| The relationships between genetic structure of larval odonates and water chemistry was examined in the Raccoon Creek basin in southeastern Ohio. The Raccoon Creek basin is affected by drainage from coal mines which produce acidic conditions and high concentrations of metals in adjacent streams. This study examined larval Gomphus graslinellus and G. lividus (Odonata: Gomphidae). Sites without larval G. graslinellus were only characterized by low pH. Sites without larval G. lividus were characterized by low pH, low alkalinity, high acidity, and high concentrations of iron and magnesium. Allozyme electrophoresis resolved 15 presumptive loci on nine enzyme systems. Direct count heterozygosity, Ho, ranged from 0.180 to 0.269 for G. graslinellus and from 0.140 to 0.325 for G. lividus. Measurements of inbreeding within populations, f, and the variance of allele frequencies between individuals, theta, revealed measurable degrees of inbreeding and a significant amount of among population variability for both gomphid species. A combination of clinal variation in allele frequency and water chemistry revealed possible selective pressure on some alleles by acid mine drainage. In G. graslinellus, clines in ACP-2*b and ALP-1*b reflected clines in acidity and alkalinity. In G. lividus, clines in ALP-1*c and LAP-2* c reflected clines in iron concentration. There is a relationship of ALP-1*c to iron concentration seen at both the allelic and genotypic level. Although the congeners G. graslinellus and G. lividus apparently respond differently to acid mine drainage conditions, it is possible that the high degree of genetic variability seen in each species contributes to its ability to survive such conditions. Gomphus graslinellus may occur at fewer sites than G. lividus because it may experience a higher metabolic cost to acid mine drainage tolerance. Localized selection pressures for particular alleles and genotypes in gomphid odonates may contribute to the measured levels of inbreeding and among population variability seen in this study. |
