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Abstract:
Cooperative interactions among species, termed mutualisms, have played a crucial role in the evolution of life on Earth. However, despite
key potential benefits to partners, there are many cases in which two
species cease to cooperate and mutualisms break down. What factors
drive the evolutionary breakdown of mutualism? We examined the
pathways toward breakdowns of the mutualism between plants and
arbuscular mycorrhizal fungi. By using a comparative approach, we
identify ∼25 independent cases of complete mutualism breakdown
across global seed plants. We found that breakdown of cooperation
was only stable when host plants (i) partner with other root symbionts
or (ii) evolve alternative resource acquisition strategies. Our results
suggest that key mutualistic services are only permanently lost if hosts evolve alternative symbioses or adaptations.