Symbioses shape feeding niches and diversification across insects

For over 300 million years, insects have relied on symbiotic microbes for nutrition and defence. However, it is unclear whether specific ecological conditions have repeatedly favoured the evolution of symbioses, and how this has influenced insect diversification. Here, using data on 1,850 microbe-insect symbioses across 402 insect families, we found that symbionts have allowed insects to specialize on a range of nutrient-imbalanced diets, including phloem, blood and wood. Across diets, the only limiting nutrient consistently associated with the evolution of obligate symbiosis was B vitamins. The shift to new diets, facilitated by symbionts, had mixed consequences for insect diversification. In some cases, such as herbivory, it resulted in spectacular species proliferation. In other niches, such as strict blood feeding, diversification has been severely constrained. Symbioses therefore appear to solve widespread nutrient deficiencies for insects, but the consequences for insect diversification depend on the feeding niche that is invaded. Insects rely on symbiotic microbes for nutrition and defence. Analysing a large dataset of microbe-insect symbioses, the authors show that symbiosis evolved in response to nutrient deficiencies but its impacts on insect diversification depend on their feeding niche.

Automated summary

Insects have depended on symbiotic microbes for nutrition and defence for more than 300 million years. The evolution of symbioses and its impact on insect diversification under specific ecological conditions remain unclear. This study analyzed 1,850 microbe-insect symbioses across 402 insect families and found that symbionts allowed insects to specialize on nutrient-imbalanced diets, with B vitamins consistently associated with obligate symbiosis. The consequences of shifting to new diets with the help of symbionts varied, leading to species proliferation in some cases (e.g. herbivory) and severe diversification constraints in others (e.g. strict blood feeding).