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<br />INTROGRESSION IN COLORADO RIVER CATOSTOMIDS
<br />
<br />109
<br />
<br />limited published data for fishes (e.g., Selander
<br />1976). A more appropriate perspective might be
<br />limited to variation in cypriniform fishes (A vise
<br />1977; Buth 1978, 1984), which is marked by a
<br />wide range of values for measures of genetic vari-
<br />ability. While the razorback sucker is below the
<br />mean for genetic variation in catostomid fishes, it
<br />is far from the low end of the spectrum. Several
<br />abundant catostomid species, e.g., black redhorse
<br />Moxostoma duquesnei, suckermouth redhourse M.
<br />pappillosum, and blacktail redhorse M. poeci/u-
<br />rum, have far lower levels of genetic variability
<br />than razorback sucker (Buth 1978). Genetic vari-
<br />ability in razorback suckers is similar to that for
<br />tlannelmouth suckers within the Colorado drain-
<br />age (Table 2). We believe that as long as the breed-
<br />ing stock continues to be obtained in sufficient
<br />quantity from natural populations, the breeding
<br />program for razorback suckers at the Dexter
<br />Hatchery can be quite successful. Programs that
<br />select subsequent breeding stock from their own
<br />reared stock run the risk of reducing variation by
<br />taking a subsample from a subsample; we advise
<br />against such a program for razorback sucker.
<br />
<br />Acknowledgments
<br />This study was supported by the U.S. Fish and
<br />Wildlife Service (20181-0643 FY 82), the UCLA
<br />Department of Biology Fisheries Program, the
<br />University of California at Los A~geles (UCLA)
<br />Biomedical Support Grant, and the UCLA Com-
<br />mittee on Research (U.R. 3674 to D.G.B.). We
<br />thank Jim Bennett, Gerald Burton, Leslie Fitz-
<br />patrick, Dean Hendrickson, Buddy Jensen, James
<br />E. Johnson, Gene Wilde, and especially W. L.
<br />Minckley for their assistance in obtaining speci-
<br />mens for this study. We appreciate the support
<br />and assistance of the Lower Basin Native Fishes
<br />Committee. Analyses of the allozyme data were
<br />conducted with the BIOSYS- I computer program
<br />(Swofford and Selander 1981) supplied by D. L.
<br />Swofford. We thank Walter J. Rainboth for his
<br />suggestions and critical evaluation of the manu-
<br />script.
<br />
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