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Anthropogenic and environmental drivers shape diversity of naturalized plants across the Pacific
(2021)
Aim
The Pacific exhibits an exceptional number of naturalized plant species, but the drivers of this high diversity and the associated compositional patterns remain largely unknown. Here, we aim to (a) improve our understanding of introduction and establishment processes and (b) evaluate whether this information is sufficient to create scientific conservation tools, such as watchlists.
Location
Islands in the Pacific Ocean, excluding larger islands such as New Zealand, Japan, the Philippines and Indonesia.
Methods
We combined information from the most up‐to‐date data sources to quantify naturalized plant species richness and turnover across island groups and investigate the effects of anthropogenic, biogeographic and climate drivers on these patterns. In total, we found 2,672 naturalized plant species across 481 islands and 50 island groups, with a total of 11,074 records.
Results
Most naturalized species were restricted to few island groups, and most island groups have a low number of naturalized species. Island groups with few naturalized species were characterized by a set of widespread naturalized species. Several plant families that contributed many naturalized species globally also did so in the Pacific, particularly Fabaceae and Poaceae. However, many families were significantly over‐ or under‐represented in the Pacific naturalized flora compared to other regions of the world. Naturalized species richness increased primarily with increased human activity and island altitude/area, whereas similarity between island groups in temperature along with richness differences was most important for beta diversity.
Main conclusions
The distribution and richness of naturalized species can be explained by a small set of drivers. The Pacific region contains many naturalized plant species also naturalized in other regions in the world, but our results highlight key differences such as a stronger role of anthropogenic drivers in shaping diversity patterns. Our results establish a basis for predicting and preventing future naturalizations in a threatened biodiversity hotspot.
The term ‘urban beekeeping’ connotes a host of meanings—sociopolitical, commercial, ecological and personal—beyond the mere description of where bees and beekeepers happen to coincide. Yet, these meanings are seldom articulated explicitly or brought into critical engagement with the relevant fields of urban ecology and political ecology.
Beginning with a brief account of the history of urban beekeeping in the United States, we draw upon urban ecological theory to construct a conceptual model of urban beekeeping that distinguishes beekeeping in, of and for the city. In our model, beekeeping in the city describes the mere importation of the traditionally rural practice of beekeeping into urban spaces for the private reasons of the individual beekeeper, whereas beekeeping of the city describes beekeeping that is consciously tailored to the urban context, often accompanied by (semi)professionalization of beekeepers and the formation of local expert communities (i.e. beekeeping associations). Beekeeping for the city describes a shift in mindset in which beekeeping is directed to civic ends beyond the boundaries of the beekeeping community per se.
Using this framework, we identify and discuss specific socioecological assets and liabilities of urban beekeeping, and how these relate to beekeeping in, of and for the city. We then formulate actionable guidelines for maturing the practice of urban beekeeping into a beneficent and self‐critical form of urban ecological citizenship; these include fostering self‐regulation within the beekeeping community, harnessing beekeeping as a ‘gateway’ experience for a broader rapprochement between urban residents and nature, and recognizing the political‐ecological context of beekeeping with respect to matters of socioecological justice.
Cryptic species and hidden ecological interactions of halictine bees along an elevational gradient
(2021)
Changes of abiotic and biotic conditions along elevational gradients represent serious challenges to organisms which may promote the turnover of species, traits and biotic interaction partners. Here, we used molecular methods to study cuticular hydrocarbon (CHC) profiles, biotic interactions and phylogenetic relationships of halictid bees of the genus Lasioglossum along a 2,900 m elevational gradient at Mt. Kilimanjaro, Tanzania. We detected a strong species turnover of morphologically indistinguishable taxa with phylogenetically clustered cryptic species at high elevations, changes in CHC profiles, pollen resource diversity, and a turnover in the gut and body surface microbiome of bees. At high elevations, increased proportions of saturated compounds in CHC profiles indicate physiological adaptations to prevent desiccation. More specialized diets with higher proportions of low‐quality Asteraceae pollen imply constraints in the availability of food resources. Interactive effects of climatic conditions on gut and surface microbiomes, CHC profiles, and pollen diet suggest complex feedbacks among abiotic conditions, ecological interactions, physiological adaptations, and phylogenetic constraints as drivers of halictid bee communities at Mt. Kilimanjaro.
Most parasites and parasitoids are adapted to overcome defense mechanisms of their specific hosts and hence colonize a narrow range of host species. Accordingly, an increase in host functional or phylogenetic dissimilarity is expected to increase the species diversity of parasitoids. However, the local diversity of parasitoids may be driven by the accessibility and detectability of hosts, both increasing with increasing host abundance. Yet, the relative importance of these two mechanisms remains unclear. We parallelly reared communities of saproxylic beetle as potential hosts and associated parasitoid Hymenoptera from experimentally felled trees. The dissimilarity of beetle communities was inferred from distances in seven functional traits and from their evolutionary ancestry. We tested the effect of host abundance, species richness, functional, and phylogenetic dissimilarities on the abundance, species richness, and Shannon diversity of parasitoids. Our results showed an increase of abundance, species richness, and Shannon diversity of parasitoids with increasing beetle abundance. Additionally, abundance of parasitoids increased with increasing species richness of beetles. However, functional and phylogenetic dissimilarity showed no effect on the diversity of parasitoids. Our results suggest that the local diversity of parasitoids, of ephemeral and hidden resources like saproxylic beetles, is highest when resources are abundant and thereby detectable and accessible. Hence, in some cases, resources do not need to be diverse to promote parasitoid diversity.
The response of populations and species to changing conditions determines how community composition will change functionally, including via trait shifts. Selection from standing variation has been suggested to be more efficient than acquiring new mutations. Yet, studies on community trait composition and trait selection largely focus on phenotypic variation in ecological traits, whereas the underlying genomic traits remain understudied. Using a genome‐explicit, niche‐ and individual‐based model, we address the potential interactions between genomic and ecological traits shaping communities under an environmental selective forcing, namely temporal positively autocorrelated environmental fluctuation. In this model, all ecological traits are explicitly coded by the genome. For our experiments, we initialized 90 replicate communities, each with ca 350 initial species, characterized by random genomic and ecological trait combinations, on a 2D spatially explicit landscape with two orthogonal gradients (temperature and resource use). We exposed each community to two contrasting scenarios: without (i.e. static environments) and with temporal variation. We then analyzed emerging compositions of both genomic and ecological traits at the community, population and genomic levels. Communities in variable environments were species poorer than in static environments, and populations more abundant, whereas genomes had lower genetic linkage, mean genetic variation and a non‐significant tendency towards higher numbers of genes. The surviving genomes (i.e. those selected by variable environments) coded for enhanced environmental tolerance and smaller biomass, which resulted in faster life cycles and thus also in increased potential for evolutionary rescue. Under temporal environmental variation, larger, less linked genomes retained more variation in mean dispersal ability at the population level than at genomic level, whereas the opposite trend emerged for biomass. Our results provide clues to how sexually‐reproducing diploid plant communities might react to variable environments and highlights the importance of genomic traits and their interaction with ecological traits for eco‐evolutionary responses to changing climates.
Like human Th1 cells, mouse Th1 cells also secrete IFN‐γ upon stimulation with a superagonistic anti‐CD28 monoclonal antibody (CD28‐SA). Crosslinking of the CD28‐SA via FcR and CD40‐CD40L interactions greatly increased IFN‐γ release. Our data stress the utility of the mouse as a model organism for immune responses in humans.
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.
An adequate task allocation among colony members is of particular importance in large insect societies. Some species exhibit distinct polymorphic worker classes which are responsible for a specific range of tasks. However, much more often the behavior of the workers is related to the age of the individual. Ants of the genus Cataglyphis (Foerster 1850) undergo a marked age-related polyethism with three distinct behavioral stages. Newly emerged ants (callows) remain more or less motionless in the nest for the first day. The ants subsequently fulfill different tasks inside the darkness of the nest for up to four weeks (interior workers) before they finally leave the nest to collect food for the colony (foragers).
This thesis focuses on the neuronal substrate underlying the temporal polyethism in Cataglyphis nodus ants by addressing following major objectives:
(1) Investigating the structures and neuronal circuitries of the Cataglyphis brain to understand potential effects of neuromodulators in specific brain neuropils.
(2) Identification and localization of neuropeptides in the Cataglyphis brain.
(3) Examining the expression of suitable neuropeptide candidates during behavioral maturation of Cataglyphis workers.
The brain provides the fundament for the control of the behavioral output of an insect. Although the importance of the central nervous system is known beyond doubt, the functional significance of large areas of the insect brain are not completely understood. In Cataglyphis ants, previous studies focused almost exclusively on major neuropils while large proportions of the central protocerebrum have been often disregarded due to the lack of clear boundaries. Therefore, I reconstructed a three-dimensional Cataglyphis brain employing confocal laser scanning microscopy. To visualize synapsin-rich neuropils and fiber tracts, a combination of fluorescently labeled antibodies, phalloidin (a cyclic peptide binding to filamentous actin) and anterograde tracers was used. Based on the unified nomenclature for insect brains, I defined traceable criteria for the demarcation of individual neuropils. The resulting three-dimensional brain atlas provides information about 33 distinct synapse-rich neuropils and 30 fiber tracts, including a comprehensive description of the olfactory and visual tracts in the Cataglyphis brain. This three-dimensional brain atlas further allows to assign present neuromodulators to individual brain neuropils.
Neuropeptides represent the largest group of neuromodulators in the central nervous system of insects. They regulate important physiological and behavioral processes and have therefore recently been associated with the regulation of the temporal polyethism in social insects. To date, the knowledge of neuropeptides in Cataglyphis ants has been mainly derived from neuropeptidomic data of Camponotus floridanus ants and only a few neuropeptides have been characterized in Cataglyphis. Therefore, I performed a comprehensive transcriptome analysis in Cataglyphis nodus ants and identified peptides by using Q-Exactive Orbitrap mass spectrometry (MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS. This resulted in the characterization of 71 peptides encoded on 49 prepropeptide genes, including a novel neuropeptide-like gene (fliktin). In addition, high-resolution MALDI-TOF MS imaging (MALDI-MSI) was applied for the first time in an ant brain to localize peptides on thin brain cryosections. Employing MALDI-MSI, I was able to visualize the spatial distribution of 35 peptides encoded on 16 genes.
To investigate the role of neuropeptides during behavioral maturation, I selected suitable neuropeptide candidates and analyzed their spatial distributions and expression levels following major behavioral transitions. Based on recent studies, I suggested the neuropeptides allatostatin-A (Ast-A), corazonin (Crz) and tachykinin (TK) as potential regulators of the temporal polyethism. The peptidergic neurons were visualized in the brain of C. nodus ants using immunohistochemistry. Independent of the behavioral stages, numerous Ast-A- and TK-immunoreactive (-ir) neurons innervate important high-order integration centers and sensory input regions with cell bodies dispersed all across the cell body rind. In contrast, only four corazonergic neurons per hemisphere were found in the Cataglyphis brain. Their somata are localized in the pars lateralis with axons projecting to the medial protocerebrum and the retrocerebral complex. Number and branching patterns of the Crz-ir neurons were similar across behavioral stages, however, the volume of the cell bodies was significantly larger in foragers than in the preceding behavioral stages. In addition, quantitative PCR analyses displayed increased Crz and Ast-A mRNA levels in foragers, suggesting a concomitant increase of the peptide levels. The task-specific expression of Crz and Ast-A along with the presence in important sensory input regions, high-order integration center, and the neurohormonal organs indicate a sustaining role of the neuropeptides during behavioral maturation of Cataglyphis workers.
The present thesis contains a comprehensive reference work for the brain anatomy and the neuropeptidome of Cataglyphis ants. I further demonstrated that neuropeptides are suitable modulators for the temporal polyethism of Cataglyphis workers. The complete dataset provides a solid framework for future neuroethological studies in Cataglyphis ants as well as for comparative studies on insects. This may help to improve our understanding of the functionality of individual brain neuropils and the role of neuropeptides, particularly during behavioral maturation in social insects.
Analysis of \(Trypanosoma\) \(brucei\) motility and the infection process in the tsetse fly vector
(2021)
African trypanosomes are protist pathogens that are infective for a wide spectrum of mammalian hosts. Motility has been shown to be essential for their survival and represents an important virulence factor. Trypanosoma brucei is transmitted by the bite of the bloodsucking tsetse fly, the only vector for these parasites. The voyage through the fly is complex and requires several migration, proliferation and differentiation steps, which take place in a defined order and in specific fly tissues.
The first part of this doctoral thesis deals with the establishment of the trypanosome tsetse system as a new model for microswimmer analysis. There is an increasing interdisciplinary interest in microbial motility, but a lack of accessible model systems. Therefore, this work introduces the first enclosed in vivo host parasite system that is suitable for analysis of diverse microswimmer types in specific microenvironments. Several methods were used and adapted to gain unprecedented insights into trypanosome motion, the fly´s interior architecture and the physical interaction between host and parasite. This work provides a detailed overview on trypanosome motile behavior as a function of development in diverse host surroundings. In additional, the potential use of artificial environments is shown. This can be used to partly abstract the complex fly architecture and analyze trypanosome motion in defined nature inspired geometries.
In the second part of the thesis, the infection of the tsetse fly is under investigation. Two different trypanosome forms exist in the blood: proliferative slender cells and cell cycle arrested stumpy cells. Previous literature states that stumpy cells are pre adapted to survive inside the fly, whereas slender cells die shortly after ingestion. However, infection experiments in our laboratory showed that slender cells were also potentially infective. During this work, infections were set up so as to minimize the possibility of stumpy cells being ingested, corroborating the observation that slender cells are able to infect flies. Using live cell microscopy and fluorescent reporter cell lines, a comparative analysis of the early development following infection with either slender or stumpy cells was performed. The experiments showed, for the first time, the survival of slender trypanosomes and their direct differentiation to the procyclic midgut stage, contradicting the current view in the field of research. Therefore, we can shift perspectives in trypanosome biology by proposing a revised life cycle model of T. brucei, where both bloodstream stages are infective for the vector.
Effects of dopamine on BDNF / TrkB mediated signaling and plasticity on cortico-striatal synapses
(2021)
Progressive loss of voluntary movement control is the central symptom of Parkinson's disease (PD). Even today, we are not yet able to cure PD. This is mainly due to a lack of understanding the mechanisms of movement control, network activity and plasticity in motor circuits, in particular between the cerebral cortex and the striatum. Brain-derived neurotrophic factor (BDNF) has emerged as one of the most important factors for the development and survival of neurons, as well as for synaptic plasticity. It is thus an important target for the development of new therapeutic strategies against neurodegenerative diseases. Together with its receptor, the Tropomyosin receptor kinase B (TrkB), it is critically involved in development and function of the striatum. Nevertheless, little is known about the localization of BDNF within presynaptic terminals in the striatum, as well as the types of neurons that produce BDNF in the cerebral cortex. Furthermore, the influence of midbrain derived dopamine on the control of BDNF / TrkB interaction in striatal medium spiny neurons (MSNs) remains elusive so far. Dopamine, however, appears to play an important role, as its absence leads to drastic changes in striatal synaptic plasticity. This suggests that dopamine could regulate synaptic activity in the striatum via modulation of BDNF / TrkB function. To answer these questions, we have developed a sensitive and reliable protocol for the immunohistochemical detection of endogenous BDNF. We find that the majority of striatal BDNF is provided by glutamatergic, cortex derived afferents and not dopaminergic inputs from the midbrain. In fact, we found BDNF in cell bodies of neurons in layers II-III and V of the primary and secondary motor cortex as well as layer V of the somatosensory cortex. These are the brain areas that send dense projections to the dorsolateral striatum for control of voluntary movement. Furthermore, we could show that these projection neurons significantly downregulate the expression of BDNF during the juvenile development of mice between 3 and 12 weeks.
In parallel, we found a modulatory effect of dopamine on the translocation of TrkB to the cell surface in postsynaptic striatal Medium Spiny Neurons (MSNs). In MSNs of the direct pathway (dMSNs), which express dopamine receptor 1 (DRD1), we observed the formation of TrkB aggregates in the 6-hydroxydopamine (6-OHDA) model of PD. This suggests that DRD1 activity controls TrkB surface expression in these neurons. In contrast, we found that DRD2 activation has opposite effects in MSNs of the indirect pathway (iMSNs). Activation of DRD2 promotes a rapid decrease in TrkB surface expression which was reversible and depended on cAMP. In parallel, stimulation of DRD2 led to induction of phospho-TrkB (pTrkB). This effect was significantly slower than the effect on TrkB surface expression and indicates that TrkB is transactivated by DRD2. Together, our data provide evidence that dopamine triggers dual modes of plasticity on striatal MSNs by acting on TrkB surface expression in DRD1 and DRD2 expressing MSNs. This surface expression of the receptor is crucial for the binding of BDNF, which is released from corticostriatal afferents. This leads to the induction of TrkB-mediated downstream signal transduction cascades and long-term potentiation (LTP). Therefore, the dopamine-mediated translocation of TrkB could be a mediator that modulates the balance between dopaminergic and glutamatergic signaling to allow synaptic plasticity in a spatiotemporal manner. This information and the fact that TrkB is segregated to persistent aggregates in PD could help to improve our understanding of voluntary movement control and to develop new therapeutic strategies beyond those focusing on dopaminergic supply.