Differences in survival functions of mosquitofish (Gambusia affinis) and sand shiner (Notropis ludibundus) genotypes exposed to pesticides

Differential genotypic tolerance of two species of fish native to the Great Plains of North America (the western mosquitofish [Gambursia affinis] and the sand shiner [Notropis ludibundus]) was examined in 96-h acute exposures to the pesticides lindane and parathion. Although a significant amount of data is available indicating that heavy metals cause selective genotypic mo rtality in aquatic organisms, very few studies have focused on the effects of pesticides on population genetic structure. Fish used in this experiment were captured from field populations in Kansas, USA, and acclimated to lab oratory conditions for I month before the acute toxicity tests. Two hundred individuals of each species were exposed, in two separate experiments, to estimated LC70 concentrations of each pesticide for 96 h. Dead individuals were removed at 3-h intervals allowing for comparison of genotypic times-to -death. Individuals of each species were electrophoretically examined at tw o polymorphic loci. Phenotypes of mosquitofish were determined for phosphog lucose mutase (PGM) and malic enzyme (ME). Phenotypes of sand shiners were determined for PGM and aspartate aminotransferase (AAT). Three of eight sta tistical tests (two species x two loci x two pesticides) indicated signific ant differences among survival curves of genotypic classes. Genotypes of,ME and PGM of mosquitofish exhibited significantly different survivorship fun ctions in the parathion and lindane time-to-death tests, respectively. Geno types of AAT of sand shiners exhibited significantly different survivorship curves when exposed to lindane. Given certain experimental limitations, th ese results support a continued examination of population genetic character istics as biomarkers of environmental contamination.