Diploma theses 0607
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On this page you find a selection of Diploma theses from the academic year 2006-2007. If you would like to have your Diploma-thesis added to this list, please send an e-mail to Pleuni Pennings.
Contents |
Name: Stephan Behl
Title: „ EINFLUSS DER ARTENDIVERSITÄT AUF DIE LICHT- UND NÄHRSTOFFNUTZUNG DES PHYTOPLANKTONS“
Supervisor: Herwig Stibor
CV: link
Abstract:
In den meisten aquatischen Ökosystemen bildet die Primärproduktion des Phytoplanktons die energetische und materielle Grundlage des gesamten Systems und nimmt deshalb eine herausragende Stellung an der Basis der Nahrungsnetze ein. Folglich können im Phytoplankton stattfindende Prozesse wie Konkurrenz oder unterschiedliche Ressourcennutzung Auswirkungen auf Sekundärproduzenten und das gesamte Nahrungsnetz haben.
Als Beispiel für eine solche Auswirkung kann die Kohlenstoff:Phosphor Quote (C:P Quote) der Biomasse von Phytoplanktongemeinschaften dienen, welche ein Futterqualitätsmaß für Zooplankter darstellt. Die Ausprägung dieser C:P Quote der Algenbiomasse ist hoch variabel und abhängig sowohl von Licht- und Phosphorangebot als auch von der Möglichkeit der verschiedenen Algentaxa diese zu nutzen (Ressourcennutzung). Weicht die C:P Quote der Algenbiomasse zu stark von der relativ konstanten Biomasse C:P Quote des Zooplanktons ab, kann es zu einer Limitierungen des Zooplanktonwachstums kommen.
Ein bisher wenig beachteter Faktor, welcher die Ausprägung der Biomasse C:P Quote von Phytoplanktongemeinschaften beeinflussen kann, ist deren Diversität. Diversere Algengemeinschaften enthalten mit großer Wahrscheinlichkeit im Mittel mehr verschiedene Photosynthesepigmente als weniger diverse. Dadurch ist theoretisch eine bessere Ausnutzung des eingestrahlten Lichtspektrums möglich, was zu einer höheren Kohlenstoffassimilationsrate führen kann. Da bei Phytoplanktern Kohlenstoff- und Phosphorassimilation weitgehend unabhängig voneinander ablaufen, kann in einem Phosphor-limitierten Gewässer eine diversere Algengemeinschaft zu höheren Biomasse C:P Quoten führen.
In einem Freilandexperiment sollte dieser Einfluss der Phytoplanktondiversität auf die lichtbedingte Ausprägung der Biomasse C:P Quote der Phytoplankter untersucht werden. Dazu wurden natürliche Algengemeinschaften aus dem Epilimnion voralpiner Seen entnommen, jede Probe auf zwei durchsichtige PET-Flaschen aufgeteilt und alle im Epilimnion eines Sees eine Woche inkubiert. Dabei wurde je eine Flasche den natürlichen Lichtbedingungen ausgesetzt, die andere auf ca. 20% der natürlichen Lichtintensität abgedunkelt. Durch Bestimmung der Phytoplanktondiversität in den einzelnen Seenproben und Messen der Biomasse C:P Quoten in den Hell- und Dunkelansätzen konnte der Einfluss der Diversität auf die unterschiedliche Ausprägung der Biomasse C:P Quoten zwischen Hell- und Dunkelansätzen bestimmt werden. Daneben wurde die Totalphosphorkonzentration der Seenproben bestimmt und auch deren Einfluss auf die Ausprägung der Biomasse C:P Quoten zwischen Hell- und Dunkelansätzen untersucht. Außerdem wurde von jeder Seeprobe eine Pigmentanalyse durchgeführt, um die Pigmentdiversität mit der Algendiversität zu vergleichen.
Begleitend wurden zwei Laborversuche ähnlichen Designs durchgeführt, bei welchen aus Laborkulturen unterschiedlich diverse Algengemeinschaften zusammengestellt wurden, welche ebenfalls in Hell- und Dunkelansätzen inkubiert wurden. Die beiden Laborversuche unterschieden sich in den verwendeten Algentaxa und den Diversitätsstufen, vor allem aber in der jeweiligen Phosphorkonzentration des Mediums.
Auch hier wurden die lichtbedingten Unterschiede in der Ausprägung der Biomasse C:P Quoten bestimmt und deren Abhängigkeit von der Algendiversität ermittelt. Um die im Vorfeld getroffenen, theoretischen Überlegungen zum physiologischen Mechanismus der Abhängigkeit der Biomasse C:P Quoten von der Diversität zu überprüfen, wurden weitere Laborversuche durchgeführt: Die Primärproduktivität verschieden diverser Algengemeinschaften (Laborkulturen, wiederum Hell- und Dunkelansätze) wurde mit Hilfe der Sauerstoff-Methode gemessen. Des weiteren wurde die relative Absorption im PAR-Bereich und die Pigmentausstattung verschieden diverser Algengemeinschaften (Laborkulturen) untersucht. Es konnte, sowohl mit natürlichen als auch mit im Labor zusammengestellten Algengemeinschaften gezeigt werden, dass eine höhere taxonomische Diversität mit einer höheren Pigmentdiversität einhergeht. Des weiteren fanden wir einen positiven Zusammenhang zwischen der Diversität von Phytoplanktongemeinschaften und der relativen Absorption von eingestrahltem Licht.
Der entscheidende Punkt war, ob es - ausgehend von einer höheren Lichtabsorption durch höhere Pigmentdiversität – zu einer höheren C-Assimilationsrate, das heißt Primärproduktionsrate in diverseren Gemeinschaften kommt. Der dazu durchgeführte Laborversuch bestätigte diese Annahme weitgehend. Im Freilandversuch zeigte sich zwar auch eine Zunahme der C-Assimilation mit zunehmender Phytoplanktondiversität, diese wurde aber stark von der Totalphosphorkonzentration beeinflusst. Bei meso- und eutrophen Seen war ein ursächlicher Zusammenhang zwischen Diversität und Änderung des POC nicht nachweisbar.
Name: Melanie Böhm
Title: Evolution of virulence and resistance: Behavioural and chemical adaptations in a social parasite system
Supervisor: Susanne Foitzik
CV: link
Abstract:
Harpagoxenus sublaevis is a small slavemaking ant that is common throughout the boreal regions of Western Eurasia. As an obligate parasite it is dependant on the occurrence of its host species Leptothorax acervorum and Leptothorax muscorum. Regular raids are conducted by H. sublaevis workers, during which they steal especially the pupae of their host colonies to raise them as a slave workforce. Slavemaker colonies can contain slaves of either host species, or even of both host species at the same time.
Colonies of each of the three species were collected in Bavaria, Germany, as well as in South Tyrol, Italy. Former studies have ascertained local adaptation for H. sublaevis and its larger host species, L. acervorum. Until now, however, co-evolutional interactions between H. sublaevis and its smaller host species L. muscorum have not been investigated.
Therefore, three experimental series were conducted, analysing raiding behaviour and defences, effectiveness of the Dufour's gland secretion, and cuticular hydrocarbon profiles. The main aim was to look for local adaptation in this host-parasite system with regard to the smaller host species, L. muscorum. Additionally, the adaptations of both host species to their sympatric slavemaker were compared.
Raiding experiments were conducted in a cross-fostering design. Comparisons with respect to the smaller host species L. muscorum showed that German colonies fared better than Italian colonies during raids conducted by either German or Italian slavemaker colonies. Moreover, German slavemaker colonies were more successful at acquiring brood than Italian slavemaker colonies. Contrary to former studies with L. acervorum, no interaction effects between slavemaker and host origins were detected. Thus, local adaptation for this host-parasite system cannot be assumed.
The larger host species L. acervorum turned out to be a stronger adversary for the slavemaker than L. muscorum, regardless of population. Contrary to L. muscorum colonies, which reacted to the invasion by a slavemaker mainly by fleeing, L. acervorum colonies attacked the slavemakers, thus killed or severely injured more of them than L. muscorum colonies.
H. sublaevis queens and workers can daub host workers with a secretion from their Dufour's gland. This secretion causes the host workers to attack each other and thus distracts them from the invading slavemaker. As this manipulation of host behaviour should be under strong selection pressure, trials were conducted to ascertain the effectiveness of this gland secretion. Again, a cross-fostering design was used.
As expected, aggressive behaviour increased, while peaceful interactions occurred less often. German L. muscorum exhibited stronger reactions to the gland secretion than Italian L. muscorum, indicating that they were less well adapted to this chemical attack. The German gland secretion provoked more behavioural changes than the Italian gland secretion and thus was more effective. As in the raiding experiments, no local adaptation was found.
Contrary to L. muscorum workers, who primarily showed an increase in flight behaviour, L. acervorum workers showed a strong increase in aggressive behaviour. Still, both host species were manipulated by the gland secretion.
These two experimental series indicated the occurrence of universal co-evolution of the host-parasite system regarding H. sublaevis and the smaller host species L. muscorum. Co-evolution of the German host-parasite system appeared to be further advanced, showing adaptations superior to those in the Italian system.
Demographic data suggested that, in Germany, a shift from the larger host species L. acervorum to the smaller host species was taking place, while the Italian system revealed no such changes.
Finally, the cuticular hydrocarbon profiles of workers from all three species were analysed and compared. The two host species L. acervorum and L. muscorum differed significantly in their profiles, even when enslaved. Still, H. sublaevis workers were able to imitate the profiles of either host species. Therefore, it was sometimes possible for a slavemaker worker or queen to enter a host colony without being detected, indicating that it could even overcome the enemy recognition of the host species.
The only difference between the populations was marked by non-enslaved L. muscorum workers. German profiles differed significantly from Italian profiles. However, there was no indication that the interactions between slavemaker and host workers during the raiding experiments were influenced by this difference in any way.
Name: Claudia Burger
Title: Kin recognition in the absence of social learning in the zebra finch (Taeniopygia guttata)
Supervisor: Wolfgang Forstmeier
CV: link
Abstract:
A small number of recent studies suggested that birds might be able to discriminate kin from non-kin in the total absence of learning from genetic relatives. The primary aim of the present study was to test this hypothesis, using the zebra finch as a model organism. A cross-fostering design was used, where birds grew up with only unrelated nest siblings and raised by unrelated foster parents. Despite a large sample size, we found, contrary to a previous study on the same population, that females did not avoid associating with unfamiliar brothers in a mate choice test. Also, females did not preferentially associate with their unfamiliar sisters.
Inspired by earlier studies, a second aim was to study whether distance calls could serve as a genetically inherited cue that could allow kin discrimination. In accordance with this idea we found that ‘goodness of pitch’ (i.e. the pureness of a harmonic stack) showed a high heritability. Interestingly, this acoustic trait was not only correlated between sisters, but also between sisters and brothers, despite the fact that male calls are known to have a strong learned component.
Third, the study allowed us to test whether females remembered their nest siblings from which they had been separated at the age of 35 days, but no evidence was found.
Finally, the design also allowed us to test for effects of sexual imprinting on heritable traits of the foster father, but again no evidence was found.
In the absence of experimental cross-fostering, some recognition mechanisms like individual recognition or learning of family traits might well be working in zebra finches, but this was beyond the scope of the present study.
In summary, the present study shows that call characteristics could potentially be used for kin recognition in the absence of social learning, but at least within the experimental setup used this does not seem to be happening. In an attempt to reconcile this with the previous study showing that females avoided unfamiliar brothers, one could speculate that there might be a tendency to mate disassortatively with regard to heritable traits, but those tendencies might be expressed only under some circumstances.
Name: C. Grundmann
Title: Computer aided 4D-reconstruction of the flatfish head during metamorphosis in the turbot (Psetta maxima)
Supervisor: Martin Heß
CV: link
Abstract:
The metamorphosis of flatfishes is one of the most striking morphological events in the ontogeny of vertebrates. The animals change from a pelagic way of life with a bilateral symmetric body and a "normal" swimming posture to a benthic life permanently lying on onebody side. This requires the migration of the downward directed eye to the new upper body side and, entailed with this, more or less asymmetric deformations of other organ systems in the head region.
In this study the development of the left-eyed turbot (Psetta maxima, three selected larval stages) is investigated morphologically in detail. Using computer aided means of digital imaging, organ classification and 3D-reconstruction based on semithin section series the following organ systems of the head region can be displayed in free combination and perspective: integument with side channel system, chondro- and osteocranium, jaw muscles, brain, olfactory organ, eyes with optical nerve and eye muscles as well as the labyrinth organ with its sensory epithelia. This is complemented by scanning electron microscopy of the integument.
The virtual "fish from glas" in combination with the histological slices allows a detailed morphological and morphometrical description of complex relative organ positions and developmental processes in the turbot head (e.g. growth, more or less asymmetric changes of organ shapes and relative positions, degenerations etc.). Most remarkable are the asymmetries of the retrorbital vesicles and of the integument still before the onset of eye migration, the resorption events in the chondral skeleton during eye migration, the persisting shape and orientation of the labyrinth organ despite the permanent side posture and the formation of a special bone only in the right half of the head.
The new image data are compared with previous findings published on flatfishes and discussed critically, last but not least in the sense of functional eco-morphology.
Name: Kristin Haebler
Title: Living conditions and mobility in early medieval Perlach
Supervisor: Gisela Grupe
CV: link
Abstract
The present study focuses on the lifestyle and mobility of individuals originating from a burial site at Munich-Perlach at roughly 500 AD by the utilization of various archaeometric methods. The sex, age at death, body height, degenerative joint disease and pathologies of each individual was ascertained based on traditional and accepted morphological examination techniques. Immigrants to the site were identified by the stable isotopic signatures of oxygen and strontium.
The skeletal series is characterized by a balanced sex distribution and life expectancy figures for the individual age categories which are characteristic for that time. Age at death was assessed by both morphological methods (biological age at death) and histologically by tooth cementum annulation (calender age at death).These two methods combined led to corresponding results especially for individuals younger than 40 years. Most of the joints exhibited – probably age-related – symptoms of degenerative disease. The lumbar vertebrae were particularly seriously affected, indicative of carrying heavy loads. The degenerative changes of the lower extremities of several individuals could aready indicate a high mobility. A considerable percentage of the examined individuals exhibited squatting facets, acquired by various daily activities such as milking, pottery manufacture, or simply a squatting position while relaxing. The rare pathology of multiple osteochondritis dissecans was diagnosed for the individual P3.
The stable isotope analysis of oxygen and strontium carried out on the inhumations of the Munich-Perlach medieval cemetery site indicates that a considerable number of people buried there were of non-local origin. The strontium signatures of four individuals were indicative of a granite or volcanic geologic substrate, which identified them as foreign to the site which is dominated by carbonate soils. In an effort to define a specific geological region as a potential candidate for places of provenance, archaeological findings were also taken into consideration. However, an unambiguous interpretation based upon a synthesis of the anthropological and archaeological information was not possible. A comparison of the δ18O ratios measured in the structural carbonate of tooth enamel and bone with the respective strontium signatures revealed that one of the immigrated individuals, who was identified as a foreigner through strontium isotope analysis, had moved to Perlach as late as in the last few years of its life. Furthermore, it was possible to identify five additional individuals that exhibited significantly different oxygen isotopic ratios in their bone carbonate than the rest of the group. At least one of these persons should also have been a late immigrant to the site, with its place of origin most probably located in western Bavaria. The oxygen isotopic signature of the other four people buried at the site indicate that they had either spent their last years in life at considerable higher alpine elevations, or they will at least have utilized a different drinking water source fed by cold glacier melt water.
Name: Anja Hörger
Title: Sequence evolution of the disease resistance genes Rcr3 and Rin4 in wild tomato (Lycopersicon peruvianum)
Supervisor: Wolfgang Stephan
CV: link
Abstract:
The objective of my diploma thesis was to reveal evolutionary forces, which are working on the two disease resistance genes Rcr3 and Rin4 in the wild tomato species Lycopersicon peruvianum. Both genes are involved in different disease resistance pathways. Knowledge of evolutionary mechanisms shaping these two genes will contribute to the understanding of the evolution of disease resistance pathways in plants. To reveal the evolutionary history of Rcr3 and Rin4 I amplified and sequenced both genes and analyzed them with population genetic methods. As basic material I used ten individuals of the L. peruvianum accession LA2744 and one individual of the species Solanum lycopersicoides as outgroup.
Rcr3 revealed itself as putative paralogue within an old gene family, which occurs in several Lycopersicon species. There is also evidence that Rcr3 was duplicated within the genome of L. peruvianum again. The Rcr3 interacting guard molecule Cf-2 is part of a gene family as well. Therefore, duplication events of both interaction partners could be the consequence of specific coadaption of these two genes.
The Rcr3 gene shows evidence of purifying selection. There is little nucleotide diversity within the gene and expectations under neutrality were not met in almost all kinds of neutrality tests I performed. These observations support the assumption that Rcr3 is tightly integrated in its disease resistance network and therefore has to be highly conserved. Additionally, the specific interaction between Rcr3 and Cf-2 should contribute to purifying selection as well.
For the Rin4 gene I reported a very low level of nucleotide diversity as well. Tests of neutrality could not be rejected significantly, but all results tended to show a limitation of the variation due to purifying selection. These findings are very likely for the Rin4 gene as well. The Rin4 protein is involved in an extremely complex signaling system of herbal disease resistance. It is known to interact with at least seven - probably even more - different resistance-mediating factors. All these interactions are realized in different ways. To keep all these ways of interaction stable, a high level of conservation within the Rin4 gene is required.
Name: Petra Koch
Title: Computer aided 4D-reconstruction of the flatfish head during metamorphosis in the sole (Solea solea)
Supervisor: Martin Heß
CV: link
Abstract:
The metamorphosis of flatfishes (Pleuronectiformes) is characterized by numerous morphological changes and asymmetries in the head region - the most striking of them is the migration of one eye to the opposite body side (zenithal or "upper" side). With increasing lateral compression of the body and a 90°-turn of the nadiral side towards the bottom entails a change form pelagic to benthic way of life.
In this study the development of the right-eyed sole Solea solea (Soleidae) is investigated using five selected larval stages. By means of scanning electron microscopy, semithin section series and modern 3D-visualization software (Amira) the following organ systems are displayed: integument, side channel system, chondrocranium, osteocranium, jaw muscles, brain, olfactory organ, eyes, optical nerves, eye muscles and the labyrinth organ. A detailed morphological analysis is facilitated by the comparison of the "original" histological sections and freely rotable 3D-visualizations of any organ system. Developmental events as well as occurring asymmetries are described, displayed and analyzed semi-quantitatively (morphometry).
In the course of eye migration no solid obstacles are found; the shape and positioning of the labyrinth organ do not change during metamorphosis despite of the high degree of asymmetry in the frontal parts of the head; and contrary to pervious statements no transient asymmetry of any brain part is observable. The new data are compared with published knowledge and discussed critically.
Name: Thomas Kunze
Title: Computer-aided 3D-reconstruction and comparative anatomy of the skeneimorph Microgastropods Bathyxylophila excelsa Marshall, 1988 and Ventsia tricarinata Warén & Bouchet, 1993
Supervisor: Gerhard Haszprunar
CV: link
Abstract:
The family Skeneidae (Vetigastropoda, Trochoidea/Turbinoidea) is currently regarded as a polyphyletic lumping pot for small (max. 3 mm), rhipidoglossate gastropods ("skeneimorph") showing signs of internal fertilisation. Recent methodological progress including serial semithin sectioning combined with computer-aided (software AMIRA) 3D-reconstruction enables the detailed anatomical investigation of such small, helicoid gastropods. Here I describe the microanatomy of the small (max. 1.5 mm) Bathyxylophila excelsa Marshall, 1988, found on sunken wood (800 m depth) near Chatham Rise, New Zealand, and the hot-vent inhabitant Ventsia tricarinata Warén & Bouchet, 1993, (max. 2.5 mm) from the Lau Basin, Fiji (1800 m depth). Both species were placed originally inside the family Skeneidae.
Ventsia tricarinata has papillate cephalic and epipodial tentacles, a single left monopectinate ctenidium with skeletal roots and bursicles, a monotocard heart penetrated by the rectum, a left papillate and a right excretory organ, a rhipidoglossate radula with one pair of radula cartilages, two intestinal loops, a papillate oesophagus a hypoathroid nervous system, two statocysts with several statoconia, a single left osphradium, a subradulary organ and one pair of ESO-tentacles. The sexes are separated, the female genital systems consists of an ovary with big yolky eggs covered by a vitellin layer, a simple urinogenital duct, and a separated receptaculum seminis.
Bathyxylophila excelsa differs as follows: The heart does not encircle the rectum, the oesophagus lacks papillae. Due to insufficient fixation, many histological details could not be cleared up.
All anatomical data strongly suggest a position of both species inside the Vetigastropoda. The distinct appearance of epipodial tentacles and the lack of a combined epipodial sense organ strictly argues against an inclusion into Trochoidea/Turbinoidea and Skeneidae, where combined epipodial tentacles are always present. However, the combination of characters exclude both species from all currently defined subclades of the Vetigastropoda. Until more data on possibly related forms are collected they remain as Vetigastopoda "incertae sedis".
Name: Sofia Lizon
Title: Chemical Communication of the invasive ant Anoplolepis gracilipes
Supervisor: Volker Witte
CV: link
Abstract:
The ecological success of ants is generally based on their highly collective behaviour and thus also on their communicational abilities. Most important in the communication of ants are chemical signals, so called pheromones. A few ant species can even be invasive due to their extraordinary competitive abilities, among them the formicine ant Anoplolepis gracilipes. Although well known as very important, the chemical communication system of this ant, has not been studied until now. In this work, the functions of the most important pheromone sources, including poison gland, Doufour’s gland, hindgut, and mandibular gland were investigated. Especially recruitment and alarm communication were studied as these are fundamentally involved in ecological interactions. For this purpose, gland extracts were prepared, which were then subjected to specific bioassays, concerning orientation, attraction, and alarm behaviour. In addition, the longevity of the pheromone signals was studied. After the behavioural effects of the different glands were clarified, their pheromone contents were analysed chemically by coupled gas chromatography and mass spectrometry (GC-MS). Furthermore, synthetic compounds were examined with the previously established bioassays to confirm their behavioural effects. Finally, pheromone signals were analysed in situ by detecting bioactive compounds with solid phase-microextraction (SPME) directly in the ant trails. The bioassays showed clearly, that the hindgut is a source of long lasting orientation cues. Because of the longevity, secretes of the hindgut are most likely used to establish persistent trails between nests and stable food sources. In combination with this basic cue, poison gland and Dufour’s gland are used for regulation of recruitment rate and speed. Both are working as short-lived attractants and the Dufour’s gland is exclusively responsible for the acceleration during recruitment. Because of their volatile contents, both glands are applied in particular on trails which lead to food sources of high quality and/or short duration. Besides the remarkable recruitment communication, a weak alarm communication could also be demonstrated for A. gracilipes. Pheromone glands associated with the mandibles are involved in “panic alarm” behaviour that is mainly characterised by avoidance and defensive behaviour. Chemical analyses by GC-MS showed that the Dufour’s gland contain mainly n-alkanes and their corresponding alkenes from decane to tricosane, which is typical for formicine ants. Undecane was the main component of the gland followed by heneicosane and nonadecane. N-alkanes were also present in the hindgut, however it contained squalene and decanal in addition. The three main compounds of the poison gland were in decreasing order heneicosane, undecane and 13-methyl-heptacosane. Knowing the characteristic compounds of each gland, bioassays with the SPME-fiber prove that hindgut and Dufour’s gland pheromones were applied in recruitment trails of A. gracilipes. Behavioural assays of synthetic substances showed that the short chained alkanes (decane to tridecane) had the strongest effect on the ants. These results are in accord with observations showing that Dufour’s gland pheromones elicit short-term accelaration and attraction of ants. The same behaviour occurs on trails that lead to high quality food sources that are exploited very fast and efficiently. As could be shown in this thesis, A. gracilipes possesses a very sophisticated chemical communication system, well suited for the coordination of the highly collective and efficient foraging behaviour of these opportunistic ants. Consequently, the outstanding communication of A. gracilipes could contribute greatly to their success, because their invasive lifestyle is at least partly based on optimal exploitation of resources.
Name: Wolfgang Niggl
Title: Die zeitliche Komponente und die Rolle von Korallenmucucs bei Coral Bleaching
Supervisor: Christian Laforsch
CV: link
Abstract:
Hermatypic corals, which are the most important contributors to coral reef framework build-up, constantly release coral mucus. This organic exudate functions as an energy carrier and nutrient trap and therefore remarkably contributes to the high productivity and biodiversity in the coral reef ecosystem which offers habitat to hundreds of thousands of animals and plants. This fragile ecosystem is threatened by the global climate change, especially by global warming which leads to increased frequencies of coral bleaching events. This term describes the whitening of corals which results from the loss of symbiotic dinoflagellates, the zooxanthellae, from the coral host. Coral bleaching in most cases leads to the death of the coral colony. Stressors such as air exposure, pollution, high turbidity or coral bleaching are considered to be responsible for increased coral mucus release. However, data verifying increased coral mucus release during a bleaching event resulting from elevated temperatures is missing. In the conducted diploma thesis, the influence of elevated temperatures and a therby induced bleaching event on the release of coral mucus was investigated.
The release rates by two species of hermatypic corals, Acropora spec. and Echinopora spec. subject to coral bleaching was examined. Therefore, ten colonies (5 controls) of each species where placed in beakers containing 0,2 µm filtered sea water and exposed to elevated temperatures. Temperature was adjusted by thermostats and raised by 1° C every 12 h up to a maximum temperature of 32° C. Water temperature of the controls was kept at 25° -28° C. Every 12 h, the release of mucus by the coral colonies was determined. Therefore the coral colonies where exposed to air, turned upside down and the released mucus was collected in tubes. In order to verify the induction of a bleaching event the number of released zooxanthellae in the incubation water and in the collected mucus was determined via microscopy. The amount of released mucus and the number of zooxanthellae was correlated to the coral surface area. For determination of the coral surface area a new method using computerized tomography and subsequent 3-dimensional modelling was invented and successfully applied.
The determination of the number of released zooxanthellae showed that a bleaching event was successfully induced. In contrast to consensus in literature (without appropriate data), this study revealed no evidence for increased release rates of coral mucus per coral surface area (ml/cm²) due to elevated temperatures. By using computerized tomography and 3-dimensional modelling a new, very accurate, non-invasive and non-destructive method of calculating the coral surface area could be invented. This method promises further application by reef scientists as on the one hand the coral surface area is a very important ecological parameter in coral reef science and on the other hand, previously applied methods are either lethal for the coral colony or rather an inaccurate estimation than an accurate determination.
Name: Andrea Riebler
Title: Bayesian Methods for Detecting Selection in the Genome
Supervisor: Wolfgang Stephan
CV: link
Abstract:
The identification of loci affected by selection has become an area of intense research. Differential adaptation of populations to the environment can lead to large betweenpopulation differences in allele-frequency. Using the Fst-coefficient it is possible to quantify the amount of genetic differentiation. In this work two extensions of an Fst-based Bayesian hierarchical algorithm are presented. Gibbs variable selection is introduced to automatically select non-neutrally behaving loci and as a by-product the efficiency of the algorithm is improved by using a reparameterization.
Name: Corinna Steinmeyer
Title: Population genetics, colony structure and competition in a dense population of the native ant Lasius flavus FABRICIUS 1781
Supervisor: Susanne Foitzik
CV: link
Abstract:
In this study I investigated the colony and population structure of a very dense L. flavus population in southern Germany. Microsatellite analyses at six different highly variable loci revealed that this population does not show unicoloniality despite the high density and proximity of nests. In general each ant mound was inhabited by only one colony of L. flavus. Nevertheless seven colonies (=10%) where found to be polydomous which has not been described for this species yet. Although L. flavus is considered to be a monogynous species, less than 50% of the studied colonies (n=70) originated from a singly mated queen. More than half a year later the majority of the mounds were still inhabited by the same colony.
All examined colonies (n=21) produced sexual progeny whereas less than half of the colonies only invested in the production of one sex. Surprisingly, the proportion of produced males increased with increasing intracolonial relatedness of the workers.
Behavioural assays showed that L. flavus workers are able to distinguish between nestmates and strangers although encounters between workers from different colonies in a neutral arena took place without aggressive behaviour. Strange workers which had been introduced in a nest were encountered with more aggression when they originated from a colony of the same population than of a more distant population.
Chemical analyses were carried out in a GC-MS to examine the hydrocarbon profile of the cuticula. It was not possible to separate individuals from the two studied populations due to their hydrocarbon profile.
Name: Angelika Studeny
Title: Asymptotics of genetic Hitchhiking - a multi-locus approach
Supervisor: Peter Pfaffelhuber
CV: link
Abstract:
This diploma thesis project is rooted in the field of mathematical population genetics and focuses on the analysis of patterns left in genetic data by a selectice sweep. Since the introduction of the model of selective sweeps by Maynard-Smith and Haigh (1974), most studies concentrated on the the situation of one selective and one neutral locus considering the influence of selection on the allelic frequencies at one neutral site alone. However, molecular data is frequently available for many partially linked loci. This raises the question of whether selective sweeps generate distinct patterns of multi-locus allele frequencies. Therefore, this diploma thesis project does not rest on the visible effects in allelic frequencies within a region around a locus where selection led to fixation of a mutant type, but takes a closer look at the association between loci (linkage disequilibrium). While the first part of this thesis is dedicated to the exact mathematical formulation of the situation considered and the proof of certain convergence results for Markov processes, the second part concentrates on the analysis of the influence of selection on linkage disequilibrium by a genealogical approach. An enhanced version of the coalescent process, the ancestral recombination graph, is introduced to model the ancestries of two partially linked neutral loci under a selective sweep. You can see an example of an ancestral recombination graph in Fig.1.
As an exact analysis for this model is hard to obtain, an alternative approach is seaked. The idea is to use a two-step procedure generating first the genealogy of the selective locus and adding the one of the neutral loci afterwards. In case of two loci and in the regime of strong selection (i.e. assuming a large (scaled) selection coefficient alpha = Ns >> 1) a Yule process, i.e. a pure birth process, has been suggested to approximate the genealogy at the selected site by Etheridge, Pfaffelhuber, Wakolbinger (2006). In the present work (Chapter 3, Theorem 1) it is shown that the analysis which led to their result may be extended to the three loci case (see Fig.2 for an illustration of the Yule process approximation).
