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Aussiger Beiträge : 4. Jahrgang
(2010)
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Aussiger Beiträge : 3. Jahrgang
(2009)
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Aussiger Beiträge : 2. Jahrgang
(2008)
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Aussiger Beiträge : 1. Jahrgang
(2007)
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Climate-linked temporal and spatial patterns in the evolution of African bovidae
(2012)
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Tim Frederic Schikora
- Climate and subsequent environmental changes are regarded as one driver of species evolution. Against this background the present study investigates the evolutionary history of the mammalian family Bovidae (Cetartiodactyla, Mammalia), today the most species-rich family of large herbivores on the African continent. Temporal and spatial patterns in that group’s evolution are the focus of the present study and were investigated using methods and data deriving from multiple disciplines (palaeontology, genetics, climatology, conservation biology). The results serve as a validation of macroevolutionary hypotheses of species evolution.
A major proportion of African mammalian fossils can be assigned to that family. Due to their morphological adaptations, bovid species are highly indicative of their habitats. Hence, bovids are of great importance for paleontology. However, a strong taphonomic bias is present in the fossil record of bovids, favoring large and arid- adapted species. Molecular phylogenies of extant species and species distribution modelling combined with climate reconstructions can help to overcome these limitations.
A molecular phylogeny, based on the cytochrome b gene of 136 bovid species served as basis for analysis of temporal patterns. Divergence events were dated using the relaxed molecular clock approach. The tree was time calibrated at 30 nodes using information inferred from the fossil record. Lineage-Through-Time plots and the respective statistical analyses reveal detailed temporal patterns in the evolutionary history of tribes and groups combining arid- and humid-adapted tribes. The resulting pattern shows three distinct phases. Phase 1 (P1) is dominated by speciation events within the humid group, while the second phase (P2) is marked by a dominance of speciation within the arid group. The switch in diversification rates (BDS) from P1 to P2 is dated to 2.8 million years ago. The third phase (P3) shows low diversification rates for all groups, starting around 1.4 million year ago and culminates in a significantly reduced diversification rate for the complete family at 0.8 million years ago. Both transitions are contemporaneous with global climate changes and turnover events in fossil faunal communities.
To investigate the impact of climate changes onto the habitat availability within the last 3 million years and its putative influence on diversification rates, the species distribution modeling method was applied. For 85 African species and subspecies the climate niches were established and grouped into 5 climate-groups based on their climate preferences. For each group the available habitat for the period before and after the BDS was calculated on continental scale using reconstructed climate scenarios. To evaluate the modeled habitat distributions, regional analyses were performed in test areas surrounding well studied fossil sites (Laetoli, Olduvai, Chiwondo Beds, Lothagam, Koobi Fora, West Turkana, Swartkrans, Sterkfontain und Toros-Menalla). Habitat profiles (HP) permitted the comparison of the model based habitat reconstruction with the interpretations of classic paleontological reconstruction. The validity of the habitat modeling has been shown in particular for East African test areas. The reconstructions for the northern and southern fossil sites does not support the modeled habitats in these areas. Yet, the method of habitat- profiling may serve as suitable tool for environmental reconstruction of areas lacking sufficient paleontological material. A comparison of habitat availability before and after the BDS on continental scale identified a significant loss of habitat for humid adapted groups (7-22%) and habitat gain for arid adapted groups (19-173%). The climatically intermediate group experiences a tremendous gain of habitat (3366%). The greatest environmental change was modeled for East Africa, initiated by a progressive regional aridification.
In addition to the distribution modeling for past climate conditions, the geographical distribution was modeled for the future, i.e. for climate scenarios representing the years 2050 and 2080 under a putative climate change scenario (global surface warming). It was shown that in particular the arid groups have to expect a remarkable loss of habitat (41-76%), while a gain of available habitat can be expected for the humid adapted groups (114-577%). The climatically intermediate group suffers the strongest habitat loss (85%). Regions with locally stable climate conditions were detected and may serve as potential refugia and are already today known as Africa’s hot spots of biodiversity.
The results show a positive correlation of high diversification rates and increasing habitat availability. None of the tested speciation hypotheses taken alone explains the observations (e.g., Turnover-pulse Hypothesis, Relay Model). A major element in these hypotheses is the passive fragmentation of populations induced by unfavorable climate changes. In contrast, the Periodic Model (Grubb 1999) considers natural, periodically recurring climate changes and moreover, the active dispersal of individuals and resulting founder events. I added the effect of a superimposed directed climate trend – like the progressive aridification since the late Pliocene in Africa – which leads to a bias in the proportion and probability towards leading edge effects. This Directed Periodic Model explains the patterns found in the evolution of Bovidae.
The combination of a molecular phylogeny and species distribution modeling, together with information inferred from the fossil record, reveals remarkable temporal and spatial patterns in the evolution of bovids, and helps overcome the limitations of the fossil record. The present study highlights the importance of active dispersal and founder populations in speciation processes. A point widely unattended in speciation hypotheses. The fully dated molecular phylogeny is the most densely sampled tree for the family Bovidae to date and may serve as a framework for a connection of present and future population studies, permitting the connection of medium-scale with long- term effects induced by climate and environmental changes.
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Resonant pickups for non-destructive single-particle detection in heavy-ion storage rings and first experimental results
(2013)
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Mohammad Shahab Sanjari
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Soziale Interaktion auf Finanzmärkten
(2013)
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Frederik König
- Ziel meiner Dissertation ist die empirische Analyse von Auswirkungen der sozialen Interaktion zwischen Akteuren auf Finanzmärkten.
In meinem ersten Aufsatz stelle ich ein Marktpreismodell vor, welches dem Einfluss durch soziale Interaktion Rechnung trägt. Mit Hilfe dieses Modells gehe ich der Fragestellung nach, ob soziale Interaktion zwischen Marktteilnehmern eine stabilisierende oder eine destabilisierende Wirkung auf Finanzmärkte hat. Mit meinem zweiten Aufsatz untersuche ich das Verhalten von Aktienanalysten, die als wesentlicher Impulsgeber für Finanzmärkte gelten. Konkret stelle ich heraus, ob Analysten stärker von anderen Analysten beeinflusst werden, wenn diese im gleichen Land bzw. in der gleichen Stadt arbeiten oder wenn sogar ein regelmäßiger Meinungsaustausch erfolgt. Beides setzte ich ins Verhältnis zum vorherrschenden Marktumfeld. In meinem dritten Aufsatz beschäftige ich mich mit der sozialen Interaktion zwischen Fondsmanagern. Diese verwalten in etwa ein Drittel des frei handelbaren Aktienvermögens und haben folglich einen nennenswerten Einfluss auf Finanzmärkte. Mit Hilfe einer neuartigen Schätzmethode bestimme ich die Größe des sozialen Einflusses und untersuche auch hier temporale Variationen im Verhältnis zum zu Grunde liegenden Marktumfeld. Des Weiteren zerlege ich die Gesamtgröße des sozialen Einflusses in zwei Komponenten, die zum einen den Einfluss im Rahmen der reinen Beobachtung und zum anderen den Einfluss durch Kommunikation reflektieren.
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Aussiger Beiträge : germanistische Schriftenreihe aus Forschung und Lehre / Katedra Germanistiky FF UJEP
(2007)
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Buchbesprechung: Science Press, Beijing, China: Fauna Sini.ca Arachnida: Araneae
(2000)
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Martin Kreuels
- Alle drei Bücher wurden Überwiegend in chinesisch verfaßt. Es findet sich jedoch ein englischer Bestimmungsschlüssel am Ende jedes Werkes. Ihm angeschlossen• ist ein Artregister in lateinischer Schrift. Die Zeichnungen der Genitalien und des Habitus sind sehr deutlich und lassen sich in ihrer Genauigkeit sicherlich mit den Zeichnungen M.J. Roberts vergleichen. Die Beschreibungen zur Biogeographie werden zwar im Einführungsteil (Karten) dargestellt, die zugehörigen Textpassagen sind aber in chinesisch geschrieben worden.
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CD69 Is a TGF-β/1α,25-dihydroxyvitamin D3 Target Gene in Monocytes
(2013)
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Thea K. Wöbke
Andreas von Knethen
Dieter Steinhilber
Bernd L. Sorg
- CD69 is a transmembrane lectin that can be expressed on most hematopoietic cells. In monocytes, it has been functionally linked to the 5-lipoxygenase pathway in which the leukotrienes, a class of highly potent inflammatory mediators, are produced. However, regarding CD69 gene expression and its regulatory mechanisms in monocytes, only scarce data are available. Here, we report that CD69 mRNA expression, analogous to that of 5-lipoxygenase, is induced by the physiologic stimuli transforming growth factor-β (TGF-β) and 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) in monocytic cells. Comparison with T- and B-cell lines showed that the effect was specific for monocytes. CD69 expression levels were increased in a concentration-dependent manner, and kinetic analysis revealed a rapid onset of mRNA expression, indicating that CD69 is a primary TGF-β/1α,25(OH)2D3 target gene. PCR analysis of different regions of the CD69 mRNA revealed that de novo transcription was initiated and proximal and distal parts were induced concomitantly. In common with 5-lipoxygenase, no activation of 0.7 kb or ~2.3 kb promoter fragments by TGF-β and 1α,25(OH)2D3 could be observed in transient reporter assays for CD69. Analysis of mRNA stability using a transcription inhibitor and a 3′UTR reporter construct showed that TGF-β and 1α,25(OH)2D3 do not influence CD69 mRNA stability. Functional knockdown of Smad3 clearly demonstrated that upregulation of CD69 mRNA, in contrast to 5-LO, depends on Smad3. Comparative studies with different inhibitors for mitogen activated protein kinases (MAPKs) revealed that MAPK signalling is involved in CD69 gene regulation, whereas 5-lipoxygenase gene expression was only partly affected. Mechanistically, we found evidence that CD69 gene upregulation depends on TAK1-mediated p38 activation. In summary, our data indicate that CD69 gene expression, conforming with 5-lipoxygenase, is regulated monocyte-specifically by the physiologic stimuli TGF-β and 1α,25(OH)2D3 on mRNA level, although different mechanisms account for the upregulation of each gene.
