CHOUDHURY, A*; PEREZ-PONCE DE LEON, G; St. Norbert College, DePere; Universidad Nacional Autonoma de Mexico, Mexico D.F.: Parascript studies and the historical biogeography of North American freshwater fishes

The historical biogeography of enduring associations between North American freshwater fishes and their metazoan parasites is explored in the tradition of parascript studies (using the language of parasites to reveal the history and biology of the hosts). Patterns of associations of selected groups of parasites (trematode flukes and nematodes) in three groups of freshwater fishes, the basal Acipenseriformes, and the ostariophysian families Ictaluridae and Catostomidae are examined/reviewed. Results suggest that: a) acipenserids were primitively diadromous, b) catostomidae are strong candidates as basal cypriniforms, and c) ictalurids do not have close biogeographical relationships with neotropical siluriforms, rather their affinities likely lie with the Afro-Asian siluriforms. The nature of such associations in the Mexican transition zone indicates little parasite exchange between neotropical and nearctic siluriforms. Hypotheses of historical colonization of North American freshwater environments from marine environments by ancestors of hosts such as Centrarchidae and Aplodinotus grunniens (the only truly freshwater Nearctic sciaenid) are strongly corroborated by the evidence from parasite systematics.