Mutualism at the leading edge: insights into the eco-evolutionary dynamics of host-symbiont communities during range expansion

Abstract

The evolution of mutualism between host and symbiont communities plays an essential role in maintaining ecosystem function and should therefore have a profound effect on their dynamics of range expansion. In particular, the presence of mutualistic symbionts at the leading edge of a host-symbiont community should enhance its propagation in space. We develop a theoretical framework that captures the eco-evolutionary dynamics of host-symbiont communities, to investigate how the evolution of resource exchange may shape community structure during range expansion. We consider a community which includes symbionts that are mutualistic or parasitic to various degrees, where parasitic symbionts receive the same amount of resource from the host as mutualistic symbionts, but at lower cost. The selective advantage of parasitic over mutualistic symbionts is strengthened with resource availability (i.e. with host density), promoting mutualism at the range edges, where host density is low, and parasitism in the population core, 1 .