8081 - Laserfiche WebLink

Home Browse Search

rlG-7 t) ~~h Transactions of the American Fisheries Society 116: 103-110. 1987 @ Copyright by the American Fisheries Society 1987 t~<6 [ Population Differentiation and Introgressive Hybridization of the Flannelmouth Sucker and of Hatchery and Native Stocks of the Razorback Sucker DONALD G. BUTH Department of Biology. University of California Los Angeles. California 90024. USA ROBERT W. MURPHY Department of Ichthyology and Herpetology. Royal Ontario Museum 100 Queen's Park. Toronto. Ontario M5S 2C6. Canada LINDA ULMER California Department of Fish and Game Post Ojfu:e Box BD. Blythe, California 92225. USA Abstract. -lntrogressive hybridization has important management and evolutionary conse- quences in regard to the maintenance of the integrity of gene pools and the acquisition of new alleles by means other than mutation. Among North American cypriniform fishes, hybridization often occurs between historically allopatric forms placed into sympatry via human activities and between sympatric forms inhabiting a modified environment. In the Colorado River system, several native catostomids are known to hybridize, including flannel mouth sucker Catostomus latipinnis and razorback sucker Xyrauchen texanus. AlIozymic data enabled direct quantification of presumed introgression which was in the range of 0-5% toward flannel mouth sucker and 0-3% toward razorback sucker. Levels of presumably introgressed genes in the stock of razorback sucker from the Dexter Fish Hatchery were as low as or lower than those of the parental stock population from Lake Mohave. The razorback sucker Xyrauchen texanus is a merri!Jer of the "big-river" ichthyofaunal assem- blage of the Colorado River basin whose decline in recent years has gained attention and prompted action to reverse this trend (Minckley 1983). The historical and present distribution of razorback sucker has been mapped by Holden (1980), to which corrections and additions have been pro- vided by Minckley (1983). The biology of this species has been discussed by Minckley (1973, 1983), Moyle (1976), and Wick et aI. (1982). The razorback sucker is recognized as a "vulnerable" species (Williams et aI. 1985) whose management and recovery has included large-scale artificial propagation, which is currently based at the Dex- ter Fish Hatchery, Dexter, New Mexico. A problem regarding the management of any fish species that is artificially mass-produced con- cerns the maintenance of the natural gene pool (Shaklee 1983). The parental stock chosen for the mass production of offspring is, necessarily, a small subsample of the total number of individuals in the natural population. "Sampling error" resulting in the enhancement of the frequencies of some alleles and the reduction of others due to chance can affect the hatchery population. This genetic drift occurs in all natural populations, but has the greatest influence on the genetic composition of populations in which the effective breeding stock is small, and is expected in hatchery situations. Additional complications arise in the mainte- nance of an independent gene pool for razorback sucker due to the phenomenon of introgressive hybridization. The razorback sucker is known to hybridize with species of Catostomus in the Col- orado River system, including flannelmouth suck- er C. latipinnis. Sonora sucker C. insignis. and Utah sucker C. ardens (Hubbs and Miller 1953; Wick et al. 1982). Of these three species of Ca- tostomus. the largest number of hybridization re- ports involve flannelmouth sucker (Wick et al. 1982). The Dexter Hatchery breeding stock of ra- zorback sucker was obtained from Lake Mohave, one of the few locations where the species is locally abundant (Minckley 1983). However, hybridiza- tion with flannelmouth sucker in Lake Mohave has been suspected, and doubts have thus been cast on the genetic composition of the hatchery stock of razorback sucker. The issue is not one of generating a stock of razorback sucker that is any 103