Genotype and toxicity relationships among Hyalella azteca: I. Acute exposure to metals or low pH

Comparative genotype and toxin interactions at three polymorphic enzyme loc i were examined in a laboratory population of amphipods (Hyalella azteca) d uring acute exposure to cadmium, zinc, copper, lead, or low pH. Significant toxin-genotype interactions were observed using logistic regression to mod el mortality in ten of 15 analyses. Both stressor-specific and nonspecific modes of selection were observed. In general, low DH selected for different genotypes than those selected by metals, especially zinc. Different modes of selection were also observed when amphipods were exposed to different me tals. These results suggest that exposure to low pH would significantly red uce the ability of H. azteca survive subsequent contamination by metals; ex posure to stressors in the reverse order would also compromise a population 's chance of survival. A genetic distance analysis showed that the magnitud e of genetic differentiation consistently increased among survivors compare d with that of the initial populations. These increases in genetic divergen ce estimates suggest that acute exposure to metals or low pH may have an ev olutionarily significant impact on the species. They also suggest that both genotype frequency and genetic distance measures (based on allozyme data) may be used as bioindicators for environmental monitoring programs. Validat ion of such bioindicators requires an understanding of the population's gen etic background, genetic structure, and history.