Abstract
Although many ecological risk assessments of hazardous chemicals have been
conducted with test organisms, such procedures may be insufficient for establishing
reliable hazard assessments in wild organisms. The genetic variation within a species is
rarely considered in such assessments. Here, the relationship between variability in
susceptibility to fenvalerate, an agrochemical toxicant, and the degree of divergence in
allele frequencies at six microsatellite loci were assessed in Daphnia galeata
populations in Lake Kasumigaura and an adjacent local pond. The acute EC50, based
on changes in neonate immobility, in isofemale lines from three populations in Lake
Kasumigaura was 5–10 times that observed in lines from the local pond population;
however, the degree of divergence in allele frequencies was much larger among the Lake
Kasumigaura populations than between the lake and local pond populations. These
results suggest that the level of resistance to the toxicant was determined primarily by
the gradient of pollutants resulting from water flow and did not reflect the genetic
divergence of local populations. I also discuss a possible causal link between
susceptibility against toxicant and genetic variation for future perspectives of ecological
risk assessments.
