EFFECT OF ZINC ON 4 POPULATIONS AND 2 GENERATIONS OF GAMMARUS-PULEX (L)

1. The amphipod Gammarus pulex (L.) is increasingly used in toxicity assessments and is usually obtained from wild populations. Interpopulation variability in response to toxicants may be due to genetic or phenotypic differences and could be large in wild-caught organisms exposed to different environmental conditions. This paper describes an investigation designed to assess the extent of lethal and sublethal variability between four different G. pulex populations when exposed to zinc, and to determine whether differences observed in the parental generation were also apparent in offspring bred in the laboratory. 2. The mortality of G. pulex from one of the four field-caught populations (Crags Stream) was significantly lower than for animals from the other three populations for the first 2 days of exposure. After 6 days' exposure the LC(50) values for all four populations did not differ significantly, and were approximately 1.0 mg Zn l(-1). Sublethal effects on feeding rate after 6 days' exposure were also similar for all four populations (feeding rate EC(50) approximately 0.5 mg Zn l(-1)). 3. Lethal effects on the F-1 generation were similar among the four populations, in contrast to the short-term differences observed in the parental generation. These results suggest that interpopulation differences in zinc tolerance in G. pulex are short-lived, and phenotypically rather than genetically based.