Department of Ecology, Evolution and Behavior, A. Silberman Institute of Life Sciences, Faculty of Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
CMPS Department (Mathematics), University of British Columbia Okanagan, Kelowna, BC, Canada.
J Math Biol. 2024 Feb 2;88(2):24. doi: 10.1007/s00285-023-02037-w.
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 range expansion dynamics. 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 with 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 a lower cost. The selective advantage of parasitic symbionts over mutualistic ones is increased with resource availability (i.e. with host density), promoting mutualism at the range edges, where host density is low, and parasitism at the population core, where host density is higher. This spatial selection also influences the speed of spread. We find that the host growth rate (which depends on the average benefit provided by the symbionts) is maximal at the range edges, where symbionts are more mutualistic, and that host-symbiont communities with high symbiont density at their core (e.g. resulting from more mutualistic hosts) spread faster into new territories. These results indicate that the expansion of host-symbiont communities is pulled by the hosts but pushed by the symbionts, in a unique push-pull dynamic where both the host and symbionts are active and tightly-linked players.
宿主与共生体群落之间相互作用的进化在维持生态系统功能方面起着至关重要的作用，因此应该对它们的分布范围扩展动态产生深远的影响。特别是，共生体在宿主-共生体群落的前沿存在，应该会增强其在空间中的传播。我们提出了一个理论框架，该框架捕捉了宿主-共生体群落的生态进化动态，以研究资源交换的进化如何在分布范围扩展过程中塑造群落结构。我们考虑了一个具有共生体的群落，这些共生体在不同程度上是互利共生或寄生的，其中寄生共生体从宿主那里获得与互利共生体相同数量的资源，但成本更低。寄生共生体相对于互利共生体的选择优势随着资源的可用性（即宿主密度）而增加，从而促进了在宿主密度较低的分布范围边缘的互利共生，以及在宿主密度较高的种群核心的寄生。这种空间选择也会影响传播速度。我们发现，在分布范围边缘，宿主的增长率（这取决于共生体提供的平均收益）最大，那里的共生体更加互利共生，而核心共生体密度较高（例如，由于更多互利共生的宿主）的宿主-共生体群落会更快地向新领地扩散。这些结果表明，宿主-共生体群落的扩展是由宿主拉动的，但同时也受到共生体的推动，这是一种独特的推拉动态，其中宿主和共生体都是活跃的、紧密联系的参与者。
