Testing the Context and Extent of Host-Parasite Coevolution

Abstract

Brooks, D. R. (Department of Biology, University of Notre Dame, Notre Dame, Indiana 46556) 1979. Testing the context and extent of host-parasite coevolution. Syst. Zool. 28:299307.-Coevolution is defined as a combination of two processes: co-accommodation between host and parasite with no implication of host or parasite speciation and co-speciation, indicating concomitant host and parasite speciation. Parasite speciation in is viewed as primarily the result of allopatric speciation processes regardless of host speciation or changes in host type. The observation that co-speciation of hosts and parasites forms a predominant pattern relates to a more principle of biotic allopatric speciation explicit in the vicariance biogeography model, more than to an assumption that host speciation somehow causes parasite speciation. The close ecological relationship between hosts and parasites, which may be depicted using a variation of the MacArthur-Wilson island biogeography model, explains their spatial proximity at any time during which an isolating event occurs and thus may be necessary in some cases, but is not sufficient to explain parasite speciation, coevolution, or parasite phylogeny. [Parasitology; coevolution; allopatric speciation; island biogeography; vicariance biogeography; speciation.] No science can free itself from its traditions; it is a difficult matter suddenly and entirely to give up doctrines which for generations have been regarded almost as axioms, even when the erroneous character of the doctrines in question can no longer be doubted. (Arthur Looss, 1911:185.) Given the name of a parasite species, a parasitologist can tell, with a great deal of consistency, the type of host and geographical locality in which the parasite occurred. Virtually any biologist, given a species of plant or animal with which he is familiar, can also predict accurately the geographical distribution and of that species, but this has assumed greater significance with parasites because their general habitat is another living organism. Parasitologists have assumed that, whereas free-living organisms might be free to move from one locality or to another, parasites are so dependent upon their hosts that evolutionarily they have no life of their own. Historically, parasites have often been studied in an attempt to elucidate aspects of host paleobiology (phylogeny or biogeography). Only in a few cases have hosts been utilized to examine aspects of parasite phylogeny and biogeography, but the conclusions have been the same whether one takes the host's view or the parasite's view, namely that host and parasite phylogenies and geographical distributions are highly correlated. Those conclusions led to the formulation of several Rules (see Inglis, 1971) concerning host-parasite coevolu-