Researchers at the Max Planck Institute for Chemical Ecology have discovered that the insect brain's sex pheromones as well as the corresponding olfactory pathways evolve quickly and independently by analysing the genomes 99 varieties of vinegar fly species. The odor profiles of conspecific males can be used by female flies to identify them. It is interesting to note that closely related species have distinct odor profiles which help prevent mating between species. In turn, males chemically mark females in mating to make them less attractive to other males. This study provides valuable information to understand how pheromones are produced, processed in the brain and how they affect behavior.Large family with many extravagant relativesVinegar flies, like most animals, choose their mate mainly based on chemical signals. The genus Drosophila is well-suited to study the evolution and diversity in sex hormones. There are more than 1.500 species of vinegar fly known to exist in the world. They can be found in all kinds of habitats including deserts, forests, caves and swamps. The primary food source for many species is rotting fruits and the yeasts that cause fermentation. Fresh fruit, mushrooms and tree bark are all important food sources for some species. Frog spawn is also a common food source. The brain's ability to process olfactory information has been well documented in many species, including the Drosophila melanogaster model organism. The receptors that detect the scent of the conspecific partner are tuned precisely to the sex hormones.Researchers led by Markus Knaden and Mohammed Khallaf examined how sex hormones developed in 99 species of Drosophila. Mohammed Khallaf was the first author of this study. 41 species of the species under study had been fully sequenced. The scientists have presented the most complete phylogenetic analysis of Drosophila by sequencing the entire genomes of 58 more species.It was possible to genetically match chemical profiles and differences in odor detection, processing, and detection using genomic data. The researchers collected the odors from individual flies. They analyzed the odors for five males and five virgin females. This resulted in over 1500 flies. Markus Knaden (head of the Odor-guided Behavior project in the Department of Evolutionary Neuroethology), summarized: "While the comparison of virgin male flies informed me about sex-specific variations, variations between virgin and mated females informed me about male-specific compounds transfer to females during mating."Detail is what makes the difference52 different odor compounds have been identified in all 99 fly species. The scientists discovered pheromones only produced by male flies in 81 species. Male flies produce 58 different scent blends from these species. These can include up to seven distinct odors. The males are known for their sophisticated chemistry and attract attention, but it is the females that decide whether or not mating takes place. "Interestingly, closely related species often have clear differences in the pheromone profiles. Individual pheromones can also be found repeatedly along the phylogenetic tree. One example is that 34 males from 99 species produce cisvaccenyl–acetate (cVA), which is a well-described Drosophila melanogaster hormone. The majority of male-derived pheromones serve the same purpose: They attract females, and secondly they transfer to females during mating to make them less attractive to other males. Markus Knaden said that this ensures male reproductive success.There are significant differences in the pheromone profiles of males from closely related species, which suggests that there is a high selection pressure to stop them mating with species that evolved from the same ancestor. However, 34 species have cis-vaccenyl alcohol acetate produced as a sex hormone. This suggests that only a few genes are responsible for producing pheromones. Different species can produce the same pheromone as long as evolutionary pressure is not applied.One key observation is that the Drosophila male fly is the main transmitter of chemical signals. The female Drosophila fly is the receiver and interprets the signal. The diversity and abundance in male-specific compounds is remarkable compared to the females: 43 of 52 odor compounds are exclusively produced by males while 9 are created by females. Mohammed Khallaf said that 81 species of Drosophila communicate through male pheromones while only 15 species use female pheromones.From odor to behaviourThis study is the first to provide a comprehensive analysis of mating behavior of many Drosophila species. "We noticed that certain species displayed very specific behaviors while we were doing mating experiments. Some were driven by smell and would only start their mating dance when their partner had the right scent. The right wing pattern of the male's song or the right wing pattern of the female could trigger the female's mating behaviour." Bill Hansson, head of the Department of Evolutionary Neuroethology, explained the findings in the mating arena. As the first cue to find the right partner, sex hormones are likely to play an important role. After a female is attracted to another male, she may initiate other mating rituals, such as song, dance, nuptial gift, or song. Researchers will continue to evaluate the recordings of mating experiments in the hope that they can inspire other research groups to examine the different mating strategies of different Drosophilids.###Original publication:Khallaf M. A.., Cui R.. Weiflog J.. Svato A.., Dweck H. Valenzano D. R. Hansson B. S. Knaden M. (2021). Large-scale characterisation of Drosophila's sex pheromone communication system. Nature Communications, DOI. 10.1038/s41467-24395-z https:/// /www. Nature. http:// com/ articles/ S41467-021-24395 - Z
