Zugl.: Berlin, Humboldt-Univ., Diss., 2007 u.d.T.: Grah, Gunnar: Dreidimensionale Orientierung anhand vereinfachter Repräsentationen von Routen und Räumen / Hergestellt on demand

The desert ant Cataglyphis fortis is one of the hyperthermophilic species of Cataglyphis. It lives in the Sahara desert and forages during the hottest hours of the day when it can get up to 70˚C in the sand. The body temperature of the ant during the foraging runs can reach a maximum of 55˚C. Since C.fortis is one of few eukaryotic hyperthermophilic species, its proteins probably have a high thermostability. Investigating the thermostability can give valuable information about the principles of protein folding and stability in hyperthermophiles.Fatty acid binding proteins (FABPs) have an important role in the cell taking up and transporting fatty acids and regulating metabolic and inflammatory pathways. FABPs have been extensively studied and structures from several species have been determined. The determined structures of all FABPs are very similar why thermostability studies of FABP from C.fortis are highly relevant.Fluorescence spectroscopy is an easy and fast method to measure intrinsic protein fluorescence. Tryptophans were genetically introduced into three different positions in FABP to be used as environmental sensitive probes. Complementing the measurement results with a model of the 3D structure of FABP from C.fortis gave additional information about the ligand binding.The (local) thermostability of the mutants can be detected by shift in wavelength maximum during temperature ramping experiments. All mutants are stabilised in the presence of fatty acids. The mutant with tryptophan positioned closest to the supposed ligand binding residues (Y11W) is most affected. The mutant with tryptophan situated farthest from the supposed binding residues (Y52W) shows a stabilisation of Tm less evident than for Y11W. Thus, the structural changes following fatty acid binding are more obvious in the environment close to the binding site.However, the third mutant C87W shows no significant stabilisation although positioned closer to the fatty acid binding site than Y52. This is probably due to the size difference between the original and introduced amino acid in the mutation. Since the high value of the starting λmax for C87W implies that C87W is quite exposed to the aqueous solvent, the residue is likely to not have subsumed in the protein tertiary structure.Further, the myristic acid stabilise the melting temperature of all the mutants while octanoic acid only has a local effect of Y11W increasing the cooperativity. This implies different binding properties and that myristic acid stabilise the entire protein while octanoic acid only has a local stabilisation effect around the ligand binding site.

Many insights into ecological and evolutionary processes have come from studies of island systems. Diversity, abundance, and movement of species are restricted on smaller islands, but these dynamics can become increasingly complex as island size increases. In recent decades urbanization and the human population on the Galápagos islands has increased rapidly, affecting wildlife in unknown ways. During 2005 and 2006, we sampled birds along a 4-km transect extending northeast of the city of Puerto Ayora, Santa Cruz Island. This allowed us to collect data on the potential impacts of rapidly growing urban center on passerine bird diversity and abundance. We also documented movement patterns of the medium ground finch (Geospiza fortis), the most abundant species on the transect, with a mark/recapture protocol. Although Darwin's finches have been an influencial model for the last 150 years, little is known about their movements on larger islands. Avian species diversity did not vary significantly along a transect from a periurban area into more remote habitat. Avian abundance, however, was inversely correlated with distance from the urban center. This latter finding is consistent with a well-documented trend in urban ecology, in which periurban areas show higher abundance as compared to adjacent, less developed regions. We also found recapture/re-sight rates for G. fortis within years were 7% and 11% in 2005 and 2006, respectively. The mean distance traveled by individual birds between recaptures or re-sightings was 430.4 m. The majority of movements were less than 500 m from the location of previous sighting. There was no relationship between the distance moved and the time between captures or re-sightings; birds were equally likely to move large distances over short intervals (days) as over longer intervals (years). There was no significant difference in movement distances between males and females. These data document the movement of G. fortis on a larger island. Further studies of gene flow among populations may provide further insight into the genetic and evolutionary consequences of movement patterns documented here.

Wüstenameisen (Cataglyphis fortis) orientieren sich mittels Wegintegration sowie, in visuell abwechslungsreichem Gelände, anhand von Landmarken. In der vorliegenden Arbeit wurden in Verhaltensexperimenten die Orientierungsmechanismen von C. fortis im Kontext dreidimensionaler Routen untersucht. 1. Wüstenameisen sind in der Lage, Steigungen und Gefälle eines dreidimensionalen Laufs mit den korrespondierenden Grunddistanzen in ihren Heimvektor zu integrieren. Hierdurch bleibt eine zweidimensionale Wegintegration selbst in hügeligem Gelände akkurat. 2. Entlang bekannter Routen werden Eigenschaften eines Aufstiegs wie Winkel und Länge gespeichert. Wenn Auf- und Abstiege nur auf dem Hinweg zu einer Futterquelle auftreten, werden sie trotzdem auch auf dem Rückweg akzeptiert. 3. Erfolgreiche Aufstiege führen zu einer neu erlernten, generellen Akzeptanz von Rampen, selbst wenn ihr Auftreten inkongruent mit dem aktuell erlernten Lauf ist. 4. Haben Wüstenameisen im Test die Wahl zwischen einem Auf- bzw. Abstieg und einem horizontalen Kanal, entscheiden sie sich häufiger für die Rampen und legen auf ihnen größere Distanzen zurück, wenn auch das vorherige Training geneigte Streckenabschnitte besaß. Dies gilt auch, wenn die Kombination eines Auf- und Abstiegs im Training einen horizontalen Vektor zur Folge hatte. Die Reihenfolge von Auf- und Abstiegen wird jedoch nicht gespeichert, ebenso wenig die Distanz einer Rampe von Nest und Futterstelle. 5. Erzwungene vertikale Ablenkungen im Lauf einer Ameise werden nicht kompensiert. Der Heimvektor besitzt demnach keine vertikale Komponente, sondern funktioniert auf Basis der Korrektur geneigter Wegstrecken zu ihren entsprechenden Grunddistanzen. Cataglyphis fortis verfügt demnach nicht über eine tatsächlich dreidimensionale Repräsentation ihrer Routen. Stattdessen ermöglicht ihr wahrscheinlich das Zusammenspiel einer Reihe einfacherer Navigationsmechanismen eine genaue Orientierung auch in hügeligem Terrain. / Desert ants (Cataglyphis fortis) orientate by means of path integration, and the use of landmarks, if available. In this thesis, behavioural experiments were conducted to elucidate C. fortis’ orientation mechanisms in the context of three-dimensional routes. 1 Along a three-dimensional route, desert ants are able to incorporate the ground distances of slopes into their home vector. Thus, two-dimensional path integration remains accurate also in hilly terrain. 2 Along familiar routes, ants store and recall a slope’s properties such as inclination and length. Even if ascents and descents only occur on the outbound trip, they are also accepted on the homebound run nevertheless. 3 Successful ascents result in a newly learnt, general acceptance of ramps, even if their occurrence is incongruent with a currently learnt route. 4 Given that desert ants can choose between a horizontal continuation of a channel and a ramp, they decide more often to walk on ramps if earlier training included sloped path segments, and continue to walk on them for greater distances. This is also the case if a combination of an ascent and descent results in a horizontal home vector during training. Neither their sequence nor the distance of a ramp from nest and feeder is stored and subsequently recalled. 5 Forced vertical detours in an ant’s run are not compensated for. The home vector consequently possesses no vertical component, and instead is functional due to the correction of sloped path segments to their respective ground distances. In summary, three-dimensional orientation in C. fortis is carried out by the combination of several mechanisms, namely (1) a global vector that corresponds to a plane projection of a route in the horizontal plane; (2) behavioural rules that are generally learnt; and (3) the storing and recollection of specific information along familiar routes.

Die Wüstenameise, Cataglyphis, orientiert sich vor allem mittels Wegintegration. Über einen Heimvektor, den sie aus Distanz und Richtung einzelner Wegabschnitte berechnet, kann sie auf dem kürzesten Weg zu ihrem Ausgangspunkt zurückkehren. Zur Bestimmung der zurückgelegten Strecken verwendet sie einen Schrittintegrator. Die Laufrichtung wird hauptsächlich über Himmelsinformationen (Polarisationsmuster, Sonnenstand und Spektral- und Intensitätsgradienten) definiert. In dieser Arbeit über die Orientierungsfähigkeit von Cataglyphis fortis wird die Rolle des Polarisationskompasses bei der Bestimmung der Laufrichtung untersucht. In verschiedenen Versuchen wurden der Polarisationskompass der Ameise mit Hilfe eines Polarisationsfilters gezielt manipuliert und künstliche Konfliktsituationen erzeugt. Die Richtungsbestimmung wurde vom Polarisationskompass dominiert, wenn allein die Information des Polarisationskompass und idiothetische Richtungsinformation zur Verfügung standen. Erfuhren die Ameise widersprüchliche Informationen von Sonnen- und Polarisationskompass, berechneten sie eine mittlere Heimlaufrichtung, was eine gemeinsame neuronale Verarbeitung der beiden Signale voraussetzt. Diese These wurde durch Transferexperimente gestützt. In einer weiteren Versuchsreihe wurde die Wahrnehmung des Polarisationsmusters durch direkte Manipulation der entsprechenden Region (DRA) im Ameisenauge untersucht. Standen der Ameise in beiden Augen die frontale oder caudale DRA zur Verfügung führte dies zu einem deutlichen Orientierungsverlust. Die intakte DRA eines Auges erlaubte eine zielgerichtete Fortbewegung, die jedoch von der Erwartungsrichtung abwich. Zusammenfassend zeigen die Ergebnisse der vorliegenden Studie, dass der Polarisationskompass die präziseste Richtungsinformation liefert und den Himmelskompass der Wüstenameise dominiert. / The desert ant, Cataglyphis, navigates predominantly by means of path integration. The information about the distance and direction of individual path segments is integrated into a home vector, which allows the ant to return to the starting point on the shortest way. The distances covered are determined by a stride integrator. The heading direction is inferred mainly via celestial cues: the sky’s polarization pattern, the position of the sun, and the spectral and intensity gradient. This thesis focuses generally on the orientation abilities of Cataglyphis fortis and particularly on the role of the polarization compass to determine the heading direction. In the experiments, the ant’s polarization compass was selectively manipulated using a polarization filter and artificial cue conflict situations were created. The ants relied exclusively on the polarization compass to determine their heading direction if only idiothetic information and information from the polarization compass were available. When the ants experienced contradicting information detected via the sun and the polarization compass systems, an intermediate homing direction was calculated, suggesting a combined neural processing of both signals. This statement was supported by transfer experiments. In a further series of experiments, the input part of the polarization compass was manipulated. Particular regions of the ant’s eye (DRA) that detect polarized light were occluded. Ants with only the frontal or caudal parts of the DRA became disoriented, whereas ants with the entire DRA of one eye were able to perform more precise paths, although deviated from the expected direction. Overall, the results from this thesis suggest that the polarization compass provides the most accurate directional information and dominates the celestial compass system of the desert ant.

<p>The desert ant Cataglyphis fortis lives in the Sahara desert where it is exposed to extreme temperatures up to 70° C. In other words, the organism is considered as a thermophile. Until now the genome remains unknown but the fact that C. fortis provides heat stable proteins makes it very interesting in the field of protein studies and maybe even therapeutical research later on. This thesis focuses on trying to find genes that are expressed in C. fortis. Different genes were chosen and capable primers designed. After fishing for the enzyme GAPDH a fragment was found and sequenced. The sequence showed 31% homology on amino acid level with protein disulfide isomerase (PDI) in Apis mellifera (honey bee) and Drosophila melanogaster (fruitfly). The received sequence can be used to design new primers that match exactly. Gene fishing can also be continued by using the other primers that were designed during this project.</p>

The desert ant Cataglyphis fortis lives in the Sahara desert where it is exposed to extreme temperatures up to 70° C. In other words, the organism is considered as a thermophile. Until now the genome remains unknown but the fact that C. fortis provides heat stable proteins makes it very interesting in the field of protein studies and maybe even therapeutical research later on. This thesis focuses on trying to find genes that are expressed in C. fortis. Different genes were chosen and capable primers designed. After fishing for the enzyme GAPDH a fragment was found and sequenced. The sequence showed 31% homology on amino acid level with protein disulfide isomerase (PDI) in Apis mellifera (honey bee) and Drosophila melanogaster (fruitfly). The received sequence can be used to design new primers that match exactly. Gene fishing can also be continued by using the other primers that were designed during this project.

Inaug.-Diss.--Munich. / Vita. Bibliography: p. 504-514.

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