Altered Olfactory Receptor Neuron Responsiveness I

Authors: Michael J Domingue Kenneth F Haynes Julie L Todd Thomas C Baker

Publish Date: 2009/04/24

Volume: 35, Issue: 4, Pages: 405-415

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Abstract

There is little understanding of how sex pheromone blends might change during speciation events For the cabbage looper Trichoplusia ni there is a mutant laboratory strain that has exhibited characteristics of a shift to a new pheromone blend Mutant females produce a blend that is significantly different from wildtype females in having a much higher proportion of a minor pheromone component and lower quantity of the major component Males in this colony have changed over the years to become more broadly tuned and fly upwind equally well to both the wildtype and mutant female pheromone blends They also exhibit reduced overall sensitivity to pheromone flying upwind to either blend at a lower success rate than is typical when wildtype males respond to the wildtype blend Using singlecell recordings we examined the olfactory receptor neurons ORNs of males from evolved and wildtype colonies for evidence of changes in response characteristics that might explain the abovedescribed behavioral evolution We found that in evolvedcolony males the ORNs tuned to the major sex pheromone component exhibited a somewhat lower responsiveness to that compound than the ORNs of wildtype males In addition the minor pheromone component emitted at excessively high rates by mutant females elicited a drastically reduced ORN responsiveness in evolvedcolony males compared to wildtype males This alteration in ORN responsiveness may be responsible for allowing evolved males to tolerate the excessive amounts of the minor pheromone component in the mutant female blend which would normally antagonize the upwind flight of unevolved males Thus peripheral olfactory alterations have occurred in T ni males that are correlated with the evolution of the more broadly tuned but less sensitive behavioral response profile

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