Multiple genetic control of acetate-induced olfactory responses in Drosophila melanogaster larvae

Abstract

Behavioural responses of Drosophila melanogaster larvae were measured in response to olfactory stimulation with an homologous series of eight aliphatic n-acetates (methyl... octyl actetate) and with cis-vaccenyl acetate. Larvae tended to be attracted to short-chain acetates (methyl. . . pentyl) and repelled by longer chain acetates (hexyl, heptyl and octyl acetate). All larvae were strongly attracted to propyl acetate, irrespective of the dose studied. Larval olfactory responses generally declined with age. Two geographical strains showed specific anosmias. Katsunuma (Japan) larvae showed no response to hexyl acetate; chromosome substitution showed this behaviour to be controlled by genes on chromosome II. Tai (Ivory Coast) larvae showed no response to pentyl acetate; chromosome substitution showed that two genetic factors were primarily involved, on the X chromosome and chromosome III. The response was modulated by chromosome II. No effect of the Y chromosome was found. Two olfactory mutants were studied, olfC (X chromosome) and Indf (chromosome III); both mutants showed abnormal responses to certain acetates. The results are discussed in terms of various models of olfactory processing and the implications of these models for the number of genes involved in olfaction.

Olfactory coding in Drosophila larvae investigated by cross-adaptation

“…Hexyl and heptyl acetate appear to be processed separately from the other odours, as shown by the lack of cross-adaptation shown by test responses to these two odours (with the exception of methyl and ethyl acetate on hexyl acetate). The existence of a specific anosmia to hexyl acetate (Cobb and Dannet, 1994) confirms this. Taken as a whole, these data show no clear evidence for any of the 16 odours studied here being odour equivalents.…”

“…As expected (Cobb and Dannet, 1994), unadapted larvae were strongly attracted to ethyl and pentyl acetate and repulsed by heptyl acetate (Fig.·1). Following pre-stimulation, larvae showed auto-adaptation to each odour, as shown by nonsignificant 2 tests comparing the observed distribution of larvae with those observed following control tests with no odour (data not shown).…”

“…The data in Table·1 show that maggots respond to butyl and pentyl acetate in very similar manners, but the existence of a J. Boyle and M. Cobb Olfactory coding in Drosophila larvae specific genetic anosmia to pentyl acetate (Cobb and Dannet, 1994) shows that larvae can discriminate the two odours. Hexyl and heptyl acetate appear to be processed separately from the other odours, as shown by the lack of cross-adaptation shown by test responses to these two odours (with the exception of methyl and ethyl acetate on hexyl acetate).…”

“…Here, we use adaptation to study the olfactory responses of Drosophila larvae to another homologous series of ecologically meaningful odours -short-chain acetic esters or aliphatic acetates. The genetic bases of larval responses to these odours have been studied and have been shown to include factors on all major chromosomes, with specific and separate anosmias to pentyl acetate and hexyl acetate, indicating that these odours can be distinguished by larvae (Cobb and Dannet, 1994). The present study not only provides information about the organisation of the olfactory response to these important odours but it also enables us to test the generality of the lateral inhibition model we developed for the coding of alcohols.…”

“…This test does not involve any 'stampede effect'; the response of each individual larva is independent from the behaviour of those around it (M. Kaiser and M. Cobb, manuscript in preparation). The response index is a sensitive and robust phenotype that has enabled genetic factors controlling quantitative variation in the olfactory response to be localised (Cobb and Dannet, 1994).…”