Biochemical Genetics of Colorado Pikeminnow

Abstract

We evaluated the genetic relationships among two captive populations of Colorado pikeminnow Ptychocheilus lucius from the Dexter National Fish Hatchery and Technology Center, New Mexico, and 15 samples of wild adult, juvenile, and age-0 fish from the Green, Yampa, Colorado, and San Juan rivers. The products of 89 or more loci were resolved by starch gel electrophoresis and histochemical staining; 8 loci were polymorphic in at least one sample. Minimally invasive sampling of fin and skeletal muscle tissue resulted in data from wild adults and juveniles (N = 207) and hatchery-produced adults (N = 60) with no mortality. Additionally, 426 wild and 34 hatchery-reared age-0 fish were sampled by necropsy. Allele frequencies did not differ significantly among geographically separated breeding populations, suggesting essential panmixia. Mean F _ST values ranged from 0.003 among wild age-0 Green and Colorado River fish to 0.108 among all wild adult fish and captive broodfish. Significant deviations from Hardy−Weinberg equilibrium were observed at four loci in the Colorado and Green River samples of adult, juvenile, and age-0 fish. No hatchery samples showed such deviations. The most striking geographic variability observed was the presence of the rare private alleles GR*b and TPI-2*c in Green River basin samples and GPI-2*c, PEPB*a, and PEPS*b in Colorado River basin samples. The lowest genetic variability was observed in the San Juan River tributary of the Colorado River, possibly as a result of prior population bottlenecks. Our gene frequency and genetic divergence results do not support the proposition that there is significant genetic differentiation among populations of Colorado pikeminnow. Rather, the significant heterozygote deficiencies at several loci suggest that although geographic differentiation may have existed in the past, current barriers to fish movement and widespread stocking of hatchery fish now mask it.