Insect pheromones are odor molecules used for chemical communication within a species, particularly in the mating of many insects. Species-specific odors attract males and females of the same species while maintaining natural boundaries between different species. However, research led by Nanji Jiang, Bill Hansson, and Markus Knaden from the Max Planck Institute for Chemical Ecology has shown that elevated ozone levels disrupt chemical communication within fly species by breaking down carbon-carbon double bonds found in insect pheromones. This results in male flies being unable to distinguish between females and other males and courting both sexes.
In a new study, the researchers investigated whether the degradation of sex pheromones by ozone also affects mating boundaries between different species. They found that even slightly elevated ozone levels can cause flies to hybridize more frequently with closely related species, potentially leading to a decline in insect populations due to the infertility of resulting hybrids. The experiments involved exposing four species of the genus Drosophila to ozone concentrations commonly found on hot days in cities and observing changes in mating behavior. Female flies exposed to ozone were less able to discriminate between conspecifics and males of other species, resulting in increased hybridization compared to flies exposed to ambient air.
Hybrid offspring resulting from inter-species mating are typically sterile or less fertile than non-hybrids, particularly male hybrids. This can lead to a wasted investment for the flies and contribute to the extinction of populations. However, female hybrids are usually fertile and can lead to continuous gene flow, potentially giving rise to hybrid species in the long term. The researchers suggest that pollutant-induced hybridization in closely related species pairs could lead to hybrid speciation, further impacting insect populations. They also highlight the importance of understanding and addressing factors such as air pollution that may contribute to the decline in insect populations.
Insects rely on odors for various types of communication beyond mating, including aggregation pheromones, alarm pheromones, and social cues. Many of these odor molecules also contain carbon-carbon double bonds, which can be broken by ozone. The researchers warn that ozone could disrupt the chemical communication of insects, and plan to investigate this further in future studies, particularly in ant species. Other oxidizing pollutants such as nitrogen oxides, which cannot be tested in laboratory experiments due to their toxicity, can also amplify the effects of ozone on insect populations.
The researchers argue that the limits for air pollutants should be re-evaluated, considering the significant impact even small amounts of these substances can have on the chemical communication of insects. They emphasize the need to better understand and counteract factors that may contribute to the decline in insect populations, including pollution-induced hybridization and other environmental stressors. With insect populations facing a dramatic decline in biomass and biodiversity, efforts to protect and preserve these crucial species are essential for maintaining healthy ecosystems.
