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The native fish fauna of the American southwest is in decline as a result of habitat destruction, disruption of natural water flows, and introduction of nonnative species. The status of several members of the cyprinid genus Gila occurring in the upper Colorado River basin is particularly tenuous, in part because of uncertainty regarding their taxonomic status. To examine this uncertainty, we have sampled 363 specimens of G. robusta and G. cypha from eight localities in the upper Colorado River basin and the Grand Canyon and used canonical discriminant and cluster analysis to categorize patterns of morphological variation at three levels of biological organization. At the population level, all sampled populations...
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Morphological and genetic characters from cyprinid fishes of the genus Gila were examined to assess a hypothesized hybrid origin of Gila seminuda from the Virgin River, Arizona-Nevada-Utah. The presumed parents, Gila robusta robusta and Gila elegans, are clearly differentiated from one another based on morphology, allozymes, and mtDNA haplotypes. G. seminuda is morphologically intermediate and polymorphic at allozyme loci diagnostic for the parental species. Restriction endonuclease analysis of mtDNA showed G. seminuda nearly identical to G. elegans. These results support an origin of the bisexual taxon G. seminuda through introgressive hybridization. The Gila population in the Moapa River, Nevada, also appears...
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Univariate and multivariate techniques were used to evaluate sexual dimorphism in 53 morphometric measures taken from 63 adult specimens of an endangered cyprinid, the humpback chub (Gila cypha). Specimens were filmed and released unharmed after their capture in the Colorado and Little Colorado rivers of the Grand Canyon (Arizona). Morphometric data were later extracted from film using a microcomputer and image analysis software. Because of the unique morphology of this fish, analyses emphasized its anterodorsal hump. Only two of 53 characters (3.8%) revealed significant sexual dimorphism in an analysis of covariance; approximately what one would expect from chance alone (i.e., one in 20, or 5%). A discriminant...
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Qualitative scoring is frequently overlooked in preference to counts or measurements of individual characters, particularly for species whose overlap in morphology makes clear separation difficult. Quantitative measurements and counts of single characters were compared to qualitative rankings of selected morphological features of chubs (genus Gila) from the Yampa River, Colorado. Data were collected by technicians with no specialized training in systematics. A high degree of morphological variability confounded identification using the quantitative data set, while principal components analysis of qualitative data clearly separated Gila cypha (humpback chub) and G. robusta (roundtail chub). Totals of 32 G. cypha...
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