North american fresh water ancyrocephalids (Monogenea) with articulating haptoral bars: host-parasite coevolution

-A previously derived parasite cladogram for North American fresh water ancyrocephalids with articulating haptoral bars was compared with one obtained for their centrarchid hosts. Mapping of the parasite phylogeny on the host phylogeny gave a consistency index of only 0.38. Host-parasite coevolution was attributed solely to ecological association (co-accommodation). Absence of historical association (co-speciation) was correlated with lack of host specificity and host hybridization. Both broad and narrow co-accommodation were demonstrated and attributed to a combined effect of host hybridization and differential geographic distribution of hosts and parasites in response to Pleistocene glaciation events. [Ancyrocephalids; Monogeniids; host-parasite coevolution; parasite phylogeny.] Parasitologists have long recognized historical relationships between parasites and their hosts, and several "rules" concerning host-parasite coevolution have been proposed to elucidate these relationships (see Eichler, 1948; Wardle et al., 1974; Brooks, 1979, 1981; Price, 1980; Noble and Noble, 1982; Mitter and Brooks, 1983). Only recently, however, was an objective, falsifiable protocol for testing hypotheses on host-parasite coevolutionary relationships proposed. Brooks (1979) defined coevolution as a combination of two processes: co-accommodation (ecological association) and cospeciation (historical association) and provided a protocol whereby a comparison of host and parasite cladograms may lead one to detect instances of co-speciation. He stated that ". . . if the major pattern of parasite evolution has been co-speciation, the biology of parasites would indicate a nonrandom association with their hosts...." Brooks (1981) then refined the protocol providing a methodology for transforming a parasite cladogram into a character state tree for host classification. Brooks (1985) stated that "... points of agreement between host phylogeny and parasite-de1 Current address: Department of Zoology, University of Toronto and Department of Ichthyology and Herpetology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada. rived host relationships support association by descent; points of disagreement represent episodes of colonization...." Klassen and Beverley-Burton (1987) applied a similar protocol to study host-parasite coevolution for the genus Ligictaluridus (Monogenea: Ancyrocephalidae) and their hosts (Ictaluridae). They believed the degree of correspondence of host (Ictaluridae) and parasite (Ligictaluridus spp.) cladograms to be better explained by ecological than historical association between hosts and parasites. Hybridization, in nature, among species of the Centrarchidae, the major host group for the North American Ancyrocephalidae, is well documented (Ricker, 1948; Hubbs, 1955; Birdsong and Yerger, 1967; Childers, 1967). However, the occurrence of host hybrids appears inconsistent with a method designed to depict hierarchies (Funk, 1985) and so far has not been taken into account in analyses of host-parasite coevolution. This omission is potentially important when considering that comparisons of host and parasite cladograms, from the parasitologists point of view, ". . . require a host cladogram designated as true ." (Brooks, 1979). The present paper is the second involving the interpretation of phylogenetic relationships among Ancyrocephalidae (sensu Murith and Beverley-Burton [1984]) with articulating haptoral bars. In the first paper