Research
Bernhard Ronacher
Research interests:
- Neuronal processing of acoustic communication signals in grasshoppers >>
- Evolutionary changes in auditory communication systems >>
- 3-D spatial orientation of desert ants >>
- Learning and recognition of visual patterns by honey bees >>
A) Neuronal processing of acoustic communication signals in grasshoppers:
The acoustic signals produced by many grasshoppers serve two main functions: they must enable the receiver to recognize and to localize a potential mate. Both tasks are not easy to solve. The recognition, for example, is rendered difficult by noise and distortions of the signal imposed on its way through the biotope. Directional hearing is impeded by the small size of the animals, which leads to a deterioriation of directionality cues. On the other hand, since mate finding obviously will affect the fitness, there is a high selective pressure working on the optimization of neuronal processing of such communication signals. Correspondingly, the grasshopper Chorthippus biguttulus shows a remarkable performance in gap detection and directional hearing, which in several respects is not inferior to that of vertebrates, including man. These capacities must be based on an "innate hardware" - the grasshoppers overwinter as eggs, and therefore have no chance to learn from their parents. Furthermore, the animals must solve these tasks with not too many auditory receptors and interneurones (many of which can be identified). These features of the grasshopper's communication make it a system, which is very well suited to investigate how a small nervous system extracts the relevant features from noisy and distorted signals. A second factor that might further delimit the precision of neuronal processing is a considerable variability visible in the spiking responses of receptors and interneurones. Due to their rather small NS, grasshoppers probably cannot get rid of thisvariability by simply averaging over a large population of parallel neuronal elements.
We use behavioural experiments as well as electrophysiological methods in order to better understand how the animals’ nervous system processes information on sound patterns and on sound direction. In addition, in a collaboration with Andreas Herz’ group in the SFB 618 at the Humboldt University, we applied stimulus reconstruction and modelling techniques to the spike train data from auditory receptors and interneurons. By these approaches we intend to reveal how much and what kind of information is transmitted by different neurones. We also aim at understanding the evolutionary lines along which such communication systems may have evolved. The limitations imposed by a rather small number of neurons available for such tasks could give more general insights into the selective forces that have shaped the evolution of small brains.
B) Evolutionary changes in auditory communication systems (with M. Hennig)
Project in the newly established GK 837 (“Functional Insect Science”) in collaboration with M. Hennig and H. Saumweber.
How are changes at the level of genes expressed in specific behavioural traits? During speciation in the communication systems of closely related cricket and grasshopper species both the generation of species-specific signals as well as the corresponding neuronal recognition filters must have changed. We intend to study such questions in these systems at three levels, that is, behaviour, neuronal processing, and genetic correlations.
C) 3-D spatial orientation of desert ants
Joint project with Rüdiger Wehner (Zürich), R. Blickhan (Jena) and H. Wolf (Ulm), sponsored by the Volkswagen Stiftung
Desert ants of the genus Cataglyphis are famous for their ability to perform large scale foraging excursions from which they precisely return to their nest by path integration. To compute and continuously update their ‘home vector’, the ants need two types of information: about the momentary direction of their path, and about the respective travelling distance covered in that direction. While the celestial compass that is used by ants and bees to infer their travelling direction is fairly well understood (e.g. Wehner 1992, 1997), the ant’s distance estimation, the ‘odometer’, remains enigmatic. Recent experiments in which the ants were trained to walk over a series of hills have added a further twist to this story. They revealed unexpected capabilities of these animals to perform path integration in the third dimension. These results indicate that the ant’s odometer is much more elaborate than previously thought. We now aim at a better understanding (i) of how these ants measure traveling distances in hilly terrain, (ii) how they achieve the necessary accuracy since path integration is prone to error accumulation, and (iii) which algorithms underly the ant’s 3-D path integration. This system may serve to address the general question of brain function, that is, how complex computational tasks can be reduced to simpler approximative solutions.
D) Learning and recognition of visual patterns by honey bees:
The central questions of this project are: How do insects learn, store and recall information about visual patterns, how do they classify visual patterns, and how does their performance relate to the abilities of higher vertebrates. By comparing the performances of organisms with different evolutionary history and very differently organized sensory and nervous systems we may be able to extract more general principles how nervous systems process sensory signals. An extension of this comparison to different sensory
modalities (e.g. visual and acoustic) would be demanding as well as fruitful. We train bees to recognize visual patterns and then test whether at all and to what degree the bees do generalize a learned pattern to others. In addition we performed also similar experiments with human observers, in order to enable a direct comparison between the two species. There appears to exist a number of commonalities between visual pattern recognition of insects and humans (cf. Ronacher 1998).
Publication list since 1998
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