@phdthesis{Paul2001,
  author    = {Paul, J{\"u}rgen},
  title     = {The Mouthparts of Ants},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-1179130},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2001},
  abstract  = {Ant mandible movements cover a wide range of forces, velocities and precision. The key to the versatility of mandible functions is the mandible closer muscle. In ants, this muscle is generally composed of distinct muscle fiber types that differ in morphology and contractile properties. Volume proportions of the fiber types are species-specific and correlate with feeding habits. Two biomechanical models explain how the attachment angles are optimized with respect to force and velocity output and how filament-attached fibers help to generate the largest force output from the available head capsule volume. In general, the entire mandible closer muscle is controlled by 10-12 motor neurons, some of which exclusively supply specific muscle fiber groups. Simultaneous recordings of muscle activity and mandible movement reveal that fast movements require rapid contractions of fast muscle fibers. Slow and accurate movements result from the activation of slow muscle fibers. Forceful movements are generated by simultaneous co-activation of all muscle fiber types. For fine control, distinct fiber bundles can be activated independently of each other. Retrograde tracing shows that most dendritic arborizations of the different sets of motor neurons share the same neuropil in the suboesophageal ganglion. In addition, some motor neurons invade specific parts of the neuropil. The labiomaxillary complex of ants is essential for food intake. I investigated the anatomical design of the labiomaxillary complex in various ant species focusing on movement mechanisms. The protraction of the glossa is a non muscular movement. Upon relaxation of the glossa retractor muscles, the glossa protracts elastically. I compared the design of the labiomaxillary complex of ants with that of the honey bee, and suggest an elastic mechanism for glossa protraction in honey bees as well. Ants employ two different techniques for liquid food intake, in which the glossa works either as a passive duct (sucking), or as an up- and downwards moving shovel (licking). For collecting fluids at ad libitum food sources, workers of a given species always use only one of both techniques. The species-specific feeding technique depends on the existence of a well developed crop and on the resulting mode of transporting the fluid food. In order to evaluate the performance of collecting liquids during foraging, I measured fluid intake rates of four ant species adapted to different ecological niches. Fluid intake rate depends on sugar concentration and the associated fluid viscosity, on the species-specific feeding technique, and on the extent of specialization on collecting liquid food. Furthermore, I compared the four ant species in terms of glossa surface characteristics and relative volumes of the muscles that control licking and sucking. Both probably reflect adaptations to the species-specific ecological niche and determine the physiological performance of liquid feeding. Despite species-specific differences, single components of the whole system are closely adjusted to each other according to a general rule.},
  subject      = {Ameisen},
  language  = {en}
}
@phdthesis{Ruchty2010,
  author    = {Ruchty, Markus},
  title     = {Sensory basis of thermal orientation in leaf-cutting ants},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-48906},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {Leaf-cutting ants have a highly developed thermal sense which the insects use to regulate the own body temperature and also to optimize brood and fungus development. Apart from the already described temperature guided behaviors inside the nest it is unknown to what extent the ants may use their thermal sense outside the nest. As part of the present thesis, the question was addressed whether leaf-cutting ants (Atta vollenweideri) are able to learn the position of a warm object as landmark for orientation during foraging. Using absolute conditioning, it was shown that ten training trials are sufficient to elicit the association be-tween food reward and the temperature stimulus. In the test situation (without reward) a significantly higher amount of ants preferred the heated site compared to the unheated con-trol. Importantly, thermal radiation alone was sufficient to establish the learned association and served as orientation cue during the test situation (chapter IV). Based on the experi-mental design used in the previous chapter, the localization of thermosensitive neurons, which detect the underlying thermal stimuli, is restricted to the head or the antennae of the ants. The antennal sensillum coeloconicum is a potential candidate to detect the thermal stimuli during the orientation behavior. In chapter V the sensillum coeloconicum of Atta vollenweideri was investigated concerning its gross morphology, fine-structure and the phy-siology of the associated thermosensitive neuron. The sensillum is predominantly located on the apical antennal segment (antennal tip) where around 12 sensilla are clustered, and it has a peg-in-pit morphology with a double walled, multiporous peg. The sensory peg is deeply embedded in a cuticular pit, connected to the environment only by a tiny aperture. The sen-sillum houses three receptor neurons of which one is thermosensitive whereas the sensory modality of the other two neurons remains to be shown. Upon stimulation with a drop in temperature, the thermosensitve neuron responds with a phasic-tonic increase in neuronal activity (cold-sensitive neuron) and shows rapid adaptation to prolonged stimulation. In ad-dition, it is shown that thermal radiation is an effective stimulus for the thermosensitive neuron. This is the first evidence that sensilla coeloconica play an important role during the thermal orientation behavior described in chapter IV. During the test situation of the classic-al conditioning paradigm, the ants showed rapid antennal movements, indicating that they scan their environment in order to detect the heated object. Rapid antennal movements will result in rapid discontinuities of thermal radiation that re-quire thermosensitive neurons with outstanding sensitivity and high temporal resolution. In Chapter VI the question was addressed whether the thermosensitive neuron of the sensilla coeloconica fulfils these preconditions. Extracellular recordings revealed that the neuron is extremely sensitive to temperature transients and that, due to the response dynamics, an estimated stimulus frequency of up to 5 Hz can be resolved by the neuron. Already a tem-perature increase of only 0.005 °C leads to a pronounced response of the thermosensitive neuron. Through sensory adaptation, the sensitivity to temperature transients is maintained over a wide range of ambient temperatures. The discovered extreme sensitivity, the high temporal resolution and the pronounced adaptation abilities are further evidence support-ing the idea that sensilla coeloconica receive information of the thermal environment, which the ants may use for orientation. In order to understand how the ants use their thermal environment for orientation, it is ne-cessary to know where and how thermal information is processed in their central nervous system. In Chapter VII the question is addressed where in the brain the thermal information, specifically received by the thermosensitive neuron of sensilla coeloconica, is represented. By selectively staining single sensilla coeloconica, the axons of the receptor neurons could be tracked into the antennal lobe of Atta vollenweideri workers. Each of the three axons termi-nated in a single functional unit (glomerulus) of the antennal lobe. Two of the innervated glomeruli were adjacent to each other and are located lateral, while the third one was clear-ly separate and located medial in the antennal lobe. Using two-photon Ca2+ imaging of an-tennal lobe projection neurons, the general representation of thermal information in the antennal lobe was studied. In 11 investigated antennal lobes up to six different glomeruli responded to temperature stimulation in a single specimen. Both, warm- and cold-sensitive glomeruli could be identified. All thermosensitive glomeruli were located in the medial half of the antennal lobe. Based on the correlative evidence of the general representation of thermal information and the results from the single sensilla stainings, it is assumed that thermal information received by sensilla coeloconica is processed in the medial of the three target glomeruli. This part of the thesis shows the important role of the antennal lobe in temperature processing and links one specific thermosensitive neuron to its target region (a single glomerulus). In chapter V it was shown that the sensilla coeloconica are clustered at the antennal tip and have an extraordinary peg-in-pit morphology. In the last chapter of this thesis (Chapter VIII) the question is addressed whether the morphology of the sensilla coeloconica predicts the receptive field of the thermosensitive neuron during the detection of thermal radiation. The sensory pegs of all sensilla coeloconica in the apical cluster have a similar orientation, which was not constraint by the shape of the antennal tip where the cluster is located. This finding indicates that the sensilla coeloconica function as a single unit. Finally the hypothesis was tested whether a single sensillum could be direction sensitive to thermal radiation based on its eye-catching morphology. By stimulating the thermosensitive neuron from various angles around the sensillum this indeed could be shown. This is the last and most significant evi-dence that the sensilla coeloconica may be adapted to detect spatially distributed heated objects in the environment during the thermal landmark orientation of ants.},
  subject      = {Neurobiologie},
  language  = {en}
}