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Mutualisms are ubiquitous in nature and shape whole ecosystems. Although species benefit by interacting with each other, they permanently act selfishly. As a consequence, the involved partners must balance gaining the maximal benefit while accepting a certain amount of costs. Changes in the environment, however, may alter selection pressures and lead to a shift in the relative costs and benefits for both involved species. Due to this complexity, many mutualisms and their underlying processes, such as the dependence of the involved species on each other, are only poorly understood. Moreover, in several so-called mutualistic interactions it is unclear if they are in fact beneficial for all partners because detailed cost-benefit analyses are missing. The aim of my thesis was to contribute to a better understanding of the basic principles of mammal-plant mutualisms with special emphasis on the interdependence of the involved species. Using the interaction between an insectivorous bat species (Kerivoula hardwickii) and carnivorous pitcher plants (genus Nepenthes) as a model system, I conducted a detailed cost-benefit analysis to test if the partners interact mutualistically and are strongly dependent on one another. I hypothesised that pitchers of these plants serve as high quality roosts for the bats while the bats in turn fertilise the plants via their nutritious faeces. For the involved species the costs of the interaction should be lower than the gained benefits, but general costs should increase in the absence of the partner. Over the course of my field research, I found the bats roosting in three Nepenthes species, but the bats occupied intact pitchers of only one species, Nepenthes hemsleyana. In Nepenthes bicalcarata and Nepenthes ampullaria, the bats used senescing or damaged pitchers whose high amount of digestive fluid had drained off. Thus, only N. hemsleyana was potentially able to digest bat faecal matter, and thereby benefit from the bats. My cost-benefit analysis showed that N. hemsleyana plants strongly benefited from their bat interaction partner: In feeding experiments the plants gained between 34% and 95% of their nitrogen from bat faeces, which significantly improved their growth, photosynthesis and survival. In contrast, plants without access to faeces could not fully compensate the induced lack of nutrients by using arthropod prey. Field observations revealed no obvious costs for the pitcher plant. N. hemsleyana pitchers occupied by bats did not differ in their lifespan from unoccupied ones as bats did not injure the plants’ tissue. The interaction was also advantageous for K. hardwickii because N. hemsleyana offered high quality roosts with a favourable microclimate and low parasite infestation risk. Consequently, bats roosting in N. hemsleyana pitchers were in better condition than those roosting in dead N. bicalcarata pitchers. Although N. hemsleyana pitchers are rare in the natural habitat, bats could easily find and identify them due to an echo reflector, which reduces time and energy costs for roost detection. Most N. hemsleyana plants continuously provided at least one intact pitcher meaning bats could return to the same plants over a period of several months or even years. The interaction between K. hardwickii and N. hemsleyana can be classified as an asymmetric facultative mutualism with stronger dependence of the plant partner. N. hemsleyana has outsourced arthropod capture and digestion to its mutualistic bat partner while arthropod attraction is strongly reduced. Contrastingly, several populations of K. hardwickii frequently use alternative roosts. Strong selective pressure on the plants could be the consequence to attract bats with a potential stabilising effect on the interaction: N. hemsleyana has to outcompete the involuntarily offered roosts of the other Nepenthes species in terms of quality and accessibility. My thesis revealed complex interdependencies in an animal-plant mutualism. This study exemplifies that rigorous cost-benefit analyses are crucial for the classification of interspecific interactions and the characterisation of how the involved species affect and depend on each other.
Human habitat disturbance affects both species diversity and intraspecific genetic diversity, leading to correlations between these two components of biodiversity (termed species–genetic diversity correlation, SGDC). However, whether SGDC predictions extend to host‐associated communities, such as the intestinal parasite and gut microbial diversity, remains largely unexplored. Additionally, the role of dominant generalist species is often neglected despite their importance in shaping the environment experienced by other members of the ecological community, and their role as source, reservoir and vector of zoonotic diseases. New analytical approaches (e.g. structural equation modelling, SEM) can be used to assess SGDC relationships and distinguish among direct and indirect effects of habitat characteristics and disturbance on the various components of biodiversity.
With six concrete and biologically sound models in mind, we collected habitat characteristics of 22 study sites from four distinct landscapes located in central Panama. Each landscape differed in the degree of human disturbance and fragmentation measured by several quantitative variables, such as canopy cover, canopy height and understorey density. In terms of biodiversity, we estimated on the one hand, (a) small mammal species diversity, and, on the other hand, (b) genome‐wide diversity, (c) intestinal parasite diversity and (d) gut microbial heterogeneity of the most dominant generalist species (Tome's spiny rat, Proechimys semispinosus). We used SEMs to assess the links between habitat characteristics and biological diversity measures.
The best supported SEM suggested that habitat characteristics directly and positively affect the richness of small mammals, the genetic diversity of P. semispinosus and its gut microbial heterogeneity. Habitat characteristics did not, however, directly impact intestinal parasite diversity. We also detected indirect, positive effects of habitat characteristics on both host‐associated assemblages via small mammal richness. For microbes, this is likely linked to cross species transmission, particularly in shared and/or anthropogenically altered habitats, whereas host diversity mitigates parasite infections. The SEM revealed an additional indirect but negative effect on intestinal parasite diversity via host genetic diversity.
Our study showcases that habitat alterations not only affect species diversity and host genetic diversity in parallel, but also species diversity of host‐associated assemblages. The impacts from human disturbance are therefore expected to ripple through entire ecosystems with far reaching effects felt even by generalist species.
Abstract
Social organisation in species with fluctuating population sizes can change with density. Therefore, information on (future) density obtained during early life stages may be associated with social behaviour. Olfactory cues may carry important social information. We investigated whether early life experience of different experimental densities was subsequently associated with differences in attraction to adult conspecific odours. We used common voles (Microtus arvalis), a rodent species undergoing extreme density fluctuations. We found that individuals originating from high experimental density populations kept in large outdoor enclosures invested more time in inspecting conspecific olfactory cues than individuals from low‐density populations. Generally, voles from both treatments spent more time with the olfactory cues than expected by chance and did not differ in their latency to approach the odour samples. Our findings indicate either that early experience affects odour sensitivity or that animals evaluate the social information contained in conspecific odours differently, depending on their early life experience of conspecific density.
Main drivers for biodiversity loss in terrestrial ecosystems are changes in land use, climate change, enhanced nitrogen deposition and biotic exchange (invasive species). These drivers also affect dry, nutrient-poor open anthropo-zoogenic inland and coastal heathlands which often harbor a high biodiversity. To counteract biodiversity loss in coastal ecosystems, a basic step is the assessment of the various threats. Therefore it is important to select suitable model organisms for analyses of biodiversity dynamics. In this thesis the three arthropod groups Orthoptera (Ensifera and Caelifera), carabid beetles (Coleoptera: Carabidae) and spiders (Araneae) were studied, as they are very useful indicators. Besides sampling of the three arthropod groups vegetation and microclimate parameters were recorded. The studies were done between 2008 and 2010 in the coastal heathland on the Baltic island of Hiddensee, Germany. The main aim of the thesis was to analyze the impact of three drivers of heathland biodiversity loss (succession, grass encroachment, moss invasion) on the selected indicator arthropod groups. Based on this multi-level and -species approach, implications for the conservation of coastal heathlands are given. The results show that successional processes and grass encroachment have strong impact on species richness and abundance, species composition and functional groups, as well as life-history traits and functional diversity of the arthropod groups. Main findings were: Orthoptera species richness was highest in the intermediate stages (heath encroached by grasses and heath with shrubs) because of higher habitat heterogeneity and higher food supply (grasses). Opposed to that, species richness of ground-dwelling carabid beetles and spiders did not differ among the five successional stages, which contradicts the ‘habitat heterogeneity hypothesis’. In contrast to species richness, functional diversity differed among successional stages. The concept of functional diversity – which integrates species life-history trait data – therefore might be particularly suitable for biodiversity research, while the explanatory power of species richness alone might not be sufficient. The species compositions of all three taxa changed remarkably along the coastal heathland gradient indicating a high species turnover. In particular, open, dynamic habitats (‘grey dunes’ and ‘dwarf-shrub heath’) could be separated. Here, several specialized, xerothermic and threatened species occurred due to the extreme habitat conditions, but are displaced during grass and shrub encroachment. On a smaller spatial scale, the invasion of Campylopus introflexus alters habitat conditions in grey dunes and therefore affects carabid beetle and spider species and the dominant Orthoptera species Myrmeleotettix maculatus. Species richness of carabid beetles and spiders, and the abundance of adult M. maculatus grasshoppers were reduced. Species compositions of carabids and spiders changed remarkably with a loss of several species. These negative impacts could be explained by the vegetation structure of the moss which is unsuitable for web-building spiders or large carabid beetles, and by reduced germination of higher plants and therefore reduced food supply for M. maculatus and phytophagous carabid species. Within the open coastal heathland, the mosaic of grey dunes and adjacent dwarf-shrubs is important since many species perform a habitat change during their development and, besides the scarcely vegetated, thermally benefited grey dunes, need denser vegetation of adjacent dwarf-shrubs for shelter, as song posts, or for foraging. As grey dunes harbor a high abundance and species richness of threatened and specialized, mainly xerothermic and geobiont species and are important as oviposition and nymphal habitat, they are regarded as a keystone habitat within the coastal heathland. Besides these ecological studies, two studies focused on the method of pitfall trapping. It could have been shown, that pitfall trapping might be a useful sampling method for Orthoptera in open habitats. The other study demonstrated that sampling interval has a strong influence on the capture efficiency of several arthropod groups (‘digging-in effect’). Conservation practices should aim at maintaining a heterogeneous heathland mosaic with open grey dunes and Calluna stands, in addition to scattered grassy and shrub-encroached heath for the survival of species-rich heathland arthropod assemblages with a high proportion of specialized and threatened species.
Podocytes are highly specialized kidney cells that are attached to the outer aspect of the glomerular capillaries and are damaged in more than 75% of patients with an impaired renal function. This specific cell type is characterized by a complex 3D morphology which is essential for proper filtration of the blood. Any changes of this unique morphology are directly associated with a deterioration of the size-selectivity of the filtration barrier. Since podocytes are postmitotic, there is no regenerative potential and the loss of these cells is permanent. Therefore, identification of small molecules that are able to protect podocytes is highly important. The aim of this work was to establish an in vivo high-content drug screening in zebrafish larvae. At first, we looked for a reliable podocyte injury model which is fast, reproducible and easy to induce. Since adriamycin is commonly used in rodents to damage podocytes, we administered it to the larvae and analyzed the phenotype by in vivo microscopy, (immuno-) histology and RT-(q)PCR. However, adriamycin did not result in a podocyte-specific injury in zebrafish larvae. Subsequently, we decided to use a genetic ablation model which specifically damages podocytes in zebrafish larvae. Treatment of transgenic zebrafish larvae with 80 µM metronidazole for 48 hours generated an injury resembling focal and segmental glomerulosclerosis which is characterized by podocyte foot process effacement, cell depletion and proteinuria. Following this, we established an in vivo high-content screening system by the use of a specific screening zebrafish strain. This screening strain expresses a circulating 78 kDa eGFP-labeled Vitamin D-binding fusion protein, which passes the filtration barrier only after glomerular injury. Therefore, we had an excellent readout to follow podocyte injury in vivo. We generated a custom image analysis software that measures the fluorescence intensity of podocytes and the vasculature automatically on a large scale. Furthermore, we screened a specific drug library consisting of 138 compounds for protective effects on larval podocytes using this in vivo high-content system. The analysis identified several initial hits and the subsequent validation experiments identified belinostat as a reliable and significant protective agent for podocytes. These results led to a patent request and belinostat is a promising candidate for a clinical use and will be tested in mammalian podocyte injury models.
Abstract
Surface waters are warming due to climate change, potentially pushing aquatic organisms closer to their thermal tolerance limits. However, cyanobacterial blooms are expected to occur more often with rising temperature, increasing the likelihood of poor‐quality food available for herbivorous zooplankton. Zooplankton can adapt locally by genetic differentiation or via adaptive phenotypic plasticity to increasing temperatures, but there is limited knowledge on how these processes may be affected by food quality limitation imposed by cyanobacteria.
To test the effects of cyanobacteria‐mediated food quality on local temperature adaptation, we measured juvenile somatic growth and reproduction of five Daphnia magna clones from different latitudinal origin grown on three food qualities at 20, 24, and 28°C. Additionally we estimated short‐term heat tolerance, measured as knockout time (time to immobility) at lethally high temperature, of two clones acclimated to the three temperatures and two food quality levels to test for the effects of food quality on adaptive plastic responses.
As expected, clones from lower latitudes showed on average better somatic growth and reproduction than clones from higher latitudes at higher temperatures. However, the difference in somatic growth diminished with increasing cyanobacteria abundance in the diet, suggesting constraints on local genetic adaptation under predicted decreases in food quality. As expected, short‐term heat tolerance of the clones generally increased with increasing acclimation temperature. However, heat tolerance of animals acclimated to the highest temperature was larger when grown at medium than at good food quality, whereas the opposite response was observed for animals acclimated to the lowest temperature. This suggests a better adaptive phenotypic response of animals to elevated temperatures under higher cyanobacteria abundance, and thus shows an opposite pattern to the results for somatic growth.
Overall, we demonstrate that food quality limitation can mediate responses of D. magna life history traits and heat tolerance to increasing temperatures, and that the effects differ depending on the time scale studied, that is, mid‐term (somatic growth) versus short‐term (tolerance to acute heat stress). These aspects will need further attention to accurately predict of how organisms will cope with future global warming by local adaptation and adaptive phenotypic plasticity.
Under the influence of human activities, increased climate variability induces changes in
multiple marine environments. Especially vulnerable are the coastal ecosystems where organisms
must cope with constant extreme changes of environmental drivers, such as temperature, salinity, pH,
and oxygen content. In coastal areas, brachyuran crabs are important animals that have a high impact
on ecosystem functioning and serve as a link in food webs and pelagic-benthic coupling. Larval stages
of crabs are crucial for population persistence and dispersal. They are generally more vulnerable to
changes of environmental drivers and failure to adapt to new conditions may result in population
collapse. To analyse the effects of multiple environmental drivers on larval performance and to
elucidate interspecific and intraspecific difference, this project examined larval performance in the
European shore crab Carcinus maenas. In this study, larvae of C. maenas from three native
populations (Cádiz: Cádiz Bay, Helgoland: North Sea, Kerteminde: Baltic Sea) were reared in a
factorial design consisting of different temperature (15-24 °C) and salinity treatments (20, 25, 32.5
PSU). Results demonstrated how descriptors of larval performance (growth, physiological, and
developmental rates, and survival) were affected by combined environmental drivers. Larval
responses to temperature and salinity showed contrasting patterns and differed among native
populations originating from distant or contrasting habitats, as well as within the populations. The
highest overall performance was recorded in the Cádiz population, while the Kerteminde population
had the lowest performance in most of tested traits. The interactive effects of multiple drivers differed
among the populations. In the Cádiz and Helgoland populations, higher temperatures mitigated the
effect of lower salinity while the Kerteminde population showed a maladaptive response when
exposed to lower salinity. Differences in performance showed better locally adapted populations (e.g.
Cádiz) that could acclimate faster, have better adaptive mechanisms or stronger dispersive abilities.
Because of their wider tolerance to increased temperature and decreased salinity, interactive effects
in particular populations may favour some populations in a changing climate, especially in coastal
habitats. Variation in larval performance showed complex interactions in larval performance and
highlighted the necessity to quantify inter-population responses to climate-driven environmental
change where responses of species should not be generalised. This study emphasizes the need for
inclusion of multiple traits, drivers, and populations in experimental studies to properly characterize
performance of marine coastal animals.
The present work focusses on the mosquito populations of two zoological gardens in Germany with the aim to better understand mosquito biology of native species and to contribute to a greater awareness of mosquito and mosquito-borne disease agent surveillance in zoos. For this purpose, data on species composition, blood meal patterns and mosquito-borne pathogens were analysed. The investigated zoological gardens differed not only in their sizes and animal stocks, but also in their surrounding environments. The 160 ha Tierpark Berlin is located in a densely populated urban area, while the 15 ha Zoological Garden Eberswalde is surrounded by forest.
To gain an overview about the mosquito fauna of both zoos, adult specimens were caught by aspirating and EVS-trapping during the 2016 season. In addition, larval stages were collected from their breeding sites located in the zoo areas. In total, 2,257 mosquitoes were sampled, belonging to 20 taxa. Seasonal differences between the zoos were documented, both in terms of species composition and the relative abundance of mosquito species collected. As the studied zoos were located in the same climatic region and both locations provided similar breeding sites, differences in species composition were attributed to the entry of mosquitoes from surrounding landscapes. Influencing factors could have been the different sizes of the zoos and variations in the potential host animal populations.
According to the vector potential of most frequently collected taxa in the Zoological Garden Eberswalde (Annulipes Group, Culiseta annulata), TAHV, USUV, WNV, filariae and avian malaria parasites appear to have the highest risk of being transmitted at this location. In the Tierpark Berlin, Aedes vexans was the most frequently collected mosquito species, suggesting a theoretical risk for the transmission of a broader spectrum of pathogens due to covered vector competences. Pathogens such as BATV, SINV, TAHV, USUV and filarial worms could be of major importance regarding transmission risk to zoo animals, as they had previously been found to circulate Germany. In addition, avian malaria parasites represent a considerable risk for susceptible exotic bird species in Berlin.
Since the blood-feeding behaviour of vector-competent mosquito species has a major influence on the transmission of a mosquito-associated pathogen, the analysis of blood meal patterns is crucial to better understand vector-pathogen cycles. Therefore, blood meals of blood-fed mosquitoes caught in 2016 and 2017 by aspirating and EVS-trapping in the Tierpark Berlin and the Zoological Garden Eberswalde were analysed. The aim was to investigate to what extent native mosquito species accept exotic zoo animals, wild native animals and humans as blood hosts. In addition, it was examined whether the collected species are generalists or specialists when selecting vertebrates for blood feeding.
A total of 405 blood-fed mosquitoes from 16 taxa were collected. The genetic analysis of blood meals identified 56 host species, which – in addition to humans – mainly originated from mammals of the zoo animal populations. In agreement with the previous study on the mosquito fauna of the Tierpark Berlin and the Zoological Garden Eberswalde, the analysis of blood meals also showed differences between the two zoos. In the smaller Zoological Garden Eberswalde, a higher number of blood-fed mosquitoes was collected than in the Tierpark Berlin, probably caused by a higher host density in Eberswalde, which may have led to an overall higher mosquito density. However, no differences between both zoos were observed with respect to the blood feeding behaviour of the analysed mosquito species: Mosquitoes of both locations were rather generalistic, although species could be grouped according their blood meals into 'amphibian', 'non-human mammal' and, ‘non-human mammal and human' feeding species. The more random selection of hosts could indicate a low probability of effective pathogen transmission by applying the 'dilution effect'. Notwithstanding, since wild animals have also been accepted as hosts, pathogen transmission by bridge vectors from one vertebrate group to another could be relevant in the sampled zoos.
Adult mosquito specimens collected in 2016 and 2017 were screened for filarial nematodes, avian Haemosporidia and mosquito-borne viruses. Dirofilaria repens was detected in a mosquito from the Zoological Garden Eberswalde. Mosquitoes from Berlin and Eberswalde were tested positive for the nematode species S. tundra. Sindbis virus was found in a mosquito pool collected in the Tierpark Berlin, while no mosquito-associated viruses were detected in specimens collected in the Zoological Garden Eberswalde. Mosquitoes from both zoos were positive for the haemosporidian parasites Haemoproteus sp. and Leucocytozoon sp., and one documentation was made for avian Plasmodium sp. in the Tierpark Berlin.
The identified pathogens have the potential to cause disease in captive and wild animals, and some of them also in humans. Most of the mosquitoes tested positive had been collected in July, suggesting a high infection risk during this month. Since most pathogen detections were made from species belonging to the Cx. pipiens complex, species of this complex seem to be most relevant in the studied zoos when it comes to mosquito-borne pathogen transmission. Although mosquitoes are no proven vectors of most of the avian malaria parasite genera found, evidence for Haemoproteus sp. and Leucozytozoon sp. demonstrated a high prevalence of avian malaria parasites in the zoos.
In summary, the results of the three studies indicate regional differences both in the mosquito species composition and in the occurrence of mosquito-borne pathogens. However, no differences were found between the mosquito communities of both zoos concerning their blood feeding behaviour, suggesting that the general behaviour of the insects is location-independent.
Several potential disease agents were found in the collected mosquitoes, although not at high abundances. Whether these pathogens were found by chance in the two zoos or whether the particular zoo environment is a hot spot of arthropod-borne pathogens cannot be determined with the studies conducted. Nonetheless, it seems clear that zoological gardens are attractive to mosquito females not only in their search for breeding sites, but also when looking for blood hosts and places for mating or resting. These advantageous conditions also attract mosquito species that have their larval habitats outside the zoological gardens, which is why elimination of breeding sites on the zoo premises alone will not necessarily keep away all mosquitoes.
A closer collaboration between zoological gardens and entomologists could be beneficial for both. Zoo officials could benefit from being able to identify potential arthropod vectors on the zoo grounds and receiving information on circulating arthropod-borne disease agents, as well as on the animal species susceptible to those. For entomologists, zoological gardens are ideal research locations, as they provide an environment with a high diversity of habitats and potential blood hosts for haematophagous arthropods in a confined space.
Studying mosquito biology will become even more significant in the future, since in a world that is getting smaller, both potential vectors and pathogens are regularly introduced into areas where they did not occur before. Therefore, it would be desirable if more studies targeting ecological as well as infectiological aspects of vector species in zoological gardens in Germany were carried out.
The modification of male pedipalps into secondary sexual intromittent organs is one of the hallmark characteristics of spiders, yet understanding the development and evolution of male genitalia across the order remains a challenging prospect. The embolus – the sclerite bearing the efferent spermatic duct or spermophor, and used to deliver sperm directly to the female genitalia during copulation – has always been considered the single unambiguously homologous palpal sclerite shared by all spider species, fundamental to the bauplan of the order and to the evolution and functional morphology of spider reproductive systems. Indeed, after two centuries of comparative research on spider reproduction, the presence of a single spermophor and embolus on each of a male spider’s two pedipalps remains a central tenet of evolutionary arachnology. Our findings challenge this premise, and reveal a remarkable twin intromittent organ sperm transfer system in a lineage of Australian palpimanoid spiders, characterized by a bifurcate spermophor and the presence of two efferent ducts leading to a pair of embolic sclerites on each pedipalp. This is the first time such a remarkable conformation has been observed in any group of arachnids with direct sperm transfer, complicating our understanding of palpal sclerite homologies, and challenging ideas about the evolution of spider genitalia.
Chaetognaths are a fascinating taxon with unique features and a great impact on marine food webs as primary predators of zooplankton. Their phylogenetic position has been subject to many speculations ever since their discovery and even contemporary phylogenomic methods have not yet been able to suggest a stable hypothesis on their phylogenetic position within the Bilateria. Neuroanatomical studies may contribute new aspects to this discussion. This study aims to provide new insights into the chaetognath nervous system using a fresh set of methods to determine characters for a phylogenetic discussion. The method of choice in this case was immunohistochemistry combined with confocal microscopy. Experiments were conducted with a host of antibodies. The most effective target antigenes were RFamides (a family of neuropeptides), synapsins (synaptic proteins), tyrosinated tubulin (a cytoskeletal element, especially in neurites) and BrdU (bromodeoxyuridin, a proliferation marker). Each of those markers was of great use in highlighting certain aspects of the nervous system. A fresh look at the development of juvenile chaetognaths shortly after hatching revealed that the ventral nerve center (VNC) is developing earlier than the brain and that the production of neurotransmitters has already started at hatching. Specifically, some neurons exhibit RFmide-like immunoreactivity (ir). Neurogenesis continues for about five days after hatching and the mode of division in the neuronal stemcells is asymmetrical. In adult chaetognaths, the brain is divided into a stomatogastric anterior and a sensory posterior neuropil domain. It contains a set of individually identifiable neurons that exhibit RFamide-like ir. The study highlights the interspecific variation of brain architecture between representatives of spadellids and sagittids. The VNC consists of two lateral bands of somata that flank a central neuropil. Within the VNC exists a serial arrangement of neurons with RFamide-like ir. A variety of other neurotransmitters and related substances are also present in both, the brain and the VNC. More interspecific differences and similarities were explored in another part of the study, comparing even more different chaetognath species and focusing on the VNC and its internal structure. The two species of Krohnitta have an unusual distribution of nuclei that is not clearly separated into two lateral bands like in other species. Many of the sagittid species exhibit a striation pattern of the neuropil that is mostly absent in other groups and some of their nerve nets show varying degrees of order as opposed to the rather disorganized nerve net in other groups. In addition, immunohistochemical methods were applied to several specimens of Gnathostomula sp. in order to test one of the many hypotheses about the chaetognaths phylogenetic position, a sister-group relationship to gnathostomulids. A comparison between the two taxa, taking into account also other gnathifera and platyhelminthes, makes a sistergroup relationship between chaetognaths and gnathostomulids very unlikely. In conclusion, chaetognaths remain in an enigmatic phylogenetic position and likely branched off close to the deuterostome/protostome split.