Mutualism as a Source of Evolutionary Innovation: Insights from Insect-Plant Interactions

Mutualism is ubiquitous in nature and probably all species in the world are involved in some form of such ecological interaction. The evolution of mutualisms is often envisioned in a framework where individual selection leads to reciprocal exploitation that results in net benefits to all the interacting parties, i.e. in a framework in which individual selection intrinsically destabilises the mutualistic association. However, mutualisms are stable, and rarely turn into parasitism. At a macroevolutionary scale, mutualisms have been a source of major evolutionary innovations and have benefited all the species involved. Indeed, complementary traits of the partners enable them to colonise new ecological niches. In this chapter we discuss mutualism as a source of evolutionary innovation, using some insect-plant associations as examples. Firstly, we dedicate a topic to theoretical aspects and hypotheses on evolutionary forces stabilizing mutualisms (and their pitfalls). We present some examples of mutualisms that allowed insects and/or plants to expand their ecological niches. Finally, we focus on fig tree – animal interactions that, putatively, allowed this plant lineage to diversify in subtropical and tropical ecosystems and to form a group of keystone species for the functioning of many forest ecosystems.