Aphids, Bacteria, and the Heat Dilemma

Pea aphids have a unique relationship with a bacterium called Fukatsuia symbiotica. This bacterium is passed down from mother to offspring. It helps protect the aphids from fungal infections. However, this protection comes at a cost. When temperatures rise from cool to mildly warm, aphids with this bacterium struggle to reproduce. They produce few or no offspring. This happens because the bacterium becomes more abundant and disrupts the aphid's normal functions. The bacterium has a special gene that produces a compound similar to Herbicolin A. This compound is known for its antifungal properties. It is likely the reason aphids with Fukatsuia symbiotica are protected from fungal infections.

However, this compound also seems to interfere with the aphid's development. When aphids are injected with extracts from infected aphids, they show similar developmental issues. This suggests that the compound is responsible for the reproductive problems seen at higher temperatures. Interestingly, the compound produced by Fukatsuia symbiotica is not identical to Herbicolin A. It has both antifungal and hemolytic activities. This means it can also break down red blood cells. This relationship between aphids and Fukatsuia symbiotica is a classic example of a trade-off. The bacterium provides protection against fungi but also causes reproductive issues at higher temperatures. This trade-off is mediated by a single genetic locus in the bacterium.

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