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Interacting groups with patterns of codiversification are powerful arenas for testing the influence of selection, dispersal, and other processes on lineage diversification. When reproduction in one group is linked to reproduction in another group, codiversification may occur. For example, parasite dispersal is often linked to host dispersal, with barriers to host movement also influencing the movement of their parasites. This linkage of host and parasite dispersal is particularly common in permanent parasites, such as lice, which complete all stages of their life cycle on the body of the host. If barriers to movement contribute to lineage diversification in both host and parasite, then they will codiversify. If codiversification is simultaneous, then the host and parasite may undergo cospeciation. In this chapter we review the five main macroevolutionary events that govern patterns of cophylogenetic history. These processes are cospeciation, host switching, duplication, sorting events, and parasite cohesion. Each of these processes can influence copylogenetic patterns in different ways.

This chapter summarizes the book using a graphical framework that integrates the coadaption and codiversification ends of coevolution with five “zones” of coevolution. This framework can be applied to any host-parasite system. Indeed, it can be used with any coevolving system. Differences in the five coevolutionary zones are operational, yet subtle. Delineating these different zones helps to clarify the ways in which dispersal and selection influence the adapation, coadapation, diversification, and codiversification of interacting groups. Coevolution in this framework varies from a purely microevolutionary focus in the case of coadapation, to a purely macroevolutionary focus in the case of codiversification. These extremes are first considered in more detail. Then the three combinations of adaptation and diversification that comprise the middle portions of the framework are discussed. The importance of integrating phylogenetic, comparative, and experimental approaches cannot be overstated in studies of coevolution, or evolutionary ecology in general.

Plant–insect cophylogeny has been investigated across a range of ecological conditions including herbivory, mutualism, and seed parasitism. It has been argued from phylogeny that non-pollinating seed gallers are less closely cospeciated with figs than pollinators sharing the same hosts. It is not known if the same is true for fig wasp parasitoids. This chapter compares patterns of diversification in figs (Ficus subgenus Sycomorus) and three fig-associated insect lineages: pollinating fig wasps, non-pollinating seed gallers, and their parasitoids. Molecular phylogenies of each participant in this tritrophic interaction can illuminate histories of ancient association ranging from codivergence to host switching. This chapter distinguishes cospeciation from coevolution and discusses sampling and DNA sequencing, phylogenetic analysis, reconciliation analysis, phylogenies of figs and wasps, host specificity of non-pollinating fig wasps, and double dating of figs and fig wasps.

While coevolution may have dramatically shaped our world, it has been extremely difficult to demonstrate because the signatures of coevolution are exceptionally diverse and they are seldom exclusive to coevolutionary processes. This chapter gives a brief history of how coevolution has been studied in mutualistic and antagonistic relationships and then suggests methods which can be used to demonstrate coevolution. There are several different potential mechanisms behind the coevolutionary process and these mechanisms are likely to differ between antagonisms and mutualisms as well as from one mutualism to another. Consequently it may be expected that the signatures of coevolution may differ depending on the exact mechanisms behind the process. It is suggested how to recognize those signatures and why the phenotypes and phylogenies of interacting species may sometimes match or mismatch, and how coevolution can cause patterns of trait diversification and convergence. While patterns associated with coevolution cannot be used to prove coevolution on their own, it is argued, they remain very useful tools to test predictions about how different kinds of coevolution and relationships may affect the phenotypic and genotypic evolution of interacting species.

This chapter highlights the use of consensus techniques and other approaches for understanding historical biogeographic relationships and patterns of associations between parasites and their hosts. It deals primarily with analyses that are often placed under the heading of cospeciation or codivergence, situations in which hosts and their parasites appear to have intimate, long-standing historical connections and in which speciation in the host may result in speciation in the parasite. This type of association appears to obtain for many internal parasites and for certain external parasites, such as lice. In addition, or on the other hand, there is a whole class of host associations, such as those between herbivorous insects and their food plants, in which the relationship of the parasite and the host generally does not show such long-term fidelity but involves many apparent host shifts. These latter situations are often referred to under the more liberal heading of coevolution.