Evolution of cooperation in the legume-rhizobium symbiosis
Mutualistic symbioses include a wide range of interactions among a diverse set of organisms. The symbiosis between legumes and rhizobia (Rhizobia , Bradyrhizobium, Mesorhizobium, Sinorhizobium species) is a classic mutualistic relationship. In return for carbohydrates provided by the host legume, the rhizobia supply nitrogen to the legume. Although reciprocally beneficial, the stability of this cooperative relationship poses a dilemma to evolutionary theory. Why do symbioses persist over millennia, if additional resources could be gained by either partner through the exploitation of the mutualism? N2 fixation is clearly beneficial to the host plant because it supplies nitrogen needed for growth and photosynthesis. But N2 fixation is energetically costly to the bacteria, and hence reduces the resources that could be allocated to their growth and reproduction. Why then do rhizobia fix N2 to benefit the host plant when expending those resources on reproduction could increase the rhizobia's own fitness?
Thesis, Dissertation, English, 2005
2005