Refine
Year of publication
Document Type
- Article (73)
- Doctoral Thesis (46)
Language
- English (119) (remove)
Has Fulltext
- yes (119)
Is part of the Bibliography
- no (119)
Keywords
- - (21)
- phenotypic plasticity (9)
- climate change (8)
- Fledermäuse (7)
- Klimawandel (5)
- Anpassung (4)
- Chiroptera (4)
- genetic adaptation (4)
- Ökologie (4)
- Araneae (3)
Institute
- Zoologisches Institut und Museum (119) (remove)
Publisher
- Wiley (33)
- Frontiers Media S.A. (12)
- Springer Nature (8)
- BioMed Central (BMC) (7)
- MDPI (5)
- Nature Publishing Group (2)
- Royal Society (2)
- Company of Biologists (1)
- IOP Publishing (1)
- eLife Sciences Publications (1)
Animals face strong environmental variability even on short time scales particularly in shallow coastal habitats, forcing them to permanently adjust their metabolism. Respiration rates of aquatic ectotherms are directly influenced by water temperature, whereas ingestion rates might additionally be influenced by behavior. We aim to understand how respiration and ingestion rates of an aquatic invertebrate respond to changing temperature during a diurnal thermal fluctuation cycle and how both processes are related. We studied the benthopelagic mysid Neomysis integer as an important food web component of coastal ecosystems. Mysids were collected at the southern Baltic Sea coast and exposed in the laboratory to either constant temperature of 15°C or daily temperature fluctuation of 15 ± 5°C. Short-term (1–2 h) respiration and ingestion rates were measured at four equidistant time points within 24 h and did not differ among time points at constant temperature, but differed among time points in the fluctuating treatment. Respiration was highest at the thermal maximum and lowest at the thermal minimum. Ingestion rates showed the opposite pattern under fluctuation, likely due to differences in underlying thermal performance curves. When temperature transited the average, the direction of temperature change influenced the animals' response in respiration and ingestion rates differently. Our results suggest that respiration is not only instantaneously affected by temperature, but also influenced by the previously experienced direction of thermal change. Our experiment, using an important non-model organism, delivered new insights on the relationship between the crucial organismal processes ingestion and respiration under thermal variability.
In mandibulate arthropods, the primary olfactory centers, termed olfactory lobes in crustaceans, are typically organized in distinct fields of dense synaptic neuropils called olfactory glomeruli. In addition to olfactory sensory neuron terminals and their postsynaptic efferents, the glomeruli are innervated by diverse neurochemically distinctive interneurons. The functional morphology of the olfactory glomeruli is understudied in crustaceans compared with insects and even less well understood and described in a particular crustacean subgroup, the Peracarida, which embrace, for example, Amphipoda and Isopoda. Using immunohistochemistry combined with confocal laser scanning microscopy, we analyzed the neurochemistry of the olfactory pathway in the amphipod Parhyale hawaiensis. We localized the biogenic amines serotonin and histamine as well as the neuropeptides RFamide, allatostatin, orcokinin, and SIFamide. As for other classical neurotransmitters, we stained for γ-aminobutyric acid and glutamate decarboxylase and used choline acetyltransferase as indicator for acetylcholine. Our study is another step in understanding principles of olfactory processing in crustaceans and can serve as a basis for understanding evolutionary transformations of crustacean olfactory systems.
Hibernation is a widespread adaptation in animals to seasonally changing environmental conditions. In the face of global anthropogenic change, information about plastic adjustments to environmental conditions and associated mortality costs are urgently needed to assess population persistence of hibernating species. Here, we used a five-year data set of 1047 RFID-tagged individuals from two bat species, Myotis nattereri and Myotis daubentonii that were automatically recorded each time they entered or left a hibernaculum. Because the two species differ in foraging strategy and activity pattern during winter, we expected species–specific responses in the timing of hibernation relative to environmental conditions, as well as different mortality costs of early departure from the hibernaculum in spring. Applying mixed-effects modelling, we disentangled population-level and individual-level plasticity in the timing of departure. To estimate mortality costs of early departure, we used both a capture mark recapture analysis and a novel approach that takes into account individual exposure times to mortality outside the hibernaculum. We found that the timing of departure varied between species as well as among and within individuals, and was plastically adjusted to large-scale weather conditions as measured by the NAO (North Atlantic Oscillation) index. Individuals of M. nattereri, which can exploit milder temperatures for foraging during winter, tuned departure more closely to the NAO index than individuals of M. daubentonii, which do not hunt during winter. Both analytical approaches used to estimate mortality costs showed that early departing individuals were less likely to survive until the subsequent hibernation period than individuals that departed later. Overall, our study demonstrates that individuals of long-lived hibernating bat species have the potential to plastically adjust to changing climatic conditions, although the potential for adjustment differs between species.
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.
As the effects of anthropogenic climate change become more pronounced, it is critical to understand if and how species can persist in novel environments. Range-expanding species provide a natural experiment to study this topic: by studying the factors contributing to successful colonization of new habitats, we can gain insight into what influences organisms’ adaptive potential. The wasp spider, Argiope bruennichi, has expanded its range from warm, oceanic and Mediterranean climate zones (populations in this region are referred to as “ancestral” or “core”) into a new thermal niche, the continental climate of the Baltic States and Scandinavia (referred to as “expanding” or “edge”) within the last century. Past work demonstrated that the expanding populations are European in origin, but are more diverse than the ancestral populations, due to genetic admixture. This discovery led to the following questions, which are investigated in this dissertation: (i) Was the successful colonization of colder, more continental northern climates due to phenotypic plasticity or genetic adaptation? (ii) If A. bruennichi’s establishment of northern latitudes can be attributed to genetic adaptation, did selection act on standing genetic variation, on genetic variation introduced via admixture/introgression, on specific genomic regions, or on novel mutations? (iii) Is there a role of the microbiome in the A. bruennichi range expansion?
In Chapter 1, we assembled a chromosome-level genome for the species: the first such high-quality genome for a spider, which we made use of as a resource to provide the genomic context of single nucleotide polymorphisms in our primary study on genetic adaptation and phenotypic plasticity (Chapter 3). The genome assembly also opened the door to many new projects, such as the study presented in Chapter 2. In Chapter 2, the chromosome-level resolution of our assembly allowed us to identify the sex chromosomes in A. bruennichi. Due to the X1X20 sex chromosome system, where males have one copy of two X chromosomes, and females have two copies, the X chromosomes have a lower effective population size, and lower recombination rate, than autosomes. These characteristics give rise to the theoretical prediction of increased evolutionary rates in sex chromosomes. Knowing the identity of the sex chromosomes in our A. bruennichi genome assembly will allow us to test if there is stronger differentiation between populations on the X chromosomes.
Chapter 3 represents the central study of this dissertation. We performed a reciprocal transplant common garden experiment to assess plasticity and adaptation in cold tolerance traits, using spiderlings from the core of the range in France, and the edge of the range in Estonia. We combined this with data on clinal variation in adult phenotypes (body size, pigmentation, and fecundity) and genotypes in a transect across the European range. This study revealed a strong signature of genetic adaptation for increased cold tolerance in edge populations, and clear genetic differentiation of ancestral and expanding populations over a very short geographic distance, despite gene flow. We provide genome-wide evidence for adaptive introgression, and conclude that the A. bruennichi range
expansion was enabled by adaptive introgression, but has reached a poleward range limit.
Interactions with microbes shape all aspects of eukaryotic life. Endosymbiotic bacteria have been shown to alter the thermal tolerance of arthropod hosts, and influence dispersal behavior in spiders. With this background, in Chapter 4, we asked whether the microbiome might play a role in the rapid range expansion of A. bruennichi. We characterized the microbiome in various dissected tissues of spiders from two populations. Although we found no obvious differences between populations or tissues, this study yielded the discovery of a novel, dominant, vertically transmitted symbiont with astoundingly low similarity to all other sequenced bacteria. Since that discovery, we have found evidence of the unknown symbiont in A. bruennichi populations across the Palearctic (unpublished data), making it relatively unlikely to play a role in the range expansion.
By studying the establishment and subsequent differentiation of core versus edge populations of A. bruennichi following range expansion, we were able to gain insight into the evolutionary and ecological processes that allowed this species to successfully cope with novel environments. The rapidity with which local adaptation arose in A. bruennichi suggests that evolutionary adaptation to novel environments is possible over short time periods. However, this may only be possible in species with sufficient standing genetic variation, or with genetic variation introduced via admixture, as in A. bruennichi, which has important implications for our understanding of species responses in the face of ongoing global climate change.
American and European foulbrood (AFB and EFB) are devastating bacterial brood diseases of honey bees (Apis mellifera), which cause colony and economic losses worldwide. The causative agent of AFB, Paenibacillus larvae, are grouped into different ERIC-genotypes (Enterobacterial repetitive intergenic consensus) the two most common of which are ERIC I and ERIC II. In the field, the differentiation between the symptoms of AFB and EFB (caused by Melissococcus plutonius) can be difficult. The differentiation between the ERIC-genotypes in the field based on the symptoms is not possible at all. The differentiation between the ERIC-genotypes of P. larvae during diagnosis can help to understand the spread of the AFB disease. Hence, a tool capable of detection and distinction between the bacterial brood diseases and the P. larvae-genotypes is needed. For the optimal prevention of disease spread, the diagnosis needs to be fast, cheap and reliable.
This study focuses on the development of a diagnostic sandwich ELISA and a lateral flow device (LFD) for the detection and distinction of EFB and AFB, including the differentiation of the two main occurring P. larvae genotypes. The therefore necessary specific monoclonal antibodies (mAbs) were obtained by immunizing mice with M. plutonius or P. larvae strains belonging to either ERC I or ERIC II. The generated mAbs were characterized for their specificity towards the target bacteria and for their cross reactivity towards other bee-associated bacteria. The screening for suitable mAbs resulted in two specific mAbs against M. plutonius, two against P. larvae in general and two against ERIC II. In combination with the anti-P. larvae mAbs, the anti-ERIC II mAbs were used for genotyping.
In order to evaluate the suitability of the mAbs, their antigens were identified. The target antigens of the produced mAbs turned out to be proteins that could be of further interest as they seem to be involved in the pathogenesis and host-pathogen-interaction. The mAbs with the same antigens were used in the sandwich ELISA for testing the cross reactivity and strain detection. Suitable mAb combinations were used for LFD production. The LFDs were then successfully tested against several field isolates of AFB and EFB causing agents and no cross reactivity with bee-associated bacteria was detected. The P. larvae strains used for mAb testing were genotyped to obtain information about the respective genetic variance. In the process atypical P. larvae strains were identified and further characterized using the generated mAbs. The ability of the mAbs to also recognise the atypical strains as well indicates that the mAbs bind to an antigen that is common among different P. larvae strains.
All in all, a fast tool for detection and differentiation of EFB, AFB and the two ERIC-genotypes was developed that has to be further tested for its reliability in the field.
Bats are special: although they have a small body size, bats are extremely long-lived and have a low annual reproductive output, which puts them at the ‘slow’ end of the slow-fast continuum of mammalian life-histories. Species typically respond to climate change by genetic adaptation, range shifts or phenotypic plasticity. However, limited dispersal behavior in many bat species and long generation times make it very likely, that adaptive responses in bats are rather driven by phenotypic plasticity than by genetic adaptation or range shifts. Changing weather patterns, a higher frequency of extreme weather events and overall rising temperatures, caused by climate change, will impact phenology, energy supply and energy expenditure. In species where adult survival largely shapes population dynamics, it is thus of crucial importance to understand how climate change affects individual fitness and fitness relevant traits by altering behavior and development.
In my study, I investigated how weather impacts behavior, fitness and fitness relevant traits in free ranging Natterer’s bats from two geographical regions (south vs. north) in Germany. In the Nature Park Nossentiner/Schwinzer Heide (northern region, NSH), long-term data for investigations on population dynamics are partially collected by hibernation counts. Although counting hibernating bats is a regularly applied method, it is still unclear to which degree human visits in the hibernaculum trigger energy consuming arousals and thus increase energy expenditure. Thus, I first investigated if hibernation counts potentially threaten winter survival by assessing the number of energy consuming arousals of hibernating Natterer’s bats (Myotis nattereri) and two other bat species (Pipistrellus spp., Plecotus auritus) using thermal imaging. Additionally, I used light barriers in the hibernacula to investigate the relative impact of winter temperatures and human visits on flight activity of hibernating bats. Secondly, I investigated effects on survival and reproduction during summer by analyzing capture-mark-recapture data from summer roosts. Data from summer roosts have been collected since 2011 in Würzburg (WB, south) and 1990 in the Nature Park (NSH, north). Based on these data, I analyzed the effect of intrinsic (e.g. age) and extrinsic(e.g. different weather parameters) factors on individual survival probability and reproductive success. I further focused on the question if individual body size is a fitness relevant trait in Natterer’s bats and how body size of young bats is affected by summer temperatures.
During hibernation, ambient temperatures were the most important driver for bat activity and were positively correlated with the number of flight passes in the light barrier, suggesting that bats can exploit foraging opportunities more frequently during warm weather bouts. Monitoring caused only a small number of arousals and only a slight increase in activity, which was less severe on warmer days, when activity was generally higher. Thus, I propose that benefits of hibernation counts outweigh the costs of human presence in the hibernaculum and unlikely threaten winter survival in hibernating bats.
In spring, increased precipitation during a short time window strongly reduced the probability of successful reproduction in first-year females (females that returned from first hibernation, FY). In terms of timing, this sensitive period comprises the implantation or early pregnancy, a time before substantial investment into embryo development. Moreover, I identified a positive correlation between a large body size and reproductive success in FY females. Given the evidence that suitable weather conditions during early life support juvenile growth and thus a large body size, my findings suggest that reproduction may be condition dependent in young females. Reproductive success of older females was not affected by either weather or individual parameters. This suggests that older and experienced females can better deal with adverse conditions.
To examine if beneficial weather conditions are linked to a large body size, I investigated the effect of ambient temperatures during the growing season on body size. I found that higher ambient temperatures during summer led to larger individuals, however, only in the northern population. In the on average colder North, warmer summers may benefit juvenile growth by reducing thermoregulatory costs and increasing prey abundance, whereas in the general warmer South, this effect might not be visible or relevant. When I analyzed the link between body size and survival, I revealed that larger adult females have higher survival rates. Given the fact, that a large body size is a response to beneficial early life conditions, this demonstrates the impact of early life conditions on long lasting fitness effects.
The results of my research lead to the assumption that warmer ambient temperatures have positive effects on Natterer’s bats, both during winter and summer. However, increased activity in response to rising winter temperatures, as expected under climate change scenarios, could be a serious thread for hibernating bats, if food availability does not increase in the same amount as bat activity. During summer, warmer temperatures may have positive effects on juvenile development in northern regions, but this effect could be negative in more southern regions by exceeding heat tolerance and resulting in water stress. This research highlights, that investigating periods of weather sensitivity on a finer time scale and also in a spatial context is of crucial importance to gain a better understanding for mechanisms leading to the impacts of weather on fitness.
Relative importance of plastic and genetic responses to weather conditions in long-lived bats
(2022)
In the light of the accelerating pace of environmental change, it is imperative to understand how populations and species can adapt to altered environmental conditions. This is a crucial step in predicting current and future population persistence and limits thereof. Genetic adaption and phenotypic plasticity are two main mechanisms that can mediate the process of adaptation and are of particular importance for non-dispersing species. While phenotypic plasticity may enable individuals to cope with short term environmental changes, genetic adaptation will often be required for populations to survive in situ over longer time spans. However, a rapid genetic response is expected particularly in species with fast life histories or large population sizes, leaving species with slow life histories potentially at higher extinction risk. The Bechstein’s bat (Myotis bechsteinii) is a mammal of 10 g weight that - despite its small size - is characterized by a slow life history, with low reproductive output and long lifespan, and is already considered to be of high conservation concern. Past work demonstrated body size to be a highly fitness-relevant trait in Bechstein’s bats. Body size is further known to be a pivotal trait shaping the pace of life histories in numerous species. Simultaneously, many studies reported noteworthy changes in body size as a response to shifting environments across different taxa. This suggested a potential for high plasticity in this trait in Bechstein’s bats as well; however, changes in body size could have vital impacts on demographic rates.
Therefore, this dissertation investigated the following questions: firstly, what shapes the fundamental development of body size in M. bechsteinii, and, specifically, is there an impact of weather conditions on body size? If so, in what form and magnitude? Secondly, how does body size subsequently influence the pace of life in females? What is the cost of a faster or slower pace of life, and how does fitness compare across individuals with slow and fast life histories? And finally, to what extent can changes in body size be attributed to either phenotypic plasticity or genetic adaptation? What is the evolutionary potential of body size in the populations? And, consequently, what implications can we draw regarding population persistence of these colonies?
To answer these questions, we analyzed a long-term dataset of over two decades collected from four wild Bechstein’s bat colonies. We used individual-based data on survival, reproduction and body size, built multi-generational pedigrees, and combined everything with meteorological data. In Manuscript 1 we found that, in contrast to the declining body size observed in many species, body size in Bechstein’s bats increased significantly over the last decades. We demonstrated that ambient temperature was linked to the development of body size and identified a sensitive time period in the prenatal growth phase, in which body size was most susceptible to the impact of temperature. We established that warmer summers resulted in larger bats, but that these large bats had higher mortality risks throughout their lives. Manuscript 2 then revealed the influence of body size on the pace of life in Bechstein’s bats and demonstrated high plasticity in intraspecific life history strategies. Large females were characterized by a faster pace of life and shorter lifespans, but surprisingly, lifetime reproductive success remained remarkably stable across individuals with different body sizes. The acceleration of their pace of life means that larger females compensated for their reduced longevity by an earlier reproduction and higher fecundity to reach similar overall fitness. Ultimately, differences in body size resulted in changes in population growth rate via the impact of size on generation times. Results of Manuscript 3 were then able to clarify the extent to which changes in body size were founded on either phenotypic plasticity or genetic adaptation. We demonstrated a particularly low heritability in hot summers, indicating that variance in body size was mostly driven by phenotypic plasticity, with few genetic constraints. During cold summers, behavioural adaptations by reproducing bats seem to be able to mitigate negative effects of cold temperatures. These behaviours, such as social aggregation or preference for warm roosts, are, however, essentially irrelevant in hot environments. In addition, a low evolvability of forearm length points to a low capacity to respond to selection pressures associated with the trait.
We can conclude that body size in M. bechsteinii has increased over the last two decades as a response to global warming and is only slightly constrained by its genetic underpinnings. We can further demonstrate a direct link between body size and the pace of life histories in the Bechstein’s bat populations and how changes in body size impact demographic rates via this linkage. In the context of climate change and hotter summers, our findings consequently suggest that body size will likely increase further if warm summers continue to become more frequent. Whether this plastic response of body size proves to be adaptive in the long term, however, remains to be seen. While, up to this point, switching to a faster life history has been successful in compensating fitness losses, this strategy requires sufficient habitat quality and is likely risky in times when extreme weather events are becoming more frequent, as predicted by most climate change scenarios.
Species are the basic units of evolution and biodiversity, and the process of speciation has been one of the most important questions in biology. The evolution of species with common descent is considered to be mainly driven by natural and sexual selection. The material basis and mechanical cause of organismic evolution were recognized during the formation of the modern synthesis of the evolutionary theory in the early 20th century, providing the framework for speciation studies. During this period, the biological species concept was developed in the frame of population genetics, putting emphasis on the reproductive isolation between populations. The phylogenetic species concept developed in the 1980s, on the other hand, does not make any particular assumption about evolutionary or speciation processes. It defines species via their unique combination of character states which are compatible with phylogenetic practices. However, the aforementioned two species concepts are difficult to apply in alpha-taxonomy, where newly discovered species are largely described by the morphological (typological) species concept for practical reasons. Nevertheless, the description of morphological species provides the basis for further assessments of species delimitation via other species concepts and approaches. One of the tools for assisting the identification and discovery of animal species is DNA barcoding, which uses a standard region of mitochondrial DNA sequence as a universal DNA barcode. However, its assumption of intraspecific genetic distances being smaller than interspecific genetic distances does not always hold. Species-level poly-/paraphyly is prevalent due to the discrepancy between the phylogenies of mitochondrial DNA and species. This suggests that the application of DNA barcodes must be combined with an integrative taxonomic approach. Beside the application as a tool for assisting species identification, the information from mitochondrial DNA sequences opens up a window for looking into the complex history of species.
Sexual selection is a potential mechanism driving the evolution of species. It favors traits that increase mating probability and mating success. It can result from intrasexual competition, female preference or sexual conflict. However, previous comparative studies using the degree of sexual dimorphism as a proxy for the strength of sexual selection have yielded inconsistent results as to the relationship between sexual selection and species richness. A possible cause of the inferred low association are factors other than sexual selection, which can also lead to the evolution of sexual dimorphism, such as selection for increased female fecundity. In order to assess the effect of sexual selection on speciation, the lability and evolvability of traits need to be studied that are clearly under sexual selection.
The aim of this thesis is to improve the knowledge about dwarf spider (Erigoninae, Linyphiidae) diversity and taxonomy, and to assess the evolutionary patterns of dimorphic traits that are under sexual selection. I focused on the abundant and diverse male prosomal modifications in dwarf spiders that are linked to the transfer of secretions from the male to the female during courtship and mating (gustatory courtship). This approach explores the process of speciation and the role of sexual selection on species diversification. I described new erigonine species and revised the classification of known species based on phylogenetic analyses. I also applied X-ray micro-computed tomography (micro-CT) to investigate the distribution and evolutionary pattern of the gustatory glands to tease apart the evolution of prosomal shape and glandular equipment.
This cumulative thesis consists of three publications:
Publication 1: This publication aimed at contributing to the knowledge of erigonine diversity. The genus Shaanxinus previously contained only two species from China. I collected dwarf spiders from multiple locations in Taiwan from above-ground vegetations with a seldom applied collecting method. Inspection of the collected material resulted in the discovery of 13 Shaanxinus species. An additional species from Vietnam was described from a museum collection. I provided a revision of the genus Shaanxinus. A phylogenetic analysis using morphological characters was conducted for determining the possible generic synamomorphies. I also reconstructed the glandular distribution associated with male prosomal modifications, as well as the detailed structure of a male secondary sexual organ (pedipalp) by micro-CT. Furthermore, I conducted phylogenetic analyses based on sequences from two mitochondrial and one nuclear loci, and assessed the efficacy of different criteria in species identification using DNA barcoding. Distinction of morphologically similar species have been assisted by molecular data. The species level poly-/paraphyly found in mitochondrial DNA sequences caused the low efficacy of many distance- and tree-based species identification methods, while the nearest neighbor method showed high identification success. The non-monophyly is likely caused by instances of interspecific hybridization and recent parapatric speciation. The genus Shaanxinus thus lend itself as an ideal group for congeneric phylogeographic studies addressing the interactions between closely related species. Published in: Lin, S.-W., Lopardo, L., Haase, M. & Uhl, G. 2019. Taxonomic revision of the dwarf spider genus Shaanxinus Tanasevitch, 2006 (Araneae, Linyphiidae, Erigoninae), with new species from Taiwan and Vietnam. Organism Diversity & Evolution, 19, 211-276.
Publication 2: Sexually dimorphic prosomal modifications that are related to gustatory courtship occur in many dwarf spider species. These features evolved in the context of sexual selection, which has a potential effect on species diversification. In contrast to many
erigonine genera which present little variability in male prosomal traits, the genus Oedothorax presents higher diversity in male prosomal structures among species not only in the position and shapes of the modifications, but also in the degree of modification, ranging from absent to highly elaborated. This genus thus lends itself as a suitable target group for studying the effect of gustatory-courtship-related traits on species diversification. I conducted a revision of the 82 species previously belonging to this genus. Based on the result of a phylogenetic analysis, this genus was re-delimited with 10 species as Oedothorax sensu stricto, while taxonomic decisions were made for other species including synonymization with species from other genera and transferring species to other existing and newly defined genera. 25 species were deemed as “Oedothorax” incertae sedis. The reconstruction of character state evolution suggested multiple origins of specific prosomal modification types. Convergent evolution of these traits among different lineages suggests that sexual selection has played an important role in the species diversification of dwarf spiders. Published in: Lin, S.-W., Lopardo, L. & Uhl, G. 2021. Evolution of nuptial-gift-related male prosomal structures: taxonomic revision and cladistic analysis of the genus Oedothorax (Araneae: Linyphiidae: Erigoninae). Zoological Journal of the Linnean Society, XX, 1-168.
Publication 3: Although sexually dimorphic traits have inspired the concept of sexual selection as the driving force of their evolution, they might also have evolved due to other ecological factors. These factors include the sexual signal adaptation to the environment as well as sexual differences in ecological relations and parental investment. In contrast, the gustatory courtship in dwarf spiders is associated with sexually dimorphic male prosomal modifications, which have clearly evolved in the context of sexual selection. Multiple origins of various external prosomal modifications have been shown in erigonine phylogeny, but the evolutionary pattern of the associated glands has not been investigated. Our phylogenetic analysis incorporated the characters related to the glandular distribution in the male prosoma as well as the external shapes yielded from X-ray micro-computed-tomography showed a single origin of gland among the investigated erigonine taxa. The internal anatomy revealed previously undetected trait lability in attachments of muscles to the cuticular structures, as well as the presence/absence and differences in glandular distribution even in species without external modification. Our finding further supports that erigonine male prosomal traits are under divergent selection, and corroborates the argument that erigonines are a suitable group for investigating the effect of sexual selection on speciation. Published in: Lin, S.-W., Lopardo, L. & Uhl, G. 2021. Diversification through gustatory courtship: an X‑ray micro‑computed tomography study on dwarf spiders. Frontiers in Zoology, 18: 51.
The results of this thesis corroborate the importance of applying phylogenetic methods and an integrative approach in the description of new species, as well as in revising taxa which might not be monophyletic. Overall, the studies contributed to a more comprehensive knowledge about erigonine species diversity, phylogeny and the possible diversifying effect of sexual selection on male traits associated with gustatory courtship.
Cryptochromes are evolutionary ancient blue-light photoreceptors that are part of the circadian clock in the nervous system of many organisms. Cryptochromes transfer information of the predominant light regime to the clock which results in the fast adjustment to photoperiod. Therefore, the clock is sensitive to light changes and can be affected by anthropogenic Artificial Light At Night (ALAN). This in turn has consequences for clock associated behavioral processes, e.g., diel vertical migration (DVM) of zooplankton. In freshwater ecosystems, the zooplankton genus Daphnia performs DVM in order to escape optically hunting predators and to avoid UV light. Concomitantly, Daphnia experience circadian changes in food-supply during DVM. Daphnia play the keystone role in the carbon-transfer to the next trophic level. Therefore, the whole ecosystem is affected during the occurrence of cyanobacteria blooms as cyanobacteria reduce food quality due to their production of digestive inhibitors (e.g., protease inhibitors). In other organisms, digestion is linked to the circadian clock. If this is also the case for Daphnia, the expression of protease genes should show a rhythmic expression following circadian expression of clock genes (e.g., cryptochrome 2). We tested this hypothesis and demonstrated that gene expression of the clock and of proteases was affected by ALAN. Contrary to our expectations, the activity of one type of proteases (chymotrypsins) was increased by ALAN. This indicates that higher protease activity might improve the diet utilization. Therefore, we treated D. magna with a chymotrypsin-inhibitor producing cyanobacterium and found that ALAN actually led to an increase in Daphnia’s growth rate in comparison to growth on the same cyanobacterium in control light conditions. We conclude that this increased tolerance to protease inhibitors putatively enables Daphnia populations to better control cyanobacterial blooms that produce chymotrypsin inhibitors in the Anthropocene, which is defined by light pollution and by an increase of cyanobacterial blooms due to eutrophication.