BackgroundMate finding and recognition in animals evolves during niche adaptation and involves social signals and habitat cues. Drosophila melanogaster and related species are known to be attracted to fermenting fruit for feeding and egg-laying, which poses the question of whether species-specific fly odours contribute to long-range premating communication.ResultsWe have discovered an olfactory channel in D. melanogaster with a dual affinity to sex and food odorants. Female flies release a pheromone, (Z)-4-undecenal (Z4-11Al), that elicits flight attraction in both sexes. Its biosynthetic precursor is the cuticular hydrocarbon (Z,Z)-7,11-heptacosadiene (7,11-HD), which is known to afford reproductive isolation between the sibling species D. melanogaster and D. simulans during courtship. Twin olfactory receptors, Or69aB and Or69aA, are tuned to Z4-11Al and food odorants, respectively. They are co-expressed in the same olfactory sensory neurons, and feed into a neural circuit mediating species-specific, long-range communication; however, the close relative D. simulans, which shares food resources with D. melanogaster, does not respond to Z4-11Al.ConclusionThe Or69aA and Or69aB isoforms have adopted dual olfactory traits. The underlying gene yields a collaboration between natural and sexual selection, which has the potential to drive speciation.
Volatiles from mouse carcasses in decay stages ranging from fresh to 33 days old were used to investigate oriented flight and landings in male and female blow flies of Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae). Oriented flight increased significantly from 36% towards fresh carcasses to 68%, 61% and 65% towards carcasses aged 3 days, 6 days and 9 days, respectively. Carcasses aged 20 days and 33 days were significantly less attractive, achieving 51% and 41% attraction, respectively. No differences emerged between the sexes in oriented flight, but a significant increase in female landings at the most attractive carcasses was observed. Headspace collections from the different stages of decay showed a succession in the volatile profile emitted from the carcasses and identified nine chemicals which peak in quantity in concurrence with the most attractive stages of decay. Three of these chemicals also showed dose-response effects as indicated by a significant correlation between the amount present and the proportion of flies responding. Blow flies are important pests and efficient traps are needed. The significant interaction between fly sex and carcass age highlights behavioural differences between male and female blow flies which can be exploited in blow fly trapping. Three new volatile chemicals, butylated hydroxyl toluene, 3-hydroxy-2-butanone and nonanal, emitted from dead mice are suggested as potential attractants.
The discovery of olfactory receptors and major technological advances have greatly accelerated our 17 understanding of chemosensory mechanisms. However, some of this rapid progress may be 18 compromised by inadequate knowledge or characterization of the purity of chemical stimuli used to 19 challenge olfactory or other chemoreceptors when mapping their response profiles. Here, we provide 20 strong evidence that the presence of trace impurities in test stimuli can completely obscure true 21 ligand-receptor relationships. DmOR7a, an olfactory receptor of the vinegar fly (Drosophila 22 melanogaster) has been reported to respond to several long-chain aliphatic ligands such as a putative 23 Drosophila pheromone 1 , the pheromone of the silkworm moth Bombyx mori 2 , and a common fatty 24 acid, linoleic acid 3 . By contrast, we show that DmOR7a responds with high sensitivity to volatile 25 impurities and degradation products present in minute quantities in authentic standards of those lost activity with repeated puffs (Extended Data Fig. 1c, and Extended Data Fig. 2c). This was unexpected, 51 because these long-chain compounds have low vapour pressures and would be expected to deliver a 52 relatively constant stimulus dose over numerous puff cycles [11][12][13] . Indeed, such declines were not observed 53 (Extended Data Fig. 1a,b) when using the same protocol to stimulate the pheromone receptor of B. mori, 54BmOR1 14 (exogenously expressed in D. melanogaster T1 neurons, T1 BmOR1 ) with bombykol, or when 55 stimulating wildtype T1 neurons (expressing its cognate receptor DmOR67d 15 ) with its ligand, the long-56chain Drosophila pheromone cis-vaccenyl acetate ((Z)-11-octadecenyl acetate; cVA). 57Furthermore, AB4a neurons responded equally well to bombykol on a filter paper or in paraffin oil 11 58 (Extended Data Fig. 3a). This was counterintuitive, because non-volatile paraffin oil should retain 59 bombykol, a long-chain aliphatic compound, and significantly reduce volatilization and hence stimulus 60 intensity compared to bombykol applied to filter paper 11,13 . Indeed, responses of antennal trichoid T1 61 (sensitive to cVA) and T1 BmOR1 neurons (sensitive to bombykol) were significantly attenuated when 62 stimulated with air puffed over dilutions of cVA or bombykol dissolved in paraffin oil versus on filter paper 63 (Extended Data Fig. 3b, c). 64This cast doubt on whether the above-mentioned compounds were indeed ligands for AB4a neurons. To 65 more rigorously test this, we used coupled gas chromatography-electroantennographic detection (GC-66 EAD), which separates the injected sample into its individual components and sequentially passes these 67 over the antennal preparation. Thus, each antennal response can be unequivocally attributed to a defined 68 peak, which generally represents a single pure compound. We found that the cleanly separated bombykol 69 peak did not induce antennal depolarization in wildtype fly antennae ( Fig. 1a; Extended Data Fig. 4 and 5), 70 nor did bombykal (another reported ligand for AB4a ne...
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