the development of nocturnal macro moth species richness, abundance and biomass over four decades in forests of southern Germany. Two local scale data sets featuring a coppiced oak forest as well as an oak high forest were analysed separately from a regional data set representing all forest types in the temperate zone of Central Europe. At the regional scale species richness, abundance and biomass showed annual declines of ca. 1 %, 1.3 % and 1.4 %, respectively. These declines were more pronounced in plant host specialists and in dark coloured species. In contrast, species richness increased by ca. 1.5 % annually in the coppiced forest, while no significant trends were found in the high forest. In contrast to past assumptions, insect decline apparently affects also hyper diverse insect groups in forests. Since host specialists and dark coloured species were affected more heavily by the decline than other groups, habitat loss and climate change seem to be potential drivers of the observed trends. However, the positive development of species richness in the coppiced oak forest indicates that maintaining complex and diverse forest ecosystems through active management might compensate for negative trends in biodiversity. Chapter 4 features a study specifically aiming to investigate the long-term effect of deadwood enrichment as an integrative conservation strategy on saproxylic beetles and fungi in a central European beech forest at a landscape scale. A before–after control–impact design, was used to compare assemblages and gamma diversities of saproxylic organisms (beetles and fungi) in strictly protected old-growth forest areas (reserves) and previously moderately and intensively managed forest areas. Forests were sampled one year before and a decade after starting a landscape-wide strategy of dead-wood enrichment. Ten years after the start of the dead-wood enrichment, neither gamma diversities of saproxylic organisms nor species composition of beetles did reflect the previous management types anymore. However, fungal species composition still mirrored the previous management gradient. The results demonstrated that intentional enrichment of dead wood at the landscape scale can effectively restore communities of saproxylic organisms and may thus be a suitable strategy in addition to permanent strict reserves in order to protect wood dependent organisms in Europe. In this thesis I showed, that in contrast to what was assumed and partly reported so far, also water beetles in lentic water bodies and macro moths in forests decreased in species richness, abundance and biomass during the last three to four decades. In line with earlier studies, especially dark coloured species and specialists decreased more than light-coloured species and generalists. The reasons for these declines could partly be attributed to natural processes and pollution and possibly to climate change. However, further studies, especially experimental ones, will be needed to achieve a better understanding of the reasons for insect decline. Furthermore, analyses of time series data should be interpreted cautiously especially if the number of sampling years is smaller than ten years. In addition, validation techniques such as left- and right- censoring and cross validation should be used in order to proof the robustness of the analyses. However, the lack of knowledge, we are still facing today, should not prevent scientists and practitioners from applying conservation measures. In order to prove the effectiveness of such measures, long-term monitoring is crucial. Such control of success is essential for evidence based and thus adapted conservation strategies of threatened organisms.
Recent progress in nanotechnology has attracted interest to a biomedical application of the carbon nanoparticle C60 fullerene (C60) due to its unique structure and versatile biological activity. In the current study the dual functionality of C60 as a photosensitizer and a drug nanocarrier was exploited to improve the efficiency of chemotherapeutic drugs towards human leukemic cells.
Pristine C60 demonstrated time-dependent accumulation with predominant mitochondrial localization in leukemic cells. C60’s effects on leukemic cells irradiated with high power single chip LEDs of different wavelengths were assessed to find out the most effective photoexcitation conditions. A C60-based noncovalent nanosized system as a carrier for an optimized drug delivery to the cells was evaluated in accordance to its physicochemical properties and toxic effects. Finally, nanomolar amounts of C60-drug nanocomplexes in 1:1 and 2:1 molar ratios were explored to improve the efficiency of cell treatment, complementing it with photodynamic approach.
A proposed treatment strategy was developed for C60 nanocomplexes with the common chemotherapeutic drug Doxorubicin, whose intracellular accumulation and localization, cytotoxicity and mechanism of action were investigated. The developed strategy was revealed to be transferable to an alternative potent anticancer drug – the herbal alkaloid Berberine.
Hereafter, a strong synergy of treatments arising from the combination of C60-mediated drug delivery and C60 photoexcitation was revealed. Presented data indicate that a combination of chemo- and photodynamic treatments with C60-drug nanoformulations could provide a promising synergetic approach for cancer treatment.
Owing to climate change, natural forest disturbances and consecutive salvage logging are drastically increasing worldwide, consequently increasing the importance of understanding how these disturbances would affect biodiversity conservation and provision of ecosystem services.
In chapter II, I used long-term water monitoring data and mid-term data on α-diversity of twelve species groups to quantify the effects of natural disturbances (windthrow and bark beetle) and salvage logging on concentrations of nitrate and dissolved organic carbon (DOC) in streamwater and α-diversity. I found that natural disturbances led to a temporal increase of nitrate concentrations in streamwater, but these concentrations remained within the health limits recommended by the World Health Organization for drinking water. Salvage logging did not exert any additional impact on nitrate and DOC concentrations, and hence did not affect streamwater quality. Thus, neither natural forest disturbances in watersheds nor associated salvage logging have a harmful effect on the quality of the streamwater used for drinking water. Natural disturbances increased the α-diversity in eight out of twelve species groups. Salvage logging additionally increased the α-diversity of five species groups related to open habitats, but decreased the biodiversity of three deadwood-dependent species groups.
In chapter III, I investigated whether salvage logging following natural disturbances (wildfire and windthrow) altered the natural successional trajectories of bird communities. I compiled data on breeding bird assemblages from nine study areas in North America, Europe and Asia, over a period of 17 years and tested whether bird community dissimilarities changed over time for taxonomic, functional and phylogenetic diversity when rare, common and dominant species were weighted differently. I found that salvage logging led to significantly larger dissimilarities than expected by chance and that these dissimilarities persisted over time for rare, common and dominant species, evolutionary lineages, and for rare functional groups. Dissimilarities were highest for rare, followed by common and dominant species.
In chapter IV, I investigated how β-diversity of 13 taxonomic groups would differ in intact, undisturbed forests, disturbed, unlogged forests and salvage-logged forests 11 years after a windthrow and salvage logging. The study suggests that both windthrow and salvage logging drive changes in between-treatment β-diversity, whereas windthrow alone seems to drive changes in within-treatment β-diversity. Over a decade after the windthrow at the studied site, the effect of subsequent salvage logging on within-treatment β-diversity was no longer detectable but the effect on between-treatment β-diversity persisted, with more prominent changes in saproxylic groups and rare species than in non-saproxylic groups or common and dominant species.
Based on these results, I suggest that salvage logging needs to be carefully weighed against its long-lasting impact on communities of rare species. Also, setting aside patches of naturally disturbed areas is a valuable management alternative as these patches would enable post-disturbance succession of bird communities in unmanaged patches and would promote the conservation of deadwood-dependent species, without posing health risks to drinking water sources.
Plasma membrane receptors are the most crucial and most commonly studied components of cells, since they not only ensure communication between the extracellular space and cells, but are also responsible for the regulation of cell cycle and cell division. The composition of the surface receptors, the so-called "Receptome", differs and is characteristic for certain cell types. Due to their significance, receptors have been important target structures for diagnostic and therapy in cancer medicine and often show aberrant expression patterns in various cancers compared to healthy cells. However, these aberrations can also be exploited and targeted by different medical approaches, as in the case of personalized immunotherapy. In addition, advances in modern fluorescence microscopy by so-called single molecule techniques allow for unprecedented sensitive visualization and quantification of molecules with an attainable spatial resolution of 10-20 nm, allowing for the detection of both stoichiometric and expression density differences.
In this work, the single molecule sensitive method dSTORM was applied to quantify the receptor composition of various cell lines as well as in primary samples obtained from patients with hematologic malignancies. The focus of this work lies on artefact free quantification, stoichiometric analyses of oligomerization states and co localization analyses of membrane receptors.
Basic requirements for the quantification of receptors are dyes with good photoswitching properties and labels that specifically mark the target structure without generating background through non-specific binding. To ensure this, antibodies with a predefined DOL (degree of labeling) were used, which are also standard in flow cytometry. First background reduction protocols were established on cell lines prior analyses in primary patient samples. Quantitative analyses showed clear expression differences between the cell lines and the patient cells, but also between individual patients.
An important component of this work is the ability to detect the oligomerization states of receptors, which enables a more accurate quantification of membrane receptor densities compared to standard flow cytometry. It also provides information about the activation of a certain receptor, for example of FLT3, a tyrosine kinase, dimerizing upon activation. For this purpose, different well-known monomers and dimers were compared to distinguish the typical localization statistics of single bound antibodies from two or more antibodies that are in proximity. Further experiments as well as co localization analyses proved that antibodies can bind to closely adjacent epitopes despite their size.
These analytical methods were subsequently applied for quantification and visualization of receptors in two clinically relevant examples. Firstly, various therapeutically relevant receptors such as CD38, BCMA and SLAMF7 for multiple myeloma, a malignant disease of plasma cells, were analyzed and quantified on patient cells. Furthermore, the influence of TP53 and KRAS mutations on receptor expression levels was investigated using the multiple myeloma cell lines OPM2 and AMO1, showing clear differences in certain receptor quantities.
Secondly, FLT3 which is a therapeutic target receptor for acute myeloid leukemia, was quantified and stoichiometrically analyzed on both cell lines and patient cells. In addition, cells that have developed resistance against midostaurin were compared with cells that still respond to this type I tyrosine-kinase-inhibitor for their FLT3 receptor expression and oligomerization state.
Chlamydia trachomatis, an obligate intracellular human pathogen, is the world’s leading cause of infection related blindness and the most common, bacterial sexually transmitted disease. In order to establish an optimal replicative niche, the pathogen extensively interferes with the physiology of the host cell. Chlamydia switches in its complex developmental cycle between the infectious non-replicative elementary bodies (EBs) and the non-infectious replicative reticulate bodies (RBs). The transformation to RBs, shortly after entering a host cell, is a crucial process in infection to start chlamydial replication. Currently it is unknown how the transition from EBs to RBs is initiated. In this thesis, we could show that, in an axenic media approach, L glutamine uptake by the pathogen is crucial to initiate the EB to RB transition. L-glutamine is converted to amino acids which are used by the bacteria to synthesize peptidoglycan. Peptidoglycan inturn is believed to function in separating dividing Chlamydia. The glutamine metabolism is reprogrammed in infected cells in a c-Myc-dependent manner, in order to accomplish the increased requirement for L-glutamine. Upon a chlamydial infection, the proto-oncogene c-Myc gets upregulated to promote host cell glutaminolysis via glutaminase GLS1 and the L-glutamine transporter SLC1A5/ASCT2. Interference with this metabolic reprogramming leads to limited growth of C. trachomatis. Besides the active infection, Chlamydia can persist over a long period of time within the host cell whereby chronic and recurrent infections establish. C. trachomatis acquire a persistent state during an immune attack in response to elevated interferon-γ (IFN-γ) levels. It has been shown that IFN-γ activates the catabolic depletion of L-tryptophan via indoleamine 2,3-dioxygenase (IDO), resulting in the formation of non-infectious atypical chlamydial forms. In this thesis, we could show that IFN-γ depletes the key metabolic regulator c-Myc, which has been demonstrated to be a prerequisite for chlamydial development and growth, in a STAT1-dependent manner. Moreover, metabolic analyses revealed that the pathogen de routs the host cell TCA cycle to enrich pyrimidine biosynthesis. Supplementing pyrimidines or a-ketoglutarate helps the bacteria to partially overcome the persistent state. Together, the results indicate a central role of c-Myc induced host glutamine metabolism reprogramming and L-glutamine for the development of C. trachomatis, which may provide a basis for anti-infectious strategies. Furthermore, they challenge the longstanding hypothesis of L-tryptophan shortage as the sole reason for IFN-γ induced persistence and suggest a pivotal role of c-Myc in the control of the C. trachomatis dormancy.
The biosphere harbors a large quantity and diversity of microbial organisms that can thrive in all environments. Estimates of the total number of microbial species reach up to 1012, of which less than 15,000 have been characterized to date. It has been challenging to delineate phenotypically, evolutionary and ecologically meaningful lineages such as for example, species, subspecies and strains. Even within recognized species, gene content can vary considerably between sublineages (for example strains), a problem that can be addressed by analyzing pangenomes, defined as the non-redundant set of genes within a phylogenetic clade, as evolutionary units.
Species considered to be ecologically and evolutionary coherent units, however to date it is still not fully understood what are primary habitats and ecological niches of many prokaryotic species and how environmental preferences drive their genomic diversity. Majority of comparative genomics studies focused on a single prokaryotic species in context of clinical relevance and ecology. With accumulation of sequencing data due to genomics and metagenomics, it is now possible to investigate trends across many species, which will facilitate understanding of pangenome evolution, species and subspecies delineation.
The major aims of this thesis were 1) to annotate habitat preferences of prokaryotic species and strains; 2) investigate to what extent these environmental preferences drive genomic diversity of prokaryotes and to what extent phylogenetic constraints limit this diversification; 3) explore natural nucleotide identity thresholds to delineate species in bacteria in metagenomics gene catalogs; 4) explore species delineation for applications in subspecies and strain delineation in metagenomics.
The first part of the thesis describes methods to infer environmental preferences of microbial species. This data is a prerequisite for the analyses performed in the second part of the thesis which explores how the structure of bacterial pangenomes is predetermined by past evolutionary history and how is it linked to environmental preferences of the species. The main finding in this subchapter that habitat preferences explained up to 49% of the variance for pangenome structure, compared to 18% by phylogenetic inertia. In general, this trend indicates that phylogenetic inertia does not limit evolution of pangenome size and diversity, but that convergent evolution may overcome phylogenetic constraints. In this project we show that core genome size is associated with higher environmental ubiquity of species. It is likely this is due to the fact that species need to have more versatile genomes and most necessary genes need to be present in majority of genomes of that species to be highly prevalent. Taken together these findings may be useful for future predictive analyses of ecological niches in newly discovered species.
The third part of the thesis explores data-driven, operational species boundaries. I show that homologous genes from the same species from different genomes tend to share at least 95% of nucleotide identity, while different species within the same genus have lower nucleotide identity. This is in line with other studies showing that genome-wide natural species boundary might be in range of 90-95% of nucleotide identity. Finally, the fourth part of the thesis discusses how challenges in species delineation are relevant for the identification of meaningful within-species groups, followed by a discussion on how advancements in species delineation can be applied for classification of within-species genomic diversity in the age of metagenomics.
Nutrition facts of pollen: nutritional quality and how it affects reception and perception in bees
(2021)
Nutrients belong to the key elements enabling life and influencing an organism’s fitness. The intake of nutrients in the right amounts and ratios can increase fitness; strong deviations from the optimal intake target can decrease fitness. Hence, the ability to assess the nutritional profile of food would benefit animals. To achieve this, they need the according nutrient receptors, the ability to interpret the receptor information via perceptive mechanisms, and the ability to adjust their foraging behavior accordingly. Additionally, eventually existing correlations between the nutrient groups and single nutrient compounds in food could help them to achieve this adjustment. A prominent interaction between food and consumer is the interaction between flowering plants (angiosperms) and animal pollinators. Usually both of the interacting partners benefit from this mutualistic interaction. Plants are pollinated while pollinators get a (most of the times) nutritional reward in form of nectar and/or pollen. As similar interactions between plants and animals seem to have existed even before the emergence of angiosperms, these interactions between insects and angiosperms very likely have co-evolved right from their evolutionary origin. Therefore, insect pollinators with the ability to assess the nutritional profile may have shaped the nutritional profile of plant species depending on them for their reproduction via selection pressure. In Chapter I of this thesis the pollen nutritional profile of many plant species was analyzed in the context of their phylogeny and their dependence on insect pollinators. In addition, correlations between the nutrients were investigated. While the impact of phylogeny on the pollen protein content was little, the mutual outcome of both of the studies included in this chapter is that protein content of pollen is mostly influenced by the plant’s dependence on insect pollinators. Several correlations found between nutrients within and between the nutrient groups could additionally help the pollinators to assess the nutrient profile of pollen. An important prerequisite for this assessment would be that the pollinators are able to differentiate between pollen of different plant species. Therefore, in Chapter II it was investigated whether bees have this ability. Specifically, it was investigated whether honeybees are able to differentiate between pollen of two different, but closely related plant species and whether bumblebees prefer one out of three pollen mixes, when they were fed with only one of them as larvae. Honeybees indeed were able to differentiate between the pollen species and bumblebees preferred one of the pollen mixes to the pollen mix they were fed as larvae, possibly due to its nutritional content. Therefore, the basis for pollen nutrient assessment is given in bees. However, there also was a slight preference for the pollen fed as larvae compared to another non-preferred pollen mix, at least hinting at the retention of larval memory in adult bumblebees. Chapter III looks into nutrient perception of bumblebees more in detail. Here it was shown that they are principally able to perceive amino acids and differentiate between them as well as different concentrations of the same amino acid. However, they do not seem to be able to assess the amino acid content in pollen or do not focus on it, but instead seem to focus on fatty acids, for which they could not only perceive concentration differences, but also were able to differentiate between. These findings were supported by feeding experiments in which the bumblebees did not prefer any of the pollen diets containing less or more amino acids but preferred pollen with less fatty acids. In no choice feeding experiments, bumblebees receiving a diet with high fatty acid content accepted undereating other nutrients instead of overeating fat, leading to increased mortality and the inability to reproduce. Hence, the importance of fat in pollen needs to be looked into further. In conclusion, this thesis shows that the co-evolution of flowering plants and pollinating insects could be even more pronounced than thought before. Insects do not only pressure the plants to produce high quality nectar, but also pressure those plants depending on insect pollination to produce high quality pollen. The reason could be the insects’ ability to receive and perceive certain nutrients, which enables them to forage selectively leading to a higher reproductive success of plants with a pollinator-suitable nutritional pollen profile.