Introduction
When Carl L. Hubbs published "Materials for the revision of the catostomid fishes of eastern North America" in 1930, he commented that "...to make of this contribution a satisfactory, comprehensive synopsis of the family...will require a considerable period of time to obtain and study adequate material...". This statement applied to all eastern catostomids. However, of the three subfamilies recognized by Hubbs in 1930 (Cyclepinae, Ictiobinae and Catostominae), only the ictiobinae still awaits comprehensive systematic review.
Ictiobines are large, deep-bodied, long-finned suckers (see Body Forms) native to large rivers and lakes in eastern North America (inclusive of Mexico). The subfamily includes both fossil and living forms currently classified in four genera: Vasnetzovia of Asia (extinct), Amyzon of western North America (extinct), Carpiodes of North America, and Ictiobus of North and Central America. The fact that the oldest fossil catostomids are classified as ictiobines is consistent with the basal position of the subfamily in a recent phylogenetic treatment (Smith 1992). The wide distributions and high degree of sympatry of extant species (see Distribution) suggests that the species are older than the more allopatrically distributed species of tribe Moxostomini (Smith 1992).
The taxonomic and nomenclatural history of the Ictiobinae is much like that of other groups of North American fishes. Most of the names of currently recognized forms were established early in the 19th century, when European and early American naturalists first started describing the biota of the New World. Not surprisingly, the earliest forms named were those found along the Mid-Atlantic Coast and in the Ohio Valley. Following this was an explosive period of description of new forms and seemingly irrational taxonomic adjustments, as naturalists collected and studied material from different parts of the continent. This period started in the 1850's and concluded just after the turn of century. It involved great American naturalists such as Louis Agassiz, Edward Drinker Cope, Spencer Baird, Charles Girard, David Starr Jordan, and Seth Meek. The decades leading up to the 1960's was a period of reflection and taxonomic consolidation as ichthyologists reexamined material accumulated in museums. The 1960's to the present was a period of renewed collecting and collection building, particularly in the south (Pietsch and Anderson 1997), that contributed the material on which this revision will largely be based.
Eight species are currently recognized in the two extant genera: Carpiodes carpio (Rafinesque) C. cyprinus (LeSueur), C. velifer (Rafinesque); Ictiobus bubalus (Rafinesque), I. cyprinellus (Valenciennes), I. labiosus (Meek), I meridionalis (Gunther) and I. niger (Rafinesque). This is the same number of species recognized by Hubbs in 1930. However, most ichthyologists consider living Ictiobinae to be much more diverse (Mayden et al. 1992). Although the nomenclature is stable, modern workers attempting to describe diversity within state boundaries continue to cite problems with the current taxonomy (Burr and Warren 1986, Robison and Buchanan 1988, Jenkins and Burkhead 1994, Etnier and Starnes 1994, Mettee et al. 1996). The problems stem from the fact that: 1) most of the species are poorly diagnosed; 2) most of the currently recognized species are wide ranging , yet, comprehensive treatments of geographic variation have been attempted for only one of these (Hubbs and Black's [1940] study of variation in C. carpio. However, even this study suffered from lack of sufficient material); and 3) it is difficult to reliably assign young and juveniles to species, or even genus in some instances.
We propose to revise the two extant genera of Ictiobinae using the vast amount of material accumulated in museums since 1930, and data on genetic divergence (based on allozymic, isozymic, and mtDNA-sequence data) obtained from newly collected material. This project will increase understanding of diversity and interrelationships within in the subfamily, it will help to eliminate some of the taxonomic confusion that persists from previous treatments, and will provide characters useful for the identification of species both as adults and early life stages. A phylogeny, largely based on morphology, was recently proposed for the Catostomidae, including most of the currently recognized species of Ictiobinae (Smith 1992). This hypothesis of relationships will be useful for comparing hypotheses derived from independent data. However, many ichthyologists consider most of the terminal taxa of ictiobines in this analysis to be complexes of a few to many species. The high degree of sympatry in the distributions of these taxa (see Distribution) is suggestive of long divergence times. The present study aims to resolve interrelationships and patterns of diversification within the species complexes, as well as establish phylogenies for the genera based on genetic data. It is at this level of resolution that answers to interesting questions about patterns of speciation can be found.
