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Poxviruses are large DNA viruses with a linear double-stranded DNA genome circularized at the extremities. The helicase-primase D5, composed of six identical 90 kDa subunits, is required for DNA replication. D5 consists of a primase fragment flexibly attached to the hexameric C-terminal polypeptide (res. 323–785) with confirmed nucleotide hydrolase and DNA-binding activity but an elusive helicase activity. We determined its structure by single-particle cryo-electron microscopy. It displays an AAA+ helicase core flanked by N- and C-terminal domains. Model building was greatly helped by the predicted structure of D5 using AlphaFold2. The 3.9 Å structure of the N-terminal domain forms a well-defined tight ring while the resolution decreases towards the C-terminus, still allowing the fit of the predicted structure. The N-terminal domain is partially present in papillomavirus E1 and polyomavirus LTA helicases, as well as in a bacteriophage NrS-1 helicase domain, which is also closely related to the AAA+ helicase domain of D5. Using the Pfam domain database, a D5_N domain followed by DUF5906 and Pox_D5 domains could be assigned to the cryo-EM structure, providing the first 3D structures for D5_N and Pox_D5 domains. The same domain organization has been identified in a family of putative helicases from large DNA viruses, bacteriophages, and selfish DNA elements.
The mechanisms by which climatic changes influence ecosystem functions, that is, by a direct climatic control of ecosystem processes or by modifying richness and trait compositions of species communities, remain unresolved.
This study is a contribution to this discourse by elucidating the linkages between climate, land use, biodiversity, body size and ecosystem functions.
We disentangled direct climatic from biodiversity‐mediated effects by using dung removal by dung beetles as a model system and by combining correlative field data and exclosure experiments along an extensive elevational gradient on Mt. Kilimanjaro, Tanzania.
Dung removal declined with increasing elevation, being associated with a strong reduction in the richness and body size traits of dung beetle communities. Climate influenced dung removal rates by modifying biodiversity rather than by direct effects. The biodiversity–ecosystem effect was driven by a change in the mean body size of dung beetles. Dung removal rates were strongly reduced when large dung beetles were experimentally excluded.
This study underscores that climate influences ecosystem functions mainly by modifying biodiversity and underpins the important role of body size for dung removal.
The Role of Acid Sphingomyelinase in \(Staphylococcus\) \(aureus\) Infection of Endothelial Cells
(2022)
Staphylococcus aureus is a human bacterial pathogen responsible for a variety of diseases including bacterial pneumonia and sepsis. Recent studies provided an explanation, how S. aureus and its exotoxins contribute to the degradation of endothelial junction proteins and damage lung tissue [4]. Previous findings were indicating an involvement of acid sphingomyelinase (ASM) activity in cell barrier degradation [5]. In the presented study the impact of singular virulence factors, such as staphylococcal α-toxin, on in vitro cell barrier integrity as well as their ability to elicit an activation of ASM were investigated.
Experiments with bacterial supernatants performed on human endothelial cells demonstrated a rapid dissociation after treatment, whereas murine endothelial cells were rather resistant against cell barrier degradation. Furthermore, amongst all tested staphylococcal toxins it was found that only α-toxin had a significant impact on endothelial junction proteins and ASM activity. Ablation of this single toxin was sufficient to protect endothelial cells from cell barrier degradation and activation of ASM was absent.
In this process it was verified, that α-toxin induces a recruitment of intracellular ASM, which is accompanied by rapid and oscillating changes in cytoplasmic Ca2+ concentration and an increased exposure of Lysosomal associated membrane protein 1 (LAMP1) on the cell surface. Recruitment of lysosomal ASM is associated, among other aspects, to plasma membrane repair and was previously described to be involved with distinct pathogens as well as other pore forming toxins (PFT). However, with these findings a novel feature for α-toxin has been revealed, indicating that the staphylococcal PFT is able to elicit a similar process to previously described plasma membrane repair mechanisms.
Increased exposure and intake of surface membrane markers questioned the involvement of ASM activity in S. aureus internalization by non-professional phagocytes such as endothelial cells. By modifying ASM expression pattern as well as application of inhibitors it was possible to reduce the intracellular bacterial count. Thus, a direct connection between ASM activity and S. aureus infection mechanisms was observed, therefore this study exemplifies how S. aureus is able to exploit the host cell sphingolipid metabolism as well as benefit of it for invasion into non-professional phagocytic cells
To counteract insect decline, it is essential to understand the underlying causes, especially for key pollinators such as nocturnal moths whose ability to orientate can easily be influenced by ambient light conditions. These comprise natural light sources as well as artificial light, but their specific relevance for moth orientation is still unknown. We investigated the influence of moonlight on the reproductive behavior of privet hawkmoths (Sphinx ligustri) at a relatively dark site where the Milky Way was visible while the horizon was illuminated by distant light sources and skyglow. We show that male moths use the moon for orientation and reach females significantly faster with increasing moon elevation. Furthermore, the choice of flight direction depended on the cardinal position of the moon but not on the illumination of the horizon caused by artificial light, indicating that the moon plays a key role in the orientation of male moths.
The neuropeptide pigment-dispersing factor (PDF) plays a prominent role in the circadian clock of many insects including honey bees. In the honey bee brain, PDF is expressed in about 15 clock neurons per hemisphere that lie between the central brain and the optic lobes. As in other insects, the bee PDF neurons form wide arborizations in the brain, but certain differences are evident. For example, they arborize only sparsely in the accessory medulla (AME), which serves as important communication center of the circadian clock in cockroaches and flies. Furthermore, all bee PDF neurons cluster together, which makes it impossible to distinguish individual projections. Here, we investigated the developing bee PDF network and found that the first three PDF neurons arise in the third larval instar and form a dense network of varicose fibers at the base of the developing medulla that strongly resembles the AME of hemimetabolous insects. In addition, they send faint fibers toward the lateral superior protocerebrum. In last larval instar, PDF cells with larger somata appear and send fibers toward the distal medulla and the medial protocerebrum. In the dorsal part of the medulla serpentine layer, a small PDF knot evolves from which PDF fibers extend ventrally. This knot disappears during metamorphosis and the varicose arborizations in the putative AME become fainter. Instead, a new strongly stained PDF fiber hub appears in front of the lobula. Simultaneously, the number of PDF neurons increases and the PDF neuronal network in the brain gets continuously more complex.
Drosophila’s dorsal clock neurons (DNs) consist of four clusters (DN1as, DN1ps, DN2s, and DN3s) that largely differ in size. While the DN1as and the DN2s encompass only two neurons, the DN1ps consist of ∼15 neurons, and the DN3s comprise ∼40 neurons per brain hemisphere. In comparison to the well-characterized lateral clock neurons (LNs), the neuroanatomy and function of the DNs are still not clear. Over the past decade, numerous studies have addressed their role in the fly’s circadian system, leading to several sometimes divergent results. Nonetheless, these studies agreed that the DNs are important to fine-tune activity under light and temperature cycles and play essential roles in linking the output from the LNs to downstream neurons that control sleep and metabolism. Here, we used the Flybow system, specific split-GAL4 lines, trans-Tango, and the recently published fly connectome (called hemibrain) to describe the morphology of the DNs in greater detail, including their synaptic connections to other clock and non-clock neurons. We show that some DN groups are largely heterogenous. While certain DNs are strongly connected with the LNs, others are mainly output neurons that signal to circuits downstream of the clock. Among the latter are mushroom body neurons, central complex neurons, tubercle bulb neurons, neurosecretory cells in the pars intercerebralis, and other still unidentified partners. This heterogeneity of the DNs may explain some of the conflicting results previously found about their functionality. Most importantly, we identify two putative novel communication centers of the clock network: one fiber bundle in the superior lateral protocerebrum running toward the anterior optic tubercle and one fiber hub in the posterior lateral protocerebrum. Both are invaded by several DNs and LNs and might play an instrumental role in the clock network.
Drosophila’s lateral posterior neurons (LPNs) belong to a small group of circadian clock neurons that is so far not characterized in detail. Thanks to a new highly specific split‐Gal4 line, here we describe LPNs’ morphology in fine detail, their synaptic connections, daily bimodal expression of neuropeptides, and propose a putative role of this cluster in controlling daily activity and sleep patterns. We found that the three LPNs are heterogeneous. Two of the neurons with similar morphology arborize in the superior medial and lateral protocerebrum and most likely promote sleep. One unique, possibly wakefulness‐promoting, neuron with wider arborizations extends from the superior lateral protocerebrum toward the anterior optic tubercle. Both LPN types exhibit manifold connections with the other circadian clock neurons, especially with those that control the flies’ morning and evening activity (M‐ and E‐neurons, respectively). In addition, they form synaptic connections with neurons of the mushroom bodies, the fan‐shaped body, and with many additional still unidentified neurons. We found that both LPN types rhythmically express three neuropeptides, Allostatin A, Allostatin C, and Diuretic Hormone 31 with maxima in the morning and the evening. The three LPN neuropeptides may, furthermore, signal to the insect hormonal center in the pars intercerebralis and contribute to rhythmic modulation of metabolism, feeding, and reproduction. We discuss our findings in the light of anatomical details gained by the recently published hemibrain of a single female fly on the electron microscopic level and of previous functional studies concerning the LPN.
Summary
Chapters I & II: General Introduction & General Methods
Agriculture is confronted with a rampant loss of biodiversity potentially eroding ecosystem service potentials and adding up to other stressors like climate change or the consequences of land-use change and intensive management. To counter this ‘biodiversity crisis’, agri-environment schemes (AES) have been introduced as part of ecological intensification efforts. These AES combine special management regimes with the establishment of tailored habitats to create refuges for biodiversity in agricultural landscapes and thus ensure biodiversity mediated ecosystem services such as pest control. However, little is known about how well different AES habitats fulfil this purpose and whether they benefit ecosystem services in adjacent crop fields. Here I investigated how effective different AES habitats are for restoring biodiversity in different agricultural landscapes (Chapter V) and whether they benefit natural pest control in adjacent oilseed rape (Chapter VI) and winter cereal fields (Chapter VII). I recorded biodiversity and pest control potentials using a variety of different methods (Chapters II, V, VI & VII). Moreover, I validated the methodology I used to assess predator assemblages and predation rates (Chapters III & IV).
Chapter III: How to record ground dwelling predators?
Testing methodology is critical as it ensures scientific standards and trustworthy results. Pitfall traps are widely used to record ground dwelling predators, but little is known about how different trap types affect catches. I compared different types of pitfall traps that had been used in previous studies in respect to resulting carabid beetle assemblages. While barrier traps collected more species and deliver more complete species inventories, conventional simple pitfall traps provide reliable results with comparatively little handling effort. Placing several simple pitfall traps in the field can compensate the difference while still saving handling effort.
Chapter IV: How to record predation rates?
A plethora of methods has been proposed and used for recording predation rates, but these have rarely been validated before use. I assessed whether a novel approach to record predation, the use of sentinel prey cards with glued on aphids, delivers realistic results. I compared different sampling efforts and showed that obtained predation rates were similar and could be linked to predator (carabid beetle) densities and body-sizes (a proxy often used for food intake rates). Thus, the method delivers reliable and meaningful predation rates.
Chapter V: Do AES habitats benefit multi-taxa biodiversity?
The main goal of AES is the conservation of biodiversity in agricultural landscapes. I investigated how effectively AES habitats with different temporal continuity fulfil this goal in differently structured landscapes. The different AES habitats investigated had variable effects on local biodiversity. Temporal continuity of AES habitats was the most important predictor with older, more temporally continuous habitats harbouring higher overall biodiversity and different species assemblages in most taxonomic groups than younger AES habitats. Results however varied among taxonomic groups and natural enemies were equally supported by younger habitats. Semi-natural habitats in the surrounding landscape and AES habitat size were of minor importance for local biodiversity and had limited effects. This stresses that newly established AES habitats alone cannot restore farmland biodiversity. Both AES habitats as well as more continuous semi-natural habitats synergistically increase overall biodiversity in agricultural landscapes.
Chapter VI: The effects of AES habitats on predators in adjacent oilseed rape fields
Apart from biodiversity conservation, ensuring ecosystem service delivery in agricultural landscapes is a crucial goal of AES. I therefore investigated the effects of adjacent AES habitats on ground dwelling predator assemblages in oilseed rape fields. I found clear distance decay effects from the field edges into the field centres on both richness and densities of ground dwelling predators. Direct effects of adjacent AES habitats on assemblages in oilseed rape fields however were limited and only visible in functional traits of carabid beetle assemblages. Adjacent AES habitats doubled the proportion of predatory carabid beetles indicating a beneficial role for pest control. My results show that pest control potentials are largest close to the field edges and beneficial effects are comparably short ranged.
Chapter VII: The effects of AES habitats on pest control in adjacent cereal fields
Whether distance functions and potential effects of AES habitats are universal across crops is unknown. Therefore, I assessed distance functions of predators, pests, predation rates and yields after crop rotation in winter cereals using the same study design as in the previous year. Resulting distance functions were not uniform and differed from those found in oilseed rape in the previous year, indicating that the interactions between certain adjacent habitats vary with habitat and crop types. Distance functions of cereal-leaf beetles (important cereal pests) and parasitoid wasps were moreover modulated by semi-natural habitat proportion in the surrounding landscapes. Field edges buffered assemblage changes in carabid beetle assemblages over crop rotation confirming their important function as refuges for natural enemies. My results emphasize the beneficial role of field edges for pest control potentials. These findings back the calls for smaller field sizes and more diverse, more heterogeneously structured agricultural landscapes.
Chapter VIII: General Discussion
Countering biodiversity loss and ensuring ecosystem service provision in agricultural landscapes is intricate and requires strategic planning and restructuring of these landscapes. I showed that agricultural landscapes could benefit maximally from (i) a mixture of AES habitats and semi-natural habitats to support high levels of overall biodiversity and from (ii) smaller continuously managed agricultural areas (i.e. smaller field sizes or the insertion of AES elements within large fields) to maximize natural pest control potentials in crop fields. I propose a mosaic of younger AES habitats and semi-natural habitats to support ecosystem service providers and increase edge density for ecosystem service spillover into adjacent crops. The optimal extent and density of this network as well as the location in which AES and semi-natural habitats interact most beneficially with adjacent crops need further investigation. My results provide a further step towards more sustainable agricultural landscapes that simultaneously allow biodiversity to persist and maintain agricultural production under the framework of ecological intensification.
We studied the impact of the neophyte tree Fraxinus pennsylvanica on the diversity of beetles in floodplain forests along the river Elbe in Germany in 2016, 2017 and in 2020, where 80% of all Fraxinus excelsior trees had died following severe droughts. Beetles were collected by insecticidal knock-down from 121 trees (64 F. excelsior and 57 F. pennsylvanica) and identified to 547 species in 15,214 specimens. The trees sampled in 2016 and 2017 showed no signs of drought stress or ash dieback and serve as a reference for the comparison with the 2020 fauna. The data proved that F. excelsior harbours the most diverse beetle community, which differed also significantly in guild composition from F. pennsylvanica. Triggered by extremely dry and long summer seasons, the 2020 ash dieback had profound and forest-wide impacts. Several endangered, red-listed beetle species of Saxonia Anhalt had increased in numbers and became secondary pests on F. excelsior. Diversity decreased whilst numbers of xylobionts increased on all trees, reaching 78% on F. excelsior. Proportions of xylobionts remained constant on F. pennsylvanica. Phytophages were almost absent from all trees, but mycetophages increased on F. pennsylvanica. Our data suggest that as a result of the dieback of F. excelsior the neophyte F. pennsylvanica might become a rescue species for the European Ash fauna, as it provides the second-best habitat. We show how difficult it is to assess the dynamics and the ecological impact of neophytes, especially under conditions similar to those projected by climate change models. The diversity and abundance of canopy arthropods demonstrates their importance in understanding forest functions and maintenance of ecosystem services, illustrating that their consideration is essential for forest adaptation to climate change.
Green plants are equipped with photoreceptors that are capable of sensing radiation in the ultraviolet‐to‐blue and the red‐to‐far‐red parts of the light spectrum. However, plant cells are not particularly sensitive to green light (GL), and light which lies within this part of the spectrum does not efficiently trigger the opening of stomatal pores. Here, we discuss the current knowledge of stomatal responses to light, which are either provoked via photosynthetically active radiation or by specific blue light (BL) signaling pathways. The limited impact of GL on stomatal movements provides a unique option to use this light quality to control optogenetic tools. Recently, several of these tools have been optimized for use in plant biological research, either to control gene expression, or to provoke ion fluxes. Initial studies with the BL‐activated potassium channel BLINK1 showed that this tool can speed up stomatal movements. Moreover, the GL‐sensitive anion channel GtACR1 can induce stomatal closure, even at conditions that provoke stomatal opening in wild‐type plants. Given that crop plants in controlled‐environment agriculture and horticulture are often cultivated with artificial light sources (i.e. a combination of blue and red light from light‐emitting diodes), GL signals can be used as a remote‐control signal that controls stomatal transpiration and water consumption.
Cellular growth is a fundamental process of life and must be precisely controlled in multicellular organisms. Growth is crucially controlled by the number of functional ribosomes available in cells. The production of new ribosomes depends critically on the activity of RNA polymerase (RNAP) II in addition to the activity of RNAP I and III, which produce ribosomal RNAs. Indeed, the expression of both, ribosomal proteins and proteins required for ribosome assembly (ribosomal biogenesis factors), is considered rate-limiting for ribosome synthesis. Here, we used genetic screening to identify novel transcriptional regulators of cell growth genes by fusing promoters from a ribosomal protein gene (Rpl18) and from a ribosomal biogenesis factor (Fbl) with fluorescent protein genes (RFP, GFP) as reporters. Subsequently, both reporters were stably integrated into immortalized mouse fibroblasts, which were then transduced with a genome-wide sgRNA-CRISPR knockout library. Subsequently, cells with altered reporter activity were isolated by FACS and the causative sgRNAs were identified. Interestingly, we identified two novel regulators of growth genes. Firstly, the exon junction complex protein RBM8A controls transcript levels of the intronless reporters used here. By acute depletion of RBM8A protein using the auxin degron system combined with the genome-wide analysis of nascent transcription, we showed that RBM8A is an important global regulator of ribosomal protein transcripts. Secondly, we unexpectedly observed that the glycolytic enzyme aldolase A (ALDOA) regulates the expression of ribosomal biogenesis factors. Consistent with published observations that a fraction of this protein is located in the nucleus, this may be a mechanism linking transcription of growth genes to metabolic processes and possibly to metabolite availability.
The cryptochrome/photolyase (CRY/PL) family represents an ancient group of proteins fulfilling two fundamental functions. While photolyases repair UV-induced DNA damages, cryptochromes mainly influence the circadian clock. In this study, we took advantage of the large number of already sequenced and annotated genes available in databases and systematically searched for the protein sequences of CRY/PL family members in all taxonomic groups primarily focusing on metazoans and limiting the number of species per taxonomic order to five. Using BLASTP searches and subsequent phylogenetic tree and motif analyses, we identified five distinct photolyases (CPDI, CPDII, CPDIII, 6-4 photolyase, and the plant photolyase PPL) and six cryptochrome subfamilies (DASH-CRY, mammalian-type MCRY, Drosophila-type DCRY, cnidarian-specific ACRY, plant-specific PCRY, and the putative magnetoreceptor CRY4. Manually assigning the CRY/PL subfamilies to the species studied, we have noted that over evolutionary history, an initial increase of various CRY/PL subfamilies was followed by a decrease and specialization. Thus, in more primitive organisms (e.g., bacteria, archaea, simple eukaryotes, and in basal metazoans), we find relatively few CRY/PL members. As species become more evolved (e.g., cnidarians, mollusks, echinoderms, etc.), the CRY/PL repertoire also increases, whereas it appears to decrease again in more recent organisms (humans, fruit flies, etc.). Moreover, our study indicates that all cryptochromes, although largely active in the circadian clock, arose independently from different photolyases, explaining their different modes of action.
Humans and animals alike use the sun, the moon, and the stars to guide their ways.
However, the position of celestial cues changes depending on daytime, season, and
place on earth. To use these celestial cues for reliable navigation, the rotation of the
sky has to be compensated. While humans invented complicated mechanisms like the
Antikythera mechanism to keep track of celestial movements, animals can only rely on
their brains. The desert ant Cataglyphis is a prime example of an animal using celestial
cues for navigation. Using the sun and the related skylight polarization pattern as a
compass, and a step integrator for distance measurements, it can determine a vector
always pointing homewards. This mechanism is called path integration. Since the sun’s
position and, therefore, also the polarization pattern changes throughout the day,
Cataglyphis have to correct this movement. If they did not compensate for time, the
ants’ compass would direct them in different directions in the morning and the evening.
Thus, the ants have to learn the solar ephemeris before their far-reaching foraging
trips.
To do so, Cataglyphis ants perform a well-structured learning-walk behavior during the
transition phase from indoor worker to outdoor forager. While walking in small loops
around the nest entrance, the ants repeatedly stop their forward movements to perform
turns. These can be small walked circles (voltes) or tight turns about the ants’ body
axes (pirouettes). During pirouettes, the ants gaze back to their nest entrance during
stopping phases. These look backs provide a behavioral read-out for the state of the
path integrator. The ants “tell” the observer where they think their nest is, by looking
back to it. Pirouettes are only performed by Cataglyphis ants inhabiting an environment
with a prominent visual panorama. This indicates, that pirouettes are performed to
learn the visual panorama. Voltes, on the other hand, might be used for calibrating the
celestial compass of the ants.
In my doctoral thesis, I employed a wide range of state-of-the-art techniques from
different disciplines in biology to gain a deeper understanding of how navigational
information is acquired, memorized, used, and calibrated during the transition phase
from interior worker to outdoor forager. I could show, that celestial orientation cues that
provide the main compass during foraging, do not guide the ants during the look-backbehavior
of initial learning walks. Instead Cataglyphis nodus relies on the earth’s
magnetic field as a compass during this early learning phase. While not guiding the
ants during their first walks outside of the nest, excluding the ants from perceiving the
natural polarization pattern of the skylight has significant consequences on learning-related
plasticity in the ants’ brain. Only if the ants are able to perform their learning-walk
behavior under a skylight polarization pattern that changes throughout the day,
plastic neuronal changes in high-order integration centers are induced. Especially the
mushroom bogy collar, a center for learning and memory, and the central complex, a
center for orientation and motor control, showed an increase in volume after learning
walks. This underlines the importance of learning walks for calibrating the celestial
compass. The magnetic compass might provide the necessary stable reference
system for the ants to calibrate their celestial compass and learn the position of
landmark information. In the ant brain, visual information from the polarization-sensitive
ocelli converge in tight apposition with neuronal afferents of the mechanosensitive
Johnston’s organ in the ant’s antennae. This makes the ants’ antennae an interesting
candidate for studying the sensory bases of compass calibration in Cataglyphis ants.
The brain of the desert navigators is well adapted to successfully accomplish their
navigational needs. Females (gynes and workers) have voluminous mushroom bodies,
and the synaptic complexity to store large amount of view-based navigational
information, which they acquire during initial learning walks. The male Cataglyphis
brain is better suited for innate behaviors that support finding a mate.
The results of my thesis show that the well adapted brain of C. nodus ants undergoes
massive structural changes during leaning walks, dependent on a changing celestial
polarization pattern. This underlies the essential role of learning walks in the calibration
of orientation systems in desert ants.
Biodiversity is in rapid decline worldwide. These declines are more pronounced in areas that are currently biodiversity rich, but economically poor – essentially describing many tropical regions in the Global South where landscapes are dominated by smallholder agriculture. Agriculture is an important driver of biodiversity decline, through habitat destruction and unsustainable practices. Ironically, agriculture itself is dependent on a range of ecosystem services, such as pollination and pest control, provided by biodiversity. Biodiversity on fields and the delivery of ecosystem services to crops is often closely tied to the composition of the surrounding landscape – complex landscapes with a higher proportion of (semi-)natural habitats tend to support a high abundances and biodiversity of pollinators and natural enemies that are beneficial to crop production. However, past landscape scale studies have focused primarily on industrialized agricultural landscapes in the Global North, and context dependent differences between regions and agricultural systems are understudied. Smallholder agriculture supports 2 billion people worldwide and contributes to over half the world’s food supply. Yet smallholders, particularly in sub-Saharan Africa, are underrepresented in research investigating the consequences of landscape change and agricultural practices. Where research in smallholder agriculture is conducted, the focus is often on commodity crops, such as cacao, and less on crops that are directly consumed by smallholder households, though the loss of services to these crops could potentially impact the most vulnerable farmers the hardest. Agroecology – a holistic and nature-based approach to agriculture, provides an alternative to unsustainable input-intensive agriculture. Agroecology has been found to benefit smallholders through improved agronomical and food-security outcomes. Co-benefits of agroecological practices with biodiversity and ecosystem services are assumed, but not often empirically tested. In addition, the local and landscape effects on biodiversity and ecosystem services are more commonly studied in isolation, but their potentially interactive effects are so far little explored. Our study region in northern Malawi exemplifies many challenges experienced by smallholder farmers throughout sub-Saharan Africa and more generally in the Global South. Malawi is located in a global biodiversity hotspot, but biodiversity is threatened by rapid habitat loss and a push for input-intensive agriculture by government and other stakeholders. In contrast, agroecology has been effectively promoted and implemented in the study region. We investigated how land-use differences and the agroecological practices affects biodiversity and ecosystem services of multiple taxa in a maize-bean intercropping system (Chapter 2), and pollination of pumpkin (Chapter 3) and pigeon pea (Chapter 4). Additionally, the effects of local and landscape scale shrub- to farmland habitat conversion was investigated on butterfly communities, as well as the potential for agroecology to mitigate these effects (Chapter 5).
Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human‐induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land‐use change. Conversely, the suppression of natural disturbances threatens disturbance‐dependent biota. Using a meta‐analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α‐diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively. Disturbance was beneficial for taxonomic groups preferring conditions associated with open canopies (e.g. hymenopterans and hoverflies), whereas ground‐dwelling groups and/or groups typically associated with shady conditions (e.g. epigeic lichens and mycorrhizal fungi) were more likely to be negatively impacted by disturbance. Across all taxonomic groups, the highest α‐diversity in disturbed forest patches occurred under moderate disturbance severity, i.e. with approximately 55% of trees killed by disturbance. We further extended our meta‐analysis by applying a unified diversity concept based on Hill numbers to estimate α‐diversity changes in different taxonomic groups across a gradient of disturbance severity measured at the stand scale and incorporating other disturbance features. We found that disturbance severity negatively affected diversity for Hill number q = 0 but not for q = 1 and q = 2, indicating that diversity–disturbance relationships are shaped by species relative abundances. Our synthesis of α‐diversity was extended by a synthesis of disturbance‐induced change in species assemblages, and revealed that disturbance changes the β‐diversity of multiple taxonomic groups, including some groups that were not affected at the α‐diversity level (birds and woody plants). Finally, we used mixed rarefaction/extrapolation to estimate biodiversity change as a function of the proportion of forests that were disturbed, i.e. the disturbance extent measured at the landscape scale. The comparison of intact and naturally disturbed forests revealed that both types of forests provide habitat for unique species assemblages, whereas species diversity in the mixture of disturbed and undisturbed forests peaked at intermediate values of disturbance extent in the simulated landscape. Hence, the relationship between α‐diversity and disturbance severity in disturbed forest stands was strikingly similar to the relationship between species richness and disturbance extent in a landscape consisting of both disturbed and undisturbed forest habitats. This result suggests that both moderate disturbance severity and moderate disturbance extent support the highest levels of biodiversity in contemporary forest landscapes.
SARS-CoV-2 variants such as the delta or omicron variants, with higher transmission rates, accelerated the global COVID-19 pandemic. Thus, novel therapeutic strategies need to be deployed. The inhibition of acid sphingomyelinase (ASM), interfering with viral entry by fluoxetine was reported. Here, we described the acid ceramidase as an additional target of fluoxetine. To discover these effects, we synthesized an ASM-independent fluoxetine derivative, AKS466. High-resolution SARS-CoV-2–RNA FISH and RTqPCR analyses demonstrate that AKS466 down-regulates viral gene expression. It is shown that SARS-CoV-2 deacidifies the lysosomal pH using the ORF3 protein. However, treatment with AKS488 or fluoxetine lowers the lysosomal pH. Our biochemical results show that AKS466 localizes to the endo-lysosomal replication compartments of infected cells, and demonstrate the enrichment of the viral genomic, minus-stranded RNA and mRNAs there. Both fluoxetine and AKS466 inhibit the acid ceramidase activity, cause endo-lysosomal ceramide elevation, and interfere with viral replication. Furthermore, Ceranib-2, a specific acid ceramidase inhibitor, reduces SARS-CoV-2 replication and, most importantly, the exogenous supplementation of C6-ceramide interferes with viral replication. These results support the hypotheses that the acid ceramidase is a SARS-CoV-2 host factor.
Climate and land-use changes cause increasing stress to pollinators but the molecular pathways underlying stress responses are poorly understood. Here, we analyzed the transcriptomic response of Bombus lucorum workers to temperature and livestock grazing. Bumblebees sampled along an elevational gradient, and from differently managed grassland sites (livestock grazing vs unmanaged) in the German Alps did not differ in the expression of genes known for thermal stress responses. Instead, metabolic energy production pathways were upregulated in bumblebees sampled in mid- or high elevations or during cool temperatures. Extensive grazing pressure led to an upregulation of genetic pathways involved in immunoregulation and DNA-repair. We conclude that widespread bumblebees are tolerant toward temperature fluctuations in temperate mountain environments. Moderate temperature increases may even release bumblebees from metabolic stress. However, transcriptome responses to even moderate management regimes highlight the completely underestimated complexity of human influence on natural pollinators.
A fine balance of regulatory (T\(_{reg}\)) and conventional CD4\(^+\) T cells (T\(_{conv}\)) is required to prevent harmful immune responses, while at the same time ensuring the development of protective immunity against pathogens. As for many cellular processes, sphingolipid metabolism also crucially modulates the T\(_{reg}\)/T\(_{conv}\) balance. However, our understanding of how sphingolipid metabolism is involved in T cell biology is still evolving and a better characterization of the tools at hand is required to advance the field. Therefore, we established a reductionist liposomal membrane model system to imitate the plasma membrane of mouse T\(_{reg}\) and T\(_{conv}\) with regards to their ceramide content. We found that the capacity of membranes to incorporate externally added azide-functionalized ceramide positively correlated with the ceramide content of the liposomes. Moreover, we studied the impact of the different liposomal preparations on primary mouse splenocytes in vitro. The addition of liposomes to resting, but not activated, splenocytes maintained viability with liposomes containing high amounts of C\(_{16}\)-ceramide being most efficient. Our data thus suggest that differences in ceramide post-incorporation into T\(_{reg}\) and T\(_{conv}\) reflect differences in the ceramide content of cellular membranes.
Leaf-cutting ants are highly successful herbivores in the Neotropics. They forage large amounts of fresh plant material to nourish a symbiotic fungus that sustains the colony. It is unknown how workers organize the intra-nest distribution of resources, and whether they respond to increasing demands in some fungus gardens by adjusting the amount of delivered resources accordingly. In laboratory experiments, we analyzed the spatial distribution of collected leaf fragments among nest chambers in Acromyrmex ambiguus leaf-cutting ants, and how it changed when one of the fungus gardens experienced undernourishment. Plant fragments were evenly distributed among nest chambers when the fungal symbiont was well nourished. That pattern changed when one of the fungus gardens was undernourished and had a higher leaf demand, resulting in more leaf discs delivered to the undernourished fungus garden over at least 2 days after deprivation. Some ants bypassed nourished gardens to directly deliver their resource to the chamber with higher nutritional demand. We hypothesize that cues arising from that chamber might be used for orientation and/or that informed individuals, presumably stemming from the undernourished chamber, may preferentially orient to them.
Introduction
Surgical site infections (SSIs) are one of the most common postoperative complications after appendectomy leading to recurrent surgery, prolonged hospital stay, and the use of antibiotics. Numerous studies and meta-analyses have been published on the effect of open versus conventional laparoscopic appendectomy (CLA) reporting faster postoperative recovery and less postoperative pain for CLA. A development from CLA has been the single-port appendectomy (SPA), associated with a better cosmesis but seemingly having a higher risk of wound infections. The aim of this systematic literature review and meta-analysis is to investigate whether reduced port or SPA alters the ratio of SSIs.
Methods
Pubmed, Embase, and Cochrane databases were screened for suitable articles. All articles published between January 1, 2002, and March 23, 2022, were included. Articles regarding children below the age of 18 were excluded as well as manuscripts that investigated solemnly open appendectomies. Articles were screened for inclusion criteria by two independent authors. Incidence of SSI was the primary outcome. Duration of operation and length of hospital stay were defined as secondary outcomes.
Results
A total of 25 studies were found through a database search describing 5484 patients. A total of 2749 patients received SPA and 2735 received CLA. There was no statistical difference in the rate of SSI (P = 0.98). A total of 22 studies including 4699 patients reported the duration of operation (2223 SPA and 2476 CLA). There was a significantly shorter operation time seen in CLA. The length of hospital stay was reported in 23 studies (4735 patients: 2235 SPA and 2500 CLA). A shorter hospital stay was seen in the SPA group (P < 0.00001). Separately performed analysis of randomized controlled trials could not confirm this effect (P = 0.29).
Discussion
SPA is an equally safe procedure considering SSI compared to CLA and does not lead to an increased risk of SSI. A longer operation time for SPA and a minor difference in the length of stay does lead to the use of SPA in selected patients only.