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<br />104
<br />
<br />more "pure" than the native, presumably partially
<br />introgressed, population. Rather, it is introgres-
<br />sive hybridization, coupled with sampling error,
<br />which can cause the introgressed genes of flannel-
<br />mouth sucker to be grossly overrepresented in the
<br />hatchery stock of razorback sucker. The release of
<br />massive numbers of such stock would do irrepa-
<br />rable damage to the gene pool of wild razorback
<br />suckers, flooding it with introgressed genes far
<br />above the low level currently maintained by oc-
<br />casional hybridization with flannelmouth sucker.
<br />Our study evaluated the genetic composition of
<br />natural populations of razorback and flannel-
<br />mouth suckers and the hatchery stock of razor-
<br />back sucker to determine the introgressive influ-
<br />ence of flannel mouth sucker. Enzymatic (allozyme)
<br />characteristics resolved via starch gel electropho-
<br />resis, combined with specific histochemical stain-
<br />ing, are ideal for such hybridization studies be-
<br />cause of the codominant nature of expression of
<br />these gene products and because the expression of
<br />these structural products is not under environ-
<br />mental influence. Relevant electrophoretic com-
<br />parisons involved not only hatchery and Lake
<br />Mohave samples of razorqack sucker, but also a
<br />sample from at least one other native population
<br />of this species. In addition, samples of flannel-
<br />mouth sucker from several locations were studied
<br />to evaluate local geographic variability and pos-
<br />sible differentiation.
<br />
<br />Methods
<br />
<br />Specimens of flannelmouth sucker and razor-
<br />back sucker, collected from the sites listed below,
<br />were placed on dry ice shortly after capture and
<br />maintained at - 20"C until tissues were dissected
<br />for enzyme extraction. In some cases, a preserved
<br />subsample of voucher specimens was deposited in
<br />the collections of the Natural History Museum of
<br />Los Angeles County (LACM) or Arizona State
<br />University (ASU). The numbers of specimens ex-
<br />amined electrophoretically are enclosed in paren-
<br />theses.
<br />Flannelmouth sucker.-Sample I: Virgin River
<br />between La Verkin Spring and Beaver Dam Wash,
<br />Washington County, Utah, and Mohave County,
<br />Arizona (N = 15); sample 2: mouth of Pari a River,
<br />Coconino County, Arizona (N = 3); sample 3: Lit-
<br />tle Colorado River drainage, East Clear Creek be-
<br />low Blue Ridge Reservoir at Forest Road 95 cross-
<br />ing, Coconino County, Arizona, ASU collection,
<br />uncatalogued (D. Hendrickson, ASU, personal
<br />communication) (N = 16); sample 4: upper Col-
<br />
<br />BUTH ET AL.
<br />
<br />orado River near Grand Junction, Mesa County,
<br />Colorado (N = 39).
<br />Razorback sucker. -Sample la: Lake Mohave,
<br />I'\i1ohave County, Arizona (N = 18, a biased sam-
<br />pIt of adult specimens chosen on the qasis of mor-
<br />phological traits suggesting they were of hybrid
<br />origin); sample I b: same as I a (N= 100; an un-
<br />biased random sample of juveniles); sample 2:
<br />Senator Wash Reservoir, Imperial County, Cali-
<br />fornia, collected, as eggs, from several spawning
<br />sites (these eggs were hatched and specimens were
<br />raised in 380-L aquaria at the California Depart-
<br />ment ofFish and Game facility in Blythe), LACM
<br />43570-1 (N = 14); sample 3: Dexter Fish Hatch-
<br />ery, Dexter, New Mexico (N = 52).
<br />Brain, liver, heart, and skeletal muscle tissues
<br />were dissected from each specimen (except for
<br />sam pie 1 b of razorback suckers, from which m us-
<br />c1e samples were obtained for screening products
<br />of only the Ck-A and M-lcdh-A loci). The tissue
<br />sources for enzymes, preparation of extracts, and
<br />the electrophoretic procedures and conditions em-
<br />ployed followed Buth (1980) and Crabtree and
<br />Buth (in press). Gene products compared included
<br />acid phosphatase (Enzyme Commission 3.1.3.2;
<br />Acp-A), alcohol dehydrogenase (EC 1.1.1.1; Adh-
<br />A), creatine kinase (EC 2.7.3.2; Ck-A), glucose-6-
<br />phosphate isomerase (EC 5.3.1.9; G6pi-AI,
<br />G6pi-Al, G6pi-BI, G6pi-Bl), glycerol-3-phosphate
<br />dehydrogenase (EC 1.1.1.8; G3pdh-A), isocitrate
<br />dehydrogenase (EC 1.1.1.42; M-/cdh-A, S-lcdh-
<br />AI, S-/cdh-Al), L-Iactate dehydrogenase (EC
<br />1.1.1.27; Ldh-A, Ldh-BI), malate dehydrogenase
<br />(EC 1.1.1.37; M-Mdh-AI, M-Mdh-Al, S-Mdh-AI,
<br />S-Mdh-Al, S-Mdh-B), phosphoglucomutase (EC
<br />5.4.2.2; Pgm-A), and superoxide dismutase (EC
<br />1.15.1.1; S-Sod-AI, S-Sod-Al). Enzyme nomen-
<br />clature follows the recommendations of the
<br />IUBNC (1984); locus nomenclature is based on
<br />recommendations for use in teleost studies (Buth
<br />1983). Duplicate loci arising from polyploidiza-
<br />tion are identified by superscript notation as em-
<br />ployed by Engel et al. (1973). Allelic products were
<br />lettered (lowercase letters) reflecting increasing an-
<br />0da mobility. These allelic designations are rel-
<br />ative to this study alone and do not correspond
<br />to comparable designations in any other catosto-
<br />mid study.
<br />
<br />Results and Discussion
<br />Intraspecific Variation
<br />Flannelmouth sucker. - Nine of 21 loci were
<br />variable in at least one geographic sample of flan-
<br />
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