Genetics indicators of environmental tolerance among fish populations exposed to acid deposition

Abstract

Horizontal starch-gel electrophoresis was used to analyze the genetic structure of five fish species previously reported to vary in their tolerance to acid-stressed (low pH, high [Al], soft water) environments as follows: tolerant-central mudminnow ( Umbra limi) and yellow perch ( Perca flavescens); indeterminate—creek chub ( Semotilus atromaculatus); sensitive—common shiner ( Luxilus cornutus) and blacknose dace ( Rhinichthys atratulus). The relationships between direct-count heterozyosity ( H) and polymorphism (each measured in populations from non-stressed sites to indicate “natural” levels of genetic diversity) and acid tolerance were inconsistent. As predicted, H was high (21 loci; H 0.084–0.142) in central mudminnow populations and low (21 loci; H = 0.019–0.033) in the blacknose dace. Contrary to predicton, variation was generally low (25 loci; H = 0.000−0.056) among yellow perch populations and high (22 loci; H = 0.055−0.103) in common shiners. Creek chub H (24 loci; H = 0.002−0.038) was generally intermediate, but variable. Relationships based only on levels of polymorphism gave similar results, as did comparisons based on loci scored in each species. Our results suggest that any relationship between genetic variability and stress tolerance may lack predictive power when applied to specific species and specific stressors.