Edge of Survival: The Critical Role of External Microbial Symbionts in Defining the Ecological Niche of Drosophila melanogaster

Drosophila melanogaster, a generalist fruit fly, is known for its high adaptability across diverse ecological niches, underscoring its value in biological and evolutionary research. What could be the “key” to the species’ success? A number of studies indicate the major role of microbial symbionts inhabiting the fly gut and contributing to their host’s fitness. However, the ecological relevance for Drosophila is very often overlooked in those studies. The standardized diet, supplemented with antimicrobial agents, does not reflect the complex microbial environments encountered by flies in nature. Ephemeral breeding sites, such as fermenting fruits and other rotting plant material, harbour highly diverse microbial communities, which excrete toxic metabolites or block nutrients from developing larvae. During egg laying Drosophila females pass down their own beneficial microbes that can tilt the microbial composition of a breeding site towards the flies and ensure their survival, but sometimes these community shifts lead to dysbiosis of a whole environment, and in this case the fly population would collapse. Exploring these community dynamics, our research has uncovered surprising evidence that cucumber, a seemingly neutral substrate, hosts microbial communities that can significantly constrict the reproductive niche of Drosophila melanogaster. This finding challenges our understanding of niche adaptation and raises fundamental questions about the interaction between D. melanogaster and its microbial environment. Our ongoing work aims to identify the microbial species involved and understand their impact on D. melanogaster ecological success. These insights promise to broaden the existing knowledge of microbe-host interactions and underlying mechanisms behind ecological niche construction.