Revealing the faunal tapestry: co-evolution and historical biogeography of hosts and parasites in marine systems.

Parasites are integral components of marine ecosystems, a general observation accepted by parasitologists, but often considered of trifling significance to the broader community of zoologists. Parasites, however, represent elegant tools to explore the origins, distribution and maintenance of biodiversity. Among these diverse assemblages, host and geographic ranges described by various helminths are structured and historically constrained by genealogical and ecological associations that can be revealed and evaluated using phylogenetic methodologies within the context of frameworks and hypotheses for co-evolution and historical biogeography. Despite over 200 years of sporadic investigations of helminth systematics, knowledge of parasite faunal diversity in chondrichthyan and osteichthyan fishes, seabirds and marine mammals remains to be distilled into a coherent and comprehensive picture that can be assessed using phylogenetic approaches. Phylogenetic studies among complex host-parasite assemblages that encompass varying temporal and geographic scales are the critical context for elucidating biodiversity and faunal structure, and for identifying historical and contemporary determinants of ecological organization and biogeographic patterns across the marine biosphere. Insights from phylogenetic inference indicate (1) the great age of marine parasite faunas; (2) a significant role for colonization in diversification across a taxonomic continuum at deep and relatively recent temporal scales; and (3) a primary role for allopatric speciation. Integration of ecological and phylogenetic knowledge from the study of parasites is synergistic, contributing substantial insights into the history and maintenance of marine systems.

Phylogeny of Haliotrema species (Monogenea: Ancyrocephalidae) from boxfishes (Tetraodontiformes: Ostraciidae): are Haliotrema species from boxfishes monophyletic?

The hypothesis that Haliotrema species from boxfishes form a monophyletic lineage was tested. The analysis was conducted for an ingroup of 62 species (including 10 from boxfishes), in a matrix of 20 terminal taxa and 17 characters (total of 21 states). Eight equally parsimonious cladograms (c.i. = 84%, r.i. = 91%) were generated. Two Haliotrema species from boxfishes (H. lactoriae and H. triacanthi) were found to be more closely related to other Haliotrema species than to the remaining 8 from boxfishes. The remaining 8 (H. trochaderoi, H. crymanum, H. lactophrys, H. guadeloupensis, H. glandulosum, H. torridum, H. minutum, and H. kritskyi) constituted part of the bodiani group (total of 19 species). Five of the 17 characters from the analysis were hypothesized to contain homoplastic states. Missing character coding, rounding error, and "ghost characters" influenced resolution.

On the monophyly of Haliotrema species (Monogenea: Ancyrocephalidae) from boxfishes (Tetraodontiformes: ostraciidae): relationships within the bodiani group.

The hypothesis that Haliotrema species from boxfishes, which are members of the bodiani group, form a monophyletic lineage was tested. The analysis was conducted for the 19 species of the bodiani group, which includes 8 species from boxfishes, in a matrix of 13 terminal taxa and 14 characters (total of 15 states). A single, most parsimonious cladogram (c.i. = 75%, r.i. = 85%) was generated. The 8 Haliotrema species from boxfishes (H. trochaderoi, H. crymanum, H. lactophrys, H. guadeloupensis, H. glandulosum, H. torridum, H. minutum, and H. kritskyi) were found to form a monophyletic lineage within the bodiani group; 3 of the 14 characters from the analysis were hypothesized to contain homoplastic states.

A new species of Haliotrema (Monogenea: Ancyrocephalidae) from a Japanese puffer fish Takifugu niphobles (Tetraodontiformes: Tetraodontidae).

A new species of Haliotrema is described on the basis of material from the gills of the Japanese puffer fish Takifugu niphobles. The new species is compared to other ancyrocephalids from tetraodontid hosts and congeners with similar copulum morphology from unrelated hosts. It is distinguished from these species based on a combination of reproductive and haptoral characters. Comparison of the haptor musculature of the new species with that described for Haliotrema balisticus revealed a potential for additional taxonomic characters. Resolution of differences in the interpretation of the functional morphology of the muscle groups in the two species will require further investigation.

Coevolution: a history of the macroevolutionary approach to studying host-parasite associations.

The year 1991 marked 100 yr of coevolution research. I have reviewed the first 90 yr of this history. Three chronological phases are apparent: recognition of predictable associations among hosts and their parasites; search for patterns of association and their underlying causes, emphasizing either correlated biogeographic patterns or correlated phylogenies; and development of objective and repeatable methodologies for reconstructing and interpreting these patterns of association. Von Ihering, an outspoken anti-Darwinian, was undoubtedly the first to recognize and make use of predictable host-parasite associations. Kellogg and Fahrenholz, however, had more profound influence on subsequent generations, but in different directions. Kellogg attempted to meld natural selection with speciation by isolation. He also considered host specificity a component of coevolution, important but variable. His work laid the foundation for future research concentrated on biogeographic interpretations of host-parasite relationships. This emphasis and Metcalf's failed attempts to provide adequate mechanisms for reconstructing phylogenies reduced the biogeographic approach to an empirical research program in the hands of Manter. Fahrenholz, on the other hand, exposed to a strong anti-Darwinian sentiment, emphasized the importance of strict host specificity. This led to Eichler's formulation of the first 3 coevolutionary rules and the conclusion that host specificity was not a component but the cause of coevolution and ultimately the tautology inherent in the phylogenetic approach. All had to rely on 1 assumption, that host and parasite phylogenies were reflected in the taxonomic hierarchy. Hennig criticized this assumption and provided a method whereby phylogenies are reconstructed independently. Brooks melded this new phylogenetic method (cladistics) with an equally new biogeographic method (vicariance biogeography), providing the foundations for the modern macroevolutionary approach to studying host-parasite associations.

New approaches to the systematics of the ancyrocephalid Monogenea from Nearctic freshwater fishes.

A total of 133 ancyrocephalid species found on Nearctic freshwater fishes have been named. Of these, 103 are now considered valid; 14 and 16 have been declared previously as synonyms or species inquirendae, respectively, and Urocleidus rarus Mizelle, 1940, is designated as a species inquirenda in the present work. A cladistic analysis, based on 13 binary and 4 multistate characters and 32 apomorphic character states was carried out. Generalized forms of Entobdella, Gyrodactylus, and Tetraonchus were used to generate a hypothetical outgroup taxon. Thirteen terminal taxa emerged. Of these, 3 (the articulating bar group, Ligictaluridus, and Onchocleidus sensu Wheeler and Beverley-Burton, 1989) have been recognized previously as monophyletic; 3 (Aethycteron, Lyrodiscus, and Salsuginus) were shown to be monophyletic in the present study; 3 (Leptocleidus, Macrohaptor, and Tetracleidus) are monotypic genera; and 4 were identified as unresolved assemblages that contain a number of species considered to be incertae sedis as well as those assigned to the following genera: Aristocleidus Mueller, 1936, Urocleidus sensu Suriano and Beverley-Burton, 1981, Cleidodiscoides Mayes and Miller, 1973, and Cleidodiscus sensu Beverley-Burton and Suriano, 1980. The resultant cladogram was 40 steps long with a consistency index of 0.80. The monophyly of the ingroup is supported by 5 synapomorphies. Comparison and mapping of the parasite cladogram with/onto a family-level cladogram of hosts indicated that the present data provided no unequivocal evidence of cospeciation. Some possible origins for the Nearctic ancyrocephalids are discussed, and the need for further taxonomic studies on the Holarctic ancyrocephalids to explore the possible sister-group relationship between the Nearctic and Eurasian faunas is emphasized.