Impacts of Drosophila melanogaster aggregation on offspring development and microbial community structure.

Aggregating with conspecifics can lead to collective environmental manipulation, benefiting individuals, particularly in ovipositing insects where symbiotic microorganisms play a crucial role in larval development. Variability in maternal microbial communities and available habitats significantly impacts developmental habitat quality, especially for insects with limited control over their symbionts. Female insects transmitting microorganisms collected from different habitats during aggregation may increase the chance of a suitable microbiome being filtered by the current habitat. Our study on Drosophila fruit flies demonstrates that habitat type (including apple, tomato, and lemon) significantly influences the composition of symbiotic fecal microbiota in females. However, mixing maternal microbiota from different habitats, simulating aggregation, did not consistently enhance larval development success across substrates. Further investigation revealed intriguing outcomes in larval development across substrates. While larva-to-adult survival rates were high in apple and tomato substrates regardless of initial microbiota, they were lower in lemon substrates, except when inoculated with apple-derived maternal microbiota. Additionally, apple substrate not only produced the largest flies but was also associated with a species-poor Acetobacter-dominated microbiota. In contrast, diverse bacterial communities tended to hinder larval development, suggesting a complex relationship between microbial diversity and larval fitness. Furthermore, substrate type acted as a robust environmental filter, favoring specific microbial communities influenced by maternal inoculum. This phenomenon highlights the intricate interplay between habitat characteristics and microbial composition, shaping larval development outcomes. Overall, adapting as a habitat generalist may disrupt mutually beneficial symbiosis, hindering the evolution of stable host-symbiont associations across spatial and temporal scales.