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 In Focus

Evolution of the insect olfactory system

Published 2000-01-02

From 2001 Professor Bill Hansson, Department of Crop Science at the Swedish University of Agricultural Sciences. receives an annual funding of SEK 500 000 from the Institutional Grant Programme for cooperation with Professor Nicholas J Strausfeld at Arizona Research Laboratories, Division of Neurobiology, USA on the insect olfactory system.

Since 2001 we collaborate in a joint research project aimed at strengthening collaboration both scientifically and in teaching. The project has now run effectively for about three years and we have very good experiences from collaborating. A number of researchers have travelled between our laboratories, learning and teaching new techniques, thus augmenting the potential of both sites. Senior scientists have also ”changed places” and taken part in both undergraduate and graduate teaching, and occurrence much appreciated also by the students at the two host universities. The collaboration has produced very interesting results, and presently these are starting to emerge also in published form. The project will continue also during 2004-05 and as a concluding event we will arrange a mini conference for researchers involved in mushroom body research (see below).

This project thus deals with how the insect sense of smell has evolved. Insects rely to a very high degree on the sense of smell, olfaction, for more or less all important aspects of their lives. Partners are located by sexual pheromones, food is found by olfactory cues and suitable oviposition sites are identified using the smell emanating from i.e. leafs and flowers. Being such an extremely important sensory system has put the olfactory system under unusually harsh evolutionary pressures to develop into a highly specific and sensitive system. In this project we study brain structure and function involved in olfaction in a number of different insects. We also study how transition from a marine environment to land has affected peripheral olfactory functions, i.e. the nose, in land crabs.

We concentrate on two important smell centres in the insect brain: the antennal lobe and the mushroom bodies. The antennal lobe is equivalent to our olfactory bulb and is the primary olfactory centre of the brain. The mushroom bodies are the next level of the brain, where integration with other sensory modalities and with memory functions is occurring. By comparing a beetle, a moth, a sawfly and a fly we study how these structures have changed through evolution, and how different selection pressures have affected structure and function.

In the antennal lobe odours are coded as a topographical map among glomeruli, little balls of neural tissue. Each ball receives information regarding a certain class of odours. Here we have studied how conserved the map is among a number of more or less related moths. The map is remarkably conserved, also among widely distant species. We have also started investigating how a specific neurochemical affects olfactory coding in the antennal lobe, and were in this project first in the world to register nitric oxide signalling as part of the olfactory map in the antennal lobe.

In the mushroom bodies we have investigated the detailed morphology in a beetle and in a moth. This has given us important new insights into how these brain centres are organised in different insects. We have also developed a new and unique method allowing us to record from tiny neurons present in the mushroom bodies.

One of the major transitions of a chemosensory system is to move from detecting molecules in water to do it in air. This is just what has happened in a numbed of land crabs that today are obligatory terrestrial and will drown if submerged in water. What we have found is that these animals have developed an olfactory system extremely similar to the insect system. Marine crabs have a very different system as compared to insects, so the transition to air has caused a very clear case of convergent evolution.

We find that this project has allowed us to deepen the relationship between our two laboratories to a very significant extent. We have learned much from each other and we have achieved results that we would not have otherwise. The possibility to go through with this project has been based entirely on our grant from STINT.

Bill S. Hansson and Nicholas J. Strausfeld

Senast uppdaterad: 05-01-10 09:03

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