Refine
Has Fulltext
- yes (131)
Is part of the Bibliography
- yes (131)
Year of publication
- 2020 (131) (remove)
Document Type
- Journal article (99)
- Doctoral Thesis (32)
Keywords
- biodiversity (5)
- autophagy (4)
- Apis mellifera (3)
- Drosophila melanogaster (3)
- Staphylococcus aureus (3)
- cell death (3)
- colorectal cancer (3)
- diversity (3)
- evolution (3)
- foraging (3)
Institute
- Theodor-Boveri-Institut für Biowissenschaften (131) (remove)
Sonstige beteiligte Institutionen
- Core Unit Systemmedizin (1)
- Interdisciplinary Center for Clinical Research (1)
- Lehrstuhl für Translationale Onkologie (1)
- Technische Hochschule Nürnberg Georg Simon Ohm (1)
- Zentrum für Innere Medizin I, Städtisches Klinikum Brandenburg GmbH, Hochschulklinikum der MHB Theodor Fontane (1)
- eXcorLab GmbH (1)
EU-Project number / Contract (GA) number
- 311781 (1)
- 765937 (1)
- CoG 721016–HERPES (1)
Staphylococcus aureus is a Gram-positive commensal bacterium, that asymptomatically colonizes human skin and mucosal surfaces. Upon opportune conditions, such as immunodeficiency or breached barriers of the host, it can cause a plethora of infections ranging from local, superficial infections to life-threatening diseases. Despite being regarded as an extracellular pathogen, S. aureus can invade and survive within non-phagocytic and phagocytic cells. Eventually, the pathogen escapes from the host cell resulting in killing of the host cell, which is associated with tissue destruction and spread of infection. However, the exact molecular mechanisms underlying S. aureus-induced host cell death remain to be elucidated.
In the present work, a genome-wide haploid genetic screen was performed to identify host cell genes crucial for S. aureus intracellular cytotoxicity. A mutant library of the haploid cell line HAP1 was infected with the pathogen and cells surviving the infection were selected. Twelve genes were identified, which were significantly enriched when compared to an infection with a non-cytotoxic S. aureus strain.
Additionally, characteristics of regulated cell death pathways and the role of Ca2+ signaling in S. aureus-infected cells were investigated. Live cell imaging of Ca2+ reporter cell lines was used to analyze single cells. S. aureus-induced host cell death exhibited morphological features of apoptosis and activation of caspases was detected. Cellular H2O2 levels were elevated during S. aureus intracellular infection. Further, intracellular S. aureus provoked cytosolic Ca2+ overload in epithelial cells. This resulted from Ca2+ release from endoplasmic reticulum and Ca2+ influx via the plasma membrane and led to mitochondrial Ca2+ overload. The final step of S. aureus-induced cell death was plasma membrane permeabilization, a typical feature of necrotic cell death.
In order to identify bacterial virulence factors implicated in S. aureus-induced host cell killing, the cytotoxicity of selected mutants was investigated. Intracellular S. aureus employs the bacterial cysteine protease staphopain A to activate an apoptosis-like cell death characterized by cell contraction and membrane bleb formation. Phagosomal escape represents a prerequisite staphopain A-induced cell death, whereas bacterial intracellular replication is dispensable. Moreover, staphopain A contributed to efficient colonization of the lung in a murine pneumonia model.
In conclusion, this work identified at least two independent cell death pathways activated by intracellular S. aureus. While initially staphopain A mediates S. aureus-induced host cell killing, cytosolic Ca2+-overload follows later and leads to the final demise of the host cell.
1.Honeybees Apis mellifera and other pollinating insects suffer from pesticides in agricultural landscapes. Flupyradifurone is the active ingredient of a novel pesticide by the name of ‘Sivanto’, introduced by Bayer AG (Crop Science Division, Monheim am Rhein, Germany). It is recommended against sucking insects and marketed as ‘harmless’ to honeybees. Flupyradifurone binds to nicotinergic acetylcholine receptors like neonicotinoids, but it has a different mode of action. So far, little is known on how sublethal flupyradifurone doses affect honeybees.
2. We chronically applied a sublethal and field‐realistic concentration of flupyradifurone to test for long‐term effects on flight behaviour using radio‐frequency identification. We examined haematoxylin/eosin‐stained brains of flupyradifurone‐treated bees to investigate possible changes in brain morphology and brain damage.
3. A field‐realistic flupyradifurone dose of approximately 1.0 μg/bee/day significantly increased mortality. Pesticide‐treated bees initiated foraging earlier than control bees. No morphological damage in the brain was observed.
4. Synthesis and applications. The early onset of foraging induced by a chronical application of flupyradifurone could be disadvantageous for honeybee colonies, reducing the period of in‐hive tasks and life expectancy of individuals. Radio‐frequency identification technology is a valuable tool for studying pesticide effects on lifetime foraging behaviour of insects.
Following natural disturbances, additional anthropogenic disturbance may alter community recovery by affecting the occurrences of species, functional groups, and evolutionary lineages. However, our understanding of whether rare, common, or dominant species, functional groups, or evolutionary lineages are most strongly affected by an additional disturbance, particularly across multiple taxa, is limited. Here, we used a generalized diversity concept based on Hill numbers to quantify the community differences of vascular plants, bryophytes, lichens, wood‐inhabiting fungi, saproxylic beetles, and birds in a storm‐disturbed, experimentally salvage logged forest. Communities of all investigated species groups showed dissimilarities between logged and unlogged plots. Most species groups showed no significant changes in dissimilarities between logged and unlogged plots over the first seven years of succession, indicating a lack of community recovery. In general, the dissimilarities of communities were mainly driven by rare species. Convergence of dissimilarities occurred more often than divergence during the early stages of succession for rare species, indicating a major role in driving decreasing taxonomic dissimilarities between logged and unlogged plots over time. Trends in species dissimilarities only partially match the trends in dissimilarities of functional groups and evolutionary lineages, with little significant changes in successional trajectories. Nevertheless, common and dominant species contributed to a convergence of dissimilarities over time in the case of the functional dissimilarities of wood‐inhabiting fungi. Our study shows that salvage logging following disturbances can alter successional trajectories in early stages of forest succession following natural disturbances. However, community changes over time may differ remarkably in different taxonomic groups and are best detected based on taxonomic, rather than functional or phylogenetic dissimilarities.
Sexually reproducing organisms depend on meiosis for the generation of haploid, genetically diverse gametes to maintain genome stability and the potential to adapt to changing environments. Haploidization is achieved through two successive rounds of cell division after a single initial pre-meiotic DNA replication. Meiosis I segregates the homologous chromosomes, followed by the segregation of the sister chromatids in meiosis II. Genetic diversity is achieved through the process of recombination that de-scribes the exchange of genetic material between the maternal and paternal homolog. Recombination and the initial steps of haploidization are executed already early on in prophase I. Both essential processes depend on a variety of multiprotein complexes, such as the linker of nucleo- and cytoplasm (LINC) complex and the synaptonemal complex (SC). The structure of multiprotein complexes is adjusted according to their function, environment, and the forces they are subjected to. Coiled-coil domains typical in load-bearing proteins characterize the meiotic mechanotransducing LINC complexes. SCs resemble ladder-like structures that are highly conserved amongst eukaryotes, while the primary sequence of the proteins that form the complex display very little if any sequence homology. Despite the apparent significance of the structure to their function, little quantitative and topological data existed on the LINC complexes and the SC within their morphological context prior to the present work. Here, the molecular architecture of the meiotic telomere attachment site where LINC complexes reside and the SC have been analyzed in depth, mainly on the basis of electron microscope tomography derived 3D models complemented by super-resolution light microscopic acquisitions of the respective protein components.
SLAC/SLAH Anionenkanäle, die zur Familie der langsamen Anionenkanäle gehören, repräsentieren Schlüsselproteine in der pflanzlichen Stressantwort. Neben ihrer Aufgabe in Stresssituationen, ist eine Untergruppe der Kanäle für die Beladung der Leitgefäße mit Nitrat und Chlorid in der Stele der Pflanzenwurzeln verantwortlich. Biophysikalische und pflanzenphysiologische Studien stellten heraus, dass vor Allem der Anionenkanal SLAH3 für die Beladung der Xylem Leitgefäße mit Nitrat und Chlorid verantwortlich ist. Ihm zur Seite gestellt werden noch die elektrisch inaktiven Homologe SLAH1 und SLAH4 in der Wurzel exprimiert. Sie steuern die Aktivität von SLAH3 durch die Assemblierung zu SLAH1/SLAH3 oder SLAH3/SLAH4 Heteromeren. Neben der Kontrolle durch Heteromerisierungsereignisse, werden SLAH3 Homomere sehr spezifisch und schnell durch zytosolische Ansäuerung aktiviert. Obwohl bereits die Kristallstruktur des bakteriellen Homologs HiTehA zu pflanzlichen SLAC/SLAH Anionenkanälen bekannt ist, welche HiTehA als Trimer charakterisiert, sind die Stöchiometrie und der Polymerisierungsgrad der pflanzlichen SLAC/SLAHs bisher noch unbekannt.
Die Fluoreszenzmikroskopie umfasst viele etablierte Anwendungsmethoden, wie die konfokale Laserrastermikroskopie (CLSM), Techniken mit verbesserter Auflösung, wie die Mikroskopie mit strukturierter Beleuchtung (SIM) und hochauflösende Methoden, welche durch die Lokalisationsmikroskopie (z.B. dSTORM und PALM) oder die Expansionsmikroskopie (ExM) vertreten werden. Diese unterschiedlichen Mikroskopie-methoden ermöglichen neue Einblicke in die Organisation von Proteinen in biologischen Systemen, die bis auf die molekulare Ebene hinunterreichen. Insbesondere im Bereich der hochauflösenden Fluoreszenzmikroskopie sind im Gegensatz zu tierischen Frage-stellungen bisher jedoch nur wenige Untersuchungen in pflanzlichen Geweben durchgeführt worden.
Die Lokalisationsmikroskopie ermöglicht die Quantifizierung einzelner Moleküle in nativen Systemen und lässt überdies Rückschlüsse auf den Polymerisierungsgrad von Proteinen zu. Da Poly- und Heteromerisierung von Proteinen oftmals mit der Funktionalität eines entsprechenden Proteins einhergeht, wie es bei den SLAC/SLAH Anionenkanälen der Fall ist, wurden in dieser Arbeit PALM Messungen zur Untersuchung des Polymerisierungsgrades und Interaktionsmuster der Anionenkanäle angewendet. Ferner wurden Expressionsmuster der SLAC/SLAHs untersucht und zudem Mikroskopieanwendungen im Pflanzengewebe etabliert und verbessert.
In Bezug auf die Mikroskopieanwendungen konnten wir in Arabidopsis thaliana (At) Wurzeln die polare Verteilung von PIN Proteinen mittels SIM bestätigen und die gruppierte Verteilung in der Plasmamembran am Zellpol auflösen. In Wurzel-querschnitten war es möglich, Zellwände zu vermessen, den Aufbau der Pflanzenwurzel mit den verschiedenen Zelltypen zu rekonstruieren und diesen in Zusammenhang mit Zellwanddicken zu bringen. Anhand dieser Aufnahmen ließ sich die Auflösungsgrenze eines SIM-Mikroskops bestimmen, weshalb diese Probe als Modellstruktur für Auflösungsanalysen, zur Kontrolle für die korrekte Bildverarbeitung bei hochauflösender Bildgebung und andere Fragestellungen empfohlen werden kann.
Für die Expansionsmikroskopie in pflanzlichen Proben konnten ein enzym- und ein denaturierungsbasiertes Präparationsprotokoll etabliert werden. Dabei wurden ganze At Setzlinge, Wurzelabschnitte und Blattstücke gefärbt, expandiert und mit zwei bis drei Mal verbesserter Auflösung bildlich dargestellt. In diesem Zusammenhang waren Aufnahmen ganzer Wurzel- und Blattproben mit beeindruckender Eindringtiefe und extrem geringem Hintergrundsignal möglich. Zudem wurden die Daten kritisch betrachtet, Probleme aufgezeigt, gewebespezifische Veränderungen dargestellt und limitierende Faktoren für die ExM in Pflanzenproben thematisiert.
Im Fokus dieser Arbeit stand die Untersuchung der SLAC/SLAH Proteine. SLAH2 wird in den Wurzeln vornehmlich in Endodermis- und Perizykelzellen exprimiert, was anhand verschiedener At SLAH2 YFP Mutanten untersucht werden konnte. Dies unterstützt die Annahme, dass SLAH2 bei der Beladung der Leitgefäße mit Nitrat maßgeblich beteiligt ist. Es ist denkbar, dass SLAH2 ebenfalls eine wachstumsbeeinflussende Funktion über die Regulation von Nitratkonzentrationen zugeschrieben werden kann. Darauf deuten vor allem die verstärkte Expression von SLAH2 im Bereich der Seitenwurzeln und die heterogene Expression in der Elongations-, Differenzierungs- und meristematischen Zone hin. Die Membranständigkeit von SLAH4 konnte nachgewiesen werden und FRET FLIM Untersuchungen zeigten eine hohe Affinität von SLAH4 zu SLAH3, was die beiden Homologe als Interaktionspartner identifiziert.
Für die Bestimmung des Oligomerisierungsgrades mittels PALM wurden die pflanzlichen Anionenkanäle in tierischen COS7-Zellen exprimiert. Die elektrophysiologische Funktionalität der mEOS2-SLAC/SLAH-Konstrukte wurde mit Hilfe von Patch-Clamp-Versuchen in COS7-Zellen überprüft. Um Expressionslevel, Membranständigkeit und die Verteilung über die Membran der SLAC/SLAHs zu verifizieren, wurden dSTORM-Aufnahmen herangezogen
Schließlich ermöglichten PALM-Aufnahmen die Bestimmung des Polymerisierungs-grades der SLAC/SLAH Anionenkanäle, die stöchiometrischen Veränderungen bei Heteromerisierung von SLAH3 mit SLAH1 oder SLAH4 und auch der Einfluss einer zytosolischer Ansäuerung auf den Polymerisierungsgrad von SLAH3 Homomeren. Zudem weisen die Oligomerisierungsanalysen von SLAH3 Mutanten darauf hin, dass die Aminosäuren Histidin His330 und His454 entscheidend an der pH sensitiven Regulierung von SLAH3 beteiligt sind.
Durch die erhobenen Daten konnten also entscheidende, neue Erkenntnisse über die Regulationsmechanismen von pflanzlichen Anionenkanälen auf molekularer Ebene gewonnen werden: Unter Standardbedingungen liegen SLAC1, SLAH2 und SLAH3 hauptsächlich als Dimer vor. Auf eine zytosolische Ansäuerung reagiert ausschließlich SLAH3 mit einer signifikanten stöchiometrischen Veränderung und liegt im aktiven Zustand vor Allem als Monomer vor. Der Oligomerisierungsgrad von SLAC1 und SLAH2 bleibt hingegen bei einer zytosolischen Ansäuerung unverändert. Ferner kommt es bei der Interaktion von SLAH3 mit SLAH1 oder SLAH4 zur Formierung eines Heterodimers, welches unbeeinflusst durch den zytosolischen pH bleibt. Im Gegensatz dazu bleiben die elektrisch inaktiven Untereinheiten SLAH1 und SLAH4 monomerisch und assemblieren ganz spezifisch nur mit SLAH3. Die hochauflösende Fluoreszenz-mikroskopie, insbesondere PALM erlaubt es also Heteromerisierungsereignisse und Änderungen im Poylmerisierungsgrad von Membranproteinen wie den SLAC/SLAHs auf molekularer Ebene zu untersuchen und lässt so Rückschlüsse auf physiologische Ereignisse zu.
Resource availability in agricultural landscapes has been disturbed for many organisms, including pollinator species. Abundance and diversity in flower availability benefit bee populations; however, little is known about which of protein or carbohydrate resources may limit their growth and reproductive performance. Here, we test the hypothesis of complementary resource limitation using a supplemental feeding approach. We applied this assumption with bumble bees (Bombus terrestris), assuming that colony growth and reproductive performance should depend on the continuous supply of carbohydrates and proteins, through the foraging for nectar and pollen, respectively. We placed wild‐caught bumble bee colonies along a landscape gradient of seminatural habitats, and monitored the colonies’ weight, foraging activity, and reproductive performance during the whole colony cycle. We performed supplemental feeding as an indicator of landscape resource limitation, using a factorial design consisting of the addition of sugar water (carbohydrate, supplemented or not) crossed by pollen (protein, supplemented or not). Bumble bee colony dynamics showed a clear seasonal pattern with a period of growth followed by a period of stagnation. Higher abundance of seminatural habitats resulted in reducing the proportion of pollen foragers relative to all foragers in both periods, and in improving the reproductive performance of bumble bees. Interestingly, the supplemental feeding of sugar water positively affected the colony weight during the stagnation period, and the supplemental feeding of pollen mitigated the landscape effect on pollen collection investment. Single and combined supplementation of sugar water and pollen increased the positive effect of seminatural habitats on reproductive performance. This study reveals a potential colimitation in pollen and nectar resources affecting foraging behavior and reproductive performance in bumble bees, and indicates that even in mixed agricultural landscapes with higher proportions of seminatural habitats, bumble bee populations face resource limitations. We conclude that the seasonal management of floral resources must be considered in conservation to support bumble bee populations and pollination services in farmlands.
Preventing malnutrition through consuming nutritionally appropriate resources represents a challenge for foraging animals. This is due to often high variation in the nutritional quality of available resources. Foragers consequently need to evaluate different food sources. However, even the same food source can provide a plethora of nutritional and non‐nutritional cues, which could serve for quality assessment. We show that bumblebees, Bombus terrestris , overcome this challenge by relying on lipids as nutritional cue when selecting pollen. The bees ‘prioritised’ lipid perception in learning experiments and avoided lipid consumption in feeding experiments, which supported survival and reproduction. In contrast, survival and reproduction were severely reduced by increased lipid contents. Our study highlights the importance of fat regulation for pollen foraging bumblebees. It also reveals that nutrient perception, nutrient regulation and reproductive fitness can be linked, which represents an effective strategy enabling quick foraging decisions that prevent malnutrition and maximise fitness.
Chlamydia trachomatis is the main cause of sexually transmitted diseases worldwide. As obligate intracellular bacteria Chlamydia replicate in a membrane bound vacuole called inclusion and acquire nutrients for growth and replication from their host cells. However, like all intracellular bacteria, Chlamydia have to prevent eradication by the host's cell autonomous system. The chlamydial deubiquitinase Cdu1 is secreted into the inclusion membrane, facing the host cell cytosol where it deubiquitinates cellular proteins. Here we show that inactivation of Cdu1 causes a growth defect of C. trachomatis in primary cells. Moreover, ubiquitin and several autophagy receptors are recruited to the inclusion membrane of Cdu1‐deficient Chlamydia . Interestingly, the growth defect of cdu1 mutants is not rescued when autophagy is prevented. We find reduced recruitment of Golgi vesicles to the inclusion of Cdu1 mutants indicating that vesicular trafficking is altered in bacteria without active deubiquitinase (DUB). Our work elucidates an important role of Cdu1 in the functional preservation of the chlamydial inclusion surface.
Aim:
Temperature, food resources and top‐down regulation by antagonists are considered as major drivers of insect diversity, but their relative importance is poorly understood. Here, we used cavity‐nesting communities of bees, wasps and their antagonists to reveal the role of temperature, food resources, parasitism rate and land use as drivers of species richness at different trophic levels along a broad elevational gradient.
Location:
Mt. Kilimanjaro, Tanzania.
Taxon:
Cavity‐nesting Hymenoptera (Hymenoptera: Apidae, Colletidae, Megachilidae, Crabronidae, Sphecidae, Pompilidae, Vespidae).
Methods:
We established trap nests on 25 study sites that were distributed over similar large distances in terms of elevation along an elevational gradient from 866 to 1788 m a.s.l., including both natural and disturbed habitats. We quantified species richness and abundance of bees, wasps and antagonists, parasitism rates and flower or arthropod food resources. Data were analysed with generalized linear models within a multi‐model inference framework.
Results:
Elevational species richness patterns changed with trophic level from monotonically declining richness of bees to increasingly humped‐shaped patterns for caterpillar‐hunting wasps, spider‐hunting wasps and antagonists. Parasitism rates generally declined with elevation but were higher for wasps than for bees. Temperature was the most important predictor of both bee and wasp host richness patterns. Antagonist richness patterns were also well predicted by temperature, but in contrast to host richness patterns, additionally by resource abundance and diversity. The conversion of natural habitats through anthropogenic land use, which included biomass removal, agricultural inputs, vegetation structure and percentage of surrounding agricultural habitats, had no significant effects on bee and wasp communities.
Main conclusions:
Our study underpins the importance of temperature as a main driver of diversity gradients in ectothermic organisms and reveals the increasingly important role of food resources at higher trophic levels. Higher parasitism rates at higher trophic levels and at higher temperatures indicated that the relative importance of bottom‐up and top‐down drivers of species richness change across trophic levels and may respond differently to future climate change.
We are living in a system that underlies permanent environmental changes due to the rotation of our planet. These changes are rhythmic with the most prominent one having a period of about 24 hours, but also shorter and longer rhythms characterize our environment. To cope with the ever-changing environmental conditions, it is thought to be beneficial if an organism can track and anticipate these changes. The so called endogenous clocks enable this and might provide a fitness advantage. To investigate and unravel the mechanism of endogenous clocks Chronobiologists have used different model organisms. In this thesis Drosophila melanogaster was used as model organism with its about 150 clock neurons representing the main endogenous clock of the fly in the central brain.
The molecular mechanisms and the interlocked feedback loops with the main circadian key players like period, timeless, clock or cycle are under investigation since the 1970s and are characterized quite well so far. But the impact of a functional endogenous clock in combination with diverse factors and the resulting fitness advantages were analysed in only a few studies and remains for the most part unknown. Therefore the aim of this thesis was to unravel the impact of Drosophila melanogaster`s endogenous clock on the fitness of the fly. To achieve this goal different factors – like day length, humidity and food composition – were analyzed in wild type CS and three different period mutants, namely perL, perS and per01, that carry a point mutation altering or abolishing the free-running period of the fruit fly as well as a second arrhythmic strain, clkAR.
In competition assay experiments wild type and clock mutant flies competed for up to 63 generations under a normal 24 hour rhythm with 12 hours light/day and 12 hours darkness/night (LD12:12) or T-cycles with 19 or 29 hours, according to the mutants free-running period, or constant light (LL) in case of the arrhythmic mutant as well as under natural-like outdoor conditions in two consecutive years. Overall the wild type CS strain was outcompeting the clock mutant strains independent of the environmental conditions. As the perL fly strain elongated their free-running period, the competition experiments were repeated with naturally cantonized new fly strains. With these experiments it could be shown that the genetic background of the fly strains – which are kept for decades in the lab, with backcrosses every few years – is very important and influences the fitness of flies. But also the day length impacts the fitness of the flies, enabling them to persist in higher percentage in a population under competition. Further factors that might influence the survival in a competing population were investigated, like e.g. mating preferences and locomotor activity of homo- and heterozygous females or sperm number of males transferred per mating. But these factors can still not explain the results in total and play no or only minor roles and show the complexity of the whole system with still unknown characteristics.
Furthermore populations of flies were recorded to see if the flies exhibit a common locomotor activity pattern or not and indeed a population activity pattern could be recorded for the first time and social contact as a Zeitgeber could be verified for Drosophila melanogaster.
In addition humidity and its impact on the flies´ fitness as well as a potential Zeitgeber was examined in this thesis. The flies experienced different relative humidities for eclosion and wing expansion and humidity cycle phase shifting experiments were performed to address these two different questions of fitness impact and potential Zeitgeber. The fruit fly usually ecloses in the morning hours when the relative humidity is quite high and the general assumption was that they do so to prevent desiccation. The results of this thesis were quite clear and demonstrate that the relative humidity has no great effect on the fitness of the flies according to successful eclosion or wing expansion and that temperature might be the more important factor. In the humidity cycle phase shifting experiments it could be revealed that relative humidity cannot act as a Zeitgeber for Drosophila melanogaster, but it influences and therefore masks the activity of flies by allowing or surpressing activity at specific relative humidity values.
As final experiments the lifespan of wild type and clock mutant flies was investigated under different day length and with different food qualities to unravel the impact of these factors on the fitness and therefore survival of the flies on the long run. As expected the flies with nutrient-poor minimum medium died earlier than on the nutrient-rich maximum medium, but a small effect of day length could also be seen with flies living slightly longer when they experience environmental day length conditions resembling their free-running period. The experiments also showed a fitness advantage of the wild type fly strain against the clock mutant strains for long term, but not short term (about the first 2-3 weeks).
As a conclusion it can be said that genetic variation is important to be able to adapt to changing environmental conditions and to optimize fitness and therefore survival. Having a functional endogenous clock with a free-running period of about 24 hours provides fitness advantages for the fruit fly, at least under competition. The whole system is very complex and many factors – known and unknown ones – play a role in this system by interacting on different levels, e.g. physiology, metabolism and/or behavior.