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. ' DOUGLAS-SEXUAL DIMORPHISM IN GILA. CYPHA. 335 leading ventra-posteriorly directly to the upper part of the gill openings, allow water to irrigate the gills when the mouth and body are pressed downward. The ventral mouth would therefore be usable, when protected from the onrushing water by the snout (in a manner similar to that occurring in some swift-water suckers)." In spite of Miller's (1946) diagnosis, the tax- onomic validity ofG. cypha has been questioned, most often by personnel from state and federal agencies who monitored and assessed riverine populations of Gila (Holden, 1991). In the 1950s and 1960s, these individuals commonly recog- nized only two subspecies of chub in the Colo- rado River: Roundtail (G. r. robus/a) and bon- ytail (G. r. ('legalls). The humpback chub was simply considered a male bony tail, with the nu- chal hump a secondary sexual characteristic (re- viewed by Holden, 1991 :49). Several studies (e.g., Holden and Stalnaker, 1970: Suttkus and Clemmer, 1977; Smith et aI., 1979) have since recognized the three Colorado River chubs as distinct species (see Douglas et aI., 1989 for a review of the nomenclatorial history of the G. robusta complex). The nuchal hump as a sexual characteristic has yet to be addressed. Gila cYPha is part of an endemic Colorado River Basin fauna that extends at least as far back as the Miocene (Miller, 1959: Minckley et aI., 1986). It has been recorded from deposits dated to 4000 B.C. in the Grand Canyon (Miller and Smith, 1984) and from Native American ruins near Hoover (Boulder) Dam (Miller, 1955). There are only a few published studies on the ecology of G. cypha (Kaeding and Zimmerman, 1983; Kaeding et a\., 1990), and knowledge about its morphological variation is primarily comparative (i.e., relative to other members of the G. Tobusta complex: Douglas et a!., 1989; Kaeding et aI., 1990; R. Valdez, Bureau of Rec- lamation. 1990, unpubl., and references there- in). Suttkus and Clemmer (1977) evaluated morphological variation within G. cypha. but their results were limited by small samples for various size-groups and by modest statistical analyses. There are reasons for the paucity of pub- lished data on G. cypha. Most research on this species has been government sponsored (accom- plished either directly by agency employees or via contracts from agencies to independent re- searchers). Results of these studies are pro- duced as "technical reports" or other agency- sponsored (i.e., "gray") literature, which are published without adequate review and without broad distribution (Collette, 1990). These re- ports do have a function in that they provide the agency with a record of the type of research A Fig. 1. (A): Fifty-three-character truss superim- posed upon the phenotype of an adult Gila c.~plra: (B): An adult Gila cypha without truss; (C): Fifty-three- character truss framework alone. performed and the results obtained. Yet, agen- cy reports are often cited as if they are readily available, when in fact they often are not. Many journals (such as Copeia) will not, in fact, accept as valid literature citations technical reports published by the majority of state and federal agencies. To circumvent this problem, agencies should either avoid (Collette, 1990), or at least minimize (Wilbur, 1990), production of gray literature and instead emphasize publishing of technical results in the formal literature. Limited published data on G. cypha also re- flects the biology of the species itself. For ex- ample, humpback chub inhabit narrow, canyon- bound segments of the Colorado River and its major tributaries (Minckley, 1973; Holden and Minckley, 1980; Tyus et aI., 1982). Access to these sites is difficult or impossible; research on the species is thus logistically difficult and ex- pensive. In addition, the species has only been recognized for less than 50 years: as a result the literature base is quite modest, and museum specimens suitable for morphological study are scarce. Field studies to collect additional spec- imens are further constrained by its endangered status. The present study was undertaken with twO goals in mind: (1) to quantitatively evaluate morphological variation in this species, with particular emphasis on sexual dimorphism as it