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)
In agricultural grasslands, management practice highly determines reproductive success for ground-nesting bird species. The most effective conservation measure is the delay of first mowing dates until broods fledge or bird friendly mowing. Late mowing often implies economical losses for farmers and may increase land use abandonment, which will, in turn, cause habitat deterioration. Thus, grassland bird conservation involves the challenge to protect broods against land use and to promote an appropriate management to sustain habitat quality at the same time. Because of their late and extended breeding season Corncrakes Crex crex are in particular vulnerable to frequent mowing which increases nest destruction, chick mortality and habitat loss.
This thesis aims to gain knowledge on favourable habitat characteristics and brood protection in relation with grassland management to derive implications for the conservation of Corncrake breeding sites in floodplain meadows. Study area is the Lower Oder Valley National Park in northeastern Germany that holds a Corncrake population of 50 to 250 calling males. The study covered two study periods, before (1998-2000) and after (2012-2015) the implementation of new Corncrake conservation measures allowing inferences on the effects of different timing and intensity of mowing for brood protection and habitat conservation.
Breeding was only confirmed on meadows with high forb cover, low sedge cover, low litter heights and a close location to ditches. Radio-tracked females preferred areas with high cover of forbs (> 30%) and a distinct relief heterogeneity, which was associated with increased vegetation diversity. Vegetation characteristics on sites with day calling activity of males showed more similarity with breeding sites than with sites only used for nocturnal calling, supporting the assumption that diurnal calling indicates the occurrence of females. Favoured vegetation structure was best provided by mowing in the preceding year. Low-intensity grazing was less effective in reducing litter and sedge cover, especially when conducted late in the season. In the absence of management, meadows rapidly overgrow and dense litter accumulates from dead plant material in eutrophic floodplains, which increases walking resistance for Corncrakes and may impede prey accessibility. Plant species richness and forb cover declined after land use cessation. Male Corncrakes abandoned calling sites on meadows unmanaged for longer periods.
Besides the availability of suitable nesting sites, food supply and nest predation risk are also related to vegetation structure and may indirectly influence the habitat quality. Faecal samples of Corncrakes consisted mainly of beetles and their larvae, followed by snails, spiders and earthworms. Invertebrate biomass, sampled with pitfall-traps, was twice as high, the numbers of large ground beetles even five times higher on previously unmanaged than on managed meadows. Invertebrate abundance was highest in the first and second years after land use abandonment, but strongly decreased afterwards to a similar level like under annual management. Therefore, unmown refuge strips for Corncrake protection and alternating mowing also enhance invertebrate prey resources in floodplain meadows.
Mammals caused the majority of all observed artificial ground nest predations. Nest predation risk was higher on previously unmanaged than on managed sites. Unmanaged meadows probably attract mammalian predators, because they provide a more favourable vegetation structure for foraging and harbour high numbers of small rodents, increasing also the risk of incidental nest predations. These findings suggest that an annual removal of vegetation, if conducted late in the season to protect grassland birds may reduce predation risk of ground nests in the subsequent year.
Whereas during 1998-2000 half of the study area was managed by the end of July, land use was delayed on meadows occupied by Corncrakes until at least 15 July or 15 August during 2012-2015. On meadows mown between 15 July and 15 August refuge strips were applied. The majority of Corncrake broods were started in the second half of May and mowing postponement until 15 August allows 80% of chicks to fledge without disturbance in the study area. In 65% of broods chicks reach independence (> 14 days old) until 15 July and can be protected by Corncrake friendly mowing because then they are large enough to successfully escape during mowing. Both adults and chicks survived in 10 m wide refuge strips. Because most birds tried to leave the unmown block for the first time when it was up to 30 m wide and only 15 to 30 m wide strips served as temporary habitat for unfledged chicks from mowing to departure, 10 m should be considered as the absolute minimum width for refuge strips.
The strong reduction of land use especially during July should have allowed more chicks to survive until fledging in 2012-2015 than 1998-2000. Besides the protection of nests and higher chick survival, the decline of mowing intensity increased the extent of habitat available for second breeding attempts. In 2012-2015, broods were initiated until late July in the study area. Male Corncrakes showed continuous arrival and departure during the breeding season. Similar departure rates were estimated by a multi-state occupancy model and for radio-tracked males in the same study area and periods, which both left their home ranges spontaneous and due to the impact of mowing. Compared to 1998-2000, total departure of males during June and July was reduced by 50% in 2012-2015, when more calling sites were protected from mowing. Although male Corncrakes show high intra-seasonal dispersal due to their sequential polygamous breeding system, postponed land use should have increased mating opportunities and re-nesting at first breeding sites.
Therefore, future directions of Corncrake conservation in eutrophic floodplains should address the increase of annual late mowing to protect broods and maintain favourable habitat conditions by creating a more flexible mowing regime adjusted to actual occurrence of Corncrakes. This requires expert advice to farmers based on an intense monitoring of calling Corncrakes. Repeated nocturnal surveys during May and June are highly recommended because low detection probability in combination with constant departure substantially underestimated the number of males present. Additionally, diurnal calling activity could improve the identification of breeding sites and timing could be used to estimate chick age in July to select sites for Corncrake friendly mowing. Because currently late mowing dates are unattractive for farmers conservation actions should along with financial compensations for mowing after 15 August promote the utilization of late-cut grass with poor nutrient quality for combustion. Energy production could provide an alternative income for farmers operating in conservation areas with delayed land use dates and will increase their acceptance of Corncrake protection measures.
Background
Haemosporidian parasites of the genus Polychromophilus infect bats worldwide. They are vectored by obligate ectoparasitic bat flies of the family Nycteribiidae. Despite their global distribution, only five Polychromophilus morphospecies have been described to date. The two predominant species, Polychromophilus melanipherus and Polychromophilus murinus, are broadly distributed and mainly infect miniopterid and vespertilionid bats, respectively. In areas where species from different bat families aggregate together, the infection dynamics and ability of either Polychromophilus species to infect other host families is poorly characterized.
Methods
We collected 215 bat flies from two bat species, Miniopterus schreibersii and Rhinolophus ferrumequinum, which sometimes form mixed clusters in Serbia. Miniopterus schreibersii is known to be frequently infected with P. melanipherus, whereas R. ferrumequinum has been observed to be incidentally infected with both Polychromophilus species. All flies were screened for Polychromophilus infections using a PCR targeting the haemosporidian cytb gene. Positive samples were subsequently sequenced for 579 bp of cytochrome b (cytb) and 945 bp of cytochrome oxidase subunit 1 (cox1).
Results
Polychromophilus melanipherus DNA was detected at six out of nine sampling locations and in all three examined bat fly species collected from M. schreibersii (Nycteribia schmidlii, n = 21; Penicillidia conspicua, n = 8; Penicillidia dufourii, n = 3). Four and five haplotypes were found for cytb and cox1, respectively. Evidence for multiple Polychromophilus haplotypes was found in 15 individual flies. These results point to a high diversity of P. melanipherus parasites in Miniopterus hosts and efficient transmission throughout the study area. A single Phthiridium biarticulatum bat fly collected from R. ferrumequinum screened positive for P. melanipherus, but only yielded a partial cox1 sequence fragment. Nevertheless, this result suggests that secondary hosts (both bat and fly species) are regularly confronted with this parasite.
Conclusions
The results of this study provide new insights into the prevalence and distribution of Polychromophilus parasites in European bats and their nycteribiid vectors. The use of bat flies for the non-invasive investigation of Polychromophilus infections in bat populations has proven to be efficient and thus represents an alternative for large-scale studies of infections in bat populations without the need to invasively collect blood from bats.
Urbanization, industrialization, and intensification of agriculture have led to considerable heavy metal pollution across the globe, harming our ecosystems. Concentrations of arsenic (As), cadmium (Cd), copper (Cu), and lead (Pb) have been analysed in 249 eggshells collected between 2006 and 2021 from 83 female Common Cranes (Grus grus) nesting within north-eastern Germany. Information on the presence of trace elements in cranes from Europe and their potential adverse effects on the reproduction are largely missing. Only Cu and Pb were found to be present in eggshell samples. Levels of both metals did not exceed concentrations considered potentially toxic in birds and unhatched eggs did not contain higher metal concentrations compared to eggshell residues from hatched eggs. Statistical analysis revealed that trace element concentrations decreased significantly over the course of the study period. The ban of leaded gasoline in the early twenty-first century and strict limitations of heavy metal-based biocontrol products are likely responsible for this decrease over the years. However, as Cu levels gradually increase with increasing proportions of agricultural areas within the cranes’ home ranges, we suggest that considerable amounts of Cu originating from agricultural practises are still being released into the environment. We found no increase in metal concentrations in eggshells with increasing female age, suggesting that heavy metals do not accumulate in the circulatory systems of the adults over time. This study is the first to assess heavy metal contamination in Common Cranes and indicates the suitability of crane’s eggshells as bioindicator for monitoring environmental pollution.
Background
Phylogenomic studies over the past two decades have consolidated the major branches of the arthropod tree of life. However, especially within the Chelicerata (spiders, scorpions, and kin), interrelationships of the constituent taxa remain controversial. While sea spiders (Pycnogonida) are firmly established as sister group of all other extant representatives (Euchelicerata), euchelicerate phylogeny itself is still contested. One key issue concerns the marine horseshoe crabs (Xiphosura), which recent studies recover either as sister group of terrestrial Arachnida or nested within the latter, with significant impact on postulated terrestrialization scenarios and long-standing paradigms of ancestral chelicerate traits. In potential support of a nested placement, previous neuroanatomical studies highlighted similarities in the visual pathway of xiphosurans and some arachnopulmonates (scorpions, whip scorpions, whip spiders). However, contradictory descriptions of the pycnogonid visual system hamper outgroup comparison and thus character polarization.
Results
To advance the understanding of the pycnogonid brain and its sense organs with the aim of elucidating chelicerate visual system evolution, a wide range of families were studied using a combination of micro-computed X-ray tomography, histology, dye tracing, and immunolabeling of tubulin, the neuropil marker synapsin, and several neuroactive substances (including histamine, serotonin, tyrosine hydroxylase, and orcokinin). Contrary to previous descriptions, the visual system displays a serial layout with only one first-order visual neuropil connected to a bilayered arcuate body by catecholaminergic interneurons. Fluorescent dye tracing reveals a previously reported second visual neuropil as the target of axons from the lateral sense organ instead of the eyes.
Conclusions
Ground pattern reconstruction reveals remarkable neuroanatomical stasis in the pycnogonid visual system since the Ordovician or even earlier. Its conserved layout exhibits similarities to the median eye pathway in euchelicerates, especially in xiphosurans, with which pycnogonids share two median eye pairs that differentiate consecutively during development and target one visual neuropil upstream of the arcuate body. Given multiple losses of median and/or lateral eyes in chelicerates, and the tightly linked reduction of visual processing centers, interconnections between median and lateral visual neuropils in xiphosurans and arachnopulmonates are critically discussed, representing a plausible ancestral condition of taxa that have retained both eye types.
Abstract
Two decades after the discovery of adult‐born neurons in the brains of decapod crustaceans, the deutocerebral proliferative system (DPS) producing these neural lineages has become a model of adult neurogenesis in invertebrates. Studies on crayfish have provided substantial insights into the anatomy, cellular dynamics, and regulation of the DPS. Contrary to traditional thinking, recent evidence suggests that the neurogenic niche in the crayfish DPS lacks self‐renewing stem cells, its cell pool being instead sustained via integration of hemocytes generated by the innate immune system. Here, we investigated the origin, division and migration patterns of the adult‐born neural progenitor (NP) lineages in detail. We show that the niche cell pool is not only replenished by hemocyte integration but also by limited numbers of symmetric cell divisions with some characteristics reminiscent of interkinetic nuclear migration. Once specified in the niche, first generation NPs act as transit‐amplifying intermediate NPs that eventually exit and produce multicellular clones as they move along migratory streams toward target brain areas. Different clones may migrate simultaneously in the streams but occupy separate tracks and show spatio‐temporally flexible division patterns. Based on this, we propose an extended DPS model that emphasizes structural similarities to pseudostratified neuroepithelia in other arthropods and vertebrates. This model includes hemocyte integration and intrinsic cell proliferation to synergistically counteract niche cell pool depletion during the animal's lifespan. Further, we discuss parallels to recent findings on mammalian adult neurogenesis, as both systems seem to exhibit a similar decoupling of proliferative replenishment divisions and consuming neurogenic divisions.
Abstract
Nervous system development has been intensely studied in insects (especially Drosophila melanogaster), providing detailed insights into the genetic regulatory network governing the formation and maintenance of the neural stem cells (neuroblasts) and the differentiation of their progeny. Despite notable advances over the last two decades, neurogenesis in other arthropod groups remains by comparison less well understood, hampering finer resolution of evolutionary cell type transformations and changes in the genetic regulatory network in some branches of the arthropod tree of life. Although the neurogenic cellular machinery in malacostracan crustaceans is well described morphologically, its genetic molecular characterization is pending. To address this, we established an in situ hybridization protocol for the crayfish Procambarus virginalis and studied embryonic expression patterns of a suite of key genes, encompassing three SoxB group transcription factors, two achaete–scute homologs, a Snail family member, the differentiation determinants Prospero and Brain tumor, and the neuron marker Elav. We document cell type expression patterns with notable similarities to insects and branchiopod crustaceans, lending further support to the homology of hexapod–crustacean neuroblasts and their cell lineages. Remarkably, in the crayfish head region, cell emigration from the neuroectoderm coupled with gene expression data points to a neuroblast‐independent initial phase of brain neurogenesis. Further, SoxB group expression patterns suggest an involvement of Dichaete in segmentation, in concordance with insects. Our target gene set is a promising starting point for further embryonic studies, as well as for the molecular genetic characterization of subregions and cell types in the neurogenic systems in the adult crayfish brain.
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.
Many of the world’s most biodiverse regions are found in the poorest and second most populous continent of Africa; a continent facing exceptional challenges. Africa is projected to quadruple its population by 2100 and experience increasingly severe climate change and environmental conflict—all of which will ravage biodiversity. Here we assess conservation threats facing Africa and consider how these threats will be affected by human population growth, economic expansion, and climate change. We then evaluate the current capacity and infrastructure available to conserve the continent’s biodiversity. We consider four key questions essential for the future of African conservation: (1) how to build societal support for conservation efforts within Africa; (2) how to build Africa’s education, research, and management capacity; (3) how to finance conservation efforts; and (4) is conservation through development the appropriate approach for Africa? While the challenges are great, ways forward are clear, and we present ideas on how progress can be made. Given Africa’s current modest capacity to address its biodiversity crisis, additional international funding is required, but estimates of the cost of conserving Africa’s biodiversity are within reach. The will to act must build on the sympathy for conservation that is evident in Africa, but this will require building the education capacity within the continent. Considering Africa’s rapidly growing population and the associated huge economic needs, options other than conservation through development need to be more effectively explored. Despite the gravity of the situation, we believe that concerted effort in the coming decades can successfully curb the loss of biodiversity in Africa.
Organisms often employ ecophysiological strategies to exploit environmental conditions and ensure bio-energetic success. However, the many complexities involved in the differential expression and flexibility of these strategies are rarely fully understood. Therefore, for the first time, using a three-part cross-disciplinary laboratory experimental analysis, we investigated the diversity and plasticity of photoresponsive traits employed by one family of environmentally contrasting, ecologically important phytoflagellates. The results demonstrated an extensive inter-species phenotypic diversity of behavioural, physiological, and compositional photoresponse across the Chlamydomonadaceae, and a multifaceted intra-species phenotypic plasticity, involving a broad range of beneficial photoacclimation strategies, often attributable to environmental predisposition and phylogenetic differentiation. Deceptively diverse and sophisticated strong (population and individual cell) behavioural photoresponses were observed, with divergence from a general preference for low light (and flexibility) dictated by intra-familial differences in typical habitat (salinity and trophy) and phylogeny. Notably, contrasting lower, narrow, and flexible compared with higher, broad, and stable preferences were observed in freshwater vs. brackish and marine species. Complex diversity and plasticity in physiological and compositional photoresponses were also discovered. Metabolic characteristics (such as growth rates, respiratory costs and photosynthetic capacity, efficiency, compensation and saturation points) varied elaborately with species, typical habitat (often varying more in eutrophic species, such as Chlamydomonas reinhardtii), and culture irradiance (adjusting to optimise energy acquisition and suggesting some propensity for low light). Considerable variations in intracellular pigment and biochemical composition were also recorded. Photosynthetic and accessory pigments (such as chlorophyll a, xanthophyll-cycle components, chlorophyll a:b and chlorophyll a:carotenoid ratios, fatty acid content and saturation ratios) varied with phylogeny and typical habitat (to attune photosystem ratios in different trophic conditions and to optimise shade adaptation, photoprotection, and thylakoid architecture, particularly in freshwater environments), and changed with irradiance (as reaction and harvesting centres adjusted to modulate absorption and quantum yield). The complex, concomitant nature of the results also advocated an integrative approach in future investigations. Overall, these nuanced, diverse, and flexible photoresponsive traits will greatly contribute to the functional ecology of these organisms, addressing environmental heterogeneity and potentially shaping individual fitness, spatial and temporal distribution, prevalence, and ecosystem dynamics.
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.