Dynamics of symbiotic relationships

The symbiotic relationship between legumes and nitrogen-fixing bacteria is ancient—but why is this relationship sometimes lost, when in other cases it plays a crucial role in evolution?

GBIF-mediated data resources used : 3.2 million species occurrences
Lotus corniculatus

Lotus corniculatus, member of the legumes (Fabaceae). Photo by Andreas Rockstein, licensed under CC BY-SA 2.0.

Symbiotic relationships are an important driver of diversification of organisms. The connection between legumes and nitrogen-fixing bacteria, for example, is ancient—but why is this relationship sometimes lost, when in other cases it plays a crucial role in evolution? In this study, researchers used more than three million GBIF-mediated legume occurrences in hope of shedding light on this mystery, testing whether certain traits or ecological factors might lead to persistence of symbiosis. The results showed that half the species analysed remain highly likely to maintain the symbiotic relationship over time, even if it isn’t absolutely necessary. Such species tend to have high nitrogen and phosphorus leaf content and are located in climates with low mean annual temperatures.

Evolutionary signals of symbiotic persistence in the legume–rhizobia mutualism

Werner GDA, Cornwell WK, Cornelissen JHC and Kiers ET (2015) Evolutionary signals of symbiotic persistence in the legume–rhizobia mutualism. Proceedings of the National Academy of Sciences. Proceedings of the National Academy of Sciences, 10262–10269. Available at doi:10.1073/pnas.1424030112.